DOI: 10.1002/cphc.201200350

Tetrathiafulvalene-Fused Porphyrins via QuinoxalineLinkers: Symmetric and Asymmetric Donor–AcceptorSystemsHongpeng Jia,[a] Belinda Schmid,[a] Shi-Xia Liu,*[a] Michael Jaggi,[a] Philippe Monbaron,[a]

Sheshanath V. Bhosale ,*[b] Shadi Rivadehi,[b] Steven J. Langford,[b] Lionel Sanguinet,[c]

Eric Levillain,[c] Mohamed E. El-Khouly,[d] Ysushi Morita,[e] Shunichi Fukuzumi ,*[d, f] andSilvio Decurtins[a]

1. Introduction

There is considerable interest in developing multi-chromophor-ic arrays as a way to gain insight into the fundamental aspectsof energy- and electron-transfer processes and to mimic multi-step charge-separation processes in natural photosynthesisand ultimately organic-based solar energy conversion technol-ogies.[1] Porphyrins (P) are prominent molecular components ofsuch donor–acceptor (D–A) arrays and have found widespreaduse in the development of artificial light-harvesting antennae,[2]

photonic wires,[3] redox switches,[4] efficient sensitizers in dye-sensitized solar cells[5] and molecular shuttles.[6] A wide rangeof electron acceptor- or donor-linked porphyrins have been in-tensively studied.[1, 7–10] Among them, however, only a fewpapers on molecular systems that include the well-known elec-tron donor tetrathiafulvalene (TTF) as an annulated moiety tothe porphyrin core have appeared in the literature,[10, 11] per-haps due to synthetic difficulties. In all cases, the TTF unit actsas an electron donor and the porphyrin core as an electron ac-ceptor leading to photoinduced intramolecular charge transferfrom the TTF donor to the porphyrin chromophore. However,no TTF-fused porphyrin conjugates in which two porphyrinrings are directly annulated to the central TTF core through p

linkers have been reported.Based on our experience in the functionalization of TTF[12]

and our keen interest in molecular (opto)electronic devices, we

A tetrathiafulvalene (TTF) donor is annulated to porphyrins (P)via quinoxaline linkers to form novel symmetric P–TTF–P triads1 a–c and asymmetric P–TTF dyads 2 a,b in good yields. Theseplanar and extended p-conjugated molecules absorb lightover a wide region of the UV/Vis spectrum as a result of addi-tional charge-transfer excitations within the donor–acceptorassemblies. Quantum-chemical calculations elucidate thenature of the electronically excited states. The compounds areelectrochemically amphoteric and primarily exhibit low oxida-tion potentials. Cyclic voltammetric and spectroelectrochemicalstudies allow differentiation between the TTF and porphyrinsites with respect to the multiple redox processes occurringwithin these molecular assemblies. Transient absorption meas-urements give insight into the excited-state events and deliver

corresponding kinetic data. Femtosecond transient absorptionspectra in benzonitrile may suggest the occurrence of fastcharge separation from TTF to porphyrin in dyads 2 a,b butnot in triads 1 a–c. Clear evidence for a photoinduced and rela-tively long lived charge-separated state (385 ps lifetime) is ob-tained for a supramolecular coordination compound built fromthe ZnP–TTF dyad and a pyridine-functionalized C60 acceptorunit. This specific excited state results in a (ZnP–TTF)· +

···(C60py)·� state. The binding constant of ZnII···py is evaluatedby constructing a Benesi–Hildebrand plot based on fluores-cence data. This plot yields a binding constant K of 7.20 �104

m�1, which is remarkably high for bonding of pyridine to

ZnP.

[a] Dr. H. Jia, B. Schmid, Dr. S.-X. Liu, M. Jaggi, P. Monbaron, Prof. S. DecurtinsDepartement f�r Chemie und BiochemieUniversit�t Bern, Freiestