Synthesis, spectroscopy, and molecular orbital calculations of subazaporphyrins, subphthalocyanines, subnaphthalocyanines, and compounds derived therefrom by ring expansion

9096

J. Am. Chem. Soc. 1999, 121, 9096-9110

Synthesis, Spectroscopy, and Molecular Orbital Calculations of

Subazaporphyrins, Subphthalocyanines, Subnaphthalocyanines, and

Compounds Derived Therefrom by Ring Expansion¹

Nagao Kobayashi,*^,†Takeo Ishizaki,^†Kazuyuki Ishii,^†and Hideo Konami^‡

Contribution from the Department of Chemistry, Graduate School of Science, Tohoku UniVersity,

Sendai 980-8578, Japan, and Miyagi National College of Technology, Natori 981-1239, Japan

ReceiVed September 17, 1998

Abstract: A subazaporphyrin (SubAP), tert-butylated and crowned subphthalocyanines (tBSubPc and SubCRPc),

a µ-oxo dimer of tert-butylated SubPc {(tBSubPc)₂O}, a subnaphthalocyanine (SubNc), and monosubstituted

type unsymmetrical phthalocyanine (Pc) and naphthalocyanine (Nc) analogues have been synthesized. In

particular, unsymmetrical Pc’s and Nc’s have been prepared in moderate yields by the ring expansion reaction

of structurally distorted SubPc’s and SubNc’s with isoindolediimine derivatives in dimethyl sulfoxide-

chloronaphthalene (or chlorobenzenes or aromatic hydrocarbons such as toluene and xylene) mixtures. The

compounds have been characterized by electronic absorption, magnetic circular dichroism (MCD), fluorescence

emission, and nuclear magnetic resonance spectroscopy. Both the Soret bands and Q-bands shift to longer

wavelength and gain intensity in the order SubAP, SubPc, and SubNc. Fluorescence quantum yields and lifetimes

generally decrease with decreasing molecular symmetry. Circular dichroism and NMR spectroscopy have

revealed that a SubPc with three 15-crown-5 ether voids having a phenyl group as an axial ligand (SubCRPc)

forms inclusion complexes with 2,6-dimethyl-â-cyclodextrin in acetonitrile or water-acetonitrile mixtures,

while the electronic absorption spectroscopy suggests that it is not dimerized by the addition of cations such

as K⁺, Rb⁺, Ce⁺, i.e., cations which are effective in dimerizing Pc’s with 15-crown-5 ether voids. Molecular

orbital (MO) calculations within the framework of the Pariser-Parr-Pople approximation have succeeded in

reproducing the optical absorption experimental data of not only the parent subazamacrocycles but also Pc

derivatives with lower symmetry obtained by the ring expansion reaction. The correspondence between MO

calculations and experiments suggests strongly that, in the metal-free unsymmetrical Pc’s, two pyrrole hydrogen

atoms are bound to the nitrogens along the short axis. Comparison of formation, bonding, and donation energies

between SubPc and typical Pc, i.e., MgPc by natural bond orbital analysis, suggests that the distortion energy

is not the major reason for the ring expansion reactivity of SubPc, and that the lack of donor-acceptor

stabilization in B-N(pyrrole) bonds destabilizes SubPc. Band deconvolution of the electronic absorption and

MCD spectra of SubPc with the same set of bands (with the same centers and width) experimentally identified

that the excited state of the Q-band of SubPc is orbitally degenerate, with three degenerate transitions located

in the 250-450-nm region. In particular, the transition at 359 nm corresponds to a shoulder seen on the red

side of the Soret band tail. Time-resolved EPR analysis has shown that the size of the π-system of SubPc is,

indeed, smaller than that of Pc’s.

Introduction

several groups have reported many new monosubstituted type

Pc’s.⁴However, most papers have been concerned only with

the synthesis of SubPc’s, and the spectroscopic characterization

of these compounds has not been examined in detail. In this

In 1990, we reported a new method for preparing monosub-

stituted type phthalocyanines (Pc’s) via the so-called subph-

thalocyanines (SubPc’s).¹Among various Pc analogues, mono-

substituted C_2Vtype Pc’s had previously been prepared either

by mixed condensation reaction²or by a polymer support³

method. The former method gave mixtures of products that

could not be readily separated by chromatographic methods,

while the latter method required a functional group which is

linked to a polymer and which could be cleaved therefrom after

synthesis. Following our introduction of this new method,

(4) (a) Kobayashi, N. J. Chem. Soc., Chem. Commun. 1991, 1203. (b)

Musluoglu, E.; Gurec, A.; Ahsen, V.; Gul, A.; Bekaroglu, O. Chem. Ber.

1992, 125, 2337. (c) Kasuga, K.; Idehara, T.; Hamada, M.; Isa, K. Inorg.

Chim. Acta 1992, 196, 127. (d) Danak, S.; Gul, A.; Bekaloglu, O. Chem.

Ber. 1994, 127, 2009. (e) Hanack, M.; Geyer, M. J. Chem. Soc., Chem.

Commun. 1994, 2253. (f) Rauschnabel, J.; Hanack, M. Tetrahedron Lett.

1995, 1629. (g) Weitmeyer, A.; Kliesch, H.; Wohrle, D. J. Org. Chem.

1995, 60, 4900. (h) Sastre, A.; Torres, A.; Hanack, M. Tetrahedron Lett.

1995, 8501. (i) Diaz-Garcia, M. A.; Agullo-Lopez, F.; Sastre, A.; Torres,

T.; Torruellas, W. E.; Stegeman, G. I. J. Phys. Chem. 1995, 99, 14988. (j)

Sastre, A.; Torres, T.; Diaz-Garcia, M. A.; Agullo-Lopez, F.; Dhenaut, C.;

Brasselet, S.; Ledoux, I.; Zyss, J. J. Am. Chem. Soc. 1996, 118, 2746. (k)

Sastre, A.; Rey, B.; Torres, T. J. Org. Chem. 1996, 61, 8591. (l) Geyer,

M.; Plenzig, F.; Rauschnabel, J.; Hanack, M.; Rey, B.; Sastre, A.; Torres,

T. Synthesis 1996, 1139. (m) Kasuga, K.; Idehara, T.; Handa, M.; Ueda,

Y.; Fujiwara, T.; Isa, K. Bull. Chem. Soc. Jpn. 1996, 69, 2559. (n)

Kudrevich, S.; Brasseur, N.; Madeleine, C. L.; Gilbert, S.; van Lier, J. E.

J. Med. Chem. 1997, 40, 3897.

^†Tohoku University.

^‡Miyagi National College of Technology.

(1) Preliminary results have been published: Kobayashi, N.; Kondo, R.;

Nakajima, S.; Osa, T. J. Am. Chem. Soc. 1990, 112, 9640.

(2) (a) Konami, H.; Hatano. H. Chem. Lett. 1988, 1359. (b) Piechocki,

C.; Simon, J. J. Chem. Soc., Chem. Commun. 1985, 259.

(3) Leznoff, C. C. In PhthalocyaninessProperties and Applications;

Leznoff, C. C., Lever, A. B. P., Eds.; VCH: New York, 1989; Chapter 1.

Published on Web 09/15/1999

Subazaporphyrins and Subphthalo- and Subnaphthalocyanines

J. Am. Chem. Soc., Vol. 121, No. 39, 1999 9097

electronic absorption spectra of the product.⁵The desired SubAP

suitable for spectroscopic study was synthesized without bro-

mination, although the yield was not high (1.9%).

Substituent-free SubNc was initially synthesized from 2,3-

dicyanonaphthalene and BBr₃in chloronaphthalene according

to the procedure reported by Meller and Ossko.⁶The problem

of partial bromination was greatly diminished when 6-tert-butyl-

2,3-dimethylnaphthalene, obtained by Friedel-Crafts butylation

of 2,3-dimethylnaphthalene, was used as a solvent, since

bromination occurred mostly on this compound due to electron-

rich character of the molecule.

To synthesize (SubPc)₂O, we first changed the axial bromine

atom of tert-butylated subphthalocyanines (tBSubPc’s) to an

OH group using an ion-exchange resin,⁷and the resultant

tBSubPc with the OH group was heated at ca. 200 °C under

vacuum for 21 h. After cooling, the residue was imposed on a

gel permeation chromatography column for complete separation

from the monomeric tBSubPc.

Boron tribromide is an effective cutter of ether linkages.⁸

Accordingly, triphenylborane^4ewas used instead of BBr₃for

the synthesis of SubCRPc, to avoid cleavage of the crown ether

unit. The reaction was carried out in naphthalene in the presence

of 1,8-diazabicyclo[5,4,0]-7-undecene (DBU), but the yield was

very low (ca. 0.4%). This low yield is ascribed to the difficulty

of the elimination of two phenyl groups from triphenylborane.

Even with such a low yield, SubCRPc is requisite for the cation

complexation studies (for details, see section III).

Figure 1. Structures and abbreviations of the subazamacrocycles

studied.

NMR signals of protons of tBSubPc were observed at 8.63-

8.71 (m, 3H, arom), 8.50-8.56 (m, 3H, arom), 7.82-7.90 (m,

3H, arom), and 1.48-1.57 ppm (m, 27H, butyl). The positions

of these signals did not change at 0.07 < [tBSubPc] < 5 mM,

suggesting that the aggregation trend is very small.⁹In

comparison with these, in the corresponding zinc phthalocya-

nine, i.e., tetra-tert-butylphthalocyaninatozinc(II) (tBZnPc), the

corresponding proton signals appear at 8.3-8.9 (br, 8H, arom),

7.90-8.08 (br, 4H, arom), and 1.72-1.77 ppm (m, 36H, butyl)

at 0.1 mM. Although there is almost no difference in the

positions of aromatic proton signals between tBSubPc and

tBuZnPc, the position of tert-butyl protons suggests that the

ring current of a SubPc skeleton is smaller than that of the Pc

skeleton.

(b) Unsymmetrical Pc Analogues. Monosubstituted type Pc

analogues (Figure 2) were obtained by reacting tBSubPc^4a(1

equiv) and 1H-isoindole-1,3(2H)-diimine¹⁰or its analogues Nil,

Ben, Nap, An, or Py (typically ca. 7 equiv) at 80-90 °C in a

mixture of dimethyl sulfoxide (DMSO) and either chloroben-

zene, dichlorobenzene, toluene, xylene, or 1-chloronaphthalene

(CNP) (mostly 5:1-1:3 v/v) for 5-30 h (Figure 3). To find

the optimum solvent ratio in the reaction, the solvent ratio was

continuously varied (from 10:0 to 0:10 v/v) between DMSO

and CNP, and the above experiments were repeated at fixed

[SubPc] and [isoindolediimine], keeping other conditions exactly

the same. We were unable to obtain any BenPc in pure DMSO

or CNP. However, when the more soluble 5-tert-butyl-1H-

Figure 2. Synthetic routes to various low-symmetrical Pc derivatives

NilPc-PyPc from tBSubPc. The resultant Pc derivatives are expressed

using abbreviations of the molecules introduced. BenPc, NapPc, AnPc,

and PyPc represent, therefore, a benzene-, naphthalene-, anthracene-,

and pyridine unit-introduced Pc, respectively, while NilPc means Pc

analogue without fused ring.

paper, we have initially synthesized a subazaporphyrin (SubAP),

several SubPc’s, and a subnaphthalocyanine (SubNc) (Figure

1) and then further obtained new compounds by ring expansion

reaction of these (Figure 2). Most of the new compounds have

been characterized by various spectroscopic techniques, and

some of the data has been reproduced by molecular orbital (MO)

calculations. We have also considered, through quantum chemi-

cal calculations, why SubPc’s can be utilized for ring expansion

reactions.

Results and Discussion

I. Synthesis and NMR. (a) SubAP, tBSubPc, SubNc,

(tBSubPc)₂O, and SubCRPc. Syntheses of normal SubPc’s

have been reported in several publications.⁴Accordingly, we

comment here only on the syntheses of SubAP, SubNc, and

crowned subphthalocyanines (SubCRPc). As a starting material

for SubAP, we used 2-(o-trifluoromethyl)phenyl-1,1,2-tricya-

noethylene because of (i) its accessibility,⁵(ii) the high solubility

we expected for the resulting macrocycles, (iii) the low

temperature that we expected cyclization to require, (iv) the low

possibility of bromination during cyclization with boron tribro-

mide, and (v) the small substituent effect we anticipated on the

(6) (a) Meller, A.; Ossko, A. Monatsh. Chem. 1972, 103, 150. (b)

Kietaibl, H. Monatsh. Chem. 1974, 105, 405.

