Synthesis and properties of fused-ring-expanded porphyrins that were core-modified with Group 16 heteroatoms

DOI: 10.1002/chem.201200956

Synthesis and Properties of Fused-Ring-Expanded Porphyrins that were

Core-Modified with Group 16 Heteroatoms

Hai-Jun Xu,^[a]John Mack,^{[b, d]}Di Wu,^[a]Zhao-Li Xue,^[a]Ana B. Descalzo,^{[c, e]}

Knut Rurack,*^[c]Nagao Kobayashi,*^[b]and Zhen Shen*^[a]

Dedicated to Professor Noboru Ono on the occasion of his 70th birthday

Abstract: The synthesis of a series of

novel core-modified and fused-ring-ex-

panded tetraphenylporphyrins is re-

ported. Theoretical calculations and

magnetic circular dichroism (MCD)

and fluorescence spectroscopic meas-

urements were used to analyze the

effect of core modification with

Group 16 oxygen, sulfur, selenium, and

tellurium atoms on the optical proper-

ties and electronic structures of the

porphyrins. Marked redshifts of the Q

and B bands and accelerated intersys-

tem-crossing rates were observed, thus

making these compounds potentially

suitable for use in a variety of applica-

tions. The scope for further fine-tuning

of these optical properties based on ad-

ditional structural modifications, such

as the incorporation of fused benzene

rings to form ABAB structures by

using a thiophene precursor with a

fused bicycloACTHNUGRTENUNG[2.2.2]octadiene ring and

Keywords: density functional calcu-

lations · fluorescence · MCD spec-

troscopy · porphyrinoids · ring ex-

pansion

the introduction of various substituents

onto the meso-phenyl rings, is also ex-

amined.

Introduction

Porphyrins have long been the focus of intense research in-

terest due to the key role that porphyrinoid p-systems play

in various biological processes, such as photosynthesis and

respiration. In recent years, research has focused, to a signif-

icant extent, on the use of porphyrinoids as opto-electronic

materials. Structurally modified porphyrins with strong ab-

sorption bands at the red end of the visible-light region and

in the 700–1000 nm portion of the near-infrared (NIR) spec-

trum have been investigated extensively, due to their poten-

tial future use in photodynamic therapy^[1–3]and in key mate-

rial-science applications, such as fluorescent probes,^[4]solar-

energy conversion,^[5]nonlinear optical materials,^[6]and NIR

dyes.^[5,7–9]In the future, there is likely to be a growing focus

on porphyrinoids that absorb and fluoresce significantly in

the second and third telecom windows (1260–1675 nm). Var-

ious strategies, such as peripheral fused-ring-expansion,^[10]

the introduction of meso-alkynyl substituents,^[11,12]and the

formation of porphyrin oligomers,^[13]have been adopted to

redshift the band centers of the Q and B (or Soret) bands.

The most-widely applicable approach is the fusion of aro-

matic rings onto the b-pyrrole carbon atoms. Although there

have been a large number of reports on the effect of periph-

eral-fused-ring expansion on conventional tetrapyrrole por-

phyrins,^[14]the fused-ring expansion of core-modified por-

phyrins has only been studied to a limited extent.^[15]Herein,

we report an in-depth analysis of the optical properties of

porphyrinoids with Group 16 heteroatoms, by replacing the

two protonated pyrrole nitrogen atoms, and we explore the

effect of fused-ring-expansion, the incorporation of addition-

[a] Dr. H.-J. Xu,⁺Dr. D. Wu,⁺Dr. Z.-L. Xue,⁺Prof. Z. Shen

State Key Laboratory of Coordination Chemistry

Nanjing National Laboratory of Microstructures

School of Chemistry and Chemical Engineering

Nanjing University, Nanjing 210093 (P.R. China)

Fax : (+86)25–8331–4502

E-mail: zshen@nju.edu.cn

[b] Dr. J. Mack, Prof. N. Kobayashi

Department of Chemistry, Graduate School of Science

Tohoku University, Sendai 980–8578 (Japan)

Fax : (+81)22–795–7719

E-mail: nagaok@m.tohoku.ac.jp

[c] Dr. A. B. Descalzo, Dr. K. Rurack

Division 1.9 Sensor Materials

BAM Federal Institute for Materials Research and Testing

Richard-Willstꢀtter-Strasse 11, 12489 Berlin (Germany)

Fax : (+49)30–8104–1157

E-mail: knut.rurack@bam.de

[d] Dr. J. Mack

Current address: Department of Chemistry

Rhodes University, Grahamstown (South Africa)

[e] Dr. A. B. Descalzo

Current address: Department of Organic Chemistry

Faculty of Chemical Sciences

Complutense University of Madrid

Avda. Complutense s/n, 28040 Madrid (Spain)

[⁺] These authors contributed equally to this work.

Supporting information for this article is available on the WWW

under http://dx.doi.org/10.1002/chem.201200956.

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Chem. Eur. J. 2012, 18, 16844 – 16867

FULL PAPER

al pyrrole moieties, ligand nonplanarity, and the electron-do-

nating properties of meso-aryl substituents on their electron-

ic structures.

5,10,15,20-tetraphenyl-21-oxaporphyrin can stabilize nick-

el(I),^[18]which is not possible with 5,10,15,20-tetraphenylpor-

phyrin (TPP), due to the presence of an N₃O (rather than

an N₄) core. The use of thia- and oxaporphyrin as terminolo-

gy to describe core-modified porphyrinoids was originally

introduced by Johnson and co-workers^[19]and is now well-

established in the literature^[20]despite the fact that it would

normally only be applied to the replacement of a carbon

atom rather than a nitrogen atom. Most of the recent re-

search on core-modified porphyrins has focused on N₃S and

N₂S₂compounds;^[20]there have been relatively few reports

of compounds that contain O, Se, and Te atoms.

The influence of the heteroatoms on the electronic struc-

ture and optical properties of the porphyrinoids is examined

in-depth based on TD-DFT calculations and magnetic circu-

lar dichroism (MCD) and fluorescence measurements

(Figure 1). MCD measurements were carried out on a series

of compounds with n-hexadecyloxy groups incorporated at

the para positions of the phenyl substituents (N2Y2-

OC16H33), since this enhances the solubility in optically

We have recently demonstrated that meso-tetraphenyl

ACHTUNGTNERtNUNG et-

ACHTUNGTRENNUNGraphenanthroporphyrins (TPTPhenPs) have remarkably

redshifted B bands, due to the introduction of peripheral-

fused phenanthrene rings.^[16]Similar results had previously

been reported by Lash and co-workers for compounds with

peripheral-fused acenaphthalene rings.^[10a,b]This work

prompted us to explore the effect of introducing fused-phen-

ACHTUNGTRENNUNGanthrene rings at the b-pyrrole carbon positions of core-

modified porphyrins to synthesize new porphyrinoids with

optical properties in the NIR region that would be suitable

for use in various applications. For example, water-soluble

core-modified porphyrins have recently emerged as poten-

tially useful agents for photodynamic therapy (PDT).^[17]

Herein, we report the synthesis of N₂O₂, N₂S₂, N₂Se₂, and

N₂Te₂tetraphenyldiphenanthroporphyrins (this terminology,

used throughout, refers to the four core atoms on the inner

perimeter of the p-system that can coordinate a central

metal atom; Figure 1 and the Supporting Information, Fig-

transparent solvents. Electron-donating OMe and NACHTUNGTRENNUNG(CH₃)₂

ure S1), in which Group 16 hetero

atoms replace the proto-

groups (N₂Se₂-OMe and N₂Se₂-NMe₂) and electron-with-

drawing F atoms (N₂O₂-F and N₂S₂-F) have been used to ex-

amine the extent to which the aryl substituents can be used

to fine-tune the optical properties, whilst Cl, Br, and I atoms

(N₂O₂-Cl, N₂O₂-Br, and N₂O₂-I) were introduced so that the

nated pyrrole nitrogen atoms along the y axis and peripher-

al-fused-phenanthrene rings are substituted onto the pyrrole

moieties on the x axis. These macrocycles can potentially

stabilize metals in unusual oxidation states. For example,

Figure 1. Left: Cross-section views in the yz plane of the B3LYP-optimized geometries of P, TPP, TPTPhenP (TPTP), N₂O₂, N₂S₂, N₂Se₂, N₂Te₂, N₂S₂-F,

P₁, P₁-Bz_y, and P₃, model compound structures (M) of TPhenP and 2Phen_xN₄, and the X-ray structures (X) of N₂Se₂-NMe₂and P₃-Bz_y, based on the use

of 6–31G(d) basis sets (3–21G** basis sets for N₂Te₂). Only the trans isomers are shown with respect to the BCOD groups in structures P₁and P₃. The

axes are orientated such that the y and z axes lie horizontally and vertically in the plane of the page, respectively. For cross-section views in the xy and

xz planes, see the Supporting Information. Right: Key trends to be analyzed by MCD and/or fluorescence spectroscopy.

Chem. Eur. J. 2012, 18, 16844 – 16867

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16845

K. Rurack, N. Kobayashi, Z. Shen et al.

relative influence of the heavy-atom effect and core modifi-

cation on the emission properties could be compared. The

effect of forming ABAB structures with differing types of

peripheral-fused-ring expansion has been explored by syn-

thesizing core-modified diphenanthro- (P₁and P₁-Bz_y) and

diacenaphthoporphyrins (P₃and P₃-Bz_y; Figure 1 and the

Supporting Information, Figure S1), which have fused

and N₂Te₂compounds by using the corresponding non-

BCOD fused furan, thiophene, selenophene, tellurophene,

dithiophene, and diselenophene diols with a phenanthro-

fused pyrrole precursor. Aryl groups with different para-

substituents can be readily introduced during the prepara-

tion of the diols. For full details, see the Experimental Sec-

tion.

bicyclo

the y axis.

[2.2.2]octadiene (BCOD) and benzene rings along

X-ray structures are reported for N₂Se₂-NMe₂and P₃-Bz_y,

which fit the tetragonal P4(2)/nmc and monoclinic P21/n

space groups, respectively (Figure 2 and the Supporting In-

formation, Figure S2 and Table S1). Steric hindrance be-

tween the meso-phenyl substituents and the peripheral-

fused-ring moieties resulted in a significant saddling distor-

tion of the p-system (see the Supporting Information,

Synthesis of core-modified porphyrins: The synthesis of

monohetero- and diheteroporphyrins was pioneered by

Ulman and Manassen in the mid-1970s, based on a reaction

between a diarylfuran/diarylthiophene diol and a pyrrole to

form a porphyrinoid compound.^[21]In recent years, Ono and

co-workers developed a breakthrough synthesis of pure p-

expanded porphyrinoids^[22]and benzo[c]heterocyclic oligo-

AHCTUNGTREGTNNUN ables S2 and S3), which rotated the meso-phenyl groups

into the plane that was formed by the four meso-carbon

atoms on the inner ligand perimeter. Recent studies on

core-modified tetrabenzoporphyrins^[15]and TPTPhenPs^[16]

have demonstrated that the results of DFT geometry optimi-

zations are very similar to those obtained by X-ray crystal-

lography when steric hindrance between peripheral-fused

rings results in severe ligand folding, due to the lack of con-

formational flexibility. Therefore, the observed trends in the

experimental data of the core-modified structures synthe-

sized herein can be readily compared to those predicted by

theoretical calculations for the B3LYP-optimized geome-

tries, even in the absence of X-ray structures.

ACHTUNGTRENNUNG

mers^[23,24]that was based on the tetramerization of BCOD-

fused pyrroles to afford peripherally substituted porphyrins,

which can subsequently be converted into tetrabenzopor-

phyrins in quantitative yield by heating at 2008C.^[25]A series

of core-modified tetrabenzoporphyrins, in which one or

both of the protonated pyrrole nitrogen atoms were re-

placed with oxygen/sulfur atoms by using BCOD-fused

furan and thiophene, respectively, were successfully synthe-

sized.^[23,26]The same synthetic approach is adopted herein to

synthesize P₁-Bz_yand P₃-Bz_ybased on the retro-Diels–Alder

reaction of P₁and P₃, respectively, which are formed from a

BCOD-fused diarylthiophene diol with either a phenanthro-

or acenaphtho-fused pyrrole. The replacement of pyrrole

moieties by other heterocycles, such as furans, thiophenes,

selenophenes, or tellurophenes, leads to the formation of

new classes of core-modified porphyrinoids. Ulman and Ma-

Electronic structure of porphyrinoids: Many key break-

throughs in understanding the electronic structure of por-

phyrinoids have been derived from MCD spectroscopy.^[27]

Analysis of the MCD spectra is based on the three Faraday

terms: a₁, b₀, and c₀. Because there are no three-fold or

higher axes of symmetry, the spectra of the core-modified

ACHTUNGTRENNUNGnasACHTUNGTRENNUNG

senꢂs methodology^[21]is used to form N₂O₂, N₂S₂, N₂Se₂,

Figure 2. Crystal structures of a) P₃-Bz_y(top) and b) N₂Se₂-NMe₂(bottom); thermal ellipsoids are set at 50% probability. Phenyl groups and solvent mol-

ecules are omitted for clarity.

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Core-Modified Fused-Ring-Expanded Porphyrins

FULL PAPER

porphyrinoids reported herein are completely dominated by

positively and negatively signed and Gaussian-shaped Fara-

day b₀terms. The application of TD-DFT techniques to

MCD spectroscopy is still being developed..^[28,29]Theoretical

approaches based on semi-empirical theoretical techniques,

such as Michlꢂs perimeter model^[30]and Goutermanꢂs 4-orbi-

tal model,^[31]continue to play an important role in the inter-

pretation of the optical spectra of porphyrinoids. These ap-

proaches provide readily accessible conceptual frameworks

for rationalizing and predicting key trends in the spectro-

scopic data. The orbital angular momentum (OAM) proper-

ties of the p-MOs of porphyrinoids can typically be de-

scribed in terms of an M_L=0, ꢀ1, ꢀ2, ꢀ3, ꢀ4, ꢀ5, ꢀ6,

ꢀ7, 8 sequence in the magnetic quantum number, in ascend-

ing energy, for thosethe p-MOs which are associated with a

2ꢁ

D_16hsymmetry of the C₁₆H₁₆parent perimeter for the 18p

electrons on the 16-atom inner ligand perimeters of conven-

tional tetrapyrrole porphyrinoids. This perimeter-model ap-

proach is based on the fact that heteroaromatic p-systems

maintain their OAM properties upon symmetry-lowering

structural perturbations. The nodal patterns of the four fron-

tier p-MOs of the free-base porphyrin (P), TPP, TPTPhenP,

N₂O₂, N₂S₂, N₂Se₂, N₂Te₂, P₁, P₁-Bz_y, P₃, and P₃-Bz_yare con-

Figure 3. Top: Origin of the Q and B bands in Goutermanꢂs 4-orbital

model.^[31]In the context of a free-electron model, the doubly degenerate

HOMO and LUMO of the inner cyclic polyene perimeter of C₁₆H₁₆ex-

2ꢁ

sistent with a C₁₆H₁₆parent perimeter (see the Supporting

hibit angular momentums of ꢀ4 and ꢀ5 b, respectively. Configurational

interaction between the four possible spin-allowed one-electron transi-

tions results in forbidden Q bands and allowed B bands. When the sym-

metry is lowered to D_2h, the zero-field splitting of the excited states split

the Q and B bands into their x- and y-polarized components. Bot-

Information, Figure S3). Because an incident photon can

only provide one quantum of orbital angular momentum,

optical spectroscopic data of the porphyrinoids can be as-

signed in the context of Goutermanꢂs 4-orbital model^[31]to

an allowed B band (“DM_L= ꢀ1”) and a forbidden Q band

(“DM_L= ꢀ9”), which arise from the four spin-allowed tran-

sitions that link the HOMOs (M_L= ꢀ4) and the LUMOs

(M_L= ꢀ5; Figure 3). When the symmetry is lowered to

form a porphyrinoid, there is a mixing of the allowed and

forbidden properties of the Q and B excited states, but the

OAM properties of the frontier p-MOs of the parent perim-

eter are largely retained.^[30]In Michlꢂs perimeter model

(Figure 4), the excited-state magnetic moments of the states

that arise from the Q and B transitions of the parent perim-

eter are referred to as m^ꢁand m⁺, respectively. The m^ꢁ

moment is relatively small and is associated with the net

charge circulation on the perimeter upon electronic excita-

tion when the circulation of the excited electron in the

LUMO level and the hole that is left in the HOMO level

are both taken into consideration. The m⁺moment is much

larger due to a reversal of the handedness properties of the

circulation of the excited electron. In the case of the parent

D_16hor D_22hsymmetry of the hydrocarbon perimeters dis-

cussed herein, the Q₀₀bands would be fully electric-dipole

forbidden and the sign and intensity of the a₁term that

arises from the B transition would be exclusively determined

by the far-weaker m^ꢁmoment. When the symmetry is low-

ered to form a porphyrin with D_4hsymmetry, there is an in-

crease in the degeneracy of the MOs that are derived from

the HOMO level of the parent perimeter but not of those

from the LUMO level (the magnitudes of these splittings

are referred to as the DHOMO and DLUMO values in the

context of Michlꢂs model). Michl^[30]demonstrated that the

2ꢁ

tom: The four frontier p-MOs of the C₁₆H₁₆parent perimeter and N₂S₂

were found to exhibit M_L= ꢀ4, ꢀ5 nodal patterns in the differences in

phase on the inner cyclic perimeter of the p-system as would be antici-

pated on the basis of Goutermanꢂs 4-orbital^[31]and Michlꢂs perimeter^[30]

model (Figure 4). The nodal patterns were generated from the Gaussian

checkpoint files using the CS Chem3D program at the 0.04 a.u. energy

level of the isosurface value for electrostatic potential. In the context of

Michlꢂs perimeter model, the MOs with nodal planes along the y axis are

referred to as “a” and “ꢁa” MOs, whereas those with large MO coeffi-

cients are referred to as “s” and “ꢁs” MOs. The nodal patterns for all of

the compounds in Figure 1 are provided in the Supporting Information,

Figure S3.

degree of mixing (a) and the magnitude of the induced mag-

netic dipole moments, which are associated with the first-de-

rivative-shaped Faraday a₁terms (the intensity of the a₁

term is associated with the differential absorbance of left-

and right-polarized light, due to the Zeeman splitting of or-

bitally degenerate excited states) of the Q and B bands (m_Q,

m_B), based on the observed dipole strengths (D₀), can be

predicted by Equations (1)–(3).

D_0ðQÞ=D_0ðBÞ¼ tan²a

ð1Þ

ð2Þ

ð3Þ

m_B¼ ꢀðcos²aÞm^ꢁꢀ ðsin²aÞm^þ

m_Q¼ ꢀðsin²aÞm^ꢁꢀ ðcos²aÞm^þ

In the case of low-symmetry chromophores, in which

DHOMO and DLUMO¼0, the MCD spectra are dominat-

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K. Rurack, N. Kobayashi, Z. Shen et al.

Results and Discussion

Recently, we showed that TPTPhenP has the most redshift-

ed B band of any radially symmetric fused-ring-expanded

porphyrinoid.^[16]Although TPTPhenPs are of considerable

academic interest, their severely saddled structure hinders

the coordination of a central metal and lowers the stability

of these compounds relative to almost-planar porphyrinoids.

Therefore, further structural modification is required to

form porphyrinoids that are suitable for practical applica-

tions. The goal of our research is the synthesis of low-sym-

metry phenanthroporphyrins that retain the markedly red-

shifted Q and B bands of TPTPhenP, but with p-systems

that are not as severely folded. Herein, our main strategy to

try to meet these goals was to synthesize a series of core-

modified porphyrins in which the protonated pyrrole rings

on the y axis were replaced by furan, thiophene, seleno-

phene, and tellurophene moieties to form N₂O₂, N₂S₂, N₂Se₂,

and N₂Te₂, respectively. Significant redshifting of the Q and

B bands has been reported previously for core-modified por-

phyrins.^[15]Because there are no fused phenanthrenes at-

tached to the furan, thiophene, selenophene, and telluro-

phene moieties, there is a markedly lower degree of folding

of the p-system (Table 1). The electronic structures of these

core-modified tetraphenyldiphenanthroporphyrins are ex-

pected to exhibit properties that are similar to those of

TPTPhenPs, due to the nature of the structural perturba-

tions. We recently reported an in-depth analysis of the opti-

cal properties of core-modified tetrabenzoporphyrins,^[15]in

Figure 4. Left: Michlꢂs perimeter model^[30]for C₁₆H₁₆^2ꢁ. The circle repre-

sents the clockwise and counterclockwise motions of the p-system elec-

trons on the inner ligand perimeter, thereby generating the M_Lvalue for

each complex p-MO. Right: The alignment and magnitude of the mag-

netic moments that are induced by the electron motion within each p-

MO can be predicted based on the right-hand rule and linear combina-

tion of atomic orbital (LCAO) calculations. The moments aligned along

the z axis with/against the applied field are shown schematically.^[31]

Right- and left-handedness are defined within classical optics by looking

towards the light source of the CD spectrometer (lcp and rcp=left and

right circularly polarized light, respectively).

ed by Gaussian-shaped Faraday b₀terms. The intensity of

the b₀term arises from the field-induced mixing of states

that are linked by a magnetic dipole transition moment;

thus, a coupled pair of oppositely signed bands replaces the

derivative-shaped a₁term, due to the zero-field splitting of

the Q and B excited states. Michl^[30]has demonstrated that,

in the context of aromatic p-systems, such as porphyACTHNUTRGENNGrU inACHTUNGTNERoNUGN ids,

the differential absorbance of left- and right-polarized light

(and, hence, the ordering of the MCD signs for the Qx, Qy,

Bx, and By bands) by the excited states of aromatic p-sys-

tems, such as porphyrinoids, is related to the alignment of

the induced magnetic moments with or against the axis of

light propagation and the applied field, and is primarily de-

termined by the relative magnitudes of the DHOMO and

DLUMO values. When a structural perturbation introduces

a large DHOMO or DLUMO value, the circulation of the

charge on the perimeter is hindered. Therefore, the relative

magnitudes of the DHOMO and DLUMO values determine

whether the circulation of the excited electron in the

LUMO level or that of the hole that is left in the HOMO

level is the dominant factor in conserving the quantum of

orbital angular momentum that is provided by the incident

photon of left- or right-circularly polarized light. Ampereꢂs

rule (right-hand rule) for conventional current flow in a sol-

enoid^[27]can be used to demonstrate that, when DHOMO>

DLUMO and electronic-charge circulation in the LUMO

predominates, the ordering of the signs of MCD intensity

for the b₀terms that are associated with the Q and B bands

is ꢁ, +, ꢁ, +, in ascending energy terms. In contrast, when

DLUMO>DHOMO and the circulation of the positive

charge that is associated with the hole that is left in the

HOMO is the dominant factor, the sequence reverses to +,

ꢁ, +, ꢁ.

which we demonstrated that a core-modified tetraphenyl

AHCTUNGTREGrNNNU abenzodithiaporphyrin that contained two thiophene moi-

ACHTUNGTRENNUNGtet-

eties, which lay on the y axis, and two benzo groups, which

were fused to the pyrrole moieties along the x axis (2Bz_x;

Figure 5), retained many of the optical properties of the

parent hydrocarbon perimeter, because DHOMOꢂ

DLUMO. Therefore, their OAM properties were similar to

those of—what Michl referred to as—double soft MCD

chromophores,^[30]such as tetraphenyltetraacenaphthopor-

phyrin (TPTANP), for which DHOMOꢂDLUMOꢂ0.

Markedly redshifted B bands tend to be observed for por-

phyrinoid chromophores of this type, because the Q and

B bands retain their ideal forbidden and allowed properties

and there is very limited configurational interaction between

the B and higher-energy pp* states.^[14]

Michlꢀs perimeter model: To perform the rational design of

new porphyrinoids, the effect of different structural pertur-

bations, such as fused-ring-expansion, must be fully under-

stood. Michlꢂs perimeter model^[30]can be used to rationalize

how different peripheral-fused rings affect the HOMO–

LUMO band gap and the DHOMO and DLUMO values

and, hence, the spectroscopic properties (Figure 6). Al-

though theoretical calculations can be used to derive quanti-

tative values for the energies of the four frontier p-MOs,

predictions of the magnitudes of the DHOMO and DLUMO

values can also be made based on a qualitative considera-

tion of the nodal patterns of the four frontier p-MOs, due to

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Core-Modified Fused-Ring-Expanded Porphyrins

FULL PAPER

Table 1. Trends in the key distances [ꢃ] in the molecular structures of P, TPP, TPhenP, TPTPhenP, N₂O₂, N₂O₂-OMe, N₂S₂, N₂S₂-OMe, N₂S₂-F, N₂Se₂,

N₂Se₂-OMe, N₂Te₂, P₁-Bz_y, and P₃-Bz_y, the trans and cis isomers of P₁and P₃, and the X-ray structures (X) of P₃-Bz_yand N₂Se₂-NMe₂.

a

b

c

d

e

f

g

h

i

j

P

TPP

–

6.88

6.93

6.80

6.75

6.72

6.73

7.10

7.18

7.19

7.26

7.31

7.09

7.06

7.15

7.12

2.50

2.52

2.46

2.47

2.48

–

4.24

4.22

4.19

4.16

4.22

4.23

3.20

3.23

3.21

3.16

3.18

3.20

3.42

3.45

3.53

3.54

3.51

3.37

3.15

3.13

5.79

5.78

5.70

5.20

5.39

5.40

5.20

5.18

5.20

5.21

5.22

5.15

5.16

5.17

5.15

5.13

5.39

5.38

5.37

8.52

8.50

8.36

6.90

7.33

7.32

7.27

7.23

7.26

7.14

7.10

7.09

7.20

6.83

6.82

6.81

6.84

6.88

7.68

7.69

7.67

7.70

4.06

4.08

4.03

4.09

4.01

4.02

4.78

4.79

4.78

4.89

4.91

4.93

5.12

5.00

4.79

4.78

4.80

4.77

4.76

4.77

4.73

4.64

5.79

5.73

5.61

5.22

5.31

6.24

6.23

6.24

8.52

8.53

8.32

6.87

7.38

8.75

8.70

8.74

15.56

–

TPhenP

TPTPhenP

N₂O₂

N₂O₂-OMe

N₂S₂

N₂S₂-OMe

N₂S₂-F

N₂Se₂

N₂Se₂-OMe

N₂Se₂-NMe₂

N₂Se₂-NMe₂(X)

N₂Te₂

P₁-trans

P₁-cis-sp²

P₁-cis-sp³

P₁-Bz_y

P₃-trans

P₃-cis-sp²

P₃-cis-sp³

P₃-Bz_y

13.14

9.67

15.36

15.07

15.06

15.21

15.27

15.18

15.17

15.22

15.34

15.55

15.17

15.40

15.41

15.45

15.67

15.66

15.65

10.88

10.89

13.10

12.97

13.09

13.

(33/6)

2.

N

6.

N

8.ACHTUNGTRENNUNG(90/3)

13.14

12.99

12.30

13.

12.25/6

12.32

12.19

12.02

–

2.47

6.35

6.34

6.42

8.83

8.77

8.41

(76/90)

2.

N

6.

N

9.ACHTUNGTRENNUNG(21/9)

2.47

2.50

2.49

6.11

6.05

6.25

6.24

6.17

8.37

8.39

8.35

8.23

8.82

8.84

8.80

8.67

P₃-Bz_y(X)

7.

(07/10)

15.

E

5.

(37/8)

7.

N

6.

N

8.ACHTUNGTRENNUNG(75/6)

tier p-MOs of P. The effect of adding fused rings onto the

periphery of the porphyrin ligand can be readily understood

with reference to the effect of symmetry-lowering structural

perturbations on the relative energies of four key frontier p-

MOs that are primarily associated with the 16-atom 18p-

electron cyclic polyene on the inner ligand perimeter. The

perimeter-model approach often enables accurate predic-

tions to be made about key aspects of the electronic struc-

ture and optical spectroscopic properties, based on a qualita-

tive consideration of the alignment of the nodal planes of

the four frontier p-MOs. In the context of 4N+2 p-electron

systems, the HOMO level has 2N nodal planes, whilst the

Figure 5. Structures of 5,10,15,20-tetraphenyldibenzo

ACHTUNGERTN[NUNG b,l]-21,23-dithiapor-

phyrin (2Bz_y) and 5,10,15,20-tetraphenyldibenzo[g,q]-21,23-dithiapor-

AHCTUNGTRENNUNG

phyrin (2Bz_x), which are core-modified tetrabenzoporphyrins with N₂S₂

structures. The pathway of the dominant ring current, which was ob-

served by NMR spectroscopic analysis, is shown in bold.^[15]The core-

modified tetraphenyldiphenanthroporphyrins reported herein have struc-

tures that are similar to that of 2Bz_x(with the exception of P₁-Bz and P₃-

Bz).

LUMO level has 2ACHTUNTRGNEUNG(N+1), thereby effectively forming either

an octagon or a decagon on the 16-atom inner perimeter

(Figure 7). Under the D_2hsymmetry of porphyrin com-

pounds, the alignment of the 2N nodal planes of the

HOMO level is defined (for symmetry reasons) by the

mirror planes that run through the pyrrole nitrogen atoms.

The alignment of the y axis through the protonated set of

the differing effects of fused-ring expansion with acenaph-

thalene, phenanthrene, and benzene rings on the four fron-

Chem. Eur. J. 2012, 18, 16844 – 16867

ꢁ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

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16849

K. Rurack, N. Kobayashi, Z. Shen et al.

Figure 7. In the context of Michlꢂs perimeter model,^[30]the nodal proper-

ties of the frontier p-MOs on the inner perimeter of the porphyrinoid lig-

2ꢁ

N

nodal planes of the MOs which are associated with the HOMO of the

4N+2 (N=4) parent perimeter form octagonal patterns on the perimeter

because there are planes running through alternating sets of atoms. In

contrast, the 2ACTHNUGTRNEUNG(N+1) nodal planes of the LUMO-level MOs form a deca-

gon in which the planes (with the exception of those lying on either the x

or y axis) do not coincide with the atomic positions. When there is a sym-

metry-lowering structural perturbation, such as fused-ring expansion or

core modification, the nodal patterns are determined by the alignment of

the yz plane of symmetry. In this context, Michl introduced “a”, “s”,

“ꢁa”, and “ꢁs” nomenclature to describe the four frontier p-MOs, based

on whether there is a nodal plane (a and ꢁa) or an antinode (s and ꢁs),

corresponding to the M_L=0 in Figure 4. Once the alignment of the nodal

planes has been clearly defined, the effect of different structural pertur-

bations can be readily conceptualized on a qualitative basis through a

consideration of the relative size of the MO coefficients on each atom on

the perimeter.

perimeter and are referred to as the “a” and “s” MOs, re-

spectively, on this basis, in the context of Michlꢂs perimeter

model (Figure 7). In both of these MOs, eight atoms of the

inner perimeter either lie on or very close to nodal planes,

whilst the other eight lie on or very close to antinodes, with

the phase sign changing as each nodal plane is crossed; thus

the nodal patterns of the “a” and “s” MOs are radially sym-

metric. The 1b_2g* and 1b_3g* MOs are referred to as the “ꢁa”

and “ꢁs” MOs, because there is, respectively, a nodal plane

and an antinode on the pyrrole nitrogen atom on the y axis,

which is regarded as the M_L=0 MO. The “a” and “s” MOs

do not have radial symmetry because a decagon (rather

than an octagon) is formed by the nodal planes on the 16-

atom perimeter. Thus the twelve atoms that do not lie on

the x and y axes no longer lie on a nodal plane or an anti-

node.

Once the alignment of the nodal planes on the inner

ligand perimeter in each of the four frontier p-MOs has

been defined, it becomes easy to determine the effect of var-

ious structural perturbations on the energy of the MOs. In

the context of porphyrin compounds, the “a” and “s” MOs

remain (accidentally) almost degenerate. The net stabilizing

effect on the “s” MO, due to the increased electronegativity

of the four pyrrole nitrogen atoms at the nodes of the “a”

MO is matched by the stabilizing effect on the “a” MO of

adding the four peripheral C₂H₂bridges at nodes of the “s”

MO (Figure 6), based on a strong bonding interaction be-

tween the “a” MO of the inner ligand perimeter and what

can be viewed as four antibonding ethylene MOs. Michl^[30]

has demonstrated that the effect on the MO energies of in-

troducing bridging atoms is primarily determined by the size

and sign of the relative phase of the MO coefficients on the

perimeter atom on which the bridge is attached and on the

Figure 6. Center: MO energies of the frontier p-MOs of P, TPP, TBP,

TPTBP, TANP, TPTANP, TPhenP (TPhen), and TPTPhenP (TPTP)

that were obtained from TD-DFT calculations with the B3LYP function-

al by using 6–31G(d) basis sets. The “a” and “ꢁa” MOs with nodal

planes on the protonated pyrrole nitrogen atoms (1a_uand 1b_2g*) are de-

noted by gray squares, whilst the “s” and “ꢁs” MOs (1b_1uand 1b_3g*),

with significant MO coefficients on these atoms, are denoted by black di-

amonds. The nodal patterns (top), arranged in an ascending order, of the

“a”, “s”, “ꢁa”, and “ꢁs” MOs of P, TBP, TANP, and TPhenP are at an

isosurface of 0.01. The average HOMO–LUMO band gap values, which

take into account all four MOs that are derived from the HOMO and

LUMO of the parent perimeter, are denoted by small dark-gray triangles

plotted against a secondary axis (center). The observed trends closely

mirror those in the observed (large light-gray diamonds) and calculated

energies (small black diamonds) of the Q and B bands (bottom).

pyrrole nitrogen atoms is used to define the identity of the

MO with M_L=0 (Figure 7). The 1a_1uand 1a_2uMOs have

nodes and antinodes at these positions on the inner ligand

16850

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Chem. Eur. J. 2012, 18, 16844 – 16867

Core-Modified Fused-Ring-Expanded Porphyrins

FULL PAPER

first atom of the bridge, because this result determines

whether there is a stabilizing bonding interaction or a desta-

bilizing antibonding interaction. When the bridges consist of

an even number of atoms, the four frontier p-MOs of the

parent perimeter will usually still be the HOMOꢁ1,

HOMO, LUMO, and LUMO+1 of the expanded p-sys-

tem.^[30c]In the case of metal complexes, symmetry considera-

tions dictate that the “ꢁa” and “ꢁs” MOs remain degener-

ate, because only the degeneracy of the M_L= ꢀ2, ꢀ4, and

ꢀ6 MOs is lifted on moving from D_16hto D_4hsymmetry

(Figure 6). However, in the context of free-base compounds,

the introduction of protonated pyrrole nitrogen atoms along

the y axis results in a slight increase in the degeneracy of

the LUMO level. In the “ꢁa” and “ꢁs” MOs, the differing

interactions with the peripheral ethylene bridges along the x

and y axes are broadly similar and only differ in their rela-

tive orientation; thus, a minor lifting of the degeneracy of

the LUMO is anticipated based on the relative size of the

MO coefficients on the protonated and nonprotonated pyr-

role nitrogen atoms.

