β,meso-Acetylenyl-bridged, asymmetrical, porphyrin dyads - synthesis, spectral, electrochemical and computational studies

FULL PAPER

DOI: 10.1002/ejoc.200901362

β,meso-Acetylenyl-Bridged, Asymmetrical, Porphyrin Dyads – Synthesis,

Spectral, Electrochemical and Computational Studies

Meesala Yedukondalu,^[a]Dilip K. Maity,*^[b]and Mangalampalli Ravikanth*^[a]

Keywords: Molecular devices / FRET / Density functional calculations / Porphyrin dyads / Heteroporphyrins / Acetylenyl

bridge

The first examples of β,meso-acetylenyl-bridged, asymmetri-

cal, covalently linked, porphyrin dyads, containing two dif-

ferent subunits, such as ZnN₄P-N₃OP (1), ZnN₄P-N₃SP (2),

ZnN₄P-N₂SOP (4) and ZnN₄P-N₂S₂P (6), were synthesized by

the coupling of a β-acetylenyl, ZnN₄porphyrin with a meso-

bromoheteroporphyrin under mild, Pd⁰-catalyzed, coupling

conditions. The dyads containing different types of metal-

free subunits, such as N₄P-N₃SP (3), N₄P-N₂SOP (5) and N₄P-

N₂S₂P (7), were synthesized by the demetallation of the cor-

responding dyads. The seven β,meso-acetylenyl dyads 1–7

were characterized by NMR, MS, absorption, fluorescence

and electrochemical techniques. The NMR, absorption and

electrochemical studies support an electronic interaction be-

tween the subunits in all seven dyads. The steady-state

fluorescence studies on dyads 1–7 support an efficient energy

transfer from the donor (ZnN₄or N₄) subunit to the acceptor

heteroporphyrin subunit upon excitation of the ZnN₄/N₄sub-

unit. First-principle-based, quantum-chemical studies car-

ried out on dyads 1, 2, 4 and 6 further support an electronic

interaction between the donor and acceptor subunits. The

computational studies also predict significant tuning of the

electronic energy levels in these dyads with the modification

of the porphyrin core of the acceptor groups. The calculations

support the experimental results of efficient donorǞacceptor

energy transfer in these dyads.

glet state from the metalloporphyrin subunit to the metal-

free subunit. However, the absorption bands of the donor

metalloporphyrin often have good overlap with the absorp-

tion bands of the acceptor porphyrin. Hence, it is often dif-

ficult to selectively excite the donor subunit. Furthermore,

the emission bands of the donor and acceptor subunits also

overlap to a great extent, which prevents the estimation of

the amount of donor emission quenched. These problems

can be circumvented by using two different types of macro-

cycles whose absorption and emission bands do not overlap

significantly. Lindsey and co-workers^[6]and others synthe-

sized porphyrin–phthalocyanine dyads and higher oligo-

mers, in which the phthalocyanine subunit absorbs at lower

energy and acts as an energy acceptor, and the porphyrin

subunit absorbs at higher energy and acts as an energy do-

nor. In porphyrin–phthalocyanine dyads, there is a good

separation between absorption and emission bands; hence,

the selective excitation of the donor subunit and the estima-

tion of energy-transfer parameters are possible in these sys-

tems. Recently, we and others synthesized several covalent,

meso-diarylethyne-bridged, asymmetrical dyads^[7]contain-

ing porphyrin (N₄core) and heteroporphyrin subunits (N₃X

and N₂X₂cores; X = O and S) and showed the possibility

of efficient energy transfer in the singlet state from the por-

phyrin to the heteroporphyrin subunit. A perusal of the lit-

erature reveals that such asymmetrical dyads are rare, and

more such systems are needed to explore their potential for

various applications. It is established that the electronic in-

Introduction

Asymmetrical porphyrin dyads containing different

macrocycles such as porphyrin–phthalocyanine,^[1]por-

phyrin–chlorin,^[2]porphyrin–corrole^[3]and porphyrin–het-

eroporphyrin^[4]have receiving attention recently, because

the singlet-state energy levels of two macrocycles in these

types of dyads are arranged favorably for efficient transfer

of energy in the metal-free state. Earlier reports on cova-

lently linked porphyrin dyads were mainly limited to systems

containing two of the same type of macrocycles such as two

normal porphyrins (N₄core). The energy gradient between

two of the same macrocycles was created by selectively

metallating one of the porphyrin units and keeping the

other macrocycle in the metal-free form. Thus, covalently

linked porphyrin dyads^[5]connected by various types of lin-

kers, containing a metalloporphyrin (e.g. as a Zn^IIor Mg^II

derivative) as an energy donor and a metal-free porphyrin

as an energy acceptor, have been synthesized. These com-

pounds demonstrated an efficient energy transfer in the sin-

[a] Department of Chemistry, Indian Institute of Technology,

Mumbai 400076, India

Fax: +91-22-25767152

E-mail: ravikanth@chem.iitb.ac.in

[b] Theoretical Chemistry Section, Chemistry Group, Bhabha

Atomic Research Centre,

Mumbai 400085, India

E-mail: dkmaity@barc.gov.in

Supporting information for this article is available on the

WWW under http://dx.doi.org/10.1002/ejoc.200901362.

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β,meso-Acetylenyl-Bridged Asymmetrical Porphyrin Dyads

teractions between the two subunits in dyads can be modu- to determine any definite orbital interaction present be-

lated by connecting two porphyrins in different orientations tween the donor and acceptor moieties of the dyads

such as meso,meso, β,meso and β,β, which facilitates elec- through the linker. Frontier orbital diagrams were also gen-

tronic delocalization within the dyads.^[8]Tuning the energy erated, and the effect of the β,meso connection in the por-

gaps between the highest doubly occupied molecular orbit- phyrin dyads on the HOMO–LUMO gap were correlated

als (HOMOs) and the lowest unoccupied molecular orbitals to the observed differences in the experimental results. The

(LUMOs) of such extended π-conjugated systems should visualization of appropriate MOs suggests an interaction

play a vital role in optimizing the performance of electronic between the donor and acceptor moieties of the dyads

devices based on these active organic components. How- through the linker.

ever, there are very few reports available on dyads in which

the β-position of the first porphyrin is connected to the

meso-position of second porphyrin. Therien et al.,^[9]Osuka

et al.^[10]and others^[11]have synthesized β,meso-linked dyads

connected either directly or by ethyne and phenyl bridges.

However, these dyads are symmetrical in nature, containing

two of the same type of subunits (N₄core).

In this paper, we report four new, asymmetrical, β,meso-

acetylenyl-bridged dyads containing porphyrin and hetero-

porphyrin subunits such as ZnN₄P-N₃OP (1), ZnN₄P-N₃SP

(2), ZnN₄P-N₂SOP (4) and ZnN₄P-N₂S₂P (6) and three

metal-free dyads such as N₄P-N₃SP (3), N₄P-N₂SOP (5)

and N₄P-N₂S₂P (7), as shown in Figure 1. The dyads 1, 2,

4 and 6 were prepared from readily available porphyrin

building blocks under Pd⁰-catalyzed coupling conditions,

and dyads 3, 5 and 7 were prepared by the demetallation of

Figure 1. β,meso-acetylenyl-bridged, asymmetrical dyads 1–7.

the corresponding dyads. Preliminary photophysical studies

supported an efficient energy transfer from the ZnN₄/N₄

subunit to the heteroporphyrin subunit upon the selective

excitation of the ZnN₄/N₄subunit. The structure and elec-

tronic properties of dyads 1, 2, 4 and 6, along with their

Results and Discussion

appropriate porphyrin monomers, were calculated by apply-

The required monofunctionalized porphyrin and hetero-

ing density-functional-based electronic-structure theory porphyrin building blocks 8–15, for the synthesis of β,meso-

with all the electron, Gaussian, atomic, basis functions. Ap- acetylenyl-bridged dyads 1–7, are shown in Figure 2. The

propriate MO contour plots were generated and visualized β-bromoporphyrin building block [2-bromo-5,10,15,20-tet-

Figure 2. Functionalized monomers 8–15.

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M. Yedukondalu, D. K. Maity, M. Ravikanth

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ra(p-tolyl)porphyrinato]zinc(II) (8) was synthesized accord- metric nature of the compound. In the absorption spectrum

ing to a literature procedure.^[12]The meso-bromoporphyrin of 9, one strong Soret band at 431 nm and two Q-bands at

building blocks such as 5-bromo-10,15,20-tri(p-tolyl)-21- 559 and 597 nm were observed, which were slightly red-

oxaporphyrin (12) and 5-bromo-10,15,20-tri(p-tolyl)-21-thia- shifted compared to 8. Compound 10 was prepared by de-

porphyrin (13) were synthesized from monomeric, meso-un- protecting 9 with KOH in C₆H₆/CH₃OH at 90 °C over-

substituted porphyrins such as 10,15,20-tri(p-tolyl)-21-oxa- night, followed by column chromatographic purification on

porphyrin (16) and 10,15,20-tri(p-tolyl)-21-thiaporphyrin silica gel. Compound 10 was confirmed by a singlet at δ =

(17), respectively, according to our previously reported pro- 3.27 ppm, corresponding to the CCH proton in the ¹H

cedure.^[13]The building block [2-ethynyl-5,10,15,20-tetra- NMR spectrum and a molecular ion peak in the ESI mass

(p-tolyl)porphyrinato]zinc(II) (10) was prepared by an alter- spectrum. Compound 11 was prepared by treating 10 with

nate route, starting from [2-{(3-methyl-3-hydroxybut-1- TFA in CH₂Cl₂, followed by column chromatographic puri-

yn-1-yl)}-5,10,15,20-tetra(p-tolyl)porphyrinato]zinc(II) (9, fication. The molecular ion peak in the ESI mass spectrum

Scheme 1). Compound 9 was prepared by treating 8 with 2- and a signal at δ = –2.58 ppm corresponding to the two

methyl-3-butyn-2-ol in the presence of a catalytic amount inner NH protons in the ¹H NMR spectrum confirmed the

of CuI/Pd(PPh₃)₂Cl₂in Et₃N/DMF at reflux for 16 h, fol- identity of 11. Porphyrins 5-bromo-10,15,20-tri(p-tolyl)-21-

lowed by silica gel column chromatographic purification. oxa-23-thiaporphyrin (14) and 5-bromo-10,15,20-tri(p-

Compound 9 was confirmed by the molecular ion peak in tolyl)-21,23-dithiaporphyrin (15) were prepared from

the ESI mass spectrum and elemental analysis, which monomeric, meso-unsubstituted porphyrins 10,15,20-tri(p-

1

matched the expected composition. In the H NMR spec- tolyl)-21-oxa-23-thiaporphyrin (18)^[13]and 10,15,20-tri(p-

trum of 9, the seven β-pyrrole signals appeared as four sets tolyl)-21,23-dithiaporphyrin (19), respectively. Compound

of signals at δ = 8.70–9.20 ppm, consistent with the asym- 18 was prepared as reported earlier,^[13]and porphyrin 19

Scheme 1. Synthesis of 2-ethynyl-5,10,15,20-tetra(p-tolyl)porphyrin (11).

Scheme 2. Synthesis of meso-free dithiaporphyrin 19.

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β,meso-Acetylenyl-Bridged Asymmetrical Porphyrin Dyads

was prepared by adopting an alternate methodology, as

shown in Scheme 2. The condensation of 1 equiv. of asym-

metrical 5-(p-tolyl)-10,15,17-trihydro-16-thiatripyrrane (20)

with 1 equiv. of symmetrical 2,5-[hydroxy(p-tolyl)methyl]-

thiophene (21) in CH₂Cl₂under mild acidic conditions,^[14]

followed by purification on silica gel, yielded 19 as single

product in decent yield. The advantage of this methodology

over our previously reported method^[13]is that no scram-

bling was noted in this reaction, and the desired compound

was obtained as a single product in higher yield. Porphyrins

14 and 15 were prepared by treating 1 equiv. of porphyrins

18 and 19, respectively, with 1 equiv. of N-bromosuc-

cinimide (NBS) in CHCl₃at room temperature (Scheme 3).

The molecular ion peak in the ESI mass spectrum con-

firmed the identity of 14 and 15. In the ¹H NMR spectrum,

Scheme 3. Synthesis of 5-bromo-10,15,20-tri(p-tolyl)-21-oxa-23-

thiaporphyrin (14) and 5-bromo-10,15,20-tri(p-tolyl)-21,23-dithia-

porphyrin (15).

the meso-proton, the signal of which generally appears at δ in 55–85% yield (Scheme 4). The coupling reactions worked

≈ 10.6–10.8 ppm in 18 and 19, was absent in 14 and 15. The smoothly and required one simple chromatographic purifi-

absorption spectra of 14 and 15 showed four Q-bands and cation to afford dyads in decent yields. Dyads 1, 2, 4 and 6

one Soret band, which were bathochromically shifted rela- were freely soluble in common organic solvents and charac-

tive to those of porphyrins 18 and 19, respectively, due to terized by various spectroscopic and electrochemical tech-

the presence of bromine at the meso position.

niques. The molecular ion peaks in the MALDI-TOF mass

Covalently linked, asymmetrical, β-meso-acetylenyl- spectrum confirmed the identity of dyads 1, 2, 4 and 6.

bridged dyads 1, 2, 4 and 6, containing two different sub- Dyads 1, 2, 4 and 6, along with their corresponding mono-

units, were prepared by coupling β-ethynyl Zn^IIporphyrin mers 10, 12, 13, 14 and 15, respectively, were characterized

10 with meso-bromoporphyrins 12, 13, 14 and 15, respec- in detail by NMR spectroscopy, and the data of selected

1

tively, in the presence of Pd₂(dba)₃/AsPh₃in C₆H₆/Et₃N at protons are presented in Table 1. The H NMR spectra of

35 °C for 4 h.^[15]The reaction progress was monitored by dyads 1, 2, 4 and 6 were very clean, and the resonances of

1

TLC analysis, and the reaction was stopped after the com- the dyads were assigned on the basis of the H NMR spec-

1

plete disappearance of the starting monomers and the ap- tra observed for the corresponding monomers and H-¹H

pearance of a new spot, corresponding to the desired dyad. COSY and NOESY spectra recorded for the dyads. A rep-

The crude, asymmetrical dyads were purified by silica gel resentative spectrum of dyad 2, along with the spectra of

column chromatography and afforded dyads 1, 2, 4 and 6 the corresponding monomers 10 and 13, over a selected re-

Scheme 4. Synthesis of asymmetrical, porphyrin dyads 1–7.

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M. Yedukondalu, D. K. Maity, M. Ravikanth

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gion, is shown in Figure 3a, and the ¹H-¹H COSY spectrum observed, due to the more basic nature of the N₃O subunit.

of dyad 2 is shown in Figure 3b. A close inspection of Fig- In addition to the observations described above, we also

ure 3 and the data presented in Table 1 indicates that only note that the meso-(p-tolyl) group of the ZnN₄subunit,

the signals of selected protons such as the β-pyrrole pro- which is adjacent to the acetylenic bridge, experienced the

tons, represented as H_a, H_b, H_cand the β-thiophene/β-fu- ring current of the heteroporphyrin subunit. The signal of

ran protons experienced downfield shifts due to the por- the meso-(p-tolyl) group, which is perpendicular to the

phyrin current effect. In general, it is apparent that there are ZnN₄subunit but coplanar with the heteroporphyrin sub-

more signals for the dyads than there are for the monomers, unit, exhibited evidence of interaction with a ring current

supporting the asymmetric nature of the dyads. In all four by its upfield shift, clearly observed for the meta-protons,

1

dyads (1, 2, 4 and 6), the signal of the β-pyrrole proton of represented as H_d, in the H NMR spectra. Furthermore,

the ZnN₄subunit, which is adjacent to the ethyne linker the signals of the methyl protons of the meso-(p-tolyl)

(H_a), experienced a ca. 0.5 ppm downfield shift relative to group, represented as H_g, also experienced a ca. 1.2 ppm

the same signal in the ZnN₄monomer 10, indicating the upfield shift, clearly seen in the NOESY spectrum (see the

alteration of the ring current of the ZnN₄subunit in the Supporting Information). This kind of upfield shift of the

dyads. The signals of the β-thiophene/β-furan and other β- central meso-(p-tolyl) groups had previously been observed

pyrrole protons of the heteroporphyrin subunits experi- for similar dimeric porphyrin systems.^[16]These observa-

enced slight alterations in their chemical shifts. Further- tions were further supported by ab initio, quantum-chemi-

more, the signal of the inner NH proton of the N₃S subunit cal calculations. Thus, the NMR study supported an inter-

in dyad 2 experienced a downfield shift of ca. 0.5 ppm, and action between the two subunits in all four β,meso-acet-

the inner NH signal of the N₃O subunit in dyad 1 was not ylenyl-bridged, asymmetrical dyads 1, 2, 4 and 6.

Figure 3. NMR spectra of dyads and their corresponding momomers. (a) Comparison of partial ¹H NMR spectra of dyads 2 and 3 with

1

monomers 10 and 13, recorded in CDCl₃. (b) H-¹H COSY spectrum of dyad 2.

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β,meso-Acetylenyl-Bridged Asymmetrical Porphyrin Dyads

Table 1. ¹H NMR chemical shifts (δ in ppm) of selected protons of dyads 1–7, along with their corresponding monomers, recorded in

CDCl₃.

Entry

Compound

β-Thiophene/β-furan

β-Pyrrole

Inner NH

H_a

H_b

H_c

1

2

3

4

5

10

11

12

13

14

–

9.13 (s)

9.15 (s)

–

–2.58 (s)

10.04 (d), 9.49 (d)

10.18 (d), 9.82 (d)

10.15 (d), 9.66 (d) (β-thio),

9.65 (d), 9.37 (d) (β-fur)

10.20 (d), 9.76 (d), 9.64 (s)

10.45 (d), 9.76 (d)

10.20 (d), 9.76 (d)

10.16 (d), 9.75 (d)

–

9.29 (d)

9.30 (d)

9.35 (d)

8.57 (d)

8.64 (d)

–

–2.62 (s)

–

6

7

8

9

15

1

2

3

–

9.31 (d)

9.03 (d)

9.24 (d)

9.22 (d)

8.70 (d)

8.66 (d)

8.65 (d)

8.63 (d)

–

9.62 (s)

9.46 (s)

–2.10 (s) (N₃SP)

–2.12 (s) (N₃SP),

–2.56 (s) (N₄P)

–

10

11

4

5

9.96 (d), 9.64 (d) (β-thio),

9.63 (d), 9.33 (d) (β-fur)

9.92 (d), 9.63 (d) (β-thio),

9.63 (d), 9.30 (d) (β-fur)

10.20 (d), 9.70 (d), 9.63 (d)

10.17 (d), 9.70 (d), 9.63 (d)

9.63 (s)

9.48 (s)

9.22 (d)

9.20 (d)

8.60 (d)

–2.56 (s) (N₄)

12

13

6

7

9.62 (s)

9.47 (s)

9.28 (d)

9.25 (d)

8.67 (d)

8.66 (d)

–

–2.56 (s) (N₄)

The metal-free dyads N₄P-N₃SP (3), N₄P-N₂SOP (5) and Absorption Properties of Dyads 1–7

N₄P-N₂S₂P (7) were synthesized by the demetallation of dy-

ads 2, 4 and 6, respectively. The demetallation was carried

The absorption spectra of dyads 1–7 and their corre-

out by treating the corresponding metallated dyad in sponding monomers in CH₂Cl₂were recorded at room tem-

CH₂Cl₂with TFA for 15 min. The progress of the reaction perature, and the results are listed in Table 2. A comparison

was monitored by TLC analysis and absorption spec- of the absorption spectra of dyads 2 and 3, along with

troscopy. After the standard workup, the crude, metal-free monomers 10 and 13, is shown in Figure 4. As is clear from

dyads were purified on a short silica gel column and af- Figure 4 and Table 2, the dyads exhibit split Soret bands

forded pure dyads 3, 5 and 7, in ca. 90% yield. The molecu- and bathochromic shifts of both the Q- and Soret bands

lar ion peak in the mass spectra and the broad signal for the relative to their corresponding monomers. For example,

two inner NH protons of the N₄subunit at δ ≈ –2.56 ppm in dyad 2, containing ZnN₄and N₃S subunits, showed four Q-

1

the H NMR spectra confirmed the identity of the dyads. bands at 528, 570, 600 and 699 nm and two Soret bands at

Dyads 3, 5 and 7 showed similar ¹H NMR spectral features 428 and 450 nm. In this dyad, the bands at 450, 528 and

and exhibited slight shifts for the signals of selected pro- 699 nm were exclusively due to the N₃S subunit; the band

tons, as observed for metallated dyads 1, 2, 4 and 6 at 428 nm was exclusively due to the ZnN₄subunit, and the

(Table 1).

bands at 570 and 600 nm were due to both the ZnN₄and

Table 2. Absorption data of dyads 1–7, along with their corresponding monomers, recorded in CH₂Cl₂.