(7) Sauer, T.; Wegner, G. Mol. Cryst. Liq. Cryst. 1988, 162B, 97.

(8) McOmie, J. F.; Watts, M. L.; West, D. E. Tetrahedron 1968, 24,

2289. Bhatt, M. V.; Kulkarnyi, S. U. Synthesis 1983, 249.

(9) Positions of NMR signals of Pc’s change on aggregation: Terekhov,

D. S.; Nolan, K. L. M.; McArthur, C. R.; Leznoff, C. C. J. Org. Chem.

1996, 61, 3034.

(10) 1H-Isoindole-1,3(2H)-diimine and its analogues were obtained by

reacting aromatic ortho-dinitriles with ammonia gas in dry methanol or

propanol containing CH₃ONa or C₂H₅ONa (Brach, P. J.; Grammatica, S.

J.; Ossanna, O. A.; Weinberger, L. J. Heterocycl. Chem. 1970, 7, 1403).

(5) Troitskaya, V. I.; Trushanina, L. A.; Kopranenkov, V. N.; Luk’yanets,

E. A.; Yagupol’skii, L. M. J. Gen. Chem. (Engl. Transl.) 1989, 25, 513.

9098 J. Am. Chem. Soc., Vol. 121, No. 39, 1999

Kobayashi et al.

Figure 3. (a) Spectroscopic change during the reaction of tSubPc and

tert-butylisoindolediimine in a 1:1 (v/v) mixture of DMSO and CNP

at 90 °C. [tSubPc]/M ) 2.21 × 10^-5and [tert-butylisoindolediimine]/

M ) 1.44 × 10^-3. Arrows indicate the direction of spectroscopic

change. (b) Absorbance change at 570 nm with time, replotted from

(a).

Figure 4. MCD (top) and electronic absorption (middle) spectra of

SubAP (s), tBSubPc (‚ ‚ ‚), and SubNc (- - -) in CHCl₃(the former

two) or in o-dichlorobenzene (the latter one). The bottom panel shows

the electronic absorption spectrum of SubCRPc in CHCl₃.

isoindole-1,3(2H)-diimine was employed instead of the less

soluble 1H-isoindole-1,3(2H)-diimine, the reaction proceeded

even in pure DMSO or CNP, and some tetra-tert-butylated H₂-

Pc was obtained. Accordingly, the solubility of the reactant is

important, as in general reactions. Next, we repeated the same

experiment using isoindolediimine derivatives Nil and Nap.

Again, the reaction did not proceed in the two single solvents,

and the optimum solvent ratio changed from system to system.

However, relatiVely good yields were attained in the range of

DMSO:CNP ) 3:1-1:2 V/V.

The formation of tetra-tert-butylated H₂Pc from tBSubPc and

5-tert-butyl-1H-isoindole-1,3(2H)-diimine was monitored spec-

troscopically (Figure 3A). The 570-nm band of tSubPc disap-

pears with concomitant increase of the absorption at ca. 600-

720 nm. The time evolution of this reaction is plotted in Figure

3B by following the change of absorbance at 570 nm. The

absorbance changes relatively rapidly initially, but the rate

decreases as the reaction proceeds, and it takes almost 1 day to

complete the reaction.

Pyrrole proton signals of porphyrins and Pc’s generally appear

at around -2 to -6 ppm,¹¹and their position is an approximate

measure of the strength of the ring current. In the order of NilPc

to PyPc, the NH proton signals of 0.1 mM solution appeared at

-1.73 to -1.97, -2.7 to -4.1, -2.35 to -3.2, -1.8 to -4.4,

and -2.3 to -2.8 ppm, respectively. In the case of Pc’s, the

position of the proton signals depends on the degree of

aggregation.⁹However, considering that tert-butyl groups reduce

the aggregation⁹and that the sizes of the π-systems of NilPc

to PyPc, which affect the degree of aggregation, do not differ

significantly, the above data at 0.1 mM concentration appear

to be directly comparable. Signals of BenPc emerged at the

highest field, indicating that the ring current in this complex is

the largest. Elimination of a benzene ring from BenPc (i.e.,

NilPc) or fusion of another benzene (i.e., NapPc) reduces the

ring current. In particular, the ring current of NilPc is much

smaller than that of BenPc, suggesting that the main contribution

to the Pc ring current is not only from the inner 16- or 20-

membered rings but also from the four benzene rings. According

to theoretical calculations on π-electron ring currents of por-

phyrins and Pc’s,¹²in tetrabenzoporphyrins and Pc’s the ring

current along the outer rim, including four benzene rings, is

predicted to exceed that along the inner 20-membered porphyrin

skeleton. Hence, the small ring current in NilPc compared to

that in BenPc may be in accord with this prediction. The slight

downfield shift of signals of NapPc and AnPc from BenPc

indicates that the further outer fused benzenes have a slight effect

on the ring current of the macrocycles. Comparison of the

position of the NH proton signals of BenPc (-2.7 to -4.1 ppm)

and PyPc (-2.3 to -2.8 ppm) reveals that fusion of a

heterocyclic aromatic ring in place of a benzene ring also

reduces the ring current in Pc’s.¹³

II. Spectroscopy. (i) Electronic Absorption and Magnetic

Circular Dichroism Spectroscopy. (a) SubAP, tBSubPc,

SubNc, (tBSubPc)₂O, and SubCRPc. The electronic absorption

and magnetic circular dichroism (MCD) spectra of SubAP,

tBSubPc, and SubNc in this study (Figure 4) clearly indicate a

tendency for both the Soret bands and Q-bands to shift to longer

(12) Vysotsky, Y. B.; Kuzmitsky, V. A.; Solovyov, K. N. Theor. Chim.

Acta (Berin) 1981, 59, 467.

(13) In fact, tetrapyradinoporphyrazines show the NH proton signals at

-1.2 to -1.5 ppm in chloroform (Tokita, S.; Kojima, M.; Kai, N.; Nishi,

H.; Tomoda, H.; Saito, S.; Shiraishi, S. Nihon Kagaku Kaishi 1990, 219).

(11) Leznoff, C. C.; Marcuccio, S. M.; Greenberg, S.; Lever, A. B. P.;

Tomer, K. B. Can. J. Chem. 1985, 63, 623, 3057. Scheer, H.; Katz, J. J. In

Porphyrins and Metalloporphyrins; Smith, K. M., Ed.; Elsevier: Amster-

dam, New York, 1975; Chapter 10.

Subazaporphyrins and Subphthalo- and Subnaphthalocyanines

J. Am. Chem. Soc., Vol. 121, No. 39, 1999 9099

wavelengths and intensify with the increase of the π-conjugation

system. The SubAP, tBSubPc, and SubNc have Q-bands at 411

(pale brown), 567 (reddish-purple), and 667 nm (greenish-blue)

and Soret bands at ca. 290, 307, and 328 nm, respectively.

Compared with the band positions of the corresponding cyclic

tetramers, i.e., tert-butylated TAP, Pc, and Nc, in the same

solvent,¹⁴the Q-bands are shifted to the blue by ca. 170-180

(ca. 7100-7400 cm^-1), 120-130 (ca. 3000-3500 cm^-1), and

100-120 nm (ca. 2000-2340 cm^-1), respectively, and the Soret

bands ca. 40-50 nm (ca. 4200-5100 cm^-1), 23-33 nm (ca.

2300-3200 cm^-1), and 5-15 nm (ca. 500-1300 cm^-1),

respectively. These data indicate that, although the bands shift

to longer wavelength with the fusion of the benzene unit, the

extent of the shift becomes smaller as the size of the molecule

increases.

It is also interesting to compare the band position among

SubPc, Pc, and superphthalocyanines (SPc’s),¹⁵i.e. for cyclic

trimers, tetramers, and pentamers of isoindolediimines having

the same or similar substituent groups. Considering that the

Q-band of SPc’s appears at ca. 910-930 nm, it is found that

the Q-band energy changes ca. 3000-3600 cm^-1per iso-

indolediimine unit. Absorption coefficients (ꢀ) in both the Soret

bands and Q-bands also increase on going from SubPc’s to Pc’s.

For example, the ꢀ values of the Q-bands of alkylated SubPc’s

are (5-6) × 10⁴dm³mol^-1cm^-1, as seen for tBSubPc and

SubCRPc in Figure 4, and those of most Pc’s¹⁴are in the range

(8-24) × 10⁴dm³mol^-1cm^-1. The Q-band of SPc’s may be

weaker since the area of the Q-band is smaller when the abscissa

of the spectrum is expressed in cm^-1unit. A severe buckling

structure of SPc^15cmay prevent a large transition moment from

being produced. The smaller Q-band intensity of SubPc’s

compared to that of general Pc’s may be attributed to their non-

flat, cone-shaped structure.^6bUnder such circumstances, transi-

tion moments, which can be expressed by linear vectors, cannot

become large.

type MCD curves are observed, corresponding to two absorption

peaks. These are also transitions to the doubly degenerate excited

states (see MO section).

Table 1 summarizes the most important electronic absorption

and MCD data in the Q-band. Apparently, the dipole strength

of SubNc is almost the same as those of BenPc, NapPc, and

PyPc (Table 1A). However, this indicates that the intensity of

the Q-band of SubNc is about half those of the latter compounds,

since the values for BenPc, NapPc, and PyPc are only for the

Q_x0-0band. Since the value for tBSubPc is even smaller, we

can conclude safely that the Q-bands of subaza compounds are

weaker than those of the corresponding tetrapyrrolytic Pc’s or

Nc’s. In addition, A/D values and magnetic moments (µ) in

Table 1B are also smaller than those of Pc’s, indicating that

the orbital angular momentum of the excited state of the

subazamacrocyclic ligand is smaller than that of Pc’s.¹⁸

The spectra of (tBSubPc)₂O are collected in Figure 5.

Compared with the spectrum of the constituting monomer,

tBSubPc, the Q-band shifts to the blue, while the position of

the Soret band is virtually the same. The blue-shift of the Q-band

can be explained on the basis of an exciton interaction. Also,

the shape of the Q-band is similar to that of the µ-oxo-dimer of

an iron Pc,¹⁹though both the Q-bands and Soret bands appear

at shorter wavelengths than the respective band of the Pc’s.

(b) Unsymmetrical Pc Analogues. Electronic absorption and

MCD spectra of NilPc to PyPc are collected in Figures 6 and

7, respectively, as solid lines. The absorption spectrum of NilPc

is similar to that of tribenzotetraazaporphine without peripheral

substituent groups,²⁰and the spectrum of BenPc is typical of

those of metal-free Pc’s.¹⁸All compounds show the split Q_0-0

-

bands due to the low symmetry of the molecules. The splitting

in NilPc (2017 cm^-1) is particularly large compared with those

of the other four compounds. Comparison of this energy in

BenPc, NapPc, and AnPc (684, 817, and 914 cm^-1, respectively)

indicates that the larger the introduced conjugation unit, the

larger will be the splitting of the Q_0-0-band, although the

molecular symmetry is C_2Vin each case. In PyPc, this splitting

is 640 cm^-1, a value slightly smaller than the benzene analogue,

i.e., BenPc.

The Q_0-0peaks shift to longer wavelength with enlargement

of the π-conjugated system, while the extent of the band shift

decreases with increasing molecular size. If we take the center

of the two split Q_0-0peaks as the positions of the Q-band, then

the energy differences of the Q-bands among NilPc to AnPc

are 1030, 506, and 463 cm^-1for NilPc-BenPc, BenPc-NapPc,

and NapPc-AnPc, respectively. The absorption coefficients (ꢀ)

of the Q-bands decrease generally with decreasing symmetry

of the molecules, i.e., BenPc > NapPc > AnPc > NilPc, while

the ratio of the actual absorption (the oscillator strength) at 500-

800 nm (the Q-band) is 0.75:1.00:1.03:0.88 for NilPc:BenPc:

NapPc:AnPc, suggesting that the Q-band does not intensify

indefinitely with increasing molecular size. Small peaks seen

at 454 nm for NapPc and at 462 nm for AnPc may not be

ascribed to the naphthalene or anthracene moiety, since the

absorption bands of naphthalene and anthracene appear generally

below ca. 300 or 400 nm, respectively.²¹

The absorption spectrum of SubCRPc is different from that

of tBSubPc in that another envelope is involved at the longer

wavelength side of the Soret band. This band has been postulated

to be an n-π transition in ether oxygen or thioether sulfur.^16,17

However, the band appears much more intense than n-π

transitions, suggesting strong intensity borrowing from the

π-system.