bonding interactions between the b-carbon atoms of the pyr-

role moieties of P and the two carbon atoms of the periph-

eral C₁₀H₆bridging units to which they are attached; howev-

er, this destabilization is relatively minor in magnitude, be-

cause the MO coefficients on the fused acenaphthalene

rings are relatively low. In contrast, there is a marked stabi-

lization of the “ꢁa” and “ꢁs” MOs because there are strong

bonding interactions along the y and x axes, respectively,

which involve relatively large MO coefficients. Therefore,

the DHOMO value of TANP is significantly lower than that

predicted for TBP and there is a markedly narrower

HOMO–LUMO band gap. This result accounts for the un-

usually large shift of the Q and B bands reported by Lash

and others,^[10a,b]which results in an unusually large redshift

of the B band and spectroscopic properties, which, in other

regards, are broadly similar to those of the parent porphyrin

compound, because DHOMOꢂDLUMOꢂ0. A similar pat-

tern is observed when fused phenanthrenes are added to

form tetraphenanthroporphyrin (TPhenP), but the stabiliza-

tion of the “ꢁa” and “ꢁs” MOs is not as large as that ob-

served for TANP and, therefore, a larger HOMO–LUMO

band gap is predicted. When phenyl substituents are added

at the meso-carbon atoms to form tetraphenyltetrabenzopor-

phyrin (TPTBP), TPTANP, and TPTPhenP, there is a desta-

bilization of the “s” MO, due to the large coefficients on

these atoms. This typically results in a decrease in both the

DHOMO value and in the intensity of the Q band, as well

as a redshift of both the Q and B bands. No significant de-

stabilization of the “a” MO is anticipated, because the

meso-carbon atoms lie on nodal planes. In the context of

TPTANP, the destabilization of the “s” MO results in a soft

MCD chromophore with DHOMOꢂDLUMOꢂ0. Howev-

er, a larger DHOMO value is predicted in the context of

TPTPhenPs, because increased steric hindrance rotates the

phenyl groups almost into the plane of the inner perimeter

of the p system. This results in a more-pronounced redshift

and a higher intensity of the Q band than is observed with

TPTANPs.^[14]

Fused-ring expansion with benzene rings: When fused ben-

zene rings are added onto the porphyrin ligand in a radially

symmetric manner to form tetrabenzoporphyrin (TBP),

there is an antibonding interaction between the “a” MO and

the C₄H₄bridge at all eight positions of attachment, thereby

resulting in a marked destabilization of the MO energy

(Figure 6). In contrast, there is a slight stabilization of the

“s” MO, due to a weak bonding interaction. The energies of

the “ꢁa” and “ꢁs” MOs of the free-base TBP remain large-

ly unchanged, because the stabilizing interaction that is in-

troduced along one axis is balanced by the destabilizing in-

teraction along the other, so that the low DLUMO value of

P is retained. The marked destabilization of the “a” MO

leads to a narrowing of the HOMO–LUMO band gap and

the introduction of a significant DHOMO value, so there is

a redshift and intensification of the Q band. Only a relative-

ly minor redshift of the B band is observed, due to an in-

creased interaction between the B and higher-energy pp*

states.^[14]Marked differences are observed in the optical

spectroscopic properties of 2Bz_xand 2Bz_y,^[15]because there

is no longer a balancing of the stabilizing and debstabilizing

effects when peripheral-fused rings are only added along

one axis. In the context of 2Bz_x, the stabilizing effect of

benzo substitution along the x axis on the “ꢁa” MO is simi-

lar to that of a stabilizing effect on the “ꢁs” MO, due to

core modification, so there is a relatively low DLUMO

value. In contrast, the DLUMO value increases markedly in

the context of 2Bz_y, in which benzo substitution results in a

stabilization of the “ꢁs” MO.

B3LYP geometry optimizations and MO energies: The pre-

dicted B3LYP-optimized geometries for P, TPP, TPhenP,

TPTPhenP, N₂O₂, N₂S₂, N₂Se₂, N₂Te₂, P₁, P₁-Bz_y, P₃, and P₃-

Bz_yare shown in Figure 1, along with the non-core-modified

tetraphenyldiphenanthroporphyrin (2Phen_xN₄) parent com-

pound for the N₂O₂, N₂S₂, N₂Se₂, and N₂Te₂series. Peripher-

al substitution with fused phenanthrene and acenaphthalene

ring systems results in severe saddling of the tetraphenylpor-

phyrins due to steric hindrance with the meso-aryl substitu-

ents.^[10,14–16]In the case of TPTPhenP, this results in a fixed

C_2v(z,s_xz,s_yz) geometry because the phenyl groups can no

longer freely rotate. When the protonated pyrroles are re-

placed by Group 16 atoms, by introducing furan, thiophene,

selenophene, or tellurophene moieties along the y axis, the

structures remain highly nonplanar but the saddling distor-

tion of the p system steadily diminishes as the heteroatoms

become progressively larger on going from O to S and then

to Se and Te to form N₂O₂, N₂S₂, N₂Se₂and N₂Te₂(Table 1).

Fused-ring expansion with acenaphthalene and phenanthrene

rings: The radially symmetric fused-ring expansion of P with

acenaphthalene moieties to form tetraacenaphthoporphyrin

(TANP) has a markedly different effect on the relative ener-

gies of the four frontier p-MOs. A destabilization of both

the “a” and “s” MOs is anticipated, because there are anti-

Chem. Eur. J. 2012, 18, 16844 – 16867

ꢁ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

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16851

K. Rurack, N. Kobayashi, Z. Shen et al.

Figure 8. Top: MO energies of free-base P, TPP, TPhenP, TPTPhenP (TPTP), 2Phen_xN₄(N₄), N₂S₂-OMe, N₂Se₂-NMe₂, N₂Te₂, N₂S₂-F, P₁, P₁-Bz_y, P₃, and

P₃-Bz_yusing 6–31G(d) basis sets; 3–21G** basis sets were used for N₂Te₂. Occupied MOs are denoted by small squares. The four key frontier p-MOs de-

2ꢁ

rived from the HOMO and LUMO of the C₁₆H₁₆parent hydrocarbon perimeter, which are used to calculate the DHOMO and DLUMO values in the

context of Michlꢂs perimeter model^[30](Figure 4), are highlighted by thicker dark-gray lines, whilst lighter-gray lines are used to highlight MOs derived

from the MOs of P, which were primarily associated with the inner perimeter of the p system (see the Supporting Information, Table S5). The “a” and

“ꢁa” MOs, which have nodal planes on the Group 16 heteroatoms (1a₂and 1b₁*), are denoted by light-gray circles (Figure 3), whilst the “s” and “ꢁs”

MOs, which have significant MO coefficients (1a₁and 1b₂*), are denoted by black triangles. MOs associated with the NMe₂para-substituents of N₂Se₂-

NMe₂, are offset to the right. The average HOMO–LUMO band gap values based on the energies of the “a”, “s”, “ꢁa”, and “ꢁs” MOs (small dark-gray

diamonds) are plotted against a secondary ordinate. The trends observed in this data series closely mirror those in the observed (large light-gray dia-

monds) and calculated energies (small black diamonds) of the Q and B bands (bottom). Experimental values for the N₂Y₂-OC₁₆H₃₃compounds are plot-

ted against the calculated values for their N₂Y₂-OMe counterparts.

There is no two-fold axis of symmetry in the optimized

structures of N₂Se₂and N₂Te₂. One of the selenophene or

tellurophene moieties tilts out of the saddled structure that

is formed by the rest of the p system, due to a marked in-

higher energy (450–600 nm) can be readily assigned to Q

and B transitions, respectively, on the basis of TD-DFT cal-

culations (Table 2) and the presence of coupled pairs of x-

and y-polarized and oppositely-signed b₀terms in the MCD

spectra. Although the B band region of each spectrum is

ꢁ

crease in the length of the C Se and C Te bonds. However,

the two-fold axis of symmetry is retained in the X-ray struc-

ture of N₂Se₂and also when the structure is optimized by

using the 3–21G** rather than the 6–31G(d) basis sets

(Figure 1 and the Supporting Information, Figure S1).

domACTHNUTRGENiNUG nated by an intense close-lying pair of b₀terms

(Figure 9 and Figure 11), the effects of incorporating fused

phenanthrenes along the y axis on the energies of the

weaker Q₀₀bands would be very challenging in the absence

of MCD data, due to the presence of relatively intense en-

velopes of vibrational bands (Figure 9). Widely separated

and almost-forbidden b₀terms are also observed in the

MCD spectra of 2Bz_xand free-base TPP for the Q₀₀bands,

along with intense pseudo-a₁terms in the B band region.^[15]

In both cases, their optical properties remain close to what

would be anticipated for a D_18h-symmetric C₁₈H₁₈parent pe-

rimeter and their major spectroscopic bands are broadly

Validation of the DFT and TD-DFT results by using MCD

spectroscopy: The MO energies of the core-modified com-

pounds can be readily compared to those of P, TPP,

TPTPhenP, and the 2Phen_xN₄model compound (Figure 8).

Trends in the UV/Vis-absorption and MCD spectra can, in

turn, be compared to the results of TD-DFT calculations

and to changes in the DHOMO and DLUMO values (Fig-

ures 9–11 and the Supporting Information, Figures S5 and

S6). The optical spectra of N₂O₂, N₂S₂, N₂Se₂, and N₂Te₂are

broadly similar (Figure 9). A weaker set of bands at lower

energy (600–1000 nm) and a more-intense set of bands at

similar to the

L

and B bands of benzene.^[14]When

DHOMOꢂDLUMO, the m⁺contribution to the Q and B ex-

cited states is eliminated and the Q₀₀bands remain forbid-

den because the ease of circulation of the excited electron

16852

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Chem. Eur. J. 2012, 18, 16844 – 16867

Core-Modified Fused-Ring-Expanded Porphyrins

FULL PAPER

nitrogen atom and the heteroa-

tom and the effect of changing

the resonance integral between

the heteroatom and the neigh-

boring a-carbon atoms can

modify the relative energies of

the four frontier p-MOs to a

limited

extent.

However,

almost no difference is predict-

ed between the DHOMO and

DLUMO values of N₂O₂, N₂S₂,

N₂Se₂, and N₂Te₂relative to

the 2Phen_xN₄model com-

pound (Figure 10A), and simi-

lar trends are predicted when

TPP, 2Bz_x, 2Bz_y, TBP, and

TPTBP are core-modified with

sulfur atoms (Figure 10B). As

is the case with 2Bz_x,^[15]

B3LYP calculations predict

that

DLUMO values of the core-

modified diphenanthropor-

the

DHOMO

and

Figure 9. Observed electronic-absorption (left) and MCD spectra (right) of N₂O₂-OC₁₆H₃₃, N₂S₂-OC₁₆H₃₃,

N₂Se₂-OC₁₆H₃₃, and N₂Te₂, as well as their calculated TD-DFT (light-gray triangles) oscillator strengths (right

axis) of N₂O₂, N₂S₂, N₂Se₂, and N₂Te₂. The Q and B bands, which are primarily associated with the four frontier

p-MOs, are indicated by large dark-gray diamonds. For details of the most intense bands, see the Supporting

Information, Table S4.

phyrins are relatively similar,

but the reasons for this differ.

In the context of the N₂Y₂

compounds, the “s” MO is the

HOMO, due to the effect of

ligand saddling on the level of

in the LUMO and that of the hole that is left in the HOMO

are roughly comparable, as is the case in the parent hydro-

carbon perimeter. The p systems of 2Bz_xand free-base TPP

are referred to as “soft MCD chromophores” in the context

of Michlꢂs perimeter model because minor structural

changes can reverse the alignment of the excited-state mag-

netic moments of the induced magnetic dipoles of the Q

and B excited states and, hence, the observed sequence of

signs in the MCD spectrum (Figure 10 and Figure 11).

Key trends in the optical properties of porphyrinoids can

be rationalized by using Michlꢂs perimeter model, based on

how different types of structural modification affect the rel-

ative magnitudes of the DHOMO and DLUMO (Figure 10).

We recently demonstrated that sign sequences observed

forthe sequence of signs of the b₀terms that are associated

with the Q and B bands of core-modified tetrabenzopor-

phyrinoids can be accurately predicted based on the

DHOMO and DLUMO values derived from the MO ener-

gies predicted in B3LYP geometry optimizations and, more-

over, that the sign sequences can be used to confirm the ac-

curacy of the DFT description of the electronic structures.^[15]

Replacing the protonated pyrrole groups at the 21 and 23

positions with a Group 16 heteroatom would not normally

be expected to have a major effect on the OAM properties

of the frontier p-MOs, because a lone pair of electrons in

the p_zatomic orbital of one of the four core heteroatoms is

directly replaced by another. Michl^[30]has demonstrated that

the difference in electronegativity between the protonated

interaction between the phenyl groups and the meso carbon

atoms. A much-larger destabilization of the “s” MO is pre-

dicted in the context of TBP, TANP, and TPhenP upon

phenACTHUNRTGNEUNGylation than for P, due to the steric hindrance between

the p system and the meso substituents (Figure 10C). How-

ever, in the context of P₃-Bz_y, the “a” MO is the HOMO,

due to the antibonding interaction between the p system of

the porphyrin core and the peripheral C₄H₄bridges

(Figure 6). In this context, partial benzo substitution results

in a stabilization of the “a” MO relative to TBP (Figure 8).

The DHOMO values of the N₂Y₂compounds decrease rela-

tive to TPTPhenP (Figure 10A) because there is a lower

degree of saddling due to the removal of the two phenan-

threnes that are aligned along the y axis, and this leads to a

slight stabilization of the “s” MO (Figure 8). A significant

DLUMO value is introduced in the context of the N₂Y₂

compounds when the stabilizing and destabilizing interac-

tions with the “ꢁs” and “ꢁa” MOs along the y axis in the

context of TPTPhenP are removed (Figure 6). With the ex-

ception of P₃and N₂S₂-F, in which DHOMOꢂDLUMO

(Figure 10A,D), and N₂Te₂, in which a marked deviation

from the C_2vgeometry is predicted (Figure 1), the sign se-

quences of the MCD bands predicted based on the B3LYP-

optimized structures matches those observed experimentally

(Table 2). Therefore, the DFT-based descriptions of the elec-

tronic structures (Table 2 and the Supporting Information,

Table S5) are validated by the application of Michlꢂs perime-

ter model and the predicted trends can be used for the ra-

Chem. Eur. J. 2012, 18, 16844 – 16867

ꢁ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

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16853

K. Rurack, N. Kobayashi, Z. Shen et al.

Table 2. Trends in the predicted MO energies [eV] in the TD-DFT calculations of C₁₆H₁₆^2ꢁ, P, TPP, TPhenP, TPTPhenP, 2Phen_xN₄, N₂O₂, N₂O₂-OMe, N₂S₂,

N₂S₂-OMe, N₂S₂-F, N₂Se₂, N₂Se₂-OMe, N₂Se₂-NMe₂, N₂Te₂, P₁-Bz_y, and P₃-Bz_y, the trans and cis isomers of P₁and P₃, and the X-ray structures (X) of P₃-Bz_yand

N₂Se₂-NMe₂(see the Supporting Information, Figure S1) and in the energies and signs of the Q bands based on B3LYP-geometry optimization and TD-DFT cal-

culations with the 6–31G(d) basis sets unless otherwise stated.

[c]

[f]

[g]

ꢁs^[a]

ꢁa^[a]

s^[a]

a^[a]

DL^[b]DH^[b]jDLjꢁjDHj

Sign^[d]HꢁL^[e]av

ACHTUNGTRENNUNG

2ꢁ

C₁₆H₁₆

P

1e_4ux+5.87 1e_4uy+5.87 1e_5gx+2.80 1e_5gy+2.80

1b_3g* ꢁ2.22 1b_2g* ꢁ2.23 1b_1uꢁ5.15 1a_uꢁ5.30

0.00

0.01

0.00

0.15 ꢁ0.14

0.00

ꢁ/+

3.07

2.92

3.07

3.00

–

ꢁ/+

2.01, 3.02, ꢁ/+

2.37 3.14

TPP

2a*

ꢁ2.19 1a*

ꢁ2.20 1a

ꢁ4.91 2a

ꢁ5.20

0.01

0.29 ꢁ0.28

ꢁ/+

2.71

2.86

1.94, 2.95, ꢁ/+

2.29 3.01

TPhenP

TPTPhenP

1b_3g* ꢁ2.46 1b_2g* ꢁ2.40 1b_1uꢁ5.18 1a_uꢁ4.98 ꢁ0.06 ꢁ0.20 ꢁ0.14

ꢁ/+

2.52

1.89

2.65

2.21

–

1b₂* ꢁ2.58 1b₁* ꢁ2.52 1a₁ꢁ4.47 1a₂ꢁ5.05 ꢁ0.06

0.58 ꢁ0.52

0.33 ꢁ0.02

1.54, 2.12, ꢁ/+

1.60 2.19

2Phen_xN₄

N₂O₂

1b₂* ꢁ2.55 1b₁* ꢁ2.24 1a₁ꢁ4.70 1a₂ꢁ5.03 ꢁ0.31

1b₂* ꢁ2.67 1b₁* ꢁ2.34 1a₁ꢁ4.69 1a₂ꢁ5.02 ꢁ0.33

1b₂* ꢁ2.48 1b₁* ꢁ2.12 1a₁ꢁ4.39 1a₂ꢁ4.85 ꢁ0.36

ꢁ/+

2.15

2.02

2.47

2.35

2.31

–

0.33

0.46 ꢁ0.10

0.00

N₂O₂-OMe^[h]

1.39, 2.36, ꢁ/+

2.06 2.50

N₂S₂

1b₂* ꢁ2.70 1b₁* ꢁ2.40 1a₁ꢁ4.78 1a₂ꢁ5.15 ꢁ0.30

1b₂* ꢁ2.53 1b₁* ꢁ2.19 1a₁ꢁ4.48 1a₂ꢁ4.98 ꢁ0.33

0.37 ꢁ0.07

0.51 ꢁ0.18

ꢁ/+

2.08

1.95

2.42

2.37

–

N₂S₂-OMe^[h]

1.43, 2.36, ꢁ/+

1.93 2.49

N₂Se₂

1a’* ꢁ2.75 1a“* ꢁ2.43 1a’

ꢁ4.78 1a” ꢁ5.14 ꢁ0.32

0.36 ꢁ0.04

0.51 ꢁ0.17

ꢁ/+

2.03

1.95

2.37

2.35

–

N₂Se₂-OMe^[h]

1b₂* ꢁ2.54 1b₁* ꢁ2.20 1a₁ꢁ4.47 1a₂ꢁ4.98 ꢁ0.34

1b₂* ꢁ2.25 1b₁* ꢁ1.89 1a₁ꢁ4.03 1a₂ꢁ4.69 ꢁ0.36

1.44, 2.29, ꢁ/+

1.88 2.43

N₂Se₂-NMe₂

0.63 ꢁ0.37

ꢁ/+

+/ꢁ

ꢁ/+

+/ꢁ

ꢁ/+

+/ꢁ

1.78

1.34

1.85

2.06

1.89

1.90

1.89

1.87

2.13

2.15

2.11

2.01

2.04

2.29

2.22

2.14

2.40

2.27

2.24

2.41

2.42

2.40

2.38

2.45

1.38, 2.23, ꢁ/+

1.80 2.35

N₂Se₂-NMe₂(X) 1b₂* ꢁ2.58 1b₁* ꢁ1.44 1a₁ꢁ3.92 1a₂ꢁ4.50 ꢁ1.14

N₂Te₂(3–21G**) 1a’* ꢁ2.86 1a“* ꢁ2.71 1a’ ꢁ4.71 1a” ꢁ5.14 ꢁ0.15

1b₂* ꢁ2.86 1b₁* ꢁ2.57 1a₁ꢁ4.92 1a₂ꢁ5.31 ꢁ0.29

1a’* ꢁ2.70 1a“* ꢁ2.56 1a’ ꢁ4.59 1a” ꢁ5.21 ꢁ0.14

0.58

0.56

1.38, 2.23, ꢁ/+

1.80 2.35

0.43 ꢁ0.28

0.39 ꢁ0.10

0.62 ꢁ0.48

0.61 ꢁ0.48

0.62 ꢁ0.48

1.29, 2.19, +/+

1.85 2.47

N₂S₂-F

1.55, 2.38, +/ꢁ

2.01 2.52

P₁-trans

P₁-cis-sp²

P₁-cis-sp³

P₁-Bz_y

1.46, 2.27, ꢁ/+

1.86 2.39

1b₂* ꢁ2.68 1b₁* ꢁ2.55 1a₁ꢁ4.58 1a₂ꢁ5.19 ꢁ0.13

1b₂* ꢁ2.71 1b₁* ꢁ2.57 1a₁ꢁ4.60 1a₂ꢁ5.22 ꢁ0.14

1b₂* ꢁ2.95 1b₁* ꢁ2.42 1a₁ꢁ4.82 1a₂ꢁ5.03 ꢁ0.53

1.46, 2.27, ꢁ/+

1.86 2.39

1.46, 2.27, ꢁ/+

1.86 2.39

0.21

0.31

1.44, 2.30, +/ꢁ

1.75 2.50

P₃-trans

P₃-cis-sp²

P₃-cis-sp³

P₃-Bz_y

1a’* ꢁ2.71 1a“* ꢁ2.47 1a’

ꢁ4.84 1a” ꢁ5.16 ꢁ0.24

0.32 ꢁ0.08

0.30 ꢁ0.06

0.34 ꢁ0.10

1.60, 2.45, +/ꢁ

1.75 2.56

1b₂* ꢁ2.70 1b₁* ꢁ2.46 1a₁ꢁ4.85 1a₂ꢁ5.15 ꢁ0.24

1b₂* ꢁ2.72 1b₁* ꢁ2.48 1a₁ꢁ4.83 1a₂ꢁ5.17 ꢁ0.24

1.60, 2.45, +/ꢁ

1.75 2.56

1.60, 2.45, +/ꢁ

1.75 2.56

1b₂* ꢁ2.96 1b₁* ꢁ2.36 1a₁ꢁ5.10 1a₂ꢁ4.97 ꢁ0.60 ꢁ0.13

2a* ꢁ2.31 1a ꢁ5.17 2a ꢁ4.98 ꢁ0.63 ꢁ0.19

ꢁ2.94 1a*

0.47

0.44

1.56, 2.35, +/ꢁ

1.67 2.42

P₃-Bz_y(X)

1.56, 2.35, +/ꢁ

1.67 2.42

[a] MO energies and symmetries of the four key frontier p-MOs derived from the HOMO and LUMO of the parent hydrocarbon perimeter. Michlꢂs “a”, “s”,

“ꢁa”, and “ꢁs” terminology is used, based on the presence of nodal planes (a, ꢁa) or large MO coefficients (s, ꢁs) on the pyrrole nitrogen atoms on the y axis

(Figure 3). [b] DLUMO (DL) and DHOMO (DH) values [eV], based on DH=sꢁa and DL=ꢁsꢁꢁa. [c] Difference between the DLUMO and DHOMO values

(jDLjꢁjDHj). [d] The predicted MCD band sign sequences. [e] HOMO–LUMO band gap (HꢁL) and the average HOMO–LUMO band gap (av(HꢁL)), which

G

takes into account all four frontier p-MOs, based on the TD-DFT calculations. [f] Average energies of the Q and B bands (Q_obs, B_obs), based on the energies of

the coupled Faraday b₀terms in the MCD spectra. [g] Observed sequences of MCD signs, in ascending energy. [h] Observed values are for the corresponding 4-

hexadecyloxy compounds.

tional design of ligands for use in practical applications. In

contrast, predictions that are made based on the MO ener-

gies predicted by using ZINDO/s calculations are more

problematic (see the Supporting Information, Table S6).

better utilized in various applications. The key to achieving

this shift is using different types of structural perturbation to

narrow the HOMO–LUMO band gap, such as core modifi-

cation with chalcogens, the inductive and mesomeric sub-

stituent effects of para substituents on the aryl groups, and

the introduction of fused benzene rings along the y axis. The

effect of forming diphenanthroporphyrins with fused-ring

moieties that are oriented along the x axis must first be

Effect of structural perturbation on the optical spectroscopy

data: A key goal of recent porphyrinoid research has been

to shift the Q band into the near-IR region, where it can be

16854

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Chem. Eur. J. 2012, 18, 16844 – 16867

Core-Modified Fused-Ring-Expanded Porphyrins

FULL PAPER

cients on the two heteroatoms that would replace the proto-

nated pyrrole-nitrogen atoms (Figure 6 and the Supporting

Information, Figure S3). The saddling of the ligand and the

incorporation of aryl groups to form the 2Phen_xN₄model

compound results in an “a”, “s”, “ꢁs”, “ꢁa” ordering be-

cause there is a marked destabilization of the “s” MO, due

to the large MO coefficients on the meso-carbon atoms

(Figure 6 and the Supporting Information, Figure S3). This

leads to a decrease in the average HOMO–LUMO band

gap (Table 2), in which the energies of “a”, “s”, “ꢁa”, and

“ꢁs” are all taken into consideration, because almost-equal

contributions of one-electron transitions between all four

frontier p-MOs contribute to the Q and B excited states of

TPP in the context of Goutermanꢂs 4-orbital model^[31]

(Table 2 and the Supporting Information, Figures S4 and

S7).

Core modification to form N₂Y₂structures: A further nar-

rowing of the average HOMO–LUMO band gap is predict-

ed upon core modification with chalcogens (Figure 8), pri-

marily based on a slight relative destabilization of the “s”

MO. Core modification results in a redshift of the lowest-

energy Q and B bands on moving from N₂S₂-OC₁₆H₃₃to

N₂Se₂-OC₁₆H₃₃and then to N₂Te₂, as well as on moving from

N₂S₂-OC₁₆H₃₃to N₂O₂-OC₁₆H₃₃, which results in band cen-

ters that lie to the red side of the corresponding band in the

spectrum of TPTPhenP (Figure 9). Although only relatively

minor changes in the DHOMO and DLUMO values are pre-

dicted when Group 16 heteroatoms are incorporated along

the y axis to form N₂O₂, N₂S₂, N₂Se₂, and N₂Te₂(Fig-

ure 10A), the absorption spectra of N₂O₂and N₂Te₂are

markedly different from those of N₂S₂and N₂Se₂and the

bands in the UV region increase in intensity relative to the

Q and B bands. This increase is probably due to the effect

of changes in the degree of saddling of the phenanthrene

moieties and, where N₂Te₂is concerned, the effect on the vi-

brational bands of tilting one of the tellurophene moieties

out of the saddled C_2v(z,s_xz,s_yz) symmetry structure

(Figure 1 and Table 1). The Q₀₀bands of N₂O₂, N₂S₂, N₂Se₂,

and N₂Te₂are relatively weak. The higher-energy Q₀₀bands

appear as relatively intense positive b₀terms in the MCD

spectrum at 600–700 nm. The band center of the MCD peak

does not correspond with the main absorption band in this

region of the spectrum, which is consistent with the B3LYP

prediction that DHOMOꢂDLUMO for these compounds

(Figure 10A). When the Q₀₀bands are almost fully forbid-

den, vibrational bands tend to dominate the Q band region

of the porphyrinoid spectra.^[14,31]

Figure 10. A) The effect of structural perturbation on the DHOMO and

DLUMO values for N₂O₂(O₂), N₂S₂(S₂), N₂S₂-F (S₂-F), N₂Se₂

ACHTUNGTNER(NUGN Se₂),

N₂Se₂-NMe₂(S₂-NMe₂), N₂Te₂(Te₂), P, TPP, TPhenP, and TPTPhenP, as

A

ACHTUNGTRENNUNG

predicted by B3LYP-geometry optimizations; calculations that were car-

ried out by using the 6–31G(d) and 3–21G** basis sets are denoted by

black and gray diamonds, respectively. In the light-gray shaded areas, for

which DHOMO>DLUMO, a ꢁ/+ MCD sign sequence is anticipated^[30]

for the Q₀₀bands in ascending energy terms, whilst a +/ꢁ sign sequence

is anticipated in the unshaded areas, for which DLUMO>DHOMO.

B) Plots of TPP, TBP, and TPTBP, their corresponding core-modified

21,23-dithiaporphyrinoid structures (TPP_N₂S₂, TBP_N₂S₂, and

TPTBP_N₂S₂), 2Bz_xand 2Bz_y(Figure 5), and their non-core-modified

parent compounds (TP2Bz_xN₄and TP2Bz_yN₄), based on the B3LYP-op-

timized geometries with 6–31G(d) basis sets (top right). Black diamonds

and gray squares are used to denote non-core-modified and core-modi-

fied compounds, respectively. C) Plots of TBP, TPhenP, TANP, and P, as

well as their corresponding tetraphenyl compounds (TPTBP, TPTPhenP,

TPTANP, and TPP), by using different sets of black and gray symbols,

respectively. D) Plots of P₁, P₁-Bz_y, P₃, and P₃-Bz_ywith black and gray

symbols for the BCOD- and benzo-fused compounds, respectively.

taken into consideration. The “ꢁs” MOs of 2Phen_xN₄and

TPTPhenP are predicted to have similar energies, whereas,

in contrast, the “ꢁa” MO of 2Phen_xN₄is similar to that of

TPP, because peripheral-fused phenanthrene rings are only

present on the x axis (Figure 8). The decrease in ligand sad-

dling (Table 1) results in a marked stabilization of the “s”

MO relative to TPTPhenP. However, the energy of the “a”

MO is largely unaffected by the removal of the two periph-

eral-fused phenanthrenes, because there is neither a bonding

nor an antibonding interaction at the points where the fused

rings are attached to the p system of the porphyrin core

(Figure 6). If the p system were planar and did not contain

any substituents on the meso-carbon atoms, the core-modi-

fied diphenanthroporphyrins would be expected to have an

“s”, “a”, “ꢁs”, “ꢁa” ordering of the four frontier p-MOs, in

ascending energy, similar to that of TPhenP, based on the

stabilization of the “s” and “ꢁs” MOs, due to large coeffi-

One clear drawback of making use of a 2Phen_x-fused-ring

substitution pattern is that the Q₀₀bands of N₂O₂, N₂S₂,

N₂Se₂, and N₂Te₂have relatively weak intensities, because

DHOMOꢂDLUMO, which could potentially limit the use

of these compounds in applications that require strong ab-

sorbance in the NIR region. Therefore, further fine-tuning

of their electronic properties could be desirable, with the

key goals being to introduce a sufficient difference in the

magnitude of the DHOMO and DLUMO values so that the

Chem. Eur. J. 2012, 18, 16844 – 16867

ꢁ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.chemeurj.org

16855

K. Rurack, N. Kobayashi, Z. Shen et al.

Figure 11. Observed electronic-absorption and MCD spectra of N₂S₂-OC₁₆H₃₃and N₂S₂-F (left), N₂Se₂-OC₁₆H₃₃and N₂Se₂-NMe₂(right), and their calcu-

lated TD-DFT oscillator strengths (light-gray triangles, right axis). Trace amounts of triethylamine were added to the solutions of N₂Se₂-NMe₂and N₂S₂-

F to prevent protonation. The Q and B bands, which are primarily associated with the four frontier p-MOs, are indicated by large dark-gray diamonds.

For details of the most intense bands, see the Supporting Information, Table S4.

allowed and forbidden properties of the Q and B bands mix

substantially, whilst retaining a narrow HOMO–LUMO

band gap and, hence, markedly redshifted Q₀₀bands. Two

approaches have been explored in this regard: modifying

the para substituents on the aryl groups at the meso-carbon

positions, and the introduction of two fused benzene rings

along the y axis. In this latter context, ABAB structures are

formed with different types of fused rings along the x and

y axes. The structures of P₁and P₃were selected because ra-

dially symmetric fused-ring expansion with acenaphthalene

rings to form TPTANP is known to result in unusually large

redshifts of the Q and B bands relative to TPP, in a similar

manner to those observed with TPTPhenP.^[10a,b,16]The MO

energies predict that this shift is due to a marked stabiliza-

tion of the LUMO relative to the parent porphyrin and

analogous benzo-fused compound (Figure 6). Because the

nodal planes of the “ꢁa” and “ꢁs” MOs do not lie on alter-

nating sets of atoms, unlike those of the “a” and “s” MOs

(Figure 7), fused-ring expansion with different fused-ring

systems can have different effects on the relative energies of

the four frontier p-MOs, depending on whether they are

aligned with the x or y axes.

Inductive effects of the aryl substituents: It has long been

known that an intensification and redshift of the Q₀₀bands

of TPPs can be obtained by introducing substituents at the

para positions of the meso-phenyl rings. In the 1970s, Kadish

and Morrison^[32]demonstrated that the redox properties of

TPPs with electron-withdrawing para-substituents could be

adjusted in a predictable manner based on their Hammett

parameter values (Table 3), due to changes in the energies

of the HOMO and LUMO. We recently reported similar

trends in the spectra of TPTPhenPs with F, Cl, Br, I, CH₃,

NO₂, and NACHTNUGTRNEUNG(CH₃)₂groups at the para positions of the four

meso-phenyl substituents.^[16]Similar trends are observed

herein for the core-modified biphenanthroporphyrins. For

example, a stabilization is predicted for the MO energies of

N₂S₂-F relative to N₂S₂(Table 2), due to the electron-with-

drawing effects of the halogen substituents. Michl demon-

strated that the inductive effect of substituents should only

16856

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Chem. Eur. J. 2012, 18, 16844 – 16867

Core-Modified Fused-Ring-Expanded Porphyrins

FULL PAPER

Table 3. Hammett parameter (s_P) of the para-substituent,^[48]the first re-

duction (1st Red.) and the first and second oxidation (1st Ox., 2nd Ox.)

potentials [V] relative to the saturated calomel electrode, and the gap be-

tween the first oxidation and reduction potentials (DE_oꢁr) of the com-

pounds in CH₂Cl₂.

MOs are stabilized or destabilized to approximately the

same extent.^[30]Only minor shifts of the Q and B bands are

observed in the spectra of N₂S₂-OC₁₆H₃₃and N₂S₂-F, as well

as for the N₂O₂-X series (Figure 11 and Table 4), based on

substitution with halogen atoms and weakly electron-donat-

ing alkoxy groups.