Entry

Compound

Soret bands

λ [nm] (logε)

Q-bands

λ [nm] (logε)

1

2

3

4

5

6

7

10

11

12

13

14

15

1

428 (5.75)

426 (5.72)

430 (5.18)

422 (5.35)

434 (5.73)

438 (5.48)

431 (5.60),

456 (5.35)

428 (5.64),

450 (5.73)

426(5.18),

449 (5.29)

429 (5.35),

450 (5.27)

425 (5.08),

454 (5.19)

427 (5.72),

455 (5.77)

428 (5.45),

453 (5.31)

–

558 (4.18)

557 (4.03)

551 (3.45)

577 (3.67)

547 (3.47)

549 (3.79)

561 (4.63)

597 (3.67)

598 (3.87)

620 (3.11)

610

–

521(4.35)

516 (4.05)

512 (4.16)

517 (4.02)

516 (4.29)

484 (4.32)

655 (3.88)

–

681 (3.23)

677

717 (3.32)

702 (3.61)

680 (3.75)

–

649 (3.14)

638 (3.12)

608 (4.60)

–

8

2

3

4

5

6

7

528 (4.42)

524 (4.24)

526 (4.32)

525 (4.16)

530 (4.55)

525 (4.58)

570 (4.81)

571 (4.25)

565 (4.49)

571 (4.19)

570 (4.86)

567 (4.57)

600 (4.41)

600(4.01)

596 (4.05)

601 (3.92)

595 (4.60)

600 (4.36)

–

699 (4.13)

699 (3.72)

733 (4.02)

721 (3.69)

721 (4.28)

734 (4.17)

9

655 (3.60)

–

10

11

12

13

657 (3.51)

–

657 (3.95)

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N₃S subunits. All these absorption bands of dyad 2 were Electrochemical Properties of Dyads 1–7

redshifted relative to those of the corresponding ZnN₄and

N₃S monomers (Table 2). Similarly, the metal-free dyad 3,

containing N₄and N₃S subunits, showed five Q-bands at

524, 571, 600, 655 and 699 nm and two Soret bands at 426

and 449 nm, which were redshifted relative to those of cor-

responding monomers. Furthermore, we note that in dyads

1–7, the absorption bands corresponding to the heteropor-

phyrin subunit exhibited more redshifts than did the ZnN₄/

N₄unit.

The electrochemical properties of dyads 1–7 were studied

by cyclic voltammetry (CV) and differential pulse voltam-

metry at a scan rate of 50 mV/s using tetrabutylammonium

perchlorate as the supporting electrolyte (0.1 ) in CH₂Cl₂.

The oxidation and reduction waves of dyads 2 and 6 are

shown in Figure 5, and the redox data along with the data

of 2, 6 and their corresponding monomers are presented in

Table 3. In general, the dyads exhibited two or three oxi-

dations and two to four reductions. The oxidations and re-

ductions are reversible or quasi-reversible (∆E_p= 60–

120 mV) and, in some cases, irreversible. The redox waves

of the dyads were assigned by comparison with the redox

potentials of the corresponding porphyrin monomers. For

example, dyad 2, containing ZnN₄and N₃S subunits, exhib-

ited four reductions at –1.03, –1.37, –1.55 and –1.68 V. The

first two reduction waves at –1.03 and –1.37 V were as-

signed to the first and second reductions of the N₃S subunit

on the basis of the fact that the N₃S porphyrin is easier to

reduce than the Zn^IIN₄porphyrin.^[17]The reductions at

–1.55 and –1.68 V were assigned to the first and second

reductions of the ZnN₄subunit. Similarly, dyad 2 showed

three oxidations at 0.80, 1.11 and 1.52 V. The first oxidation

at 0.80 V was assigned to the ZnN₄subunit since the ZnN₄

porphyrin is easier to oxidize than the N₃S porphyrin. The

oxidation at 1.52 V was exclusively assigned to the oxi-

dation of the N₃S subunit, and the oxidation at 1.11 V was

due to the oxidation of both the ZnN₄and N₃S subunits.

However, in dyads 3, 5 and 7, containing the metal-free N₄

subunit and heteroporphyrin subunit, the oxidations over-

lapped, but the reductions could be assigned to the subunits

Figure 4. Normalized Q-bands and Soret band (inset) absorption

spectra of dyads 2 and 3 along with their monomers 10 and 13,

recorded in CH₂Cl₂.

Figure 5. Oxidation and reduction waves of dyads 2 and 6 in CH₂Cl₂containing 0.1  TBAP as the supporting electrolyte, recorded at

a 50 mVs^–1scan speed.

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β,meso-Acetylenyl-Bridged Asymmetrical Porphyrin Dyads

Table 3. Electrochemical redox data [V] of dyads 2–7 and their corresponding monomers recorded in CH₂Cl₂containing 0.1  TBAP as

the supporting electrolyte at a scan rate of 50 mV/s. E_1/2values are reported relative to SCE.

Entry Compound

Oxidation

E_1/2[V] vs. SCE (∆E_P[mV])

Reduction

E_1/2[V] vs. SCE (∆E_P[mV])

E_CT

E_0–0

[M⁺, M^–] [eV]

1

2

3

4

5

6

7

10

11

13

14

15

2

0.78 (88) 1.08 (88)

–

1.41

–

1.42

–

–1.48 (97) –1.65 (108)

–

1.83

2.10

2.03

1.90

1.80

1.72

1.75

–

1.01

1.15

–

–1.12 (58)

–1.40 (89)

–

1.53 (88) –0.96 (67) –1.39 (79)

–1.18

1.58 (86) –1.14 (78) –1.25 (95)

–

–1.50

–

1.19

–

–1.68 (57)

–

0.80 (70) 1.11 (73)

1.10

1.52

–

–1.03 (52) –1.37 (94) –1.55 (74)

3

–

–1.00 (56),

–1.11 (79)

–1.17

–

–1.40 (94)

–

8

9

4

5

0.80 (70) 1.10 (80)

1.09

–

1.40

–

–1.49 (54)

–1.42 (74),

–1.48 (131)

–1.50

–1.63 (57)

1.97

2.20

–

–1.11 (57)

–

10

11

6

7

0.80 (68) 1.11 (77)

–

1.43

1.55

–

–1.22 (81)

–1.32

–1.62 (73)

2.02

2.11

–

1.01,

1.16

–1.10 (74)

–1.44 (66)

–

by comparison with the corresponding monomer data. A

close inspection of the redox data of the dyads indicated

that the subunit in the dyads exhibited slightly altered oxi-

dations and reductions compared to their corresponding

monomers, supporting an interaction between the subunits

in dyads 1–7.

Table 4. Emission data of dyads 1–7, recorded in CH₂Cl₂.

Entry Compound λ_ex[nm] Porphyrin subunit

Φ_f

% quenched

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

H₂TPP^[a]

420

550

420

430

435

550

530

550

530

550

530

550

530

420

450

420

450

420

450

–

0.11

0.033

0.037

0.016

0.005

0.007

0.0001

0.0035

0.0006

0.014

0.0002

0.0048

0.0002

0.0068

0.0015

0.015

–

97.2

–

98.2

–

99.4

–

99.4

–

98.7

–

98.7

–

99

–

ZnTPP^[a]

OTPPH^[a]

STPPH^[a]

SOTPP^[a]

S₂TPP^[a]

1

2

4

6

3

5

7

ZnN₄em

N₃Oem

ZnN₄em

N₃Sem

ZnN₄em

N₂SOem

ZnN₄em

N₂S₂em

N₄em

N₃Sem

N₄em

N₂SOem

N₄em

N₂S₂em

Excited-State Properties of Dyads 1–7

The steady-state fluorescence properties of dyads 1–7

were studied in CH₂Cl₂, and the data are presented in

Table 4. The metallated dyads 1, 2, 4 and 6 were excited at

550 nm, where the ZnN₄subunit absorbs strongly, or

530 nm, where the heteroporphyrin subunit absorbs

strongly. A comparison of the fluorescence spectra of 6 with

that of a 1:1 mixture of the corresponding monomers 10

and 15, excited at 550 nm, is shown in Figure 6. Upon exci-

tation of dyads 1, 2, 4 and 6 at 550 nm, one would expect

a strong emission from the ZnN₄subunit, as was observed

for a 1:1 mixture of 10 and 15 (Figure 6). A careful inspec-

tion of Figure 6 and the data in Table 4 indicates that the

emission from the ZnN₄subunit was quenched by ca. 99%,

and the strong emission observed originated from hetero-

porphyrin subunit. However, when dyads 1, 2, 4 and 6 were

excited at 530 nm, where the heteroporphyrin subunit ab-

sorbs strongly, the emission originated from the heteropor-

phyrin subunit. Furthermore, the excitation spectra re-

corded for all four dyads, using an emission wavelength of

730 nm, closely matched those of their respective absorp-

tion spectra. These observations strongly support an ef-

ficient energy transfer from the ZnN₄subunit to the hetero-

porphyrin subunit in dyads 1, 2, 4 and 6. Similarly, the

fluorescence properties of metal-free dyads 3, 5 and 7 were

studied by using excitation wavelengths of 420 and 450 nm.

The fluorescence spectra of dyads 3, 5 and 7, recorded at

420 nm, are shown in Figure 7, and the relevant data is pre-

sented in Table 4. When dyads 3, 5 and 7 were excited at

450 nm, where the heteroporphyrin subunit absorbs

0.0003

0.005

0.0011

0.0057

[a] Taken from ref.^[17]

Figure 6. Comparison of emission spectra of dyad 6 and a 1:1 mix-

strongly, the emission originated exclusively from the ture of monomers 10/15, recorded at λ_ex= 550 nm in CH₂Cl₂.

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1551

M. Yedukondalu, D. K. Maity, M. Ravikanth

FULL PAPER

∆G(¹ZnN₄P Ǟ N₃S) = E_CT(ZnN₄P⁺N₃S^–) – E_0–0(ZnN₄P)

∆G(¹N₄P Ǟ N₃S) = E_CT(N₄P⁺N₃S^–) – E_0–0(N₄P)

(1)

(2)

heteroporphyrin subunit, as expected. However, when dyads

3, 5 and 7 were excited at 420 nm, where the metal-free N₄

subunit absorbs strongly, the emission from the N₄subunit

was quenched by 98%, and the strong emission originated

mainly from the heteroporphyrin subunit, supporting an ef-

ficient energy transfer from the N₄subunit to the hetero-

porphyrin subunit. Thus, the steady-state fluorescence stud-

ies clearly support an efficient energy transfer from the

ZnN₄/N₄subunit to the heteroporphyrin subunit in dyads

1–7. Even though the energy transfer in the singlet state is

the major process responsible for quenching the fluores-

cence of the donor ZnN₄/N₄subunits in dyads 1–7, a pho-

toinduced electron transfer (PET) cannot be completely

ruled out in these dyads. Hence, we evaluated the relation-

ships of the energy levels for dyads 2 and 3 with Equa-

tions (1) and (2), respectively, using fluorescence and redox

potential data.^[18]

The singlet, excited and charge-transfer states for dyads

2 and 3 are shown in Figure 8. In dyad 2, the charge-trans-

fer state is lower than the singlet state of the donor ZnN₄,

whereas in dyad 3, the charge-transfer state is higher than

the singlet state of the donor N₄porphyrin. Thus, the free

energy change ∆G_PETis negative for dyad 2, indicating that

electron transfer is also possible in addition to energy trans-

fer. However, in the case of dyad 3, the ∆G_PETis positive,

indicating that the PET is not possible, and energy transfer

is the predominant process. More studies are required to

probe the excited-state dynamics of these covalently linked

dyads.