Given the somewhat cone-shaped nature of SubPc’s,^6bthe

MCD spectra of these subazacompounds can be interpreted

under the C_3Vor D_3happroximation. The Q-band MCD spectra

of tBSubPc and SubNc appear to correspond to the wavelengths

of the absorption spectra. Though the spectra are not sym-

metrical with respect to the line of [θ]_M) 0, this nonsym-

metricity is due to the superimposition of Faraday A and B terms,

as will be shown later in the sections on MO calculations and

band deconvolution. Namely, a transition to the degenerate state

is included in this region, as in general metalloPc’s.¹⁸In the

250-350-nm region of the spectra of tBSubPc, two dispersion

(14) Luk’yanets, E. A. Electronic Spectra of Phthalocyanines and Related

Compounds; NIOPIK: Moscow, 1989. Kobayashi, N. In Phthalocyaniness

Properties and Applications; Leznoff, C. C., Lever, A. B. P., Eds.; VCH:

New York, 1992; Vol. 2, Chapter 3.

(15) (a) Bloor, J. E.; Schlabits, J.; Wolden, C. C.; Demerdache, A. Can.

J. Chem. 1964, 42, 2201. (b) Cuellar, E. A.; Marks, T. J. Inorg. Chem.

1981, 20, 3766. (c) Day, V. W.; Marks, T. J.; Wacher, W. A. J. Am. Chem.

Soc. 1975, 97, 4519.

The spectra of deprotonated (-H₂) species are shown as

broken lines (Figure 6). The Q-bands of (-H₂)BenPc and

(-H₂)NapPc are close to those of MtPc’s with D_4hsym-

metry,^14,18indicating that elimination of two pyrrole protons

(16) Kobayashi, N.; Lever, A. B. P. J. Am. Chem. Soc. 1987, 109, 7433.

(17) Aoudia, M.; Cheng, G.; Kennedy, V. O.; Kenney, M. E.; Rodgers,

M. A. J. J. Am. Chem. Soc. 1997, 119, 6029.

(19) Lever, A. B. P.; Licoccia, S.; Ramaswamy, B. S. Inorg. Chim. Acta

1982, 64, L87.

(18) Stillman, M. J.; Nyokong, T. In PhthalocyaninessProperties and

Applications; Leznoff, C. C., Lever, A. B. P., Eds.; VCH: New York, 1989;

Chapter 3.

(20) Elvidge, J. A.; Linstead, R. P. J. Chem. Soc. 1955, 3536.

(21) Kobayashi, N.; Minato, S.; Osa, T. Makromol. Chem. 1983, 184,

2123.

9100 J. Am. Chem. Soc., Vol. 121, No. 39, 1999

Kobayashi et al.

Table 1. Experimental Determination of (A) the Longest Wavelength Band Parameters in Chloroform (SubAP and tBSubPc) and in

o-Dichlorobenzene (Others) and (B) the MCD Parameters of the Q-Band

(A) Longest Wavelength Band Parameters in Chloroform and in o-Dichlorobenzene

λ

_max/nm

half-width at

compd

SubAP^b

(λ_max/kcm^-1

)

ꢀ

1/e height/cm^-1

dipole strength/D²

24.57

dipole length/Å

1.034

[θ]_M

B/D × 10^{4 a}

411

12 200

3005

(24.331)

567

(17.637)

667

(14.993)

680

(14.706)

700

(14.286)

729

(13.717)

757

(13.210)

688

tBSubPc

SubNc

NilPc

51 500

62 600

58 500

122 000

91 000

41 200

112 000

378

18.00

0.885

1.116

0.869

1.210

1.103

0.777

1.167

451

30.71

267.6

241.8

258.8

273.4

249.2

17.359

33.673

27.996

13.891

31.312

-24.7

-125.6

-80.6

21.6

52.7

45.3

51.4

65.9

BenPc

NapPc

AnPc

-41.4

PyPc

-144.1

(14.535)

(B) MCD Parameters of the Q-Band^c

compd

tBSubPc^g

SubNc^h

UV/nm

Γ/cm^-1

A/D^d

µ^e

[θ]₁

[θ]₂

diff

sum

B/D × 10^{4 f}

17.99

12.75

567

667

593

715

0.846

0.972

-1.692

-1.944

-32.0

-33.1

+5.3

+10.1

-37.3

-43.2

-26.7

-23.0

^aB/D values in systems not containing transitions to the degenerate excited states. ^bThe 411-nm band is tentatively assumed as the Q-band. ^cTo

obtain A/D values by Briat’s method (Briat, B.; Schooley, D. A.; Records, R.; Bunnenberg, E.; Djerassi, C. J. Am. Chem. Soc. 1967, 89, 7062), [θ]₁

and [θ]₂in this table are expressed by molar ellipticity per unit gauss. Γ is the width at half-maximum absorption. diff ) [θ]₁- [θ]₂, sum ) [θ]₁

+ [θ]₂, and A/D ) -1.97Γ(diff)/ꢀ_m, while B/D ) -3.47(sum/ꢀ_m). Faraday A and B terms are expressed by â D²and â D²/cm^-1, respectively, as

in Stephens, P. J.; Suetaak, W.; Schatz, P. N. J. Chem. Phys. 1966, 44, 4592. ^dA/D values under a new definition (Piepho, S. B.; Schatz, P. N.

Group Theory in Spectroscopy; John Wiley & Sons: New York, Chichester, 1983) are obtained by dividing these values by 2. ^eMagnetic moment.

^fB/D values associated with A terms. ^gIn chloroform. ^hIn o-dichlorobenzene.

Figure 5. MCD (top) and electronic absorption spectra (bottom) of

tBSubPc (‚ ‚ ‚) and (tBSubPc)₂O (s) in CHCl₃. The electronic spectrum

ofµ-oxobis{tetra(dodecylsulfonamide)phthalocyaninatoiron(III)},(TdPcFe)₂O,

in DMF (bottom, - - -) is replotted for comparison from ref 19.

helps lessen the difference between the Q_x- and Q_y-bands. This

is also reflected in the spectra of (-H₂)NilPc and (-H₂)AnPc.

Differing from the case of (-H₂)BenPc, however, (-H₂)PyPc

still shows two Q_0-0-band (a peak and a shoulder), suggesting

that replacement of the benzene ring with a pyridine ring further

lowers the molecular symmetry. There is one common spec-

troscopic change in the Soret band region on deprotonation:

the relatively sharp Soret bands in NilPc to PyPc become weaker

and extend to longer wavelengths. Thus, in general, at least three

bands are seen between 300 and 500 nm.

Figure 6. UV-visible-near-IR absorption spectra of NilPc-PyPc (top

The MCD spectra of porphyrins with C_2Vsymmetry can be

interpreted as a superimposition of Faraday B terms.¹⁸MCD

spectra of neutral NilPc to PyPc (Figure 7, solid lines) can also

be interpreted as a superimposition of Faraday B terms. For

to bottom) in o-dichlorobenzene. (s) Neutral forms; (- - -) deprotonated

forms obtained by addition of tetrabutylammonium hydroxide. Because

of solution instability, a well-defined curve was not obtained in the

Soret region of deprotonated AnPc.

Subazaporphyrins and Subphthalo- and Subnaphthalocyanines

J. Am. Chem. Soc., Vol. 121, No. 39, 1999 9101

Figure 8. Fluorescence emission (solid lines) and excitation spectra

(broken lines) of SubAP, tBSubPc, SubNc, and SubCRPc (top to

bottom) in CHCl₃. Excitation wavelengths and emission wavelengths

used to record excitation spectra are shown. The absorbance at the

excitation wavelengths was always less than 0.05.

Figure 7. MCD spectra of NilPc-PyPc (top to bottom) in o-

dichlorobenzene. (s) Neutral species; (- - -) deprotonated species

obtained by addition of tetrabutylammonium hydroxide. Because of

solution instability, a well-defined curve was not recorded in the Soret

region of deprotonated AnPc.

Figure 8. All compounds exhibit so-called S₁emission, while

only SubCRPc shows S₂emission additionally, and they have

a mirror-image relationship with respect to their excitation

spectra. The S₂emission is broader than the S₁emission and

has a band shape similar to that observed for phthalocyanine^23,24

and tetrabenzoporphyrin.²⁵Interestingly, the Stokes shift for S₁

emission increases with decreasing molecular size, so that

compounds showing Q-band at shorter wavelengths have larger

shifts. The values of Stokes shift were 59064, 5988, 4902, and

roughly ca. 400-600 cm^-1in the order of SubAP, tBSubPc,

SubNc, and general Pc’s.^24aThe value of S₁Stokes shift of

SubAP is within the size of that found for S₂emission of Pc’s

(roughly 46 000-74 000 cm^-1).^24bThis result indicates experi-

mentally that the spacing of the vibrational level indeed becomes

smaller as the size of the π-system increases.

By using the known quantum yields of quinine sulfate (for

SubAP), tetraphenylporphyrin (for tBSubPc), Rhodamine B (for

SubCRPc), and compound PyPc (for SubNc) as calibrants,²⁶

the quantum yields (φ_F) of S₁emission for SubAP, tBSubPc,

SubCRPc, and SubNc were determined to be 0.034, 0.61, 0.135

(in chloroform), and 0.094 (in o-dichlorobenzene), respectively.

The value for tBSubPc is smaller than that for tBH₂Pc (0.85)^27a

but slightly larger than that for tert-butylated metal-free tetra-

example, in NilPc, the Q-band MCD maximum and minimum

appear corresponding to the two intense Q peaks, and the shape

of the Q-band MCD of BenPc and PyPc resembles that of metal-

free Pc’s with D_2hsymmetry. The Soret band MCD spectra of

NilPc to PyPc are, on the other hand, relatively simple, showing

a strong dispersion type curve corresponding to the main Soret

absorption peaks. Although these look like Faraday A terms,

they are being caused by the superimposition of close Faraday

B terms,²²since no degenerate state is expected for these

molecules theoretically.¹⁸

When the molecule is deprotonated (Figure 7, broken lines),

the Q-band MCD of (-H₂)BenPc and (-H₂)NapPc can be

interpreted as a pseudo-Faraday A term, since a single Q_0-0

-

band is seen in the absorption spectra. In contrast, the Q-band

MCD spectra of (-H₂)NilPc and (-H₂)PyPc are considered to

be a contribution of Faraday B terms, since the minimum and

maximum of MCD correspond to the two Q_0-0absorption peaks.

In the Soret region, although several Faraday A term type curves

are seen, the ones detected for (-H₂)BenPc, (-H₂)NapPc, and

(-H₂)PyPc at 440-480 nm might be pseudo-Faraday A terms,

which are often observed for MtPc’s with D_4hsymmetry (a

π-π^*transition from low-lying a_2uto the LUMO, i.e., 4a_2uto

7e_g).¹⁸

(23) Kobayashi, N.; Lam, H.; Nevin, W. A.; Janda, P.; Leznoff, C. C.;

Koyama, T.; Monden, A.; Shirai, H. J. Am. Chem. Soc. 1994, 116, 879.

(24) (a) Kobayashi, N.; Togashi, M.; Osa, T.; Ishii, K.; Yamauchi, S.;

Hino, H. J. Am. Chem. Soc. 1996, 118, 1073. (b) Kaneko, Y.; Nishimura,

Y.; Takane, N.; Arai, T.; Sakuragi, H.; Kobayashi, N.; Matsunaga, D.; Pac,

C.; Tokumaru, K. J. Photochem. Photobiol. A: Chem. 1997, 106, 177.

(25) Bajema, L.; Gouterman, M. J. Mol. Spectrosc. 1971, 39, 421.

Fielding, P. E.; Mau, A. W.-H. Aust. J. Chem. 1976, 29, 933. Aaviksoo, J.;

Freiberg, A.; Savikhin, S.; Stehlmakh, G. F.; Tsvirko, M. P. Chem. Phys.