[b]

s_P

1st Red.^[a]1st Ox.^[a]2nd Ox.^[a]DE_oꢁr

Q^[c]

TPTPhenP

N₂O₂-Br

N₂O₂-I

N₂O₂-Cl

N₂O₂-F

0.00

0.23

0.18

0.23

0.06

0.00

ꢁ0.17

ꢁ0.93

ꢁ0.60

ꢁ0.66

ꢁ0.60

ꢁ0.61

ꢁ0.64

ꢁ0.68

–

0.90

0.81

–

1.83

1.41

–

1.43

1.42

1.40

1.35

–

1.53

1.48

1.37

–

1.14

1.72

1.66

1.57

–

1.25

1.21

–

Mesomeric effects of the aryl substituents: As reported re-

cently in the context of para-substituted TPTPhenPs,^[16]

there is a strong mesomeric interaction between the NMe₂

substituents and the core of the p system when there is a

severe saddling of the p system, because the phenyl rings

are rotated into the plane of the inner-ligand perimeter due

to steric crowding. The predicted MO energies for N₂Se₂

and N₂Se₂-NMe₂(Figure 3) demonstrate that the incorpora-

tion of strongly electron-donating NMe₂groups has a more

significant effect on the relative energies of the key frontier

p-MOs on the inner-ligand perimeter than the inductive ef-

fects that are introduced by halogen atoms. Marked changes

in the wavelengths and intensities of the Q and B bands of

N₂Se₂-NMe₂and N₂Se₂-OC₁₆H₃₃compounds are observed

(Figure 10A, Figure 11, and Table 4). In contrast with the

Q bands of N₂S₂-F, which are almost fully forbidden because

DHOMOꢂDLUMO (Figure 11 and Table 2), there is a sig-

nificant intensification of the Q band region of N₂Se₂-NMe₂,

due to a mixing of the forbidden and allowed properties of

0.83

0.81

0.76

0.67

0.99

0.86

0.71

0.34

0.73

0.95

0.99

1.24

1.23

1.03

1.11

1.34

1.26

1.03

–

N₂O₂

–

N₂O₂-OMe

1.39

1.43

–

N₂S₂-OC₁₆H₃₃ꢁ0.17^[d]

N₂Se₂-Cl

N₂Se₂

0.23

0.00

ꢁ0.54

ꢁ0.62

–

N₂Se₂-OC₁₆H₃₃ꢁ0.17^[d]ꢁ0.66

1.44

1.38

1.29

1.60

1.56

N₂Se₂-NMe₂

N₂Te₂

ꢁ0.83

–

0.00

ꢁ0.41

ꢁ0.77

ꢁ0.67

1.21

1.39

1.25

P₃

P₃-Bz_y

0.06

[a] Peak potentials were determined by differential pulse voltammetry

(DPV). [b] Gap between the first oxidation and reduction potentials

(DE_oꢁr) in eV. [c] Observed energies of the lowest-energy Q₀₀bands, as

identified by MCD spectroscopy in eV. [d] Hammett parameter for

OCH₃rather than OC₁₆H₃₃.

have a minor effect on the HOMO–LUMO band gap and,

hence, on the optical properties, because the four frontier p-

Table 4. Absorption and emission data for N₂O₂, N₂S₂, N₂Se₂, N₂Te₂, and TPTPhenP, P₁-Bz_y, P₁, N₂Se₂-OMe, N₂Se₂-NMe₂, and N₂O₂-X (X=halogen) in

their free-base and protonated forms^[a](c=1 mm in CHCl₃, 298 K).

l_abs[nm] (loge^[b]/m^ꢁ1cm^ꢁ1

)

l_em

Dn˜_absꢁem

[cm^ꢁ1

F_f

ꢄ10³

t_f

k_f

[ꢄ10⁷s^ꢁ1

k_nr

[ꢄ10⁹s^ꢁ1

]

B bands

Q bands

[nm]

G

]

[ps]

E

]

U

N₂O₂

N₂O₂H₂

N₂S₂

N₂S₂H₂

N₂Se₂

N₂Se₂H₂

N₂Te₂

497 (4.92)

507 (4.98), 539 (4.87)

504 (4.75)

530 (4.67), 575 (4.70)

521 (4.98)

536 (4.80), 584 (4.88)

531 (4.72)

532 (4.77), 594 (4.89)

576 (4.92)

579 (5.04)

533 (5.18)

542 (5.08), 572 (5.08)

543 (5.32)

551 (5.31), 595 (5.43)

543 (4.99)

591

529 (5.04)

548 (4.89), 596 (4.85)

497 (4.80)

509 (4.94)

499 (4.82)

519 (4.90)

499 (4.91)

842 (3.73)

906

861

908

933

911

922

–

840

850

1.0

3.2

0.87

0.97

0.12

276

169

130

69

25

11

<3

380

420

61

68

54

57

24

<3

20

–

306

174

219

118

195

99

0.3

1.9

0.7

1.4

0.5

3.6

5.9

7.7

2+

802 (4.15)

812 (3.35)

859 (3.95)

820 (3.65)

858 (4.25)

918 (3.34)

900 (4.29)

794 (4.14)

803 (4.21)

861 (4.04)

735 (4.65), 849 (4.54)

712 (4.72), 866 (4.16)

688 (4.60), 760 (4.46), 896 (4.71)

910 (4.08)

875, 1140

843 (3.90)

1300

920

1220

810

–

2+

14.5

40.0

2+

G

(83)^[e]

–

N₂Te₂H₂

–

TPTPhenP^[b]

TPTPhenPH₂

P₁

831

838

942

918

986

966

–

560

520

1010

880

1350

810

–

1.5

1.9

0.7

1.6

0.5

1.1

–

2.6

2.4

16.4

14.7

18.5

17.5

–

2+[b]

8.0

0.40

1.1

0.27

2+

P₁H₂

P₁-Bz_y

P₁-Bz_yH₂

N₂Se₂-NMe₂

N₂Se₂-NMe₂H_n

N₂Se₂-OMe

N₂Se₂-OMeH₂

N₂O₂-F

N₂O₂-FH₂

N₂O₂-Cl

N₂O₂-ClH₂

2+

0.62

<0.1

<0.05

n+

–

940

1220

(0.05)^[e]

(0.3)^[e]

(50)^[e]

2+

[d]

763 (4.47), 934 (4.45)

851 (3.68)

804 (4.12)

854 (3.52)

809 (4.10)

(1025)^[d]

(900)^[d]

<0.05^[d]

0.70

3.1

–

915

865

913

873

913

874

913

884

820

880

760

910

770

930

730

970

0.2

1.8

0.5

1.8

0.5

1.9

3.3

5.7

4.6

8.5

4.6

8.5

2+

1.0

2.1

2+

N₂O₂-Br

N₂O₂-BrH₂

N₂O₂-I

N₂O₂-IH₂

853 (3.62)

0.95

1.9

2+

519 (4.96)

808 (4.15)

502 (4.63)^[c]

856 (3.51)^[c]

–

117

54

–

[f]

2+

525 (4.78)^[c]

814 (4.00)^[c]

0.84

1.6

18.5

[a] Protonation was carried out by adding 1% TFA (v/v) to the solution of the corresponding porphyrin in CHCl₃. [b] Taken from reference [16], except

for the lifetimes of the protonated species, which were determined herein. [c] Higher uncertainty for e (20%) because of low solubility. [d] The fluores-

cence band was too redshifted and too weak to be reliably determined. [e] High uncertainty of F_f(>30%) and high uncertainty of the photophysical

data due to weak fluorescence. [f] Could not be reliably determined because the compound decomposed in its free-base form over the long measurement

time that was required to record the weak, redshifted fluorescence.

Chem. Eur. J. 2012, 18, 16844 – 16867

ꢁ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.chemeurj.org

16857

K. Rurack, N. Kobayashi, Z. Shen et al.

tions between the fused-ring

moieties and the core porphy-

AHCTUNGTERGrNNUN in ligand at the points of at-

tachment. This interaction is

absent in the context of the

“ꢁa” MO of the N₂Y₂-core-

modified

biphenanthropor-

phyrins, because it would be

aligned with the y axis, which

is unsubstituted in this context

(Figure 1). This explains why

Figure 12. Nodal patterns of the four frontier p-MOs of N₂Se₂-NMe₂at an isosurface value of 0.015, which

demonstrate that the largest interactions between the aryl substituents and the four frontier p-MOs are pre-

dicted in the context of the “s” MO.

the Q and B bands. The observed spectroscopic properties

can be readily explained in qualitative terms using Michlꢂs

perimeter model based on the DHOMO and DLUMO

values predicted for the B3LYP-optimized geometry.

Marked differences in the DHOMO and DLUMO values

are anticipated because the NMe₂groups will have differing

effects based on the size of the MO coefficients at the para

positions of the phenyl rings and at the meso-carbon atoms.

The largest effect is anticipated for either the “a” or “s”

MO, based on mixing with close-lying occupied NMe₂MOs

of the same symmetry (Figure 8). Michlꢂs perimeter model

can be used to demonstrate that a greater destabilization is

expected for the “s” MO because there are large MO coeffi-

cients rather than nodal planes on the meso-carbon atoms at

which the aryl groups are attached (Figure 12). Because

DHOMOꢂDLUMO in the case of N₂Se₂, this destabiliza-

tion should lead to a larger DHOMO value, as is predicted

for the B3LYP-optimized geometry (Table 2). Therefore, a

ꢁ/+/ꢁ/+ sequence in the Faraday b₀terms is anticipated

with ascending energy, as observed experimentally

(Figure 11), along with an intensification of the Q₀₀bands,

due to the mixing of the forbidden and allowed properties

of the Q and B transitions that occurs when DHOMO>

DLUMO. However, the destabilization of the frontier p-

MOs leads to a marked decrease in the first oxidation po-

tential (Table 3), which could lead to issues with stability

that could potentially complicate their use in future applica-

tions. Ideally, the narrowing of the HOMO–LUMO band

gap would be achieved by a stabilization of the LUMO

rather than by a destabilization of the HOMO.

the “ꢁs” MO is consistently the LUMO in the context of

the N₂Y₂compounds (Figure 8). An examination of the

nodal patterns of the four frontier p-MOs of TBP (Figure 6)

makes it clear that benzo substitution along the y axis can

be expected to stabilize the “s” and “ꢁs” MOs and destabi-

lize the “a” and “ꢁa” MOs, based on whether there is a

bonding or antibonding interaction at the b-pyrrole carbon

atoms to which the benzo moieties are fused. The extra sta-

bilization of the “ꢁs” MO results in a significant increase in

the DLUMO values of P₁-Bz_yand P₃-Bz_yrelative to those of

P₁and P₃(Figure 13). The stabilization of the “s” MO and

destabilization of the “a” MO results in a lower DHOMO

value and a HOMO that lies at an energy comparable to

that of TPP (Figure 8), which results in a reversal of the ob-

served MCD-sign sequence of the Q and B bands of P₁-Bz_y

and P₃-Bz_y(Figure 13) and an intensification of the Q bands,

because there is a mixing of the forbidden and allowed

properties of the Q and B bands when DLUMO>DHOMO.

The redox properties of P₁-Bz_yand P₃-Bz_ycould enhance

the utility of these compounds in many applications. Al-

though the lower-energy Q band of P₁-Bz_yat 869 nm is sig-

nificantly redshifted compared with the corresponding band

of TPTPhenP (809 nm), there is a marked stabilization of

the HOMO (the “s” MO of P₁-Bz_yand the “a” MO of P₃-

Bz_y) relative to that of TPTPhenP, which leads to an in-

crease (rather than a decrease) in the first oxidation poten-

tial (Table 3). In marked contrast with the introduction of

NMe₂substituents onto the aryl groups of N₂Se₂-NMe₂, the

narrowing of the HOMO–LUMO band gap is primarily ach-

ieved through a significant stabilization of the LUMO,

rather than through a further destabilization of the HOMO,

owing to the stabilizing effects of the fused rings along both

the x and y axes.

ABAB-fused-ring expansion: The second approach that was

explored to enhance the intensity of the Q band region was

the incorporation of benzo groups along the y axis by using

a BCOD-fused-thiophene precursor. The BCOD moieties of

P₁and P₃(Figure 1) were then converted into P₁-Bz_yand

P₃-Bz_ycompounds with fused-benzene rings based on a

retro-Diels–Alder reaction.^[15]Although the incorporation of

F substituents at the para positions of the phenyl groups re-

sults in slight blueshifts of the Q and B bands, a potential

advantage is that the stabilization of the frontier p-MOs

makes these compounds more stable towards oxidative

attack (Table 3). Figure 6 demonstrates that the introduction

of either acenaphtho- or phenanthro-fused-ring moieties

along the x axis can be expected to result in a marked stabi-

lization of the “ꢁs” MO, due to the strong bonding interac-

Marked differences are observed between the spectra of

P₁and P₃, based on whether phenanthro- and acenaphtho-

fused rings are present along the x axis, respectively. A sig-

nificantly larger DHOMO value is predicted for P₁relative

to P₃(Figure 10D), due to a larger destabilization of the “s”

MO (Figure 8, Table 2), based on a greater folding of the p

system (Table 1), due to the greater steric hindrance be-

tween the phenyl groups and the larger phenanthrene-fused

rings. As a result, the B3LYP calculations predict that

DHOMO>DLUMO for P₁, whilst P₃is a soft MCD chro-

mophore with DHOMOꢂDLUMO (Figure 10D). This dif-

ference is reflected in the close alignment between the in-

tense coupled oppositely signed x- and y-polarized b₀terms

16858

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ꢁ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Chem. Eur. J. 2012, 18, 16844 – 16867

Core-Modified Fused-Ring-Expanded Porphyrins

FULL PAPER

AHCTUNGTRENNUNG

AHCTUNGTERGeNNUN rism of P₁and P₃, based on

the relative orientation of the

fused BCOD moieties, is not

expected to play a major role in

determining the optical proper-

ties.

Accuracy of the TD-DFT calcu-

lations: In many instances, the

TD-DFT calculations appear to

predict the presence of more in-

tense bands in the

B band

region than are actually ob-

served. Similar issues have pre-

viously been reported for

a

wide range of porphyrinoids.^[14]

Two intense xy-polarized elec-

tronic bands tend to be predict-

ed in the B band region of ZnP

based on TD-DFT calculation-

s,^[29a]

whilst

only

one

is observed experimentally.^[14]

ZINDO/s calculations (see the

Supporting Information, Fig-

AHCTUNGTERGuNNUN res S9–S13 and Table S7) tend

to consistently predict a single

intense pair of x- and y-polar-

ized B bands. The additional

predicted bands appear to be

associated with

a systematic

overestimation of the level of

configurational interaction be-

tween the B and higher-energy

pp* states.^[14]Reimers and co-

workers^[33]recently demonstrat-

ed that calculations that were

carried out with the BP86 and

Figure 13. Observed electronic-absorption and MCD spectra of P₁and P₃(left), P₁-Bz_yand P₃-Bz_y(right), and

their calculated TD-DFT oscillator strengths (light-gray triangles, right axis). Trace amounts of triethylamine

were added to prevent protonation. The Q and B bands, which are primarily associated with the four frontier

p-MOs, are indicated by large dark-gray diamonds. For details of the most intense bands, see the Supporting

Information, Table S4.

at 850, 668, 549, and 521 nm in the MCD spectrum of P₁

and their corresponding bands in the absorption spectrum,

whilst a much more complex spectrum is predicted for P₃

(Figure 13). When the Q₀₀bands are almost fully forbidden,

most of the intensity in the near-IR region is derived from

vibrational borrowing from the allowed B₀₀bands.^[14,31]For

this reason, the assignment of the higher-energy Q₀₀band of

P₃is problematic. There is a slight blueshift of the Q₀₀and

B₀₀bands of P₃and P₃-Bz_yrelative to the corresponding

bands in the spectra of P₁and P₁-Bz_y, due to a narrowing of

the average HOMO–LUMO band gap (Figure 8 and

Table 2). This is primarily due to the greater destabilization

of the “s” MO (Figure 8 and Table 2). It should be noted

that the calculated MO energies and the calculated TD-

DFT and ZINDO/s spectra of the cis and trans isomers of P₁

and P₃, with respect to the BCOD substituents, were very

similar to their corresponding data for the trans isomers

(Figure 3, Table 2, and the Supporting Information, Fig-

B3LYP functionals underestimated the energy of states that

was associated with the 1b_2u!1e_g* one-electron transition of

free-base porphyrins and their fused-ring-expanded ana-

logues, due to their charge-transfer character, and that a

larger Hartree–Fock component was required to compen-

sate for this. This issue has not been pursued in depth in the

context of this study because our primary goal has been to

account for the observed trends in the properties in the Q

band region based on the energies of the four “Gouterman

orbitals”.