Quantum-Chemical Studies

To support the inferences drawn from the experimental

results and to provide more insight into the electronic prop-

erties of these porphyrin-based dyads, quantum-chemical

calculations were carried out by applying density functional

theory. Equilibrium structures, calculated at the B3LYP/6-

31G(d) level of theory for the four dyads 1, 2, 4 and 6, are

displayed with selected geometrical parameters for clarity

in Figure 9. We note that the dihedral angle between the

two subunits is ca. 70°, and the distance between the two

subunits is ca. 4.05 Å in all four dyads. Furthermore, the

heteroporphyrin subunit in all four dyads deviates from

planarity, as is evident from the calculated, fully optimized

structures. The calculated distance between two opposite

Ns in the heteroporphyrin subunit is quite different in these

four dyads (Figure 9), showing a significant modification of

Figure 7. Normalized emission spectra of dyads 3, 5 and 7, re-

corded at λ_ex= 420 nm in CH₂Cl₂.

Figure 8. Energies of singlet and charge-transfer states of dyads 2 and 3.

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Eur. J. Org. Chem. 2010, 1544–1561

β,meso-Acetylenyl-Bridged Asymmetrical Porphyrin Dyads

Figure 9. Calculated, optimized structures with selected geometrical parameters of dyads (a) 1, (b) 2, (c) 4 and (d) 6 at the B3LYP/6-

31G(d) level of theory. Distances in Å; angles in °.

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1553

M. Yedukondalu, D. K. Maity, M. Ravikanth

FULL PAPER

Figure 10. Frontier orbital correlation diagram for β,meso, ZnN₄P-N₃OP, asymmetrical dyad 1.

the core (acceptor). All the final, optimized, geometrical through the acetylenic bridge. The LUMO manifests more

parameters of these dyads and their subunits are supplied extensive electronic delocalization between the two macro-

in the Supporting Information in the form of Cartesian co- cycles. Higher-energy states like LUMO + 2 and LUMO +

ordinates. Frontier orbitals (FO) were also calculated for 4 exhibit a comprehensive π-electron delocalization between

dyads 1, 2, 4 and 6 and displayed in Figures 10, 11, 12 and the donor ZnN₄and acceptor N₃O subunits. Stable states

13, respectively, in the form of orbital correlation diagrams; like HOMO – 4 show extended π-electron delocalization

the FOs and energies of the respective subunits are also within the dyad, from the acceptor N₃O subunit to the do-

shown. The present calculations also indicate that in all four nor ZnN₄subunit and extending to the meso-phenyl group

dyads, the meso-phenyl group of the ZnN₄subunit (donor) of the ZnN₄subunit, which is parallel to the acceptor N₃O

adjacent to the acetylenic bridge is parallel to the hetero- subunit. The HOMO of dyad 1 is destabilized by 0.10 and

porphyrin subunit (acceptor). This allows the meso-phenyl 0.15 eV relative to those of the acceptor and donor, respec-

group of the donor to participate in π–π interactions with tively, whereas the LUMO is stabilized by 0.10 and 0.13 eV

1

the acceptor subunit. This is clearly reflected in the H-¹H with respect to those of the acceptor N₃O and donor ZnN₄

COSY spectra, which showed a doublet at δ = 6.9 ppm for subunits, respectively (Figure 14a). These opposite energetic

the two ortho-phenyl protons of the donor subunit in all the trends of the MOs reduces the HOMO–LUMO gap sub-

dyads (Figure 3b).

stantially to 2.58 eV for 1, down from 2.86 and 2.78 eV

The HOMO in the FO correlation diagram of dyad 1 for 10 and 16, respectively. Table 5 provides the calculated

(Figure 10) indicates an extended π overlap between the HOMO–LUMO gaps for the dyads and their correspond-

N₃O acceptor and the C₁atom of the ZnN₄donor unit ing monomer subunits.

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Eur. J. Org. Chem. 2010, 1544–1561

β,meso-Acetylenyl-Bridged Asymmetrical Porphyrin Dyads

Figure 11. Frontier orbital correlation diagram for β,meso, ZnN₄P-N₃SP, asymmetrical dyad 2.

Similar results were obtained for dyad 2 in terms of the lected MOs and energy levels of dyad 6 and its monomer

extended, π-electron delocalization from the acceptor N₃S constituents are displayed in Figure 13, which shows ex-

to the donor ZnN₄subunit in the case of HOMO – 4, tended, π-electron delocalization between two subunits. The

LUMO + 2 and LUMO + 4, as depicted in Figure 11. How- HOMO of dyad 6 is destabilized by 0.21 and 0.10 eV rela-

ever, the calculated HOMO–LUMO energy gap is 2.43 eV, tive to those of the acceptor and donor, respectively,

which is lower than that of dyad 1. The HOMO of dyad 2 whereas the LUMO is stabilized by 0.13 and 0.38 eV with

is destabilized by 0.16 and 0.14 eV relative to those of the respect to those of the acceptor N₂S₂and donor ZnN₄sub-

acceptor and donor, respectively, whereas the LUMO is sta- units, respectively. Figure 14 depicts a comparative chart of

bilized by 0.16 and 0.29 eV with respect to those of the HOMO–LUMO energy gaps in these four dyads and the

acceptor N₃S and donor ZnN₄subunits, respectively. Fig- corresponding monomer donor and acceptor subunits. It

ure 12 displays the FO correlation diagram of dyad 4, show- demonstrates that the modified core alters the HOMO–

ing selected MOs of the dyad and its constituent monomers. LUMO energy gap significantly, indicating electronic inter-

The visualization of the displayed MOs suggests significant actions in these newly synthesized, β,meso dyads. Dyad 6

electronic interactions between the acceptor N₂SO and the has the largest gap between HOMO energy levels of the

donor ZnN₄subunits in the HOMO and LUMO states, as donor and the acceptor (Figure 14), indicating that 6 expe-

in dyads 1 and 2. The HOMO of dyad 4 is destabilized by riences the largest energy transfer of these four dyads. The

0.17 and 0.14 eV relative to those of the acceptor and do- HOMO orbitals of these four dyads show that, apart from

nor, respectively, whereas the LUMO is stabilized by 0.12 the linker, only atoms from the acceptors participate in this

and 0.33 eV with respect to those of the acceptor N₂SO and MO. However, atoms from both the donor and acceptor

donor ZnN₄subunits, respectively. As a result, the calcu- subunits participate in LUMO orbitals, showing that these

lated HOMO–LUMO energy gap is 2.38 eV for dyad 6. Se- systems are potential candidates for a molecular switch.

Eur. J. Org. Chem. 2010, 1544–1561

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1555

M. Yedukondalu, D. K. Maity, M. Ravikanth

FULL PAPER

Figure 12. Frontier orbital correlation diagram for β,meso, ZnN₄P-N₂SOP, asymmetrical dyad 4.

Dyad 6 has the smallest HOMO–LUMO energy gap, and ZnN₄/N₄subunit to the heteroporphyrin subunit upon exci-

therefore, is the best candidate for molecular-level device tation of the ZnN₄/N₄subunit. The computational studies

applications among the β,meso-substituted dyads reported carried out on asymmetrical dyads containing metallopor-

herein.

phyrin and heteroporphyrin subunits also support an inter-

action between the subunits. Our computational studies

indicated that β,meso-acetylenyl-bridged, asymmetrical,

ZnN₄P-N₂S₂P dyad 6 is the best potential candidate for

molecular-level applications among the dyads presented

herein. Currently, efforts are underway to explore these dy-

ads in more detail using ultra-fast, photophysical studies.

Conclusions

We synthesized the first examples of covalently linked,

β,meso-acetylenyl-bridged, asymmetrical dyads containing

a ZnN₄subunit and a heteroporphyrin subunit such as

N₃O, N₃S, N₂SO and N₂S₂by the coupling of β-ethynyl

ZnN₄with a meso-bromoheteroporphyrin under mild, Pd⁰-

catalyzed, coupling conditions. The coupling works well,

and dyads containing two different subunits such as

ZnN₄P-N₃OP (1), ZnN₄P-N₃SP (2), ZnN₄P-N₂SOP (4) and

ZnN₄P-N₂S₂P (6) were obtained in decent yields. The dyads

containing two metal-free subunits such as N₄P-N₃SP (3),

N₄P-N₂SOP (5) and N₄P-N₂S₂P (7) were obtained by de-

matallating the corresponding dyads with mild acid. The

NMR, optical and electrochemical studies support an inter-

action between the two subunits. The steady-state fluores-

Experimental Section

1

General: H NMR spectra were recorded with a Varian 400 MHz

instrument using tetramethylsilane (TMS) as an internal standard.

¹³C NMR spectra were recorded with a Varian spectrometer op-

erating at 100.6 MHz. All NMR experiments were carried out at

room temperature in CDCl₃with TMS as an internal standard.

Absorption spectra were obtained with a Perkin–Elmer Lambda-

35 instrument, and steady-state fluorescence spectra were obtained

with a PC1 photon counting spectrofluorimeter, manufactured by

ISS, USA. IR spectra were recorded with a Nicolet Imapact-400

cence studies indicate an efficient energy transfer from the FTIR spectrometer, and ESI mass spectra were recorded with a Q-

1556 Eur. J. Org. Chem. 2010, 1544–1561

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β,meso-Acetylenyl-Bridged Asymmetrical Porphyrin Dyads

Figure 13. Frontier orbital correlation diagram for β,meso, ZnN₄-N₂S₂, asymmetrical dyad 6.

TOF Micromass spectrometer. The fluorescence quantum yields

(Φ_f) of all the compounds were estimated from the emission and

absorption spectra by a comparative method using H₂TPP (Φ_f=

0.11) or ZnTPP (Φ_f= 0.033) as reference compounds. MALDI-

TOF spectra were obtained with an Axima-CFR instrument manu-

factured by Kratos Analyticals. CV and differential pulse voltam-

metric (DPV) studies were carried out with a BAS electrochemical

system utilizing the three-electrode configuration, consisting of a

glassy carbon (working) electrode, a platinum wire (auxiliary) elec-

trode and a saturated calomel (reference) electrode. These experi-

ments were performed in dry CH₂Cl₂using 0.1  tetrabutylammo-

nium perchlorate as the supporting electrolyte. Under these condi-

tions, ferrocene shows a reversible, one-electron oxidation wave

(E_1/2= 0.42 V). The solution was degassed by purging with argon,

and during the acquisition, argon was slowly passed over the solu-

tion. All general chemicals and solvents were procured from S. D.

Fine Chemicals, India. Column chromatography was performed

using silica gel obtained from Sisco Research Laboratories, India.

Tetrabutylammonium perchlorate was purchased from Fluka and

used without further purification. All other chemicals used for syn-

thesis were reagent grade, unless otherwise specified.

to determine their equilibrium structures and their electronic prop-

erties. A search for minimum energy structures was performed in

the ground electronic state (S₀), applying Becke’s three-parameter,

correlated, hybrid, density functional (B3LYP) with 6-31G(d)

atomic basis functions, which include ca. 3200 primitive Gaussian

functions in total. Equilibrium structures of these systems were cal-

culated based on a full geometry optimization without any sym-

metry restrictions according to the Newton–Raphson procedure.