Lett. 1984, 111, 275.

(ii) Emission Spectroscopy. (a) SubAP, tBSubPc, SubNc,

and SubCRPc. Fluorescence emission and excitation spectra

of monomeric subazamacrocycles in this study are shown in

(22) Tajiri, A.; Winkler, J. Z. Naturforsch. 1983, 38a, 1263. Kaito, A.;

Nozawa, T.; Yamamoto, T.; Hatano, M.; Orii, Y. Chem. Phys. Lett. 1977,

52, 154.

(26) (a) Demas, J. N.; Crosby, G. A. J. Phys. Chem. 1971, 75, 991. (b)

Seybold, P. G.; Gouterman, M. J. Mol. Spectrosc. 1969, 31, 1. (c) Strickler,

S. J.; Berg, R. A. J. Chem. Phys. 1962, 37, 814.

9102 J. Am. Chem. Soc., Vol. 121, No. 39, 1999

Kobayashi et al.

Table 2. S₁Quantum Yields (φ_F) and Lifetimes (τ) in Deaerated

Chloroform at Room Temperature^a

compd

φ_F

τ/ns

compd

φ_F

τ/ns

SubAP

0.03

0.61

0.14

0.09

2.51

2.10

1.35

1.93

NilPc

BenPc

NapPc

AnPc

PyPc

0.04

0.38

0.12

0.11

0.54

4.61

7.68

6.53

6.19

7.77

tBSubPc

SubCRPc

SubNc

^aData on SubNc alone were collected in o-dichlorobenzene due to

its low solubility in chloroform.

Figure 10. Structure of SubCRPc optimized using the UNIVERSAL

1.02 force field,⁵²which was implemented in Program Package Cerius2.

Hydrogens are omitted for clarity, and three Na⁺ions are trapped in

the 15-crown-5 moiety. Oxygen and boron atoms are represented by

large open circles, while nitrogens are by solid circles. The structure

of SubPc with a Cl axial ligand is also shown for comparison from ref

6b. Attachment of crown ether units further deforms the π-structure of

SubPc.

Figure 9. Fluorescence emission (s) and excitation spectra (- - -) of

NilPc-PyPc (top to bottom) in o-dichlorobenzene. Excitation wave-

lengths and emission wavelengths used to record excitation spectra are

shown. The absorbance at the excitation wavelengths was always less

than 0.05.

benzoporphyrin (0.57) in the same solvent.^27bThe value of 0.094

for SubNc is also smaller than that for tBH₂Nc (0.14).^27aThe

small value of 0.034 for SubAP may be related to the presence

of both CN and CF₃-phenyl group in this molecule; i.e. the

presence of two polar molecules may lead to the occurrence of

intramolecular charge transfer.

(b) Ring-Expanded Low-Symmetrical Pc Analogues. Fig-

ure 9 shows the fluorescence and excitation spectra of NilPc-

PyPc. Consistent with the absorption spectra, the main peak of

the emission generally shifts to longer wavelengths with the

enlargement of π-macrocycles, with the exception of compound

AnPc, which gave a peak at shorter wavelength than expected.

However, even in the case of AnPc, weak emission is seen at

ca. 760 nm as a shoulder corresponding to the Q-band to the

longest wavelength. The Stokes shifts are very small in each

case. In general, transitions involving emission in a condensed

organic molecule always takes place from the lowest excited

electronic level independently of the order of levels to which

the molecules was excited upon absorption of light.²⁸This

feature is typically seen for NilPc, where the intense fluorescence

symmetry and C_2Vsymmetry. It is noteworthy that the φ_Fvalue

for PyPc (0.54) is higher than that for AnPc (0.38).

The quantum yields and lifetimes of all compounds in this

study are summarized in Table 2. The lifetimes of subazamac-

rocycles are less than half of those of compounds NilPc-PyPc,

indicating that they are generally smaller for compounds having

smaller quantum yields.

III. Effect of Extraneous Cations. In the case of tetra-^16,30

or tricrowned^24aPc’s (MtCRPc’s), addition of some cations

induces dimerization. Since we succeeded in preparing Sub-

CRPc, we examined whether it can be dimerized by the addition

of some cations. As in the previous MtCRPc system, SubCRPc

was first dissolved in chloroform, and then concentrated

solutions of CH₃COOK, CH₃COOCs, CH₃COORb, or CH₃-

COONa dissolved in chloroform-methanol (9:1 v/v) were

added under stirring using a microsyringe, while the ac-

companying absorption spectroscopic changes were monitored.

However, in no case did we find any appreciable change. In

the case of MtCRPc, a hypsochromic shift accompanying a

hypochromic effect on the Q-band was the indication of

cofacial dimerization, and this was attained when cations which

form 1:2 complexes with 15-crown-5, such as K⁺, Cs⁺, and

Rb⁺, were added. From the absence of this kind of change, we

conjecture that the cone-shaped structure of SubPc^6bprevents

dimerization. The most probable structure obtained by a force

field calculation (Figure 10) suggests that three crown ether units

deviate so severely from planarity, forming a wine glass

band at 689 nm coincides with the first absorption band Q_x(0-0)

,

which is assumed to correspond to the first excited electronic

level.

The values of quantum yields (φ_F) are also given in the figure.

The value for BenPc (φ_F) 0.38) is almost 60% of that for

metal-free Pc in the same solvent (φ_F) 0.60),^26band the values

for NilPc, NapPc, and AnPc are much smaller, indicating that

lowering of molecular symmetry greatly destabilizes the S₁

state.^24a,29One possible cause for this may be the difference of

vibrational mode between Pc analogues with D_2hor D_4h

(29) Kobayashi, N.; Ashida, T.; Osa, T. Chem. Lett. 1992, 1567, 2031.

Kobayashi, N.; Ashida, T.; Osa, T.; Konami, H. Inorg. Chem. 1994, 33,

1735.

(27) (a) Kobayashi, N.; Higashi, Y.; Osa, T. Chem. Lett. 1994, 1813.

(b) Kobayashi, N.; Numao, M.; Kondo. R.; Nakajima, S.; Osa, T. Inorg.

Chem. 1991, 30, 2241.

(30) Koray, A. R.; Ahsen, V.; Bekaroglu, O. J. Chem. Soc., Chem.

Commun. 1986, 932. Sielcken, O. E.; van Tiborg, M. M.; Roks, M. F.;

Hendricks, R.; Drenth, W.; Nolte, R. J. M. J. Am. Chem. Soc. 1987, 109,

4261.

(28) Kasha, M. Discuss. Faraday Soc. 1950, 9, 14.

Subazaporphyrins and Subphthalo- and Subnaphthalocyanines

J. Am. Chem. Soc., Vol. 121, No. 39, 1999 9103

the formation constant was determined to be 516 mol^-1L in

acetonitrile-water (3:2 v/v) by the method of Rose and Drago.³⁴

The induced circular dichroism (ICD) spectra in Figure 11

are, however, different in the two solvent systems. Although

ICD spectra are seen corresponding to the absorption spectra

of SubCRPc, their sign is opposite: mainly plus in acetonitrile

and minus in the acetonitrile-water mixture. This difference

may be interpreted on the basis of hitherto accumulated

knowledge on the ICD of CDx-aromatic guest inclusion

complexes³⁵as the difference of the depth of the phenyl group

in the CDx cavity as follows. It has been established both

experimentally and theoretically that electronic transitions

parallel to the molecular axis of CDxs produce positiVe ICD,

while those normal to the axis show negatiVe ICD.^31,35Accord-

ingly, the inclusion structure in acetonitrile-water (3:2 v/v)

mixture can be inferred to be of the lid type,^35bin which the

macrocyclic plane of SubCRPc lies on the rim of DMâCDx.

The inclusion structure in acetonitrile seems similar but is an

exception of the above rule. This happens when the aromatic

guest molecules lie above the rim of the CDx by more than ca.

0.3 Å along the CDx axis,^35cand an inverse relationship with

respect to the sign of circular dichroism comes into force. Thus,

in acetonitrile, the phenyl group appears to be at the entrance

of the CDx cavity, while in solvents containing water it would

be trapped deep within the cavity. A Corey-Pauling-Koltun

molecular model suggests that more than 90% of the phenyl

group is trapped within the cavity in water. The driving force

for the inclusion of guest molecules by CDx is the hydrophobic

interaction.³¹Accordingly, in solvents containing water, hydro-

phobic aromatic guest molecules try to escape deep into the

hydrophobic CDx cavity, while in more hydrophobic organic

solvents, this kind of driving force will diminish.

V. Molecular Orbital Calculations. To deepen our under-

standing of the electronic absorption spectra of subazamacro-

cycles and their ring-expanded unsymmetrical phthalocyanine

analogues, molecular orbital calculations were performed for

both neutral protonated species (metal-free Pc derivatives) and

pyrrole proton deprotonated dianion species (subazamacro-

cycles) within the framework of the Pariser-Parr-Pople (PPP)

approximation.³⁶Although SubPc’s are not flat and have three-

fold rotation,^6bπ-electron calculations were adopted, since the

electronic spectra of buckled SPc’s have been successfully

explained using MO calculations at the PPP LCAO SCF CI

level of approximation.³⁷

(i) SubAP, SubPc, and SubNc Structures. Some frontier

MOs and MO levels of dianions of SubAP, SubPc, and SubNc

(i.e., SubAP^2-, SubPc^2-, and SubNc^2-, respectively) obtained

from our calculations are shown in Figures 12 and 13,

respectively, with the results of calculations summarized in

Table 3. The π-character in these frontier orbital is high. For

example, in SubPc^2-, the π-character of the HOMO - 1,

HOMO, and LUMOs are 83.3, 80.3, and 80.0%, respectively,

indicating that the treatment by π-electron approximation is

possible. Under C_3Vsymmetry, many transitions are doubly

degenerate, since several orbitals including LUMOs are orbitally

doubly degenerate. The LUMO and LUMO + 1 are degenerate

for all compounds, and for SubPc and SubNc the LUMO + 2

and LUMO + 3 are doubly degenerate. Of these, the latter two

Figure 11. Electronic absorption and ICD spectra of SubCRPc in the

absence (‚ ‚ ‚) and presence (s) of DMâCD in CH₃CN (top) and in

CH₃CN-H₂O (3:2 v/v) mixture (bottom). [DMâCD]/M ) 6.59 × 10^-3

.

Absorption spectra drawn with other lines are those obtained at lower

[DMâCD].

structure, that it is impossible to form a cofacial dimer on the

addition of cations.

IV. Host-Guest Complexation with 2,6-Dimethyl-â-Cy-

clodextrin. Since SubCRPc contains a phenyl group as an axial

ligand, its complexation with cyclodextrins (CDxs) was studied

using electronic absorption and circular dichroism spectroscopy.

As a CDx, 2,6-dimethyl-â-cyclodextrin (DMâCDx) was chosen

from size and solubility considerations.³¹The results in two

systems, acetonitrile and acetonitrile-water (3:2 v/v) mixtures,

are shown in Figure 11. The addition of DMâCDx to a solution

containing SubCRPc results in a small change in the absorption

spectra, suggesting interaction between SubCRPc and DMâCDx.

Inclusion of the crown moiety of the SubPc molecule is

impossible since its size is much larger than that of the CDx

cavity. Although inclusion of the phenyl moiety seems natural,

¹H NMR measurements were performed in the presence and

absence of DMâCDx in order to confirm this. In the absence

of DMâCDx, the signals of ortho, meta, and para protons of

the phenyl group appeared at 5.400, 6.641, and 6.763 ppm,

respectively. With increasing DMâCDx concentration, all

signals shifted to upper field;³²for example, at [DMâCDx] )

3.3 × 10^-3mol/L, the shifts were 0.013, 0.198, and 0.115 ppm

for ortho, meta, and para protons, respectively, in pure

acetonitrile, while in acetonitrile-water (3:2 v/v) mixture these

were 0.014, 0.203, and 0.118 ppm, respectively. Since the size

of the shift reflects the magnitude of interaction between the

inner wall of the DMâCDx and guest molecules, the above

NMR result suggests strongly the inclusion of the phenyl moiety

of SubCRPc. The 1:1 complex formation was confirmed using

Job’s continuous variation method³³(not shown), and therefore

(34) Rose, N. J.; Drago, R. S. J. Am. Chem. Soc. 1959, 81, 6138.