Effect of protonation: The optical properties of porphy

ACHTUNGTRENNUNGrin-

AHCTUNGTRENNUNG

gen atoms on the inner perimeter of the p system to form a

dicationic species.^[10b,16,31]The observed trends for the vari-

ous Group-16-substituted compounds (Table 4 and

Figure 14) mirrored those described above in the context of

Figure 9. The Q bands of N₂S₂, N₂Se₂, and TPTPhenP^[16]are

Chem. Eur. J. 2012, 18, 16844 – 16867

ꢁ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.chemeurj.org

16859

K. Rurack, N. Kobayashi, Z. Shen et al.

N₂O₂H₂²⁺, whilst the emission

band is blueshifted (from 906

to 861 nm), thereby resulting

in a virtually unchanged Stokes

shift of about 850 cm^ꢁ1. How-

ever, the increase in fluores-

cence intensity is less pro-

nounced in the case of

2+

N₂S₂H₂relative to N₂S₂and

the fluorescence maximum is

redshifted in a similar manner

to the Q₀₀absorption-band

maxima. The relatively narrow

Stokes shifts in the spectra of

N₂O₂and N₂O₂H₂²⁺, the de-

crease in the Stokes shift upon

protonation of N₂S₂, and the

increase in the radiative rate

constant (k_f) for both protonat-

ed species suggest that there is

a more rigid saddling distortion

Figure 14. Absorption (left) and emission spectra (right) of N₂O₂, N₂S₂, N₂Se₂, and N₂Te₂(top), as well as P₁

and P₁-Bz_y(bottom) in CHCl₃(black) and after the addition of 1% TFA (v/v; gray).

of the ligand upon protonation

of the core pyrrole-nitrogen

atoms and a loss of conforma-

markedly redshifted and become more intense upon proto-

nation, but a blueshift is observed in the spectra of N₂O₂

and N₂Te₂compounds. A redshift and splitting of the

B bands is consistently observed. Similar minor differences

are observed in the spectra of P₁and P₁-Bz_y(Table 4). Pro-

tonation of P₁results in a blueshift of the lowest-energy

tional flexibility. Further decreases in emission intensity are

observed for the selenophene- and, especially, the telluro-

phene-containing compounds. All of the fluorescence-decay

curves are monoexponential and display fluorescence life-

times of t_f>300 ps. Table 4 also reveals that nonradiative

processes are accelerated in the series N₂Y₂, with Y=O!

2+

Q band, but a redshift in the spectrum of P₁-Bz_yH₂

(Figure 14). Protonation further enhances the marked red-

S!Se(!Te), due to a gradual increase in k_nr. Because the

G

emission maxima remain relatively constant for the furan,

thiophene, and selenophene derivatives (906, 908, and about

910 nm, respectively, Table 4), the decrease in emissivity can

be attributed to the increasing influence of the heavy-atom

effect. The “energy-gap rule”^[35]clearly only plays a minor

role, so it is safe to assume that the difference in fluores-

cence intensity is only due to enhanced nonradiative deacti-

vation through intersystem crossing and that k_nrꢂk_isc. There-

fore, the heavy-atom effect can be quantified by using a cen-

tral-field single-electron approximation for the relationship

between k_iscand the spin-orbit coupling constant.^[36]An ex-

shifts, due to core modification and para-phenyl substitution.

2+

The lowest-energy Q₀₀band is at 900 nm for N₂Te₂H₂and

n+

at 1140 nm for N₂Se₂-NMe₂H_n(Table 4 and Figure 14).^[34]

Upon protonation, there is a redshift of the lowest-energy

Q₀₀band and a complex series of spectra that are based on

protonation at the ligand core and at the p-NMe₂substitu-

ents, similar to those reported for the analogous

2+

TPTPhenPH₂species.^[16]In the UV region, the electronic-

absorption spectra are comprised of a relatively intense en-

velope of extensively overlapping bands (Figure 9,

Figure 11, and Figure 13). These bands can be assigned to

transitions that involve MOs that are primarily associated

with the peripheral fused rings, because weak MCD intensi-

ty would be anticipated relative to bands that are primarily

associated with the “a” and “s” MOs on the inner-ligand pe-

rimeter due to the weaker OAM properties.

2+

cellent correlation is obtained for both N₂Y₂and N₂Y₂H₂

when logk_nr+logn⁶(n=quantum number) is used as a meas-

ure of the heavy-atom effect (Figure 15). An enhancement

of the spin-orbit coupling and, hence, intersystem crossing,

affords a novel set of porphyrinoids, which could potentially

be used in applications that require singlet-oxygen genera-

tion. Usually, such sensititzers contain bromo or iodo atoms

as heavy-atom substituents. An obvious question in this

regard is whether core substitution with chalcogens or the

conventional halogen substitution at the periphery provides

the best F_Dvalues. Data obtained for N₂O₂-X in both the

free-base and doubly protonated forms were analyzed, as

was data that were previously recorded for the correspond-

ing para-X-meso-phenyl-substituted TPTPhenPs.^[16]The

plots, shown in Figure 15, confirm that acceptable correla-

Fluorescence spectroscopy: The impact of core modification

with Group 16 heteroatoms on fluorescence properties has

also been studied. In general, a redshift of the S₁emission

band is observed, along with a decrease in the fluorescence

quantum yield (F_f, Table 4). The emission bands of N₂O₂

and N₂S₂are centered at l>900 nm, with fluorescence

quantum yields of about 0.1% in CHCl₃. The F_fvalue in-

creases three-fold upon the protonation of N₂O₂to form

16860

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Chem. Eur. J. 2012, 18, 16844 – 16867

Core-Modified Fused-Ring-Expanded Porphyrins

FULL PAPER

notes the slopes of the decrease in the absorption of DPBF

at 415 nm for N₂Se₂and TPP (in min^ꢁ1).

F_DðN₂Se₂Þ ¼ F_DðTPPÞ ꢃ mðN₂Se₂Þ ꢃ mðTPPÞ^ꢁ1

ð4Þ

1

Although the yield of O₂is only moderate in comparison

to that from TPP, the possibility of using irradiation at

wavelengths above 800 nm might provide advantages. Ex-

panded tests are planned as part of our future work in this

area.

Figure 15. Plot of the heavy-atom-quenching effect on the fluorescence of

the porphyrin; symbols denote the data and lines denote linear fits that

were calculated based on y=mx+b, in which m=slope and b=intercept.

Conclusion

A wide range of core modified diphenanthroporphyrins

have been prepared, in which the protonated pyrrole nitro-

gen atoms are replaced by Group 16 heteroatoms, to explore

trends in the optical properties and electronic structures and

to study the suitability of these compounds for near IR

region dye applications. The goal was to prepare compounds

with optical properties similar to those of tetraphenyltetra-

phenanthroporphyrins, which have the most redshifted Q

and B bands for a fused-ring-expanded analogue of TPP,^[16]

but with less severely saddled structures. An application of

Michlꢂs perimeter model to the MCD spectra broadly vali-

dates the DFT based descriptions of the electronic struc-

tures and provides a readily accessible conceptual frame-

work for identifying the key structure-property relationships

in a manner which can potentially enable the rational design

of novel porphyrinoids suitable for use in specific applica-

tions. The optical spectra of N₂O₂, N₂S₂, N₂Se₂and N₂Te₂

compounds are broadly similar, since in each instance the

heteroatom provides a lone pair to the p-system as would

be the case with the protonated pyrrole nitrogen atoms in

the parent diphenanthroporphyrin compound, but the spec-

tra of the N₂O₂-OC₁₆H₃₃and N₂Te₂compounds differ mark-

edly from their N₂S₂-OC₁₆H₃₃and N₂Se₂-OC₁₆H₃₃counter-

parts due to changes in the degree of ligand saddling. Al-

though the Q band of N₂Te₂is markedly redshifted relative

to TPTPhenP for this reason, the compound is unstable to

oxidation due to the destabilization of the HOMO and is

not likely to be useful for optoelectronic or photodynamic

applications. The effect of other structural modifications,

such as the introduction of different meso-aryl groups and

expansion of the inner perimeter of the ligand by incorpo-

rating two additional Group 16 heteroatoms and modifica-

tions to the fused-ring-expansion pattern, to further fine-

tune the optical properties was explored. Incorporation of

electron donating -NMe₂groups at the para-positions intro-

duces a strong mesomeric interaction with the main por-

phyrin macrocycle which results in a significant intensifica-

tion and redshift of the Q bands. A marked decrease in the

first oxidation potential due to a destabilization of the

LUMO is potentially problematic, however. The use of

BCOD-fused thiophene precursors enables the synthesis of

diphenanthro- and diacenaphtho-fused N₂S₂compounds

with ABAB structures containing two benzo-fused thio-

&

and b: the N₂O₂, N₂S₂, and N₂Se₂series (m=4.53, correlation coeffi-

2+

cient r²=0.999);

and d: the N₂O₂H₂²⁺, N₂S₂H₂²⁺, and N₂Se₂H₂

*

series (m=4.70, r²=0.999); and c: the N₂O₂-X series (X=F, Cl, Br,

~

2+

I; m=3.49, r²=0.988); and l line: the N₂O₂-XH₂series (m=3.60,

!

r²=0.988); and g: TPTPhenP derivatives that contained the same X

*

substitution pattern on the meso-phenyl rings as the N₂O₂-X series (m=

3.55, r²=0.986; data taken from ref. [16]).

tions are also obtained for the peripherally substituted com-

pounds. A comparison of the slopes of these fits suggests

that core modification accelerates intersystem crossing to a

greater extent than peripheral substitution, because m_core

ꢂ4.6 compared to m_periphery=3.5.

Performance as photosensitizers: Because the core-modified

porphyrinoids reported herein have Q or B bands that lie in

the biomedical NIR window and exhibit pronounced heavy-

atom-quenching properties, their potential suitability as pho-

tosensitizers for possible applications in photodynamic ther-

apy has also been explored. N₂Se₂, N₂Te₂, and N₂O₂-I are es-

pecially interesting in this regard, because high intersystem-

crossing yields are a prerequisite for high quantum yields of

singlet-oxygen production (F_D). Therefore, N₂O₂, N₂Se₂,

N₂Te₂, and N₂O₂-I were tested according to the following

procedure: A solution of the porphyrinoid photosensitizer

(absorbance=0.52 at 515 nm, c=5 mm) and 1,3-diphenyliso-

benzofuran (DPBF, 50 mm) was prepared in DMF and insert-

ed into a quartz cuvette. DPBF is an optical indicator for

¹O₂generation because an endoperoxide is formed upon cy-

cloaddition with singlet oxygen, thereby resulting in the dis-

appearance of its characteristic absorption band at

415 nm.^[37]The solutions were irradiated at 515 nm (in the B

band region of the porphyrins) for 30 min (Xe lamp 25.4 A)

and absorption spectra were recorded at 5 min intervals (see

the Supporting Information, Figure S14). A solution of TPP

in DMF was used as the standard for the calculation of F_D

(F_D^TPP=0.67).^[38]Unfortunately, with the exception of

N₂Se₂, the porphyrins tested herein either induced no

change in the DPBF absorption (N₂O₂and N₂Te₂) or decom-

posed upon irradiation (N₂O₂-I). A F_Dvalue of 0.13 for

N₂Se₂was calculated from the slope of the decrease in ab-

sorption intensity by using Equation (4),^[39]in which m de-

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ꢁ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

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16861

K. Rurack, N. Kobayashi, Z. Shen et al.

standard geometry, no polarizers, 600 nm cut-off filter in the emission

channel) with optically diluted solutions with an absorbance of between

0.05 and 0.1 at the maximum of the B band. Depending on the porphyrin,

a wavelength of either 525 or 535 nm was used for excitation (B band).

For all of the species studied, the fluorescence-excitation spectra matched

their absorption spectra. The fluorescence quantum yields (F_f) were de-

phene moieties. These compounds exhibit a narrowing of

the HOMO–LUMO band gap relative to TPP due primarily

to a stabilization of the LUMO rather than a destabilization

of the HOMO and enhanced absorption intensity in the

NIR region due to a significant increase in the DLUMO

value. An analysis using Michlꢂs perimeter model demon-

strates that the differing effects of incorporating benzene,

phenanthrene and acenaphthalene fused ring moieties along

the x and y-axes to form ABAB structures can substantially

modify the relative energies of the four frontier p-MOs.

Some of the core modified diphanthroporphyrins studied

are promising candidates for use in photodynamic therapy.

A fluorescence emission study was carried out which dem-

onstrates that core modification has a stronger influence on

heavy atom quenching than the introduction of peripheral

substituents such as -Br and -I.

2+

termined relative to TPTPhenPH₂(F_f=8.0ꢄ10^ꢁ3).^[16]The fluorescence

spectra presented herein were spectrally corrected.^[41]The uncertainty of

the measurements for F_fwas determined to be ꢄ ꢀ10%. Fluorescence

lifetimes (t_f) were determined by a unique customized laser-impulse flu-

orometer with picosecond time resolution.^[42]The fluorescence was col-

lected at right angles (monochromator with spectroscopic bandwidths of

16 nm). Whilst realizing typical instrument response functions of fwhm

ꢂ30 ps, the time division was 4.8 pschannel^ꢁ1and the experimental accu-

racy was ꢀ3 ps, respectively. The laser beam was attenuated by using a

double-prism attenuator (LTB) and typical excitation energies were in

the nanowatt to microwatt range (average laser power). The fluores-

cence-lifetime profiles were analyzed by a PC with the Global Unlimited

V2.2 software package (Laboratory for Fluorescence Dynamics, Universi-

ty of Illinois). The goodness of fit of the single decays, as judged by re-

duced chi-squared (c_R²) and the autocorrelation function (C(j)) of the re-

siduals, was always below c_R²<1.2.

Calculations Molecular structures were optimized and MO energies were

obtained for P, free-base tetraphenylporphyrin (TPP), TPhenP,

TPTPhenP, 2Phen_xN₄, N₂O₂, N₂O₂-OMe, N₂S₂, N₂S₂-OMe, N₂Se₂, N₂Se₂-

OMe, P₁, P₁-Bz_y, P₃, and P₃-Bz_y, and the X-ray structures of N₂Se₂-NMe₂

and P₃-Bz_y(Figure 1, Figure 6, and the Supporting Information, Fig-

Experimental Section

General: ¹H and ¹³C NMR spectra were acquired at 500 MHz and

125 MHz on a Bruker DRX500 spectrometer. NMR chemical shifts are

expressed relative to TMS as an internal standard. MS (MALDI-TOF)

was performed on an ABI Voyager De pro spectrometer. Elemental

analysis was performed on a Perkin–Elmer 240 C elemental analyzer.

Melting points were determined by using a Reichert Thermometer and

are without correction. IR spectra were recorded on a VECTOR 22 spec-

trophotometer with KBr discs in the region 4000–400 cm^ꢁ1. UV/Vis spec-

troscopy was performed on a Shimadzu UV-3100 spectrophotometer. X-

ray crystallographic analysis of N₂Se₂-NMe₂and P₃-Bz_y(Figure 2 and the

Supporting Information, Figure S2 and Tables S1–S3) was performed on

a Bruker Smart Apex CCD diffractometer with monochromated Mo_Ka

radiation (l=0.71073 ꢃ) at 293 K by using the wꢁ2q scan mode. The

data were corrected for Lorenz and polarization effects. The structures

were solved by using direct methods and refined on F²by using the full-

matrix least-squares technique on the SHELXTL-2000 program pack-

age.^[40]The redox data were obtained on a Zahner Electrochemical

Workstation. The data were measured by using a platinum working elec-

trode, a platinum-wire counter electrode, and a Ag/AgCl reference elec-

trode with Fc/Fc⁺as an internal standard. The measurements were per-

formed in CH₂Cl₂with a 0.1m Bu₄NPF₆supporting electrolyte. All of the

experiments were performed under an argon atmosphere.

AHCTUNGERTGuNNUN res S4–S6) by using the B3LYP functional of the G03W software pack-

age^[43]with 6–31G(d) basis sets and for N₂O₂, N₂S₂, N₂Se₂, and N₂Te₂with

the 3–21G** basis sets (see the Supporting Information, Figure S3). TD-

DFT calculations were performed with the same basis sets (Figure 9,

Figure 11, Figure 13, Table 1, and the Supporting Information, S1, S3–S6,

and Tables S4 and S5) and the optimized structures were also used for

ZINDO/s calculations (see the Supporting Information, Figures S7–S13

and Tables S6–S8).

Synthesis: All of the experiments were performed under an inert argon

atmosphere. Unless otherwise noted, all of the chemicals and solvents

were of analytical reagent grade and used as received. Dry CH₂Cl₂was

freshly distilled over CaH₂under a nitrogen atmosphere. Dry THF was

distilled from sodium/benzophenone under

a nitrogen atmosphere.

Column chromatography and TLC were performed on C-200 (Wakogel)

and Kieselgel 60 F254 (Merck), respectively. para-Hexadecyloxybenzal-

ACTHNUTRGNEUNG

dehyde^[44]and phenanthro[9,10-c]pyrrole^[45]were prepared according to

literature procedures.

General procedure for preparing diols: Dry and freshly distilled n-

hexane (52 mL) was added to a three-necked, round-bottomed flask

(250 mL) that was flushed with argon gas for 10 min. N,N,N’,N’-Tetra-

CCDC-905915 (P₃-Bz_y) and CCDC-639522 (N₂Se₂-NMe₂) contain the

supplementary crystallographic data for this paper. These data can be ob-

tained free of charge from The Cambridge Crystallographic Data Centre

via www.ccdc.cam.ac.uk/data_request/cif

ACHUTNGRENUmNG ethAHCUTNGTRENyNNGU lethylenediamine (TMEDA, 4.8 mL, 32 mmol) and n-BuLi (20 mL,

1.6m in n-hexane, 32 mmol) were added and the solution was stirred

under an argon atmosphere for 10 min. Then, redistilled furan, thiophene,

selenophene, or 4,7-dihydro-4,7-ethanoisothianaphthene (BCOD-fused

thiophene; 16 mmol) was added and the solution was gently heated at

reflux for 1 h (Schemes 1 and 2). The reaction mixture was cooled to 08C

Optical spectroscopy: Electronic-absorption spectra were measured on

Hitachi U-3410 and Cary 5000 UV/Vis/NIR spectrophotometers. Magnet-

ic circular dichroism (MCD) spectra were recorded on a Jasco J-725 spec-

trodichrometer with a Jasco electromagnet that produced a magnetic

field of up to 1.09 T. CHCl₃that was stabilized by 0.5% EtOH (Nacalai

Tesque) was used as the solvent for most of the MCD measurements.