All these calculations were carried out with the GAMESS suite

of programs for ab initio, electronic, structure calculations with a

LINUX cluster platform.^[19]The visualization of molecular struc-

tures and orbital contour plots were carried out using MOLDEN

visualization software.^[20]

[2-{(3-Hydroxy-3-methylbut-1-yn-1-yl)}-5,10,15,20-tetra(p-tolyl)por-

phyrinato]zinc(II) (9): To a deoxygenated solution of [2-bromo-

5,10,15,20-tetra(p-tolyl)porphyrinato]zinc(II)

(8,

200.0 mg,

0.25 mmol) in dry Et₃N/dimethylformamide (55 mL, 10:1), bis(tri-

phenylphosphane)palladium(II) chloride (17.0 mg, 0.025 mmol),

cuprous iodide (4.0 mg, 0.25 mmol) and 2-methyl-3-butyn-2-ol

(238 µL, 2.5 mmol) were added. The reaction mixture was heated

at reflux for 16 h, cooled and filtered through a short silica column

using CH₂Cl₂as the eluent. The solvent was removed under re-

duced pressure, and the crude residue was purified by silica gel

Quantum-Chemical Methods: DFT calculations were carried out on

the four dyads (1, 2, 4 and 6) shown in Figure 1 and their subunits

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1557

M. Yedukondalu, D. K. Maity, M. Ravikanth

FULL PAPER

Figure 14. Pictorial representation of Kohn–Sham HOMO and LUMO energy levels of the four dyads (a) 1, (b) 2, (c) 4 and (d) 6 and

the corresponding donor and acceptor macrocycles.

(90 mL) in a round-bottomed flask fitted with a Dean–Stark appa-

ratus and reflux condenser. Potassium hydroxide (90 mg,

1.6 mmol), dissolved in CH₃OH (30 mL), was added to it, and the

reaction mixture was stirred at 80 °C for 20 h. The solvent mixture

collected in the Dean–Stark apparatus was removed at regular in-

tervals, and the progress of the reaction was monitored by TLC

analysis. The crude compound was subjected to silica gel column

chromatography using petroleum ether/CH₂Cl₂(60:40) and af-

forded pure 10 as a purple crystalline solid (88 mg, 95%). M.p. Ͼ

300 °C. ¹H NMR (400 MHz, CDCl₃): δ = 2.70 (s, 12 H, tolyl), 3.27

(s, 1 H, CC-H), 7.45 (d, J = 7.9 Hz, 2 H, aryl), 7.53–7.55 (m, 6 H,

aryl), 7.95 (d, J = 7.9 Hz, 2 H, aryl), 8.05–8.08 (m, 6 H, aryl), 8.90

(s, 2 H, β-pyrrole), 8.92 (s, 2 H, β-pyrrole), 8.94 (s, 2 H, β-pyrrole),

9.22 (s, 1 H, β-pyrrole) ppm. ¹³C NMR (100 MHz, CDCl₃): δ =

21.8, 31.4, 78.9, 85.5, 121.2, 121.3, 121.4, 121.7, 124.8, 126.6, 126.8,

127.8, 127.9, 128.1, 132.0, 132.4, 132.5, 132.6, 133.0, 134.0, 134.6,

139.6, 142.7, 142.8, 148.0, 148.1, 150.9, 151.0 ppm. ESI-MS: m/z =

Table 5. HOMO and LUMO energy levels of dyads 1, 2, 4 and 6

and their corresponding monomers 10 and 16–19.

Entry System ε_HOMO[eV] ε_LUMO[eV] ε_HOMO– ε_LUMO[eV]

1

2

3

4

5

6

7

8

9

10

16

17

18

19

1

–4.92

–4.87

–4.94

–4.95

–5.03

–4.77

–4.78

–4.82

–2.06

–2.09

–2.19

–2.27

–2.31

–2.19

–2.35

–2.39

–2.44

2.86

2.78

2.75

2.68

2.72

2.58

2.43

2.39

2.38

2

4

6

column chromatography. Pure 9 was collected with petroleum

ether/CH₂Cl₂(20:80) and was obtained as a purple solid (148 mg,

1

63%). M.p. Ͼ 300 °C. H NMR (400 MHz, CDCl₃): δ = 1.51 (s, 6

H, C-CH₃), 2.72 (s, 12 H, tolyl), 7.53–7.57 (m, 8 H, aryl), 8.05–

8.08 (m, 8 H, aryl), 8.72 (d, J = 4.6 Hz, 1 H, β-pyrrole), 8.88 (d, J

= 4.6 Hz, 1 H, β-pyrrole), 8.91–8.92 (m, 4 H, β-pyrrole), 9.13 (s, 1

H, β-pyrrole) ppm. ¹³C NMR (100 MHz, CDCl₃): δ = 21.8, 29.9,

31.2, 65.7, 79.0, 103.2, 120.5, 120.9, 121.3, 121.6, 125.3, 127.4,

127.5, 131.9, 132.4, 132.7, 134.6, 134.8, 137.3, 137.6, 139.0, 139.9,

140.5, 147.2, 148.4, 150.4, 150.9, 151.0, 151.3 ppm. UV/Vis (tolu-

ene): λ (logε) = 431 (5.73), 559 (4.24), 597 (3.65) nm. ESI-MS: m/z

757.3 [M + H]⁺. IR (KBr film): ν = 2926, 2850, 1966, 1645, 1464,

˜

960, 800, 656 cm^–1. C₅₀H₃₆N₄Zn (756.3): calcd. C 79.20, H 4.79, N

7.39; found C 79.32, H 4.81, N 7.26.

5-Bromo-10,15,20-tri(p-tolyl)-21-oxa-23-thiaporphyrin (14): To

a

stirred solution of 10,15,20-tri(p-tolyl)-21-oxa-23-thiaporphyrin

(18, 40.0 mg, 0.066 mmol) in CHCl₃(15 mL) was added NBS

(12.0 mg, 0.066 mmol), and the mixture was stirred at room tem-

perature for 20 min. The crude compound was subjected to silica

gel column chromatography using petroleum ether/CH₂Cl₂(30:70)

as the eluent and afforded the pure bromoporphyrin 14 as a purple

= 814.2 [M]⁺. IR (KBr film): ν = 3328 (NH), 2966, 2853, 1966,

˜

1464, 1268, 960, 802, 656 cm^–1. C₅₃H₄₂N₄OZn (814.2): calcd. C

77.98, H 5.19, N 6.86; found C 77.86, H 5.25, N 6.90.

1

[2-Ethynyl-5,10,15,20-tetra(p-tolyl)porphyrinato]zinc(II) (10): Com-

pound 9 (100.0 mg, 0.13 mmol) was dissolved in dry benzene

solid (30 mg, 66%). M.p. Ͼ 300 °C. H NMR (400 MHz, CDCl₃):

δ = 2.7 (s, 9 H, 3 CH₃), 7.30–7.64 (m, 6 H, aryl), 8.03–8.10 (m, 6

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β,meso-Acetylenyl-Bridged Asymmetrical Porphyrin Dyads

H, aryl), 8.37 (d, J = 4.6 Hz, 1 H, β-pyrrole), 8.52 (d, J = 4.6 Hz,

1 H, β-pyrrole) 8.64 (d, J = 4.6 Hz, 1 H, β-pyrrole), 9.35 (d, J =

4.6 Hz, 1 H, β-furan), 9.37 (d, J = 4.6 Hz, 1 H, β-pyrrole), 9.65 (s,

1 H, β-furan), 9.66 (d, J = 5.2 Hz, 1 H, β-thiophene), 10.15 (d, J

= 5.2 Hz, 1 H, β-thiophene) ppm. ¹³C NMR (100 MHz, CDCl₃):

δ = 21.7, 110.2, 114.0, 128.4, 128.5, 134.3, 134.7, 135.2, 135.9,

J = 4.6 Hz, 1 H, β-pyrrole), 9.62–9.63 (m, 2 H, β-furan and β-

pyrrole), 9.68 (s, 1 H, β-pyrrole), 9.75 (d, J = 3.9 Hz, 1 H, β-pyr-

role) ppm. ¹³C NMR (100 MHz, CDCl₃): δ = 21.5, 21.7, 22.6, 65.2,

110.2, 121.5, 121.8, 127.5, 127.8, 128.5, 129.7, 130.5, 131.9, 132.4,

132.6, 133.0, 133.8, 134.0, 134.3, 134.7, 135.3, 136.8, 137.3, 137.5,

138.0, 138.3, 139.6, 140.0, 146.3, 147.9, 148.5, 150.4, 151.1, 151.2,

136.1, 136.3, 138.1, 138.4, 145.8, 148.3, 148.7, 156.8, 157.1, 151.3, 151.7, 156.7, 157.9, 158.8 ppm. MALDI-TOF-MS: m/z =

157.3 ppm. ESI-MS: m/z = 677.1/679.1 [M + 1]⁺(Br⁷⁹/Br⁸¹). IR

1335.2 [M]⁺. IR (KBr film): ν = 3046, 2914, 2840, 2211, 1641, 1458,

˜

(KBr film): ν = 2923, 2835, 1966, 1645, 1464, 960, 800, 645 cm^–1. 967, 820, 654 cm^–1.

˜

C₄₁H₃₃BrN₂OS (676.1): calcd. C 72.67, H 4.31, N 4.13; found C

72.75, H 4.25, N 4.26.

[5,10,15,20-Tetra(p-tolyl)-2-{2-[10Ј,15Ј,20Ј-tri(p-tolyl)-21-thiapor-

phin-5Ј-yl]ethynyl}porphryinato]zinc(II) (2): Yield: 84%. M.p. Ͼ

300 °C. ¹H NMR (400 MHz, CDCl₃): δ = –2.10 (s, 1 H, NH), 1.50

(s, 3 H, CH₃), 2.65 (s, 3 H, CH₃), 2.69 (s, 6 H, 2 CH₃), 2.70 (s, 6

H, 2 CH₃), 2.72 (s, 3 H, CH₃), 6.83 (d, J = 8.2 Hz, 2 H, aryl), 7.56–

7.72 (m, 12 H, aryl), 8.06–8.21 (m, 14 H, aryl), 8.56 (d, J = 4.6 Hz,

1 H, β-pyrrole), 8.58 (d, J = 4.6 Hz, 1 H, β-pyrrole), 8.65 (d, J =

4.6 Hz, 1 H, β-pyrrole), 8.88 (d, J = 2.1 Hz, 2 H, β-pyrrole), 8.90

(s, 2 H, β-pyrrole), 8.96 (s, 2 H, β-pyrrole), 8.99 (d, J = 4.6 Hz, 1

H, β-pyrrole), 9.03 (d, J = 4.6 Hz, 1 H, β-pyrrole), 9.24 (d, J =

4.3 Hz, 1 H, β-pyrrole), 9.62 (s, 1 H, β-pyrrole), 9.76 (d, J = 4.9 Hz,

1 H, β-thiophene), 10.20 (d, J = 4.9 Hz, 1 H, β-thiophene) ppm.

¹³C NMR (100 MHz, CDCl₃): δ = 21.5, 22.7, 23.0, 23.7, 68.1,

112.1, 121.1, 121.4, 124.4, 124.9, 125.9, 127.3, 127.6, 128.4, 128.9,

130.9, 131.0, 131.8, 132.4, 132.9, 133.6, 134.1, 134.3, 134.7, 135.2,

5-Bromo-10,15,20-tri(p-tolyl)-21,23-dithiaporphyrin (15): Com-

pound 15 was prepared under similar reaction conditions as de-

scribed above for 14 by treating 10,15,20-tri(p-tolyl)-21,23-dithia-

porphyrin (19, 55.0 mg, 0.0901 mmol) in CHCl₃(15 mL) at room

temperature with NBS (16.0 mg, 0.0901 mmol) at room tempera-

ture for 10 min. The progress of the reaction was monitored by

TLC analysis. After completion of the reaction, acetone/CH₃OH

(10 mL, 1:1) was added to quench the reaction. The solvent was

removed in a rotary evaporator under reduced pressure, and the

crude reaction mixture was purified by silica gel column

chromatography using petroleum ether/CH₂Cl₂(90:10) as the elu-

ent. The desired bromoporphyrin 15 was obtained as a purple solid

1

(58 mg, 93%). M.p. Ͼ 300 °C. H NMR (400 MHz, CDCl₃): δ =

2.7 (s, 9 H, 3 CH₃), 7.58–7.63 (m, 6 H, aryl), 8.07–8.11 (m, 6 H, 135.5, 137.1, 137.5, 137.9, 138.4, 138.7, 138.9, 139.3, 139.5, 139.8,