(35) (a) Kobayashi, N.; Osa, T. Bull. Chem. Soc. Jpn. 1991, 64, 1878.

(b) Kobayashi, N. J. Chem. Soc., Chem. Commun. 1988, 918. (c) Kobayashi,

N. In ref 31; Chapter 2, Section 6.

(36) Pariser, R.; Parr, R. G. J. Chem. Phys. 1953, 21, 466, 767. Pople,

J. A. Trans. Faraday Soc. 1953, 46, 1375.

(31) CyclodextrinssFundamentals and Applications; Toda, F., Ueno, A.

Eds.; Sangyo-Tosho: Tokyo, 1995.

(32) NMR signals of aromatic molecules shift to upper field in the cavity

of CDxs: Wood, D. J.; Hruska, F. E.; Saenger, W. J. Am. Chem. Soc. 1977,

99, 9, 1735.

(33) Job, P. Ann. Chim. Phys. 1928, 9, 113.

(37) Marks, T. J.; Stojakovic, D. R. J. Am. Chem. Soc. 1978, 100, 1695.

9104 J. Am. Chem. Soc., Vol. 121, No. 39, 1999

Kobayashi et al.

Figure 12. Four frontier orbitals of SubAP^2-, SubPc^2-, SubNc^2-, NilPc, BenPc, NapPc, and AnPc.

have larger coefficients in the outer benzene and naphthalene

moieties; i.e., these are benzene- and naphthalene-centered

orbitals. In addition, in the case of SubNc^2-, the HOMO - 1

and HOMO - 2 (naphthalene-centered orbitals) are also doubly

degenerate. As in the experiments, the calculated Q-bands and

Soret bands shift to a longer wavelength and the oscillator

strength increases with increasing area of the π-systems (for

example, the Q-bands of SubAP^2-, SubPc^2-, and SubNc^2-are

estimated at 468 (f ) 0.06), 502 (0.56), and 540 (0.91) nm,

respectively). The red-shift of the Q-band is largely explained

by destabilization of the HOMOs, rather than that of the LUMOs

(Figure 13), as in tetracyclic TAP, Pc, and Nc systems. The

Q-band of SubAP is much weaker than that of SubPc, and this

is reflected particularly in the size of the MCD magnitude (see

the magnification factor, Figure 4). Although the correspondence

between experiment and calculation is not particularly good for

SubAP, the spectra of SubPc are reproduced well in the

calculations. In particular, two strong absorption peaks in the

Soret region are predicted at 322 and 268 nm for the experi-

mental 307 and 266 nm. In addition, the calculated intensity

ratio of the Soret band to the Q-band (0.89/0.56 ) ca. 1.59) is

close to that (roughly 1.4-1.6) in the experiments. A z-polarized

transition was found at 286 nm (configurations 13f19(24%),

12f18(24%), 15f18(17%), 14f19(17%)); however, its strength

(f ) 0.009) is much less than those of the neighboring

transitions. The calculated intensity of the Q-band (f ) 0.56) is

smaller than that of Pc^2-(f ) 0.84), as is observed experimen-

tally. In addition, the predicted Q-band position (502 nm) is at

shorter wavelength than that of Pc^2-(662 nm). In the case of

SubNc, the Soret region appears to be a superimposition of

several transitions, and no transitions were predicted between

the Soret and Q-bands, although two tiny peaks are seen at ca.

404 and 475 nm (Figure 4). As in general tetracyclic TAP, Pc,

and Nc systems,³⁸the “purity” of the HOMO-LUMO transition

for the Q-band increases with increasing molecular size, as

suggested from their configuration: 57, 84, and 89% for

SubAP^2-, SubPc^2-, and SubNc^2-, respectively. However, the

Soret band region is not described by a one-electron descrip-

tion: many transitions contribute to a comparable degree, as in

the case in Pc’s. Thus, from the viewpoint of MO calculations,

it may be concluded that the properties of the Q-bands and Soret

bands are close to those of the corresponding tetracyclic

compounds (i.e., Pc and Nc). If this is the case, then the main

framework of the subazamacrocyclic chromophore may be the

innermost 12-membered rings containing six nitrogen atoms and

carrying 14 electrons.

(ii) Compounds NilPc-AnPc. (a) Metal-Free Species.

When unsymmetrical Pc and Nc analogues are prepared by the

ring expansion of SubPc’s and SubNc’s, they are obtained as

metal-free species. In contrast to the cases of normal Pc’s and

Nc’s, which have approximate square structures, however, two

cases have to be considered on the position of two pyrrole

hydrogens; i.e., they can be linked to two pyrrole nitrogens either

along the short or long axes of the molecule. Accordingly, MO

calculations have been performed for these two cases, giving

information which appears useful in interpreting the experi-

mental spectra. The main results are summarized as follows (see

(38) Kobayashi, N.; Konami, H. In PhthalocyaninessProperties and

Applications; Leznoff, C. C., Lever, A. B. P., Eds.; VCH: New York, 1996;

Vol. 4, Chapter 9, and references therein.

Subazaporphyrins and Subphthalo- and Subnaphthalocyanines

J. Am. Chem. Soc., Vol. 121, No. 39, 1999 9105

Table 3. Calculated Transition Energies, Oscillator Strength (f),

and Configurations for the Dianions of Subazamacrocycles^a

energy/eV (nm)

f

configurations^b

SubAP^2-

2.6483 (468) 0.06 11f12(57%) 10f13(38%)

2.6514 (468) 0.06 11f13(57%) 10f12(38%)

3.4229 (362) 0.17 7f13(37%) 8f13(31%) 11f12(17%)

3.4417 (360) 0.18 7f2(38%) 11f13(18%) 9f13(18%)

8f12(17%)

4.1290 (300) 1.04 10f13(40%) 9f12(21%) 8f13(18%)

11f12(16%)

4.1438 (299) 1.00 10f12(37%) 9f13(23%) 8f12(21%)

11f13(15%)

4.4566 (278) 0.73 7f13(58%) 10f13(12%) 9f12(11%)

8f13(11%)

4.4703 (277) 0.87 7f12(59%) 10f12(14%) 9f13(12%)

SubPc^2-

2.4680 (502) 0.56 17f18(84%) 16f19(15%)

2.4680 (502) 0.56 17f19 84%) 16f18(15%)

3.8525 (322) 0.89 16f18(53%) 11f18(19%)

3.8525 (322) 0.89 16f19(53%) 11f19(19%)

4.1422 (299) 0.21 17f21(38%) 15f18(16%) 14f19(16%)

11f18(11%)

4.1422 (299) 0.21 17f20(38%) 15f19(16%) 14f18(16%)

11f19(11%)

4.6321 (268) 1.17 11f18(38%) 16f18(18%)

4.6321 (268) 1.17 11f19(38%) 16f19(18%)

SubNc^2-

2.2949 (540) 0.91 23f24(89%)

2.2949 (540) 0.91 23f25(89%)

Figure 13. Partial molecular orbital energy diagram for SubAP^2-

,

SubPc^2-, SubNc^2-, NilPc, BenPc, NapPc, and AnPc. In the data of

NilPc-AnPc, solid and broken lines indicate the data when two pyrrole

protons are linked at pyrrole nitrogens along the short and long axes,

respectively.

3.8170 (325) 0.82 20f24(42%) 22f24(20%) 21f25(20%)

3.8170 (325) 0.82 20f25(42%) 22f25(20%) 21f24(20%)

4.1059 (302) 0.44 20f24(28%) 22f24(23%) 21f25(23%)

4.1059 (302) 0.44 20f25(28%) 22f25(23%) 21f24(23%)

4.3964 (282) 0.22 16f25(20%) 19f24(18%) 21f28(11%)

20f25(11%)

4.3966 (282) 0.22 16f24(20%) 19f25(18%) 22f28(11%)

20f24(11%)

4.7170 (263) 0.23 19f25(33%) 18f25(19%) 17f24(19%)

16f24(18%)

4.7171 (263) 0.23 19f24(33%) 18f24(19%) 17f25(19%)

16f25(18%)

4.8324 (257) 1.08 21f28(25%) 20f27(19%) 16f25(17%)

4.8325 (257) 1.08 22f28(25%) 20f26(19%) 16f24(17%)

also Table 4 and Figures 12 and 13). (1) The Q-band splits into

two, but the splitting is larger when the two protons are attached

along the short axis. Values are 1385 (612-685 nm), 699 (664-

697 nm), 775 (677-715 nm), and 891 cm^-1(682-726 nm) for

the π-structures of NilPc, BenPc, NapPc, and AnPc, respectively,

while the corresponding values are 274 (650-662 nm), 699

(664-697 nm), 356 (691-708 nm), and only 27 cm^-1(708-

710 nm) when protons are attached along the long axis.

Experimentally, the values of the Q_0-0-band splitting are 2017

(598-680 nm), 684 (668-700 nm), 1253 (668-729 nm), and

905 cm^-1(708-757 nm) for the above order, strongly suggest-

ing that two protons are bound to the nitrogens along the short

axis. (2) When the protons are along the short axis of the split

Q-band, the relative intensity of the lower-energy split band

becomes weaker than that at higher energy with increasing

molecular size; i.e., the ratios of f (lower energy/higher energy)

are 1.03:0.92:0.84:0.73 for NilPc:BenPc:NapPc:AnPc. There is

no such regularity if protons are along the long axis; i.e., 0.83:

0.92:1.01:0.91 for NilPc:BenPc:NapPc:AnPc. (3) The intensity

of the Q-band (the sum of the two calculated oscillator strengths,

f) is similar whether the two protons are linked to two nitrogens

along the short or long axis, although it per se increases with

increasing molecular size. That is, they are 1.45 ( 0.03, 1.82,

2.01 or 2.02, 2.12 ( 0.04 in order of NilPc to AnPc,

respectively. (4) The Q-band energy, defined as the energy

midway between the split Q-bands, shifts to longer wavelength

with increasing molecular size of the fused aromatics, but the

extent of the shift becomes smaller as the macrocyclic ligand

becomes larger. The calculated wavelengths are 646, 680, 695,

and 703 nm when protons are attached along the short axis and

656, 681, 684, and 709 nm when they are attached along the

long axis, while experimentally they are 636, 684, 697, and 731

nm in the order of NilPc to AnPc, respectively. (5) For

^aExcited states with less than 5.0 eV and f greater than 0.16 are

shown in addition to two weak transitions (f ) 0.06) of SubAP^2-at

468 nm. ^bOrbital numbers 11, 17, and 23 are HOMOs of SubAP^2-

,

SubPc^2-, and SubNc^2-, respectively. In SubNc^2-, the MOs numbered

21, 22 and 26, 27 are doubly degenerate naphthalene-centered orbitals.

compounds containing a naphthalene or an anthracene moiety,

the HOMO - 1 and LUMO + 2 orbitals are these molecule-

centered orbitals. As can be judged from the results in Table 4,

naphthalene- or anthracene-centered transitions overlap mainly

with the Soret band, while an anthracene-centered transition is

predicted between the Q-bands and Soret bands. Consistent with

this prediction, a clear peak is seen at 462 nm in the spectrum

of AnPc, although its intensity is not large. (6) Two Q-bands

are essentially described by a one-electron description (Table

4), but its purity increases with increasing molecular size. For

example, when the two protons are along the short axis, the

percentage of the HOMO to the LUMO transition of the Q-band

to lower energy increases from 87% of NilPc to 88% of BenPc,

and further to 89% of NapPc and AnPc. This is the same

phenomenon as for (pyrrole proton) deprotonated species.^24a

Thus, almost all the data for the Q-band support the case that

the two pyrrole protons are along the short axis. The features

in the shorter wavelength region are very complex. (7) The split

B1 bands are no longer described in a one-electron description,

since they appear to be mixtures of several configurations. In

9106 J. Am. Chem. Soc., Vol. 121, No. 39, 1999

Kobayashi et al.