CDCl₃was used when measurements at l>1000 nm were required. Trace

amounts of triethylamine were added to solutions of N₂Te₂, S₂N₂-F, P₁,

P₃, P₁-Bz_y, and P₃-Bz_yto prevent protonation. Steady-state fluorescence

measurements were performed on a Spectronics Instrument 8100 spectro-

fluorometer. CHCl₃and TFA, which were employed for the fluorescence

measurements, were of UV spectroscopic grade. For all of the measure-

ments, the temperature was kept constant at 298(ꢀ1) K. All of the ab-

sorption measurements were performed in 10 mm cuvettes. Molar ab-

sorption coefficients were determined from N=4 independent solutions

and only very dilute stock solutions (1–10 mm) were used to avoid aggre-

gation or solubility problems. The uncertainty of the measurements was

ꢀ10%. Fluorescence studies were performed in 10 mm cuvettes (908

Scheme 1. Synthesis of the diols: i) TMEDA, nBuLi, dry n-C₆H₁₄

;

ii) ArCHO, dry THF.

16862

www.chemeurj.org

ꢁ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Chem. Eur. J. 2012, 18, 16844 – 16867

Core-Modified Fused-Ring-Expanded Porphyrins

FULL PAPER

in an ice bath and a solution of the aromatic aldehyde (33 mmol) in dry

THF (32 mL) was added slowly. Next, the reaction mixture was allowed

to warm to RT and was stirred for 15 min. The reaction was quenched by

adding an ice-cold aqueous solution of NH₄Cl (48 mL, about 1m). The or-

ganic layer was washed with water, brine, and dried with anhydrous

Na₂SO₄. The solvent was removed on a rotary evaporator under reduced

pressure to afford the crude compounds, which were purified by column

chromatography on silica gel to obtain the target compounds as white

solids (Scheme 2).

d=7.35–7.33 (m, 4H), 6.89–6.88 (m, 4H), 6.80 (s, 2H), 5.94 (s, 2H), 3.97–

3.94 (m, 4H), 2.31 (brs, 2H), 1.81–1.76 (m, 4H), 1.46–1.43 (m, 4H), 1.27

(s, 52H), 0.91–0.88 ppm (m, 6H).

2,5-Bis[(4-N,N-dimethylphenyl)hydroxymethyl]selenophene: 6.05 g, 88%;

¹H NMR (500 MHz, CDCl₃): d=7.36–7.35 (m, 4H), 7.01–6.95 (m, 4H),

6.80 (s, 2H), 5.90 (s, 2H), 2.40 (s, 12H), 2.33 ppm (brs, 2H).

2,5-Bis(phenylhydroxymethyl)tellurophene: 2,5-Bis(phenylhydroxyACHTUNGTRENNUNGmeth-

tellurophene was synthesized according to a literature procedure^[46]

ACHUTNGRENyNUG l)ACHTUNGTRENNUGN

from NaHTe and 1,6-diphenylhexa-2,4-diyne-1,6-diol.^[47]The product was

recrystallized from n-hexane/CHCl₃.

General procedure for the preparation of N₂Y₂and BCOD-N₂S₂: The ap-

propriate diol (1 mmol) was added to a stirring solution of phenanthro-

pyrrole (217 mg, 1 mmol) in freshly dried and deoxygenated CH₂Cl₂

(100 mL) and the resulting solution was purged with argon for 10 min

(Scheme 3). BF₃·Et₂O (40 mL, 0.32 mmol) was added and the reaction

mixture was stirred for 3 h at ꢁ508C in the dark and then warmed to RT

and stirred for 24 h. After that, 2,3-dichloro-5,6-dicyano-1,4-benzoqui-

none (DDQ; 227 mg, 1 mmol) was added and the solution was stirred for

an additional 12 h; then, the solvents were removed under reduced pres-

sure by rotary evaporation. The crude product was purified by column

chromatography on silica gel and recrystallized from CH₃Cl/CH₃OH.

¹H NMR spectroscopy and MS (MALDI-TOF) are provided in the Sup-

porting Information, Figures S15–S35.

Scheme 2. Synthesis of the tellurophene diols: i) CuCl/TMEDA in ace-

tone; ii) NaHTe, CH₃OH, AgOAc, RT, 24 h.

2,5-Bis(phenylhydroxymethyl)furan: 2.01 g, 45%; ¹H NMR (500 MHz,

CDCl₃): d=7.38–7.36 (m, 10H), 6.00–5.98 (m, 2H), 5.82 (s, 2H),

4.12 ppm (s, 2H).

2,5-Bis[(4-hexadecyloxyphenyl)hydroxymethyl]furan:

5.0 g,

41%;

¹H NMR (500 MHz, CDCl₃): d=7.66–7.64 (m, 4H), 7.23–7.20 (m, 4H),

6.03–5.99 (m, 2H), 5.74 (s, 2H), 3.86 (m, 4H), 1.79–1.77 (m, 4H), 1.30–

1.26 (m, 52H), 0.91 ppm (t, 6H).

2,5-Bis(phenylhydroxymethyl)thio-

phene:

2.66 g,

56%;

¹H NMR

(500 MHz, CDCl₃): d=7.44–7.45 (m,

4H), 7.34–7.40 (m, 4H), 7.31–7.33 (m,

2H), 6.72 (s, 2H), 5.97 (s, 2H),

2.46 ppm (brs, 2H); ¹³C NMR

(125 MHz, CD₃OD): 127.7, 127.5,

126.2, 124.3, 81.0, 77.5, 77.2,

77.0 ppm.

2,5-Bis[(4-hexadecyloxyphenyl)hy-

droxymethyl]thiophene: 6.8 g, 55%;

¹H NMR (500 MHz, CDCl₃): d=7.34

(d, 4H), 6.89 (d, 4H), 6.71 (s, 2H),

5.95–5.93 (m, 2H), 3.96 (t, 4H), 2.32–

2.30 (m, 2H), 1.81–1.78 (m, 4H),

1.46–1.43 (m, 4H), 1.31–1.27 (m,

48H), 0.91 ppm (t, 6H).

2,5-Bis[(4-fluorophenyl)hydroxyl-

A

N

U

3.56 g,

67%;

¹H NMR (500 MHz, CDCl₃): d=

7.41–7.43 (m, 4H), 7.05–7.08 (m, 4H),

6.73 (s, 2H), 5.98 (s, 2H), 2.44 ppm

(brs, 2H); ¹³C NMR (125 MHz,

CD₃OD): 162.8, 148.2, 139.6, 128.2,

127.4, 123.2, 114.2, 114.1, 114.0,

70.7 ppm.

2,5-Bis[(4-fluorophenyl)hydroxymeth-

yl]4,7-dihydro-4,7-ethanoisothianaph-

thene:

1.12 g,

34%;

¹H NMR

(500 MHz, CDCl₃): d=7.39–7.36 (m,

4H), 7.05–6.99 (m, 4H), 6.43–6.39 (m,

2H), 6.02 (d, J=8.8 Hz 2H), 3.80–

3.77 (m, 2H), 2.23–2.21 (m, 2H),

1.55–1.42 ppm (m, 4H).

2,5-Bis(phenylhydroxymethyl)seleno-

phene:

2.69 g,

49%;

¹H NMR

(500 MHz, CDCl₃): d=7.49–7.26 (m,

10H), 6.88 (s, 2H), 5.97 (s, 2H),

2.42 ppm (brs, 2H).

2,5-Bis[(4-hexadecyloxyphenyl)hy-

droxymethyl]selenophene:

6.33 g,

Scheme 3. Synthesis of the core-modified porphyrins: i) BF₃·Et₂O, CH₂Cl₂, ꢁ508C, 3 h, then warm to RT, 24 h,

48%; ¹H NMR (500 MHz, CDCl₃):

then DDQ, 12 h.

Chem. Eur. J. 2012, 18, 16844 – 16867

ꢁ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.chemeurj.org

16863

K. Rurack, N. Kobayashi, Z. Shen et al.

5,10,15,20-Tetraphenyldiphenanthro[9,10-b:9,10-l]-21,23-dioxaporphyrin-

(N₂O₂): N₂O₂was prepared as described above from 2,5-bis(phenylhy-

droxymethyl)furan (280 mg, 1 mmol), phenanthro[9,10-c]pyrrole (217 mg,

8.69–8.67 (m, 8H), 8.29 (s, 4H), 7.86–7.84 (m, 8H), 7.48–7.45 (m, 4H),

7.15–7.12 ppm (m, 8H); UV/Vis (CHCl₃): l_max(e)=491 (32900), 627

(4630), 852 nm (1490 mol^ꢁ1dm³cm^ꢁ1); MS (MALDI-TOF): m/z calcd for

C₆₈H₃₆Cl₄N₂O₂: 1055.845; found: 1055.209; elemental analysis calcd (%)

for C₆₈H₃₆Cl₄N₂O₂: C 77.43, H 3.44, N 2.66; found: C 77.26, H 3.65,

N 2.76.

ACHTUNGTRENNUNG

AHCTUNGTRENNUNG

1 mmol), BF₃·Et₂O (40 mL, 0.32 mmol), and DDQ (227 mg, 1 mmol).

Column chromatography on silica gel (CHCl₃, EtOAc/petroleum ether

50%, then CHCl₃/CH₃OH 50%), followed by recrystallization from

CHCl₃/MeOH, afforded dark-green crystals (91 mg, 32%). M.p.>2508C;

¹H NMR (500 MHz, [D₆]DMSO): d=8.78 (s, 2H), 8.66–8.64 (m, 4H),

8.58–8.56 (m, 2H), 8.33–8.31 (m, 4H), 8.19 (s, 2H), 7.94–7.93 (m, 2H),

7.87–7.86 (m, 4H), 7.79–7.77 (m, 2H), 7.73–7.71 (m, 4H), 7.62–7.61 (m,

2H), 7.44–7.42 (m, 4H), 7.33–7.31 (m, 4H), 7.10–7.08 (m, 2H), 7.03–

7.01 ppm (m, 2H); UV/Vis (CHCl₃): l_max(e)=496 (75100), 576 (12700),

620 (8170), 850 nm (4670 mol^ꢁ1dm³cm^ꢁ1); MS (MALDI-TOF): m/z

calcd for C₆₈H₄₁N₂O₂: 917.057 [M+H]⁺; found: 917.366; elemental analy-

sis calcd (%) for C₆₈H₄₀N₂O₂: C 89.06, H 4.40, N 3.05; found: C 89.02,

H 4.39, N 2.99.

5,10,15,20-Tetra-4-bromophenyldiphenanthro[9,10-b:9,10-l]-21,23-dioxa-

porphyrin (N₂O₂-Br): N₂O₂-Br was prepared as described above from

2,5-bis(4-bromophenylhydroxymethyl)furan

(438 mg,

BF₃·Et₂O

1 mmol),

(40 mL,

phenanthro[9,10-c]pyrrole (217 mg, 1 mmol),

G

0.32 mmol), and DDQ (227 mg, 1 mmol). Column chromatography on

silica gel (CHCl₃, EtOAc/petroleum ether 50%, then CHCl₃/CH₃OH

50%), followed by recrystallization from CHCl₃/MeOH, afforded dark-

green crystals (121 mg, 19%). M.p.>2508C; ¹H NMR (500 MHz,

[D₆]DMSO): d=8.79–8.77 (m, 4H), 8.68–8.66 (m, 4H), 8.57–8.54 (m,

8H), 8.01–7.99 (m, 8H), 7.86–7.84 (m, 4H), 7.48–7.45 (m, 4H), 7.15–

7.12 ppm (m, 4H); UV/Vis (CHCl₃): l_max(e)=488 (94100), 580 (16000),

631 (8400), 854 nm (6210 mol^ꢁ1dm³cm^ꢁ1); MS (MALDI-TOF): m/z

calcd for C₆₈H₃₇Br₄N₂O₂: 1233.649 [M+H]⁺; found: 1233.037; elemental

analysis calcd (%) for C₆₈H₃₆Br₄N₂O₂: C 66.26, H 2.94, N 2.27; found:

C 66.20, H 2.95, N 2.17.

5,10,15,20-Tetra-4-methoxyphenyldiphenanthro[9,10-b:9,10-l]-21,23-diox-

aporphyrin (N₂O₂-OMe): N₂O₂-OMe was prepared as described above

from 2,5-bis(4-methoxyphenylhydroxymethyl)furan (340 mg, 1 mmol),

phenanthro

[9,10-c]pyrrole

(217 mg,

1 mmol),

BF₃·Et₂O

(40 mL,

0.32 mmol), and DDQ (227 mg, 1 mmol). Column chromatography on

silica gel (CHCl₃, EtOAc/petroleum ether 50%, then triethylamine

(TEA)/CHCl₃5%), followed by recrystallization from CHCl₃/MeOH, af-

forded dark-green crystals (91 mg, 32%). M.p.>2508C; ¹H NMR

(500 MHz, [D₆]DMSO): d=8.44–8.42 (m, 4H), 8.32–8.30 (m, 8H), 8.13–

8.11 (m, 4H), 8.01–7.99 (m, 4H), 7.29–7.27 (m, 4H), 7.20–7.18 (m, 8H),

7.02–7.00 (m, 4H), 3.97–3.93 ppm (m, 12H); UV/Vis (CHCl₃): l_max(e)=

508 (118100), 582 (25700), 877 nm (9410 mol^ꢁ1dm³cm^ꢁ1); MS (MALDI-

TOF): m/z calcd for C₇₂H₄₈N₂O₆: 1036.35 [M⁺]; found: 1036.55; elemen-

tal analysis calcd (%) for C₇₂H₄₈N₂O₆: C 83.38, H 4.66, N 2.70; found:

C 83.31, H 4.76, N 2.70.

5,10,15,20-Tetra-4-iodophenyldiphenanthro[9,10-b:9,10-l]-21,23-dioxa-

porphyrin (N₂O₂-I): N₂O₂-I was prepared as described above from 2,5-

bis(4-iodophenylhydroxymethyl)furan (532 mg, 1 mmol), phenanthro-

AHCTUNTGREGN[NNU 9,10-c]pyrrole (217 mg, 1 mmol), BF₃·Et₂O (40 mL, 0.32 mmol), and

DDQ (227 mg, 1 mmol). Column chromatography on silica gel (CHCl₃,

EtOAc/petroleum ether 50%, then CHCl₃/CH₃OH 50%), followed by

recrystallization from CHCl₃/MeOH, afforded dark-green crystals

(119 mg, 17%). M.p.>2508C; ¹H NMR (500 MHz, [D₆]DMSO): d=

8.49–8.47 (m, 4H), 8.15–8.13 (m, 4H), 8.08–8.05 (m, 8H), 8.00–7.99 (m,

8H), 7.90–7.89 (m, 4H), 7.37–7.34 (m, 4H), 7.07–7.04 ppm (m, 4H); UV/

Vis (CHCl₃): l_max(e)=499 (98600), 582 (17400), 631 (8510), 856 nm

(5170 mol^ꢁ1dm³cm^ꢁ1); MS (MALDI-TOF): m/z calcd for C₆₈H₃₇I₄N₂O₂:

1420.903 [M+H]⁺; found: 1420.968; elemental analysis calcd (%) for

C₆₈H₃₆I₄N₂O₂: C 57.49, H 2.55, N 1.97; found: C 57.49, H 2.69, N 1.94.

5,10,15,20-Tetra-4-hexadecyloxyphenyldiphenanthro[9,10-b:9,10-l]-21,23-

dioxaporphyrin (N₂O₂-OC₁₆H₃₃): N₂O₂-OC₁₆H₃₃was prepared as de-

ACHTUNGTRENNUNG

AHCTUNGTRENNUNG

(40 mL, 0.32 mmol), and DDQ (227 mg, 1 mmol). Column chromatogra-

phy on silica gel (CHCl₃, EtOAc/petroleum ether 50%, then CHCl₃/

CH₃OH 50%) afforded dark-green crystals (158 mg, 16%). M.p. 1428C;

¹H NMR (500 MHz, CDCl₃): d=8.47–8.44 (m, 4H), 8.32–8.25 (m, 8H),

8.16–8.14 (m, 4H), 8.04–8.02 (m, 4H), 7.27–7.30 (m, 4H), 7.12–7.20 (m,

8H), 7.02–7.05 (m, 4H), 4.09–4.12 (t, 8H), 1.90–1.88 (m, 8H), 1.56–1.55

(m, 8H), 1.35–1.30 (m, 96H), 0.93 ppm (t, 12H); UV/Vis (CHCl₃): l_max

(e)=516 (45600), 630 (6790), 877 nm (3610 mol^ꢁ1dm³cm^ꢁ1); MS

(MALDI-TOF): m/z calcd for C₁₃₂H₁₆₈N₂O₆: 1877.29; found: 1877.39; ele-

mental analysis calcd (%) for C₁₃₂H₁₆₈N₂O₆: C 84.39, H 9.01, N 1.49;

found: C 84.50, H 9.13, N 1.38.