aryl), 8.64 (s, 2 H, β-pyrrole), 8.70 (d, J = 4.6 Hz, 1 H, β-pyrrole),

9.31 (d, J = 4.6 Hz, 1 H, β-pyrrole), 9.64 (s, 2 H, β-thiophene), 9.76

(d, J = 5.2 Hz, 1 H, β-thiophene), 10.20 (d, J = 5.2 Hz, 1 H, β-

thiophene) ppm. ¹³C NMR (100 MHz, CDCl₃): δ = 21.7, 110.2,

114.0, 128.4, 128.5, 134.3, 134.7, 135.2, 135.9, 136.1, 136.3, 138.1,

138.4, 145.8, 148.3, 148.7, 156.8, 157.1, 157.3 ppm. ESI-MS: m/z =

143.3, 146.5, 148.1, 148.4, 148.9, 150.3, 150.9, 151.2, 157.6,

158.9 ppm. MALDI-TOF-MS: m/z = 1351.3 [M]⁺. IR (KBr film):

ν = 3025, 2920, 2841, 2315, 1670, 1460, 967, 812, 650 cm^–1.

˜

[5,10,15,20-Tetra(p-tolyl)-2-{2-[10Ј,15Ј,20Ј-tri(p-tolyl)-21-oxa-23-

thiaporphin-5Ј-yl]ethynyl}porphryinato]zinc(II) (4): Yield: 69 %.

M.p. Ͼ 300 °C. ¹H NMR (400 MHz, CDCl₃): δ = 1.56 (s, 3 H,

CH₃), 2.66 (s, 3 H, CH₃), 2.70 (s, 12 H, 4 CH₃), 2.73 (s, 3 H, CH₃),

6.96 (d, J = 7.3 Hz, 2 H, aryl), 7.51–7.65 (m, 12 H, aryl), 8.07–8.24

(m, 14 H, aryl), 8.37 (d, J = 4.3 Hz, 1 H, β-pyrrole), 8.52 (d, J =

4.3 Hz, 1 H, β-pyrrole), 8.60 (d, J = 4.3 Hz, 1 H, β-pyrrole), 8.85

694.2/696.3 [M + 1]⁺(Br⁷⁹/Br⁸¹). IR (KBr film): ν = 2931, 2855,

˜

1935, 1643, 1461, 964, 805 cm^–1. C₄₁H₂₉BrN₂S₂(693.2): calcd. C

70.99, H 4.21, N 4.04; found C 71.05, H 4.18, N 4.09.

General Procedure for the Synthesis of Asymmetrical, β,meso-Eth-

yne-Bridged ZnN₄Porphyrin–Heteroporphyrin Dyads 1, 2, 4 and 6: (d, J = 1.3 Hz, 1 H, β-pyrrole), 8.89 (d, J = 1.3 Hz, 1 H, β-pyrrole),

meso-Bromoporphyrin and [2-ethynyl-5,10,15,20-tetra(p-tolyl)por-

phyrinato]zinc(II) were dissolved in dry toluene/Et₃N (6 mL, 5:1)

in a 25 mL, two-necked, round-bottomed flask fitted with a reflux

condenser, gas inlet and gas outlet tubes for nitrogen purging. The

reaction vessel was placed in an oil bath preheated to 35 °C. After

purging the flask with nitrogen for 15 min, AsPh₃(3.5 equiv.) and

Pd₂(dba)₃(0.44 equiv.) were added, and the reaction mixture was

stirred at 35 °C for 4 h. TLC analysis of the reaction mixture indi-

cated the appearance of a dark new spot apart from the faded,

two starting monomeric porphyrin spots. The solvent was removed

under reduced pressure, and the crude compound was purified by

silica gel chromatography. The excess AsPh₃and the small amounts

of unreacted starting porphyrin building blocks were removed with

petroleum ether/CH₂Cl₂, and the required pure dyad was then col-

lected with CH₂Cl₂.

8.95 (d, J = 1.3 Hz, 2 H, β-pyrrole), 8.98 (d, J = 4.6 Hz, 1 H, β-

pyrrole), 9.00 (d, J = 4.6 Hz, 1 H, β-pyrrole), 9.22 (d, J = 4.6 Hz,

1 H, β-pyrrole), 9.33 (d, J = 4.6 Hz, 1 H, β-furan), 9.63 (m, 2 H,

β-furan and β-pyrrole), 9.64 (s, 1 H, β-thiophene), 9.96 (d, J =

4.0 Hz, 1 H, β-thiophene) ppm. ¹³C NMR (100 MHz, CDCl₃): δ =

20.5, 21.7, 22.8, 52.2, 110.2, 121.5, 121.6, 127.5, 127.8, 128.5, 129.7,

130.5, 131.9, 132.4, 132.6, 133.0, 133.8, 134.0, 134.3, 134.7, 135.3,

136.8, 137.3, 137.5, 138.0, 138.3, 139.6, 140.0, 146.3, 147.9, 148.5,

150.4, 151.1, 151.2, 151.3, 151.7, 156.7, 157.9, 158.8 ppm. MALDI-

TOF-MS: m/z = 1352.6 [M]⁺. IR (KBr film): ν = 3033, 2915, 2839,

˜

2223, 1665, 1458, 970, 821, 651 cm^–1.

[5,10,15,20-Tetra(p-tolyl)-2-{2-[10Ј,15Ј,20Ј-tri(p-tolyl)-21,23-dithia-

porphin-5Ј-yl]ethynyl}porphryinato]zinc(II) (6): Yield: 88%. M.p. Ͼ

1

300 °C. H NMR (400 MHz, CDCl₃): δ = 1.34 (s, 3 H, CH₃), 2.66

(s, 3 H, CH₃), 2.70 (s, 6 H, 2 CH₃), 2.71 (s, 6 H, 2 CH₃), 2.73 (s, 3

H, CH₃), 6.83 (d, J = 8.2 Hz, 2 H, aryl), 7.53–7.65 (m, 12 H, aryl),

8.09–8.22 (m, 14 H, aryl), 8.65 (s, 2 H, β-pyrrole), 8.67 (d, J =

[5,10,15,20-Tetra(p-tolyl)-2-{2-[10Ј,15Ј,20Ј-tri(p-tolyl)-21-oxapor-

phin-5Ј-yl]ethynyl}porphryinato]zinc(II) (1): Yield: 57%. M.p. Ͼ

1

300 °C. H NMR (400 MHz, CDCl₃): δ = 1.48 (s, 3 H, CH₃), 2.62 4.6 Hz, 1 H, β-pyrrole), 8.90 (s, 2 H, β-pyrrole), 8.95 (s, 2 H, β-

(s, 3 H, CH₃), 2.69 (s, 6 H, 2 CH₃), 2.71 (s, 6 H, 2 CH₃), 2.72 (s, 3 pyrrole), 8.99 (d, J = 4.9 Hz, 1 H, β-pyrrole), 9.01 (d, J = 4.9 Hz,

H, CH₃), 6.80 (d, J = 8.2 Hz, 2 H, aryl), 7.51–7.72 (m, 12 H, aryl),

8.01–8.21 (m, 14 H, aryl), 8.65 (d, J = 4.3 Hz, 1 H, β-pyrrole), 8.78

(d, J = 4.3 Hz, 1 H, β-pyrrole), 8.82 (d, J = 2.3 Hz, 1 H, β-pyrrole),

8.89 (d, J = 2.1 Hz, 1 H, β-pyrrole), 8.95 (d, J = 4.6 Hz, 1 H, β-

pyrrole), 8.97 (d, J = 4.6 Hz, 1 H, β-pyrrole), 8.98 (d, J = 4.6 Hz,

1 H, β-pyrrole), 9.00 (d, J = 4.6 Hz, 1 H, β-pyrrole), 9.22 (d, J =

4.6 Hz, 1 H, β-pyrrole), 9.33 (d, J = 4.6 Hz, 1 H, β-furan), 9.59 (d,

1 H, β-pyrrole), 9.28 (d, J = 4.6 Hz, 1 H, β-pyrrole), 9.62 (s, 1 H,

β-pyrrole), 9.63 (d, J = 1.8 Hz, 2 H, β-thiophene), 9.70 (d, J =

4.9 Hz, 1 H, β-thiophene), 10.20 (d, J = 4.9 Hz, 1 H, β-thiophene)

ppm. ¹³C NMR (100 MHz, CDCl₃): δ = 21.7, 22.8, 23.1, 23.9,68.3,

115.0, 121.3, 121.6, 125.9, 127.5, 127.8, 128.4, 128.9, 131.0, 131.9,

132.4, 132.6, 133.0, 133.7, 134.3, 134.6, 135.0, 135.5, 137.3, 137.5,

138.0, 138.3, 138.5, 138.7, 138.9, 139.5, 140.0, 147.4, 148.0, 148.4,

Eur. J. Org. Chem. 2010, 1544–1561

www.eurjoc.org

1559

M. Yedukondalu, D. K. Maity, M. Ravikanth

FULL PAPER

149.4, 150.4, 151.1, 151.2, 156.2, 156.5, 157.0, 158.2 ppm. MALDI-

135.5, 137.3, 137.5, 138.0, 138.4, 138.5, 138.7, 138.9, 139.5, 140.0,

147.3, 148.0, 148.4, 149.4, 150.4, 151.1, 151.2, 156.2, 156.5, 157.5,

159.0 ppm. MALDI-TOF-MS: m/z = 1306.5 [M + H]⁺. IR (KBr

TOF-MS: m/z = 1367.2 [M]⁺. IR (KBr film): ν = 3033, 2920, 2845,

˜

2309, 1656, 1462, 974, 811, 641 cm^–1.

film): ν = 3045, 2915, 2842, 2211, 1641, 1456, 967, 822, 653 cm^–1.