Table 4. Calculated Transition Energies, Oscillator Strength (f), and Configurations for Metal-Free NilPc-AnPc^a

energy/

eV

obsd energy/

(nm) eV

(nm)

f

configurations^b

(nm)

f

configurations^b

NilPc (two protons along the short axis)

1.8553 (668) 0.72 19f20(87%) 18f21(12%)

2.0271 (612) 0.70 19f21(87%) 18f20(12%)

3.6405 (341) 2.14 18f20(77%) 19f21(12%)

NilPc (two protons along the long axis)

(680) 1.8724 (662) 0.67 19f21(84%) 18f20(15%)

(598) 1.9064 (650) 0.81 19f20(90%)

3.2401 (383) 0.20 17f20(88%)

3.7468 (331) 1.28 18f21(42%) 15f21(37%)

3.5976 (345) 1.23 14f20(42%) 18f20(33%)

3.8027 (326) 0.37 17f21(75%) 18f21(18%)

3.8744 (320) 1.78 14f20(48%) 18f20(39%)

3.9159 (317) 1.73 18f21(46%) 17f21(24%) 15f20(21%)

4.1961 (295) 0.14 15f20(44%) 16f21(26%) 18f21(18%)

4.1961 (275) 0.16 14f21(93%)

3.9274 (316) 0.21 19f23(49%) 16f21(26%) 15f20(17%)

4.0017 (310) 0.91 16f20(54%) 18f21(27%) 15f21(12%)

4.1160 (301) 0.33 14f20(65%) 15f21(12%) 17f21(11%)

4.2072 (295) 0.17 15f20(54%) 16f21(37%)

4.2721 (290) 0.15 16f20(34%) 15f21(29%) 17f21(15%)

4.3723 (284) 0.17 17f21(57%) 19f25(14%) 14f20(12%)

4.5033

BenPc

(700) 1.7797 (697) 0.87 21f22(88%) 20f23(12%)

(668) 1.8664 (664) 0.95 21f23(91%)

3.6563 (339) 1.40 20f23(47%) 17f23(43%)

3.8200 (325) 1.96 20f22(68%) 21f26(14%)

3.9696 (312) 0.23 21f26(85%)

1.7797 (697) 0.87 21f22(88%) 20f23(12%)

1.8664 (664) 0.95 21f23(91%)

3.6563 (339) 1.40 20f23(47%) 17f23(43%)

3.8200 (325) 1.96 20f22(68%) 21f26(14%)

3.9696 (312) 0.23 21f26(85%)

4.0317 (308) 1.62 17f23(51%)

4.2268 (293) 0.17 21f27(89%)

4.0317 (308) 1.62 17f23(51%)

4.2268 (293) 0.17 21f27(89%)

4.2678 (291) 0.37 17f22(91%)

NapPc (two protons along the short axis)

1.7350 (715) 0.92 23f24(89%) 21f25(10%)

1.8311 (677) 1.10 23f25(91%)

NapPc (two protons along the long axis)

(729) 1.7520 (708) 1.01 23f25(88%) 21f24(10%)

(688) 1.7930 (691) 1.00 23f24(92%)

3.5336 (351) 1.15 22f25(66%) 21f24(24%)

3.5409 (350) 1.78 21f24(39%) 22f25(34%) 18f24(16%)

3.8899 (319) 1.82 21f25(72%)

4.0122 (309) 1.22 18f24(36%) 21f24(31%) 23f29(15%)

4.1644 (298) 0.29 23f29(67%) 20f24(15%)

4.3435 (285) 0.22 18f25(82%)

3.6890 (336) 0.19 22f24(64%) 21f25(14%) 23f28(11%)

3.7283 (333) 1.42 21f25(40%) 20f25(24%) 22f24(20%)

3.8566 (321) 0.43 23f29(60%) 21f24(19%) 22f25(15%)

3.9523 (314) 0.64 23f29(38%) 21f24(34%) 22f25(11%)

3.9730 (312) 0.69 20f25(63%) 21f25(14%) 18f25(14%)

4.1714 (297) 0.22 18f25(55%) 23f30(29%)

4.5808 (271) 0.50 22f26(60%) 16f24(21%)

4.1889 (296) 0.20 20f24(62%) 17f24(19%)

4.1993 (295) 0.24 23f30(63%) 19f24(15%) 18f25(11%)

4.6505 (267) 0.38 22f26(45%) 16f24(42%)

AnPc (two protons along the short axis)

1.7079 (726) 0.91 25f26(89%)

1.8184 (682) 1.24 25f27(92%)

AnPc (two protons along the long axis)

(757) 1.7468 (710) 0.99 25f27(93%)

(708) 1.7501 (708) 1.09 25f26(89%)

3.1889 (389) 0.35 24f27(73%)

3.2640 (380) 0.90 24f27(72%) 23f26(11%)

3.6408 (341) 0.80 20f26(44%) 23f26(36%) 24f27(11%)

3.9213 (316) 2.18 23f27(55%)

3.9681 (312) 1.50 20f26(43%) 23f26(33%) 25f32(11%)

4.1407 (299) 0.17 22f26(61%) 25f32(25%)

4.3671 (284) 0.35 20f27(73%) 22f27(11%)

3.6986 (335) 0.21 24f28(46%) 23f27(29%) 22f27(11%)

3.7826 (328) 1.68 24f28(36%) 23f27(23%) 21f27(21%)

3.7868 (327) 1.95 23f26(56%) 25f31(23%)

3.8942 (318) 0.50 25f31(74%) 23f26(15%)

4.0005 (310) 1.02 22f27(60%) 23f27(19%)

4.1266 (300) 0.24 22f26(56%) 19f26(27%)

4.2327 (293) 0.15 21f26(61%) 19f27(21%)

4.3832 (283) 0.30 20f27(50%) 21f26(19%)

^aExcited states with less than 5.0 eV and f greater than 0.14 are shown. ^bOrbital numbers 19, 21, 23, and 25 are HOMOs of NilPc, BenPc,

NapPc, and AnPc, respectively. In NapPc, the MOs numbered 22 (HOMO - 1) and 26 (LUMO + 2) are naphthalene-centered orbitals. Similarly,

in AnPc, MOs 24 (HOMO - 1) and 28 (LUMO + 2) are anthracene-centered orbitals.

particular, the naphthalene- or anthracene-centered transition is

mixed significantly in NapPc and AnPc, respectively.

and (-H₂)AnPc, naphthalene- or anthracene-centered orbitals

appear at approximately the same positions as in NapPc and

AnPc. In general, the HOMOs destabilize more than the LUMOs

with increasing size of the π-systems, both in the subazamac-

rocycles and unsymmetrical Pc analogues.

(b) Deprotonated (-H₂) Species. As in experiment (Figures

6 and 7, dotted lines), the calculated splitting of the Q-band

decreases on deprotonation, i.e., 526 (622-643 nm), 0 (662-

662 nm), 179 (673-681 nm), and 359 (676-693 nm) cm^-1for

(-H₂)NilPc, (-H₂)BenPc, (-H₂)NapPc, and (-H₂)AnPc, re-

spectively. The orders of magnitude of the experimental values

for (-H₂)NilPc (998 cm^-1), (-H₂)BenPc and (-H₂)NapPc (0

cm^-1), and (-H₂)AnPc (422 cm^-1) agree with the above

calculation trend. In addition, as shown particularly for (-H₂)-

NilPc in Figure 6, the sum of the intensity of the two Q

transitions may be smaller for deprotonated species. Changes

in the Soret region are difficult to extract.

(iii) Origin of the Reactivity of SubPc for the Ring

Expansion. We may guess intuitively that the high reactivity

of SubPc for the ring expansion reaction is related to its cone-

shaped distorted structure. Accordingly, we first calculated the

bond energies in SubPc and, for comparison, MgPc using density

functional theory (DFT)/natural bond orbital (NBO) treatment³⁹

in the ab initio MO program package Gaussian94/DFT.⁴⁰The

calculated bond energies for the C-N bonds are summarized

in Table 5. The numbers in the table show little deviation (0.4-

0.5 kJ/mol per N-C bond) between the two compounds,

suggesting that the distortion energy is not a major cause of

the ring expansion reactivity. We then investigated the reactivity

The energy levels of frontier orbitals are not compared in

Figure 13 because of the complexity of the lines. However, the

situation is very similar to that of metal-free derivatives, except

that some orbitals become doubly degenerate. In (-H₂)NapPc

Subazaporphyrins and Subphthalo- and Subnaphthalocyanines

J. Am. Chem. Soc., Vol. 121, No. 39, 1999 9107

Table 5. Bond Energies^afor the C-N Bond of the Innermost 12-Membered (SubPc) and 16-Membered (MgPc) Rings

SubPc

MgPc

bond

σ

π

total

σ

π

total

N(pyrrole)-RC

N(meso)-RC

-0.81481

-0.87521

-0.34587

-0.33179

-1.16068

-1.20700

-0.82708

-0.87290

-0.31720

-0.31230

-1.14428

-1.18520

^aIn kcal/mol.

Figure 14. Electronic absorption (top) and MCD (bottom) band analysis for SubPc with a Cl axial ligand in CHCl₃. Experimental data are plotted

by solid lines, while individual B term type bands and fitted data are by dotted lines. A term type bands and associated B term bands are drawn by

broken lines. The vertical lines show the band center positions (long lines are A terms).

of SubPc from the viewpoint of ligation energy of the pyrrole

nitrogen atoms to the central boron atom. The donor-acceptor

interaction energy is given by a second-order perturbation theory

in NBO basis.⁴¹Using this treatment, the total donating energy

of lone pairs on pyrrole N to central Mg in MgPc was calculated

to be 129 kJ/mol, while no significant donation took place in

the case of SubPc. The lack of electron donation in SubPc is

attributable to the lack of electron-accepting orbitals in boron.

Thus, at least some parts of the unstability of SubPc seems to

be caused by a lack of donor-acceptor stabilization in the B-N

(pyrrole N) bonds.

Is there any other reason for the reactivity of SubPc? To

answer this question, the structure/energy changes accompanying

elimination of the axial ligand (halogen, X) of SubPc (i.e., SubPc

f SubPc⁺+ X^-) were considered. Although this is not shown

in a figure, the shape of the main skeleton of SubPc changes

on elimination of the axial halogen atom, from a shuttlecock-

shaped form to a more planar form, and the stabilization energy

is about 100 kJ/mol. The NBO analysis has also indicated that

cationic charge on the central boron atom is delocalized over

the whole molecule, suggesting that the stability of a halogen-

eliminated intermediate is high (the calculated cationic charge

on B in SubPc⁺is only 0.277). From this, it is likely that the

initial step of the ring expansion reaction consists of a

dehalogenation process.

Finally, we attempted to obtain an approximate estimation

of the reaction enthalpy. The ring expansion reaction of SubPc

to form Pc can be written as SubPc + phthalonitrile f Pc. We

make a rather bold estimation for this reaction by using MgPc,

since boron-centered Pc does not exist. The DFT calculation

gave formation energies of 1106.263, 366.483, and 1586.389

kJ/mol for SubPc, phthalonitrile, and MgPc, respectively,

suggesting -113.642 kJ/mol for the enthalpy of the ring

expansion reaction. Although this result is very approximate,

the above value indicates that the reaction is exothermic and

apt to proceed without supplying substantial heat.

VI. Band Deconvolution of the Spectral Envelopes of

SubPc. It was suggested in the preceding section (V-i) that the

Q-bands of SubPc are orbitally doubly degenerate. Accordingly,

to verify this experimentally and to find the position (energy)

and number of transitions to the degenerate excited states, the

electronic absorption and MCD spectral envelopes of SubPc

without peripheral substituent groups were deconvoluted si-

multaneously. The deconvolution results are shown in Figure

14 (the abscissa is expressed in wavenumber units), and the

fitting parameters are summarized in Table 6. In the Q-band

(39) Foster, J. P.; Weinhold, F. J. Am. Chem. Soc. 1980, 102, 7211. Reed,

A. E.; Weinhold, F. J. Chem. Phys. 1985, 83, 1736. Reed, A. E.; Curtius,

L. A.; Weinhold, F. Chem. ReV. 1988, 88, 899.

(40) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Gill, P. M. W.;

Johnson, P. G.; Robb, M. A.; Cheeseman, J. R.; Keith, T.; Peterson, G. A.;

Montgomery, J. A.; Raghavachari, K.; Al-Laham, M. A.; Zakrzewski, V.