5,10,15,20-Tetraphenyldiphenanthro[9,10-b:9,10-l]-21,23-dithiaporphyrin

(N₂S₂): Dark-green crystals (72 mg, 15%); M.p.>2508C; ¹H NMR

(500 MHz, CDCl₃): d=8.86 (s, 4H), 8.66 (d, J=8.3 Hz, 4H), 8.41 (d, J=

7.2 Hz, 8H), 8.02 (d, J=8.3 Hz, 4H), 7.72–7.69 (m, 8H), 7.63–7.61 (m,

4H), 7.41–7.37 (m, 4H), 6.99–6.96 ppm (m, 4H); UV/Vis (CH₂Cl₂): l_max

(e)=505 (124000), 583 (25000), 817 nm (4500 mol^ꢁ1dm³cm^ꢁ1); MS

(MALDI TOF): m/z calcd for C₆₈H₄₀N₂S₂: 949.2711; found: 949.590;

HRMS (FAB): m/z calcd for C₆₈H₄₀N₂S₂: 949.2711; found: 949.2715.

5,10,15,20-Tetra-4-hexadecyloxyphenyldiphenanthro[9,10-b:9,10-l]-21,23-

dithiaporphyrin (N₂S₂-OC₁₆H₃₃): Dark-green crystals (171 mg, 18%);

M.p. 1458C; ¹H NMR (500 MHz, CDCl₃): d=8.86 (s, 4H), 8.50 (d, J=

8.5 Hz, 4H), 8.43 (d, J=8.0 Hz, 8H), 8.07 (d, J=8.5 Hz, 4H), 7.35–7.33

(m, 4H), 7.21–7.19 (m, 8H), 6.98–6.96 (m, 4H), 4.08 (t, J=6.0 Hz, 8H),

1.88–1.86 (m, 8H), 1.56–1.53 (m, 8H), 1.32–1.28 (m, 96H), 0.91 ppm (t,

J=8.5 Hz, 12H); UV/Vis (CH₂Cl₂): l_max(e)=410 (27177), 510 (141362),

588 nm (27275 mol^ꢁ1dm³cm^ꢁ1); MS (MALDI TOF): m/z calcd for

5,10,15,20-Tetra-4-fluorophenyldiphenanthro[9,10-b:9,10-l]-21,23-dioxa-

porphyrin (N₂O₂-F): N₂O₂-F was prepared as described above from 2,5-

bis(4-fluorophenylhydroxymethyl)furan (316 mg, 1 mmol), phenanthro-

ACHTUNGTRENNUNG[9,10-c]pyrrole (217 mg, 1 mmol), BF₃·Et₂O (40 mL, 0.32 mmol), and

DDQ (227 mg, 1 mmol). Column chromatography on silica gel (CHCl₃,

EtOAc/petroleum ether, then CHCl₃/CH₃OH 50%), followed by recrys-

tallization from CHCl₃/MeOH, afforded dark-green crystals (78.6 mg,

16%). M.p.>2508C; ¹H NMR (500 MHz, [D₆]DMSO): d=8.75 (s, 4H),

8.64–8.63 (m, 8H), 8.27 (s, 4H), 7.85–7.84 (m, 4H), 7.67–7.64 (m, 8H),

7.44 (s, 4H), 7.13–7.10 ppm (m, 4H); UV/Vis (CHCl₃): l_max(e)=497

(49400), 577 (10600), 622 (6740), 851 nm (2800 mol^ꢁ1dm³cm^ꢁ1); MS

(MALDI-TOF): m/z calcd for C₆₈H₃₇F₄N₂O₂: 989.279 [M+H]⁺; found:

989.347; elemental analysis calcd (%) for C₉₆H₆₂N₄: C 82.58, H 3.67,

N 2.83; found: C 82.35, H 3.65, N 2.97.

C

₁₃₂H₁₆₈N₂O₄S₂: 1909.24; found: 1909.60; elemental analysis calcd (%) for

C₁₃₂H₁₆₈N₂O₄S₂: C 82.97, H 8.86, N 1.47; found: C 82.87, H 8.89, N 1.61.

5,10,15,20-Tetra-4-fluorophenyldiphenanthro[9,10-b:9,10-l]-21,23-dithia-

porphyrin (N₂S₂-F): Dark-green crystals (67 mg, 13%); M.p.>2508C;

¹H NMR (500 MHz, [D₆]DMSO): d=8.94 (s, 4H), 8.79 (d, J=8.3 Hz,

4H), 8.56–8.53 (m, 8H), 8.07 (d, J=8.2 Hz, 4H), 7.65–7.61 (m, 8H),

7.54–7.51 (m, 4H), 7.17–7.15 ppm (m, 4H); UV/Vis (CH₂Cl₂): l_max(e)=

506 (123000), 586 (26000), 817 (4420) 500 (123000), 575 (26000), 813 nm

(4420 mol^ꢁ1dm³cm^ꢁ1); MS (MALDI TOF): m/z calcd for C₆₈H₃₆F₄N₂S₂:

1021.150; found: 1022.590; HRMS (FAB): m/z calcd for C₆₈H₃₆F₄N₂S₂:

1021.2334 [M+H]⁺; found: 1021.2337.

5,10,15,20-Tetra-4-chlorophenyldiphenanthro[9,10-b:9,10-l]-21,23-dioxa-

porphyrin (N₂O₂-Cl): N₂O₂-Cl was prepared as described above from 2,5-

bis(4-chlorophenylhydroxymethyl)furan (349 mg, 1 mmol), phenanthro-

5,10,15,20-Tetraphenyldiphenanthro[9,10-b:9,10-l]-21,23-diselenaporphyr-

in (N₂Se₂): N₂Se₂was prepared as described above from 2,5-bis(phenylhy-

ACHTUNGTRENNUNG[9,10-c]pyrrole (217 mg, 1 mmol), BF₃·Et₂O (40 mL, 0.32 mmol), and

DDQ (227 mg, 1 mmol). Column chromatography on silica gel (CHCl₃,

EtOAc/petroleum ether, then CHCl₃/CH₃OH 50%), followed by recrys-

tallization from CHCl₃/MeOH, afforded dark-green crystals (55 mg,

10%). M.p.>2508C; ¹H NMR (500 MHz, [D₆]DMSO): d=8.79 (s, 4H),

droxymethyl)selenophene (343 mg, 1 mmol), phenanthroACTHNUTRGNE[NUG 9,10-c]pyrrole

(217 mg, 1 mmol), BF₃·Et₂O (80 mL, 0.64 mmol), and DDQ (227 mg,

1 mmol). Column chromatography on silica gel (CHCl₃then EtOH/

CHCl₃2%), followed by recrystallization from CHCl₃/MeOH, afforded

16864

www.chemeurj.org

ꢁ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Chem. Eur. J. 2012, 18, 16844 – 16867

Core-Modified Fused-Ring-Expanded Porphyrins

FULL PAPER

dark-green crystals (103 mg, 19.7%). M.p.>2508C; ¹H NMR (500 MHz,

CDCl₃): d=8.71 (s, 4H), 8.65–8.63 (m, 4H), 8.50 (brs, 8H), 8.28–8.25 (m,

4H), 7.73–7.70 (m, 8H), 7.62–7.60 (m, 4H), 7.45 (m 4H), 7.10 ppm (brs,

4H); UV/Vis (CHCl₃): l_max(e)=505 (227300), 580 (54200), 810 nm

(11300 mol^ꢁ1dm³cm^ꢁ1); MS (MALDI-TOF): m/z calcd for C₆₈H₄₀N₂Se₂:

1044.152; found: 1044.477; elemental analysis calcd (%) for C₆₈H₄₀N₂Se₂:

C 78.31, H 3.87, N 2.69; found: C 78.25, H 3.71, N 2.65.

(m, 2H), 6.99–6.97 (m, 4H), 3.68–3.65 (m, 4H), 1.49–1.45 ppm (m, 8H);

UV/Vis (CH₂Cl₂): l_max(e)=533 (152000), 607 (28000), 671 (16000),

861 nm (11000 mol^ꢁ1dm³cm^ꢁ1); HRMS (FAB): m/z calcd for

C₈₀H₄₉F₄N₂S₂: 1177.3273 [M+H]⁺; found: 1177.3290.

5,10,15,20-Tetra-4-fluorophenyldiacenaphtho[1,2-b:1,2-l]-2¹,2⁴,12¹,12⁴-tet-

rahydro-2¹,2⁴,12¹,12⁴-diethano-21,23-dithiaporphyrin (P₃): Dark-green

crystals (188 mg, 48%); M.p.>3008C; ¹H NMR (500 MHz, CDCl₃): d=

8.61–8.43 (m, 8H), 7.80–7.64 (m, 12H), 7.28–7.26 (m, 4H), 6.71–6.69 (m,

2H), 6.37 (brs, 2H), 5.75 (t, J=6.8 Hz, 4H), 3.75–3.71 (m, 4H), 1.54–

1.24 ppm (m, 8H); UV/Vis (CH₂Cl₂): l_max(e)=502 (106000), 582

(23100), 612 (14500), 714 (2740), 798 nm (5000 mol^ꢁ1dm³cm^ꢁ1); HRMS

(FAB): m/z calcd for C₇₆H₄₄F₄N₂S₂: 1125.2960 [M+H]⁺; found: 1125.2961.

5,10,15,20-Tetra-4-hexadecyloxyphenyldiphenanthro[9,10-b:9,10-l]-21,23-

diselenaporphyrin (N₂Se₂-OC₁₆H₃₃): N₂Se₂-OC₁₆H₃₃was prepared as de-

scribed above from 2,5-bis(4-hexadecyloxyphenylhydroxymethyl)seleno-

phene (824 mg, 1 mmol), phenanthroACTHNUTRGNEUGN[9,10-c]pyrrole (217 mg, 1 mmol),

BF₃·Et₂O (80 mL, 0.64 mmol), and DDQ (227 mg, 1 mmol). Column chro-

matography on silica gel (CHCl₃then EtOH/CHCl₃2%), followed by re-

crystallization from CHCl₃/MeOH, afforded dark-green crystals (414 mg,

P₁-Bz_yand P₃-Bz_y: Compounds P₁-Bz_yand P₃-Bz_ywere obtained in quan-

titative yield by heating P₁and P₃in sample tubes under vacuum

(2 mmHg) at 3008C for 30 min.

1

41%). M.p. 1518C; H NMR (500 MHz, CDCl₃): d=8.68 (s, 4H), 8.63 (d,

4H), 8.43–8.41 (m, 8H), 7.30–7.27 (m, 4H), 7.44–7.41 (m, 4H), 7.25–7.21

(m, 8H), 7.14–7.11 (m, 4H), 4.13 ppm (t, 8H), 1.99–1.94 (m, 8H), 1.59–

1.46 (m, 8H), 1.35–1.27 (m, 96H), 0.93 (t, 12H); UV/Vis (CHCl₃): l_max

(e)=530 (91500), 606 (25600), 849 nm (6850 mol^ꢁ1dm³cm^ꢁ1); MS

(MALDI-TOF): m/z calcd for C₁₃₂H₁₆₉N₂O₄Se₂: 2006.14 [M+H]⁺; found:

2006.88; elemental analysis calcd (%) for C₁₃₂H₁₆₈N₂O₄Se₂: C 79.09,

H 8.45, N 1.40; found: C 79.09, H 8.43, N 1.49.

5,10,15,20-Tetra-4-fluorophenyldiphenanthro[9,10-b:9,10-l]-21,23-

dithiadibenzoACTHNUTRGNEUNG

[b,l]porphyrin (P₁-Bz_y): ¹H NMR (500 MHz, CDCl₃): d=

8.97–8.94 (m, 4H), 8.50 (d, J=8.6 Hz, 4H), 8.09–8.06 (m, 4H), 7.72 (d,

J=7.8 Hz, 4H), 7.61–7.57 (m, 4H), 7.56–7.50 (m, 4H), 7.36–7.33 (m,

4H), 7.20–7.15 (m, 4H), 7.03–6.96 ppm (m, 8H); UV/Vis (CH₂Cl₂): l_max

(e)=543

(210000),

645

(23000),

712

(53000),

869 nm

(15000 mol^ꢁ1dm³cm^ꢁ1); HRMS (FAB): m/z calcd for C₇₆H₄₁F₄N₂S₂:

1121.2647 [M+H]⁺; found: 1121.2660.

5,10,15,20-Tetra-4-methoxyphenyldiphenanthro[9,10-b:9,10-l]-21,23-dise-

lenaporphyrin (N₂Se₂-OMe): N₂Se₂-OMe was prepared as described

above from 2,5-bis(4-hexadecyloxyphenylhydroxymethyl)selenophene

5,10,15,20-Tetra-4-fluorophenyldiacenaphtho[1,2-b:1,2-l]-21,23-

dithiadibenzoACTHNUTRGNEUNG

[b,l]porphyrin (P₃-Bz_y): ¹H NMR (500 MHz, CDCl₃): d=

(824 mg, 1 mmol), phenanthroACHTNUTRGNE[UNG 9,10-c]pyrrole (217 mg, 1 mmol), BF₃·Et₂O

8.54–8.50 (m, 8H,), 7.68–7.63 (m, 17H), 7.36–7.34 (m, 4H), 7.25–7.23 (m,

3H), 5.75 ppm (d, J=7.1 Hz, 4H); UV/Vis (CH₂Cl₂): l_max(e)=516

(135000), 708 (35800), 746 nm (33600 mol^ꢁ1dm³cm^ꢁ1); HRMS (FAB):

m/z calcd for C₇₂H₃₆F₄N₂S₂: 1069.2334 [M+H]⁺; found: 1069.2335.

(80 mL, 0.64 mmol), and DDQ (227 mg, 1 mmol). Column chromatogra-

phy on silica gel (CHCl₃then EtOH/CHCl₃2%), followed by recrystalli-

zation from CHCl₃/MeOH, afforded dark-green crystals (255 mg, 44%).

M.p.>2508C; ¹H NMR (500 MHz, CDCl₃): d=8.65–8.63 (m, 8H), 8.44–

8.42 (m, 8H), 8.28 (d, J=8.5 Hz, 4H), 7.45–7.42 (m, 4H), 7.26–7.22 (m,

8H), 7.15–7.12 (m, 4H), 3.99 ppm (s, 12H); UV/Vis (CHCl₃): l_max(e)=

526 (102800), 605 (26900), 844 nm (7500 mol^ꢁ1dm³cm^ꢁ1); MS (MALDI-

TOF): m/z calcd for C₇₂H₄₈N₂O₄Se₂: 1164.194; found: 1164.891; elemental

analysis calcd (%) for C₇₂H₄₈N₂O₄Se₂: C 74.35, H 4.16, N 2.41; found:

C 74.23, H 4.13, N 2.25.

Acknowledgements

Financial support from the Major State Basic Research Development

Program of China (Grant No. 2011CB808704), the National Natural Sci-

ence Foundation of China (Nos. 20971066 and 21021062), Grants-in-Aid

for Scientific Research on Innovative Areas (No. 20108007, “p-Space”)

and for Scientific Research B (No. 23350095) to N.K. by the Ministry of

Education, Culture, Sports, Science, and Technology, Japan (MEXT), the

Alexander-von-Humboldt Foundation, the European Commissionꢂs

Human Resources and Mobility Programme for a Marie Curie Intra-Eu-

ropean Fellowship, and the Adolf-Martens Fonds is highly appreciated.

We thank Dr. Atsuya Muranaka of the Institute of Physical and Chemi-

cal Research (Riken), Saitama, Japan for help with MCD measurements

in the near-IR region.

5,10,15,20-Tetra-4-dimethylaminophenyldiphenanthro[9,10-b:9,10-l]-

21,23-diselenaporphyrin (N₂Se₂-NMe₂): N₂Se₂-NMe₂was prepared as de-

scribed above from 2,5-bis(4-hexadecyloxyphenylhydroxymethyl)seleno-

phene (429 mg, 1 mmol), phenanthroACTHNUTRGNEUGN[9,10-c]pyrrole (217 mg, 1 mmol),

BF₃·Et₂O (80 mL, 0.64 mmol), and DDQ (227 mg, 1 mmol). Column chro-

matography on silica gel (CHCl₃, EtOH/CHCl₃2%, then TEA/CHCl₃

5%), followed by recrystallization from CHCl₃/MeOH, afforded dark-

green crystals (457 mg,75%). M.p.>2508C; ¹H NMR (500 MHz,

CH₃CH₂OD/CDCl₃, 1:1): d=8.51–8.48 (m, 4H), 8.49–8.41 (m, 8H), 8.14–

8.12 (m, 4H), 7.38–7.36 (m, 4H), 7.28–7.25 (m, 4H), 7.11–7.08 (m, 4H),

6.97–6.96 (m, 8H), 3.27 ppm (s, 24H); UV/Vis (CHCl₃): l_max(e)=444

(5867), 593 nm (83841 mol^ꢁ1dm³cm^ꢁ1); MS (MALDI-TOF): m/z calcd

for C₇₆H₆₀N₆Se₂: 1215.250; found: 1215.055; elemental analysis calcd (%)

for C₇₆H₆₀N₆Se₂: C 75.11, H 4.98, N 6.92; found: C 74.99, H 4.96, N 6.78.

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Received: March 21, 2012

Revised: August 3, 2012

Published online: November 13, 2012

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Article Doi

Synthesis and properties of fused-ring-expanded porphyrins that were core-modified with Group 16 heteroatoms

DOI: 10.1002/chem.201200956

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