˜

General Procedure for the Synthesis of Asymmetrical, β,meso-Eth-

yne-Bridged, N₄Porphyrin–Heteroporphyrin Dyads 3, 5 and 7: The

corresponding ZnN₄porphyrin–heteroporphyrin dyads 2, 4 and 6

in CH₂Cl₂were treated with excess TFA for 15 min. The progress

of the reaction was monitored by absorption spectroscopy. After

the standard workup, the crude compounds were purified by silica

gel column chromatography using CH₂Cl₂, and they afforded pure

N₄porphyrin–heteroporphyrin dyads 3, 5 and 7, respectively, in ca.

90% yields.

Supporting Information (see footnote on the first page of this arti-

cle): NMR, MS and Cartesian coordinates of selected compounds.

Acknowledgments

M. R. thanks the Council of Scientific and Industrial Research

(CSIR) and the Department of Science and Technology (DST) for

financial support, and Y. K. thanks CSIR for a fellowship. The

Computer Centre, Bhabha Atomic Research Centre (BARC) is

gratefully acknowledged for generous CPU time on their ANU-

PAM, parallel, computer systems.

1-[5,10,15,20-Tetra(p-tolyl)porphin-2-yl]-2-[10Ј,15Ј,20Ј-tri(p-tolyl)-

21-thiaporphin-5Ј-yl]ethyne (3): Yield: 94%. M.p. Ͼ 300 °C. ¹H

NMR (400 MHz, CDCl₃): δ = –2.56 (s, 2 H, NH), –2.12 (s, 1 H,

NH), 1.42 (s, 3 H, CH₃), 2.66 (s, 3 H, CH₃), 2.69 (s, 6 H, 2 CH₃),

2.71 (s, 6 H, 2 CH₃), 2.73 (s, 3 H, CH₃), 6.86 (d, J = 7.6 Hz, 2 H,

aryl), 7.54–7.65 (m, 12 H, aryl), 8.05–8.22 (m, 14 H, aryl), 8.56 (d,

J = 4.6 Hz, 1 H, β-pyrrole), 8.58 (d, J = 4.6 Hz, 1 H, β-pyrrole),

8.63 (d, J = 4.6 Hz, 1 H, β-pyrrole), 8.81 (s, 2 H, β-pyrrole), 8.87

(s, 4 H, β-pyrrole), 8.94 (d, J = 4.6 Hz, 1 H, β-pyrrole), 8.99 (d, J

= 4.6 Hz, 1 H, β-pyrrole), 9.22 (d, J = 4.3 Hz, 1 H, β-pyrrole), 9.46

(s, 1 H, β-pyrrole), 9.75 (d, J = 5.2 Hz, 1 H, β-thiophene), 10.16

(d, J = 5.2 Hz, 1 H, β-thiophene) ppm. ¹³C NMR (100 MHz,

CDCl₃): δ = 21.3, 22.6, 23.5, 23.7, 67.5, 112.6, 121.1, 121.4, 124.4,

124.9, 125.9, 127.5, 127.6, 128.4, 128.9, 130.9, 131.6, 131.8, 132.4,

132.9, 133.6, 134.1, 134.3, 134.7, 135.2, 135.5, 137.1, 137.5, 137.9,

138.4, 138.7, 138.9, 139.3, 139.5, 139.8, 143.3, 146.5, 148.1, 148.4,

148.9, 150.3, 150.9, 151.4, 157.6, 158.6 ppm. MALDI-TOF-MS:

[1] a) S. Gaspard, C. Giannotti, P. Maillard, C. Schaeffer, T. H. T.

Thi, J. Chem. Soc., Chem. Commun. 1986, 1239–1241; b) H. J.

Tian, Q. F. Zhou, S. Y. Shen, H. J. Xu, J. Photochem. Photobiol.

A: Chem. 1993, 72, 163–168; c) L. Li, S. Shen, Q. Yu, Q. Zhou,

H. Xu, J. Chem. Soc., Chem. Commun. 1991, 619–620.

[2] a) R. Paolesse, R. K. Pandey, T. P. Forsyth, L. Jaquinod, K. R.

Gerzevske, D. J. Nurco, M. O. Senge, S. Licoccia, T. Boschi,

K. M. Smith, J. Am. Chem. Soc. 1996, 118, 3869–3882; b)

M. R. Wasielewski, D. G. Johnson, M. P. Niemczyk, G. L.

Gaines III, M. P. O’Neil, W. A. Svec, J. Am. Chem. Soc. 1990,

112, 6482–6488; c) G. Zheng, R. K. Pandey, T. P. Forsyth,

A. N. Kozyrev, T. J. Dougherty, K. M. Smith, Tetrahedron Lett.

1997, 38, 2409–2412; d) D. P. Arnold, R. D. Hartnell, Tetrahe-

dron 2001, 57, 1335–1345; e) A. R. Genady, D. Gabel, Tetrahe-

dron Lett. 2003, 44, 2915–2917.

m/z = 1289.5 [M + H]⁺. IR (KBr film): ν = 3031, 2925, 2860, 2212,

˜

1641, 1458, 966, 822, 656 cm^–1.

[3] a) R. Paolesse, F. Sagone, A. Macagnano, T. Boschi, L. Prodi,

M. Montalti, N. Zaccheroni, F. Bolletta, K. M. Smith, J. Por-

phyrins Phthalocyanines 1999, 3, 364–370; b) R. Guilard, C. P.

Gros, J. M. Barbe, E. Espinosa, F. Jerome, A. Tabard, Inorg.

Chem. 2004, 43, 7441–7455; c) K. M. Kadish, L. Fremond, Z.

Ou, J. Shao, C. Shi, F. C. Anson, F. Burdet, C. P. Gros, J. M.

Barbe, R. Guilard, J. Am. Chem. Soc. 2005, 127, 5625–5631;

d) J. M. Barbe, F. Burdet, E. Espinosa, R. Guilard, Eur. J. In-

org. Chem. 2005, 1032–1041; e) L. Flamigni, B. Ventura, M.

Tasior, D. T. Gryko, Inorg. Chim. Acta 2007, 360, 803–813.

[4] a) R. P. Pandian, T. K. Chandrashekar, Inorg. Chem. 1994, 33,

3311–3324; b) I. Gupta, N. Agarwal, M. Ravikanth, Eur. J.

Org. Chem. 2004, 1693–1697; c) I. Gupta, M. Ravikanth, J.

Org. Chem. 2004, 69, 6796–6811; d) S. Punidha, N. Agarwal,

M. Ravikanth, Eur. J. Org. Chem. 2005, 2500–2517; e) I.

Gupta, M. Ravikanth, Inorg. Chim. Acta 2007, 360, 1731–1742;

f) S. Punidha, J. Sinha, A. Kumar, M. Ravikanth, J. Org. Chem.

2008, 73, 323–328.

[5] a) J. S. Hsiao, B. P. Krueger, R. W. Wagner, T. E. Johnson, J. K.

Delaney, D. C. Mauzerall, G. R. Fleming, J. S. Lindsey, D. F.

Bocian, R. J. Donohoe, J. Am. Chem. Soc. 1996, 118, 11181–

11193; b) D. Holten, D. F. Bocian, J. S. Lindsey, Acc. Chem.

Res. 2002, 35, 57–69; c) R. W. Wagner, T. E. Johnson, F. Li,

J. S. Lindsey, J. Org. Chem. 1995, 60, 5266–5273; d) F. Li, S.-I.

Yang, Y. Ciringh, J. Seth, C. H. Martin, D. L. Singh, D. Kim,

R. R. Birge, D. F. Bocian, D. Holten, J. S. Lindsey, J. Am.

Chem. Soc. 1998, 120, 10001–10017; e) L. Karki, F. W. Vance,

J. T. Hupp, L. S. M. Cours, M. J. Therien, J. Am. Chem. Soc.

1998, 120, 2606–2611; f) A. K. Burrell, D. L. Officer, D. C. W.

Reid, K. Y. Wild, Angew. Chem. Int. Ed. 1998, 37, 114–117; g)

A. K. Burrell, D. L. Officer, P. G. Plieger, D. C. Reid, Chem.

Rev. 2001, 101, 2751–2796; h) N. Yoshida, T. Ishizuka, K.

Youfu, M. Murakami, H. Miyasaka, T. Okada, Y. Nagata, A.

Itaya, H. S. Cho, D. Kim, A. Osuka, Chem. Eur. J. 2003, 9,

2854–2866; i) A. Osuka, D. Fujikane, H. Shinmori, S. Koba-

take, M. Irie, J. Org. Chem. 2001, 66, 3913–3923; j) C. C. Mak,

1-[5,10,15,20-Tetra(p-tolyl)porphin-2-yl]-2-[10Ј,15Ј,20Ј-tri(p-tolyl)-

21-oxa-23-thiaporphin-5Ј-yl]ethyne (5): Yield: 90%. M.p. Ͼ 300 °C.

¹H NMR (400 MHz, CDCl₃): δ = –2.55 (s, 2 H, NH), 1.45 (s, 3 H,

CH₃), 2.66 (s, 3 H, CH₃), 2.70 (s, 12 H, 4 CH₃), 2.73 (s, 3 H, CH₃),

6.98 (d, J = 7.0 Hz, 2 H, aryl), 7.51–7.64 (m, 12 H, aryl), 8.06–8.25

(m, 14 H, aryl), 8.35 (d, J = 4.3 Hz, 1 H, β-pyrrole), 8.52 (d, J =

4.3 Hz, 1 H, β-pyrrole), 8.60 (d, J = 3.9 Hz, 1 H, β-pyrrole), 8.81–

8.95 (m, 6 H, β-pyrrole), 9.20 (d, J = 3.9 Hz, 1 H, β-pyrrole), 9.30

(d, J = 4.3 Hz, 1 H, β-furan), 9.48 (s, 1 H, β-pyrrole), 9.63–9.64

(m, 2 H, β-furan and β-thia), 9.92 (d, J = 4.8 Hz, 1 H, β-thiophene)

ppm. ¹³C NMR (100 MHz, CDCl₃): δ = 21.2, 21.7, 22.8, 52.6,

110.2, 121.5, 121.9, 127.5, 127.8, 128.5, 129.7, 130.5, 131.9, 132.4,

132.6, 133.0, 133.8, 134.0, 134.3, 134.7, 135.3, 136.8, 137.3, 137.5,

138.0, 138.3, 139.6, 140.0, 146.3, 147.7, 148.5, 150.4, 151.1, 151.2,

151.3, 151.7, 157.1, 157.9, 158.6 ppm. MALDI-TOF-MS: m/z =

1290.6 [M + H]⁺. IR (KBr film): ν = 3046, 2915, 2840, 2211, 1641,

˜

1458, 967, 820, 654 cm^–1.