G.; Ortiz, J. V.; Foresman, J. B.; Cioslowski, J.; Stephanov, B. B.;

Nanayakkara, A.; Challacombe, M.; Peng, C. Y.; Ayala, P. Y.; Chen, W.;

Wong, M. W.; Andres, J. L.; Replogle, E. E.; Gomperts, R.; Martin, R. L.;

Fox, D. J.; Binkley, J. S.; Defrees, D. J.; Baker, J.; Stewart, J. P.; Head-

Gordon, M.; Gonzalez, C.; Pople, J. A. Gaussian 94/DFT; Gaussian Inc.:

Pittsburgh, PA, 1995.

(16 500-22 000 cm^-1) and Soret band (22 000-40 000 cm^-1

)

regions, 13 and 9 bands are required in order to fill the

absorption and MCD spectral envelopes. These numbers

represent the minimum number required to obtain satisfactory

fits and are slightly smaller than those required in the band

(41) Reed, C. A.; Weinhold, F.; Curtiss, L. A.; Pochatko, D. J. Chem.

Phys. 1986, 84, 5687.

9108 J. Am. Chem. Soc., Vol. 121, No. 39, 1999

Kobayashi et al.

Table 6. Band-Fitting Parameters for SubPc in Chloroform

band

no.

position, ν/cm^-1(λ/nm)

width,^a∆ν/cm^-1

band type

band no.

position, ν/cm^-1(λ/nm)

width,^a∆ν/cm^-1

band type

1

2

3

17 163 (583)

17 581 (569)

17 823 (561)

18 210 (549)

18 423 (543)

18 808 (532)

19 093 (524)

19 410 (515)

19 808 (505)

20 314 (492)

20 801 (481)

21 305 (469)

21 767 (459)

596

448

508

591

585

584

511

560

601

617

593

544

508

B

A

B

14

15

16

23 570 (424)

25 475 (391)

27 874 (359)

30 036 (333)

32 217 (310)

33 193 (301)

36 164 (277)

37 684 (265)

42 097 (238)

1755

1598

2203

2931

2250

3683

3286

2150

2659

B

A

B

A

B

A

B

4

5

6

7

8

17

18

19

20

21

9

10

11

12

13

22

^aWidth at half-height.

deconvolution of Pc’s.^18,42In the Q-band region, each MCD

band was fitted with Faraday B terms, except for that corre-

sponding to the Q_0-0-band. Attempts to replace this A term by

two B terms of opposite sign significantly increased the residual

noise, thus confirming that the Q_0-0-band corresponds to a

transition to the orbitally degenerate state.

The Soret region is complicated by the presence of several

overlapping bands of relatively equal intensity. Deconvolution

identified three A terms at 359 (27 823 cm^-1), 301 (33 193

cm^-1), and 265 nm (37 684 cm^-1). Of these, the band at 359

nm corresponds to a weak shoulder on the long wavelength tail

of what we call the Soret band. The presence of a similar small

band has also been observed for Pc’s around 370-430 nm.^42e

Since the intensity of this band is so weak, general MO

calculations do not predict it. Judging from the intensity,

position, and similarity to Pc systems, the A term located at

301 nm appears to be the B-band of this SubPc. The third A

term at 265 nm may then be assigned to the N-band. As has

been observed for Pc’s, this A term is smaller than that at 301

nm.^18,42e

Figure 15. TREPR spectra of tBZnPc (top) and tBSubPc (bottom)

with their simulations. These spectra were observed at 20 K and 0.5

µs after laser excitation.

VII. Time-Resolved EPR. To date, the time-resolved EPR

(TREPR) technique has been used to investigate the extent of

π-delocalization in the lowest excited triplet (T₁) state and the

selectivity of the intersystem crossing (ISC) from the lowest

excited singlet (S₁) state to the T₁state.⁴³Accordingly, the

TREPR spectrum was recorded and discussed in comparison

with that of a representative MtPc, i.e., ZnPc.

Table 7. Zero-Field-Splitting Parameters and ISC Ratios Obtained

from the Simulation

compd

D/GHz

E/GHz

Px:Py:Pz

tBSubPc

tBZnPc

0.870

0.705

0.120

0.215

0:0.05:0.95

0:0.10:0.90

TREPR spectra of tBSubPc and tBZnPc are shown in Figure

15, together with their simulations, and the obtained EPR

parameters are summarized in Table 7. The zero-field-splitting

parameter, D, of tBSubPc is larger than that of tBZnPc. In

general, D values originate from the magnetic dipolar-magnetic

dipolar interaction and spin-orbit coupling (SOC). Since the

deviations of the g values from the free-electron value ()2.0023)

are so small (<0.002 and 0.005 for tBSubPc and tBZnPc,

respectively), the contribution of the SOC can be neglected for

both tBSubPc and tBZnPc.⁴⁴Therefore, the D values must only

be due to magnetic dipolar-magnetic dipolar interactions and

denote the extent of π-delocalization in the T₁state.^24aFrom

the observed D values, the extent of π-delocalization in tBSubPc

appears much smaller than that in tBZnPc in the T₁state, and

this result is consistent with the fact that the S₁energy (∼14 500

cm^-1) of tBZnPc is much lower than that (∼17 500 cm^-1) of

tBSubPc, due to the larger π-system in the former.

Our simulation reveals that the ISC from the S₁to the T_1z

sublevel is selective for tBSubPc. This selectivity in tBSubPc

is similar to that in tBZnPc but is contrary to that in MgPc or

H₂Pc.⁴⁵The selective ISC in tBZnPc is reasonably interpreted

by SOC due to the dπ atomic orbitals on the heavy zinc ion.⁴⁶

However, the contribution of the dπ atomic orbital on a central

B atom of tBSubPc can be eliminated because of the energy

difference. To clarify the origin of the selective ISC in tBSubPc,

MO calculations were carried out using the AM1 Hamiltonian.⁴⁷

After geometrical optimization, configuration interactions (CIs)

(42) (a) Ough, E.; Gasyna, Z.; Stillman, M. J. Inorg. Chem. 1991, 30,

2301. (b) Mack, J.; Stillman, M. J. J. Am. Chem. Soc. 1994, 116, 1292; J.

Phys. Chem. 1995, 99, 7935; Inorg. Chem. 1997, 36, 413. (d) Mack, J.;

Kobayashi, N.; Leznoff, C. C.; Stillman, M. J. Inorg. Chem. 1997, 36, 5624.

(e) Nyokong, T.; Gasyna, Z.; Stillman, M. J. Inorg. Chem. 1987, 26, 1087.

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Subazaporphyrins and Subphthalo- and Subnaphthalocyanines

J. Am. Chem. Soc., Vol. 121, No. 39, 1999 9109

were calculated to examine the electronic configurations in the

S₁and T₁states. In the CI calculations, only electronic

configurations whose eigenvalues were less than 8 eV were

taken into account. The calculations have revealed that the

contributions from the HOMO-to-LUMO transition are 97 and

85% for the T₁and S₁states, respectively, and that the E_xand

E_ystates are degenerate in both the S₁and T₁regions because

of the degeneracy of the LUMOs (e_xand e_y). The SOC between

stituted subphthalocyanine locates four transitions to degenerate

excited states at 561, 359, 301, and 265 nm. The values of the

zero-field-splitting parameter in the time-resolved EPR spectra

indicate that the π-system of the subphthalocyanines is, indeed,

smaller than that of the phthalocyanines.

Experimental Section

(i) Measurements. Solvents for spectroscopic measurements, o-

dichlorobenzene (Aldrich, Gold label), acetonitrile, and chloroform

(Wako, Spectrograde) were used as supplied.

1

3

the E_yand E_ystates is negligibly small, so that coupling

1

3

between the E_xand E_ystates originating from that between

the e_xand e_yMOs only is considered. From the values of

coefficients of e_xand e_yMOs, it was found that the populations

of the P_xand P_yorbitals are larger than that of the P_zorbital for

both B and Br atoms. For example, the e_yMO coefficients of

the B atom are -0.00003, -0.01903, 0.02853, and 0.00027 for

2S, 2P_x, 2P_y, and 2P_zorbitals, respectively. The e_ycoefficients

of the Br atom are, on the other hand, 0, -0.00587, 0.00882,

and 0.00008 for the 4S, 4P_x, 4P_y, and 4P_zorbitals, respectively.

Using the SOC constants of the B and Br atoms (11 and 2460

cm^-1, respectively⁴⁸), the SOC on the B and Br atoms is

estimated to be 0.013 and 0.28 cm^-1, respectively, indicating

that the SOC on the Br atom is much larger than that of the B

atom. Therefore, the selective ISC of tBSubPc can be reasonably

interpreted by SOC on the axial Br atom.

1

The 400-MHz H NMR and IR spectral measurements were made

with JEOL GSX-400 and Shimadzu FTIR-8100M spectrometers,

respectively. To eliminate the effect of aggregation, the concentration

of the samples for NMR was ca. 0.1 mM, unless otherwise noted.

Electronic spectra were recorded with a Shimadzu UV-250 spectrom-

eter. MCD spectra were run on a Jasco J-500 spectrodichrometer

equipped with a data processor and with an electromagnet which

produced magnetic fields up to 1.17 T, with parallel and then antiparallel

fields. Its magnitude was expressed in terms of molar ellipticity per

tesla, [θ]_M/10⁴deg mol^-1cm^-3cm^-1T^-1. CD spectra were recorded

on a Jasco J-720 spectrodichrometer in acetonitrile and acetonitrile-

water (3:2 v/v) in the presence of DMâCDx (Nacalai) at 20 °C.

Fluorescence spectra were obtained with appropriate filters to eliminate

scattered light. Fluorescence quantum yields (φ_F) were determined by

the use of quinine sulfate in 1 N H₂SO₄(φ_F) 0.55 at 296 K), free

base tetraphenylporphyrin in benzene (φ_F) 0.11), Rhodamine B in

ethanol (φ_F) 0.97), ZnPc (φ_F) 0.30), and H₂Pc (φ_F) 0.60) in CNP

as standards.²⁶The φ_Fvalue of SubNc alone was obtained using the φ_F

value of compound PyPc (φ_F) 0.54 in o-dichlorobenzene) as a new

standard. Data were obtained by a comparative calibration method, using

the same excitation wavelength and absorbance for the azamacrocycles,

unsymmetrical Pc analogues, and calibrants, and the same emission

energies. Fluorescence decay curves were obtained at 20 °C by a Horiba

NAES-550 series, using combinations of glass filters and a monochro-

mator for monitoring the emission. The lifetimes were determined from

the decay curves by the use of the least-squares method. All solutions

for fluorescence measurements were purged with argon before measure-

ments.

Conclusions

A subazaporphyrin, subphthalocyanines, and a subnaphtha-

locyanine have been synthesized and characterized by various

spectroscopic methods, including electronic absorption, MCD,

fluorescence emission, and NMR. Both the Q-bands and Soret

bands shift to longer wavelengths with concomitant increase in

intensity, in the order of the above compounds, i.e., with

increasing size of the π-conjugated system. Molecular orbital

calculations have succeeded in reproducing the experimental

data and have shown that the red-shift of the Q-band is due

mostly to destabilization of the HOMO level. A 15-crown-5-

ed subphthalocyanine does not dimerize following the addition

of cations which induce dimerization of 15-crown-5-ed phtha-

locyanines. As an explanation of this, force field calculations

have proposed a hemisphere structure with three crown ether

voids standing like fences. Hitherto accumulated data on induced

circular dichroism of cyclodextrin-chromophore complexes has

suggested complexation of an axial ligand of crowned subph-

thalocyanine and 2,6-dimethyl-â-cyclodextrin. In the presence

of isoindolediimine, subphthalocyanines experience ring expan-

sion reactions to monosubstituted type phthalocyanines. To attain

good yields, mixed solvent systems of DMSO and chloronaph-

thalene (or aromatic solvents such as toluene and o-dichlo-

robenzene) (3:1-1:2 v/v) are recommended at a reaction

temperature of ca. 80-90 °C and a reaction time of almost 1

day. The Q-bands of the resultant monosubstituted type phtha-

locyanines split into two and shift to longer wavelength with

increasing size of the fused aromatics. In these low-symmetrical

phthalocyanines, both the quantum yields and lifetimes of

fluorescence emission become smaller with the departure of

symmetry from D_4h. Comparison of experimental spectra and

the results of molecular orbital calculations has suggested that

two pyrrole protons are linked at pyrrole nitrogens along the

short axis. Band deconvolution analysis of the electronic

absorption and magnetic circular dichroism spectra of unsub-

TREPR measurements were carried out at 20 K on a Bruker ESP

300E spectrometer using an Oxford ESR 900 cold gas flow system.^24a

Samples were excited at 585 nm by a Lumonics HD-500 dye laser

pumped with a Lumonics EX500 excimer laser. The TREPR signals

from the EPR unit were integrated by a LeCroy 9450A oscilloscope.