1-[5,10,15,20-Tetra(p-tolyl)porphin-2-yl]-2-[10Ј,15Ј,20Ј-tri(p-tolyl)-

21,23-dithiaporphin-5Ј-yl]ethyne (7): Yield: 96%. M.p. Ͼ 300 °C. ¹H

NMR (400 MHz, CDCl₃): δ = –2.56 (s, 1 H, NH), 1.42 (s, 3 H,

CH₃), 2.66 (s, 3 H, CH₃), 2.70 (s, 6 H, 2 CH₃), 2.72 (s, 6 H, 2 CH₃),

2.73 (s, 3 H, CH₃), 6.84 (d, J = 7.6 Hz, 2 H, aryl), 7.52–7.65 (m,

12 H, aryl), 8.11–8.23 (m, 14 H, aryl), 8.65 (s, 2 H, β-pyrrole), 8.66

(d, J = 4.6 Hz, 1 H, β-pyrrole), 8.81 (d, J = 1.6 Hz, 2 H, β-pyrrole),

8.87 (s, 2 H, β-pyrrole), 8.96 (d, J = 4.6 Hz, 1 H, β-pyrrole), 8.98

(d, J = 4.6 Hz, 1 H, β-pyrrole), 9.25 (d, J = 4.6 Hz, 1 H, β-pyrrole),

9.47 (s, 1 H, β-pyrrole), 9.63 (d, J = 1.5 Hz, 2 H, β-thiophene), 9.70

(d, J = 5.2 Hz, 1 H, β-thiophene), 10.17 (d, J = 5.2 Hz, 1 H, β-

thiophene) ppm. ¹³C NMR (100 MHz, CDCl₃): δ = 21.1, 22.6,

23.15, 23.9,68.3, 115.0, 121.6, 121.6, 125.9, 127.6, 127.8, 128.4,

128.9, 131.5, 131.9, 132.4, 132.6, 133.0, 133.7, 134.3, 134.6, 135.0,

1560

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β,meso-Acetylenyl-Bridged Asymmetrical Porphyrin Dyads

N. Bampos, J. K. M. Sanders, Angew. Chem. Int. Ed. 1998, 37,

3020–3023; k) D. Kuciauskas, P. A. Liddell, S. Lin, T. E. John-

son, J. S. Weghorn, J. S. Lindsey, A. L. Moore, T. A. Moore, D.

Gust, J. Am. Chem. Soc. 1999, 121, 8604–8614; l) O. Mongin,

C. Papamicael, N. Hoyler, A. Gossauer, J. Org. Chem. 1998,

63, 5568–5580; m) R. Paolesse, L. Jaquinod, F. D. Sala, D. J.

Nurco, L. Prodi, M. Montalti, C. D. Natale, A. D’Amico,

D. A. Carlo, P. Lugli, K. M. Smith, J. Am. Chem. Soc. 2000,

122, 11295–11302; n) R. Beavington, P. L. Burn, J. Chem. Soc.

Perkin Trans. 1 2000, 1231–1240; o) K.-I. Sugiura, T. Matsum-

oto, S. Ohkouchi, Y. Naitoh, T. Kawai, Y. Takai, K. Ushiroda,

Y. Sakata, Chem. Commun. 1999, 1957–1958; p) M. J. Crossley,

P. Thordarson, Angew. Chem. Int. Ed. 2002, 41, 1709–1712; q)

M. J. Crossley, L. A. Johnston, Chem. Commun. 2002, 1122–

1123; r) A. Vidal-Ferran, Z. Clyde-Waston, N. Bampoos,

J. K. M. Sanders, J. Org. Chem. 1997, 62, 240–241.

2005, 127, 8264–8265; h) H. Hata, S. Yamaguchi, G. Mori, S.

Nakazono, T. Katoh, K. Takatsu, S. Hirot, H. Shinokub, A.

Osuka, Chem. Asian J. 2007, 2, 849–859; i) I. Hisaki, S. Hiroto,

K. S. Kim, S. B. Noh, D. Kim, H. Shinokubo, A. Osuka, An-

gew. Chem. Int. Ed. 2007, 46, 5125–5128; j) J. Song, S. Y. Jang,

S. Yamaguchi, J. Sankar, S. Hiroto, N. Aratani, J.-Y. Shin, S.

Easwaramoorthi, K. S. Kim, D. Kim, H. Shinokubo, A.

Osuka, Angew. Chem. Int. Ed. 2008, 47, 6004–6007; k) N. Arat-

ani, A. Osuka, Chem. Commun. 2008, 4067–4069; l) J. Yang,

M. Park, Z. S. Yoon, T. Hori, X. Peng, N. Aratani, P. Dedecker,

J. Hotta, H. Uji-I, M. Sliwa, J. Hofkens, A. Osuka, D. Kim, J.

Am. Chem. Soc. 2008, 130, 1879–1884.

[11] a) X. Zhou, K. S. Chan, J. Chem. Soc., Chem. Commun. 1994,

2493–2494; b) X. Zhou, K. S. Chan, J. Org. Chem. 1998, 63,

99–104; c) Y. Deng, C. K. Chang, D. G. Nocera, Angew. Chem.

Int. Ed. 2000, 39, 1066–1068.

[12] H. J. Callot, Tetrahedron Lett. 1973, 14, 4987–4990.

[13] S. Punidha, N. Agarwal, R. Burai, M. Ravikanth, Eur. J. Org.

Chem. 2004, 2223–2230.

[14] J. S. Lindsey, I. C. Schreiman, H. C. Hsu, P. C. Kearney, A. M.

Marguerettaz, J. Org. Chem. 1987, 52, 827–836.

[15] R. W. Wagner, T. E. Johnson, F. Li, J. S. Lindsey, J. Org. Chem.

1996, 60, 5266–5273.

[6] a) S. I. Yang, J. Li, H. S. Cho, D. Kim, D. F. Bocian, D. Holten,

J. S. Lindesy, J. Mater. Chem. 2000, 10, 283–296; b) J. Li, J. R.

Dires, J. Seth, S. I. Yang, D. F. Bocian, D. Holten, J. S. Lindsey,

J. Org. Chem. 1999, 64, 9090–9100; c) J. Li, J. S. Lindsey, J.

Org. Chem. 1999, 64, 9101–9108.

[7] I. Gupta, M. Ravikanth, Coord. Chem. Rev. 2006, 250, 468–

518 and references cited therein.

[8] H. Shinokubo, A. Osuka, Chem. Commun. 2009, 1011–1021

and references cited therein.

[16] a) G. Bringmann, D. C. G. Götz, T. A. M. Gulder, T. H.

Gehrke, T. Bruhn, T. Kupfer, K. Radacki, H. Braunschweig,

A. Heckmann, C. Lambert, J. Am. Chem. Soc. 2008, 130,

17812–17825; b) G. Bringmann, S. Rüdenauer, D. C. G. Götz,

T. A. M. Gulder, M. Reichert, Org. Lett. 2006, 8, 4743–4746;

c) A. Wiehe, M. O. Senge, A. Schäfer, M. Speck, S. Tannert,

H. Kurreck, B. Röder, Tetrahedron 2001, 57, 10089–10110; d)

M. O. Senge, B. Rössler, J. Von Gersdorff, A. Schäfer, H. Kur-

reck, Tetrahedron Lett. 2004, 45, 3363–3367; e) D. C. G. Götz,

T. Bruhn, M. O. Senge, G. Bringmann, J. Org. Chem. 2009, 74,

8005–8020.

[17] L. Latos-Grazynski, in The Porphyrin Handbook (Eds.: K. M.

Kadish, K. M. Smith, R. Guilard), Academic Press, New York,

2000, vol. 2, pp. 361–416.

[18] a) L. Giribabu, T. A. Rao, B. G. Maiya, Inorg. Chem. 1999,

38, 4971–4980; b) L. Giribabu, C. Vijay Kumar, P. Yella Reddy,

Chem. Asian J. 2007, 2, 1574–1580.

[9] a) V. S.-Y. Lin, S. G. DiMagno, M. J. Therien, Science 1994,

264, 1105–1111; b) P. J. Angiolillo, V. S.-Y. Lin, J. M. Vander-

kooi, M. J. Therien, J. Am. Chem. Soc. 1995, 117, 12514–12527;

c) R. Kumble, S. Palese, V. S.-Y. Lin, M. J. Therien, R. M.

Hochstrasser, J. Am. Chem. Soc. 1998, 120, 11489–11498; d)

J. T. Fletcher, M. J. Therien, J. Am. Chem. Soc. 2000, 122,

12393–12394; e) R. Shediac, M. H. B. Gray, H. Tetsuo Uyeda,

R. C. Johnson, J. T. Hupp, P. J. P. J. Angiolillo, M. J. Therien,

J. Am. Chem. Soc. 2000, 122, 7017–7033; f) K. Susumu, T. V.

Duncan, M. J. Therien, J. Am. Chem. Soc. 2005, 127, 5186–

5195; g) K. Susumu, P. R. Frail, P. J. Angiolillo, M. J. Therien,

J. Am. Chem. Soc. 2006, 128, 8380–8381; h) T. V. Duncan, P.

Ghoroghchian, I. V. Rubtsov, D. A. Hammer, M. J. Therien, J.

Am. Chem. Soc. 2008, 130, 9773–9784.

[10] a) T. Nagata, A. Osuka, K. Maruyama, J. Am. Chem. Soc.

1990, 112, 3054–3059; b) M. Ikeda, S. Shinkai, A. Osuka,

Chem. Commun. 2000, 1047–1048; c) N. Aratani, A. Osuka,

Org. Lett. 2001, 3, 4213–4216; d) A. Tsuda, A. Osuka, Science

2001, 293, 79–82; e) N. Aratani, H. S. Cho, T. K. Ahn, S. Cho,

[19] M. W. Schmidt, K. K. Baldridge, J. A. Boatz, S. T. Elbert,

M. S. Gordon, J. H. Jensen, S. Koseki, N. Matsunaga, K. A.

Nguyen, S. J. Su, T. L. Windus, M. Dupuis, J. A. Montgomery,

J. Comput. Chem. 1993, 14, 1347–1363.

D. Kim, H. Sumi, A. Osuka, J. Am. Chem. Soc. 2003, 125, [20] G. Schaftenaar, J. H. Noordik, J. Comput.-Aided Mol. Des.

9668–9681; f) N. Aratani, H. S. Cho, T. K. Ahn, S. Cho, D.

Kim, H. Sumi, A. Osuka, J. Am. Chem. Soc. 2003, 125, 9668–

9681; g) H. Hata, H. Shinokubo, A. Osuka, J. Am. Chem. Soc.

2000, 14, 123–134.

Received: November 25, 2009

Published Online: February 8, 2010

Eur. J. Org. Chem. 2010, 1544–1561

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β,meso-Acetylenyl-bridged, asymmetrical, porphyrin dyads - synthesis, spectral, electrochemical and computational studies

DOI: 10.1002/ejoc.200901362

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