For TREPR measurements, toluene was used as solvent, and samples

were deaerated by the freeze-pump-thaw method.

(ii) Synthesis. (a) tBSubPc. We reported this compound in our

previous communication.¹

(b) SubAP. A 0.81-mL portion of a 1,2-dichloroethane solution of

1 M tribromoboron (0.81 mmol) and 1-(1,2,2-tricyanoethenyl)-2-

trifluoromethylbenzene (600 mg, 2.43 mmol) were heated in chlo-

robenzene (1.5 mL) at 80 °C under nitrogen for 1 h. After cooling, the

crude product was imposed on a preparative TLC column of alumina

using chloroform as eluent, and the yellow fraction with R_f) 0.27

was collected and extracted using the same solvent. Evaporation of

the solvent, followed by recrystallization from chloroform-hexane,

afforded 4.2 mg (1.9%) of the desired triazasubporphyrin. FAB mass

(m/z): 752 (M - Br). Anal. Calcd for C₃₆H₁₂N₉BF₉: C, 51.96; H, 1.45;

N, 15.15. Found: C, 51.13; H, 1.82: N, 14.03. ¹H NMR (CDCl₃, 500

MHz): δ 7.49 (m, 3H, arom), 7.63-7.77 (m, 6H, arom), 7.87 (m, 3H,

arom). UV-vis (CHCl₃; λ_max(10^-4ꢀ)): 411 (1.22), 255 (2.70).

(c) SubNc. 2,3-Dicyanonaphthalonitrile (1.87 g, 10.5 mmol) was

dissolved in 12 g of 2,3-dimethyl-6-tert-butylnaphthalene at 80 °C under

nitrogen. Tribromoboron (1.33 g, 5.3 mmol, 0.5 mL) was added slowly,

and the temperature was maintained at ca. 180 °C for ca. 15 min. As

the reaction proceeded, the color of the solution changed from green

to dark blue. After the solution was cooled to room temperature, 120

mL of carbon tetrachloride and 40 mL of hexane were added, and the

resultant precipitate was collected by filtration and washed with 20

mL of carbon tetrachloride twice. A portion of the residue was taken

and applied to alumina column chromatography (Act. VI) using

(48) Goodman, B. A.; Raynor, J. B. Electron Spin Resonance of

Transition Metal Complexes. In AdVances in Inorganic Chemistry and

Radiochemistry; Emeleus, H. J., Sharpe, A. G., Eds.; Academic Press: New

York, 1970; Vol. 13.

9110 J. Am. Chem. Soc., Vol. 121, No. 39, 1999

Kobayashi et al.

methylene chloride-pyridine (1:1 v/v) as eluent. The first-eluted blue

band was collected, recrystallized from toluene, and used for elemental

analysis. Most of the residue was transferred to a Soxhlet apparatus

and extracted by toluene under a nitrogen atmosphere. Toluene was

evaporated from the extract to some extent to induce crystallization,

to afford, after cooling, 2.28 g (34.6%) of dark blue crystals. Anal.

Calcd for C₃₆H₁₈N₆BBr: C, 69.15; H, 2.90; N, 13.44. Found: C, 68.42;

H, 3.50: N, 12.17. This compound may be unstable in alcohol and

DMSO, since the color of the solution changed following the addition

of these solvents. UV-vis (DCB; λ_max(10^-4ꢀ)): 667 (6.26), 608 (2.06),

328 (3.09), 302 (4.62).

(d) SubCRPc. 2,3-(3′,4′-Dicyanobenzo)-1,4,7,10,13-pentaoxacyclo-

pentadeca-2-ene, the so-called 15-crown-5-ed phthalonitrile (1.59 g, 5

mmol),¹⁶triphenylboron (0.412 g, 1.7 mmol), and 1,8-diazabicyclo-

[5,4,0]-7-undecene (DBU) (0.25 g, 1.7 mmol) in naphthalene (5 g) were

heated at 218 °C for 15 min. After the solution was cooled to room

temperature, the residue was imposed on a silica gel column using

chloroform-methanol (20:1 v/v) as eluent. The reddish-purple fraction

was collected, and the solvent was removed using an evaporator. The

residue was redissolved in a small amount of chloroform and chro-

matographed on an alumina column (Act. I), followed by a gel

permeation column (Bio-beads SX-2, Bio-Rad) using chloroform as

eluent. Evaporation of the solvent, followed by recrystallization from

ethyl acetate-methanol, gave ca. 7 mg (0.4%) of reddish-purple solid

of the desired compound. FAB mass (m/z): 1042 (M⁺, 100), 965 (M⁺

- C₆H₅, 18). Anal. Calcd for C₅₄H₅₉N₆O₁₅B: C, 62.19; H, 5.70; N,

8.06. Found: C, 61.30; H, 6.25: N, 7.52. ¹H NMR (CDCl₃, 500

MHz): δ 8.19 (s, 6H, arom), 6.70 (t, J ) 7.6 Hz, 1H, arom), 6.58 (t,

J ) 7.6 Hz, 2H, arom), 5.40 (d, J ) 7.6 Hz, 2H, arom), 4.45-4.53 (m,

6H, aliph), 3.73-3.86 (m, 24H, aliph). UV-vis (CHCl₃; λ_max(10^-4

ꢀ)): 569 (5.32), 326 (3.56), 275 (4.72).

9.6 (m, 6H, arom), 1.78-1.90 (m, 27H, aliph), -2.3 to -2.8 (2 br s at

-2.43 and -2.64, 2H, pyrrole H). UV-vis-near-IR (DCB; λ_max(10^-4

ꢀ)): 688 (11.70), 659 (8.28), 635 (3.10), 605 (2.15), 343 (5.24).

(ii) Computational Method. The structures of phthalocyanine

analogues were constructed by using X-ray structural data⁵⁰of standard

phthalocyanine, naphthalene, and anthracene and by making the rings

perfectly planar and adopting the C_2Vsymmetry. Molecular orbital (MO)

calculations were performed for dianions of subazamacrocycles and

neutral protonated species of low-symmetrical Pc analogues within the

framework of the PPP approximation,³⁶where the semiempirical

parameters which were recommended in a literature^51awere modified.³⁸

The use of the latter parameters gave slightly better results. For the

calculation of (pyrrole proton) deprotonated dianions, these are atomic

valence state ionization potentials of 11.16 (carbon), 20.21 (central

nitrogen), and 14.12 eV (imino nitrogen), together with atomic valence

state electron affinities of 0.03 (carbon), 5.32 (central nitrogen), and

1.78 eV (imino nitrogen). In the case of protonated neutral species,

the values of atomic valence state ionization potentials and electron

affinities of the central nitrogens are either 27.3 and 16.44 (protonated

nitrogen) or 17.0 and 13.84 eV (nonprotonated nitrogen). For (pyrrole

proton) deprotonated species, the central nitrogen atoms were assumed

to be equivalent, supplying 1.5 electrons each to the π-system, while

the electron density at the central nitrogens of neutral protonated species

were fixed at 1.15 (nitrogens not bonding proton) and 1.85 (nitrogens

bonding proton). In addition, σ polarizability was taken into account

according to Hammond.^51bResonance integrals were taken to be -2.48

(â_CN) and -2.42 eV (â_CC).^51aTwo-center electron repulsion integrals

were computed by the method of Mataga and Nishimoto.^51bThe choice

of configurations was based on energetic considerations, and all singly

excited configurations up to 48 393 cm^-1(6 eV) were included. In the

calculation of formation, bonding, and donation energies, the ab initio

MO program package Gaussian94/DFT⁴⁰was employed with NBO

analysis.³⁹In the section entitled Origin of the Reactivity of SubPc for

the Ring Expansion, optimized structures were used throughout with

the B3LYP DFT method and the 6-31G basis set.⁴⁰Geometry

optimization on SubCRPc with three sodium cations was performed

using the UNIVERSAL 1.02 force field⁵²on a Program Package

Cerius2, to minimize the total energy of the cation-bound SubCRPc

molecule.

(e) (tBSubPc)₂O. The axial ligand (Br) of tBSubPc (210 mg, ca.

0.33 mmol) was changed to an OH group according to the literature,⁷

by using an ion-exchange resin (the IR absorption band seen at 890

cm^-1(assignable to a B-Br bond) of tBSubPc disappeared in this

process). The resulting tBSubPc having an OH group was dissolved in

2-3 mL of nitrobenzene containing a small amount of molecular sieves

(4 Å) and heated under reflux for 6 h under nitrogen. The solvent was

removed under reduced pressure, and the residue was imposed onto a

basic alumina column (Act. III, 3^φ× 10 cm^-1) using methylene chloride

as eluent. A front-running reddish-purple portion with R_f) 0.97 was

collected and further purified using gel permeation columns (Bio-beads

SX-2, Bio-Rad) to give 8.8 mg (4.7%) of the desired (tBSubPc)₂O.

FAB mass (m/z): 1143 (M + 1). Anal. Calcd for C₇₂H₇₂N₁₂OB₂: C,

Acknowledgment. We thank Ms. R. Kondo and Dr. S.

Nakajima for carrying out preliminary studies, and we gratefully

acknowledge financial support from the Asahi Glass and

Mitsubishi Foundations. We also thank Prof. M. J. Stillman for

donation of his band deconvolution program.

1

75.66; H, 6.35; N, 14.70. Found: C, 75.30; H, 6.56: N, 14.25. H

NMR(CDCl₃, 500 MHz): δ 8.64 (m, 6H, arom), 8.48 (m, 6H, arom),

7.78 (br, 6H, arom), 1.25 (br, 54H, aliph). UV-vis (CHCl₃; λ_max(10^-4

ꢀ)): 538 (3.06), 307 (2.63), 264 (3.25). This compound is unstable on

silica gel or alumina and decomposes after 3-4 h.

JA983325C

(50) Robertoson, J. M.; Woodward, I. J. Chem. Soc. 1937, 219. Barrett,

P. A.; Dent, C. E.; Linstead, R. P. J. Chem. Soc. 1936, 1719. Brown, C. J.

J. Chem. Soc. A 1968, 2488, 2494. Kirner, J. F.; Dow, W.; Scheidt, D. R.

Inorg. Chem. 1976, 15, 1685.

(51) (a) Tokita, S.; Matsuoka, K.; Kogo, Y.; Kihara, K. Molecular Design

of Functional DyessPPP MO Method and Its Application; Maruzene:

Tokyo, 1990. (b) Hammond, H. Theor. Chim. Acta 1970, 18, 239. (c)

Mataga, N.; Nishimoto, K. Z. Phys. Chem. (Frankfurt am Main) 1957, 13,

140.

(f) Monosubstituted Type Pc Compounds NilPc-PyPc. Synthesis

of NilPc-AnPc was reported previously.¹PyPc was prepared similarly

as a dark blue solid from 257 mg (0.4 mmol) of tSubPc and crude Py

obtained from 360 mg (2.8 mmol) of 2,3-dicyanopyridine and ammonia

gas.⁴⁹Yield: 71 mg (26%). Mass (m/z): 683 (M⁺). Anal. Calcd for

C₄₃H₄₁N₉: C, 75.52; H, 6.04; N, 18.43. Found: C, 75.28; H, 6.30; N,

1

18.17. H NMR (CDCl₃, 500 MHz): δ 7.7-8.5 (m, 6H, arom), 8.6-

(52) Rappe, A. K.; Casewit, C. J.; Colwell, K. S.; Goddard, W. A., III;

Skiff, W. M. J. Am. Chem. Soc. 1992, 114, 10024.

(49) Cook, A. H.; Linstead, R. P. J. Chem. Soc. 1937, 929.

Article Doi

Synthesis, spectroscopy, and molecular orbital calculations of subazaporphyrins, subphthalocyanines, subnaphthalocyanines, and compounds derived therefrom by ring expansion

DOI: 10.1021/ja983325c

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Article abstract of DOI:10.1021/ja983325c

Full text of DOI:10.1021/ja983325c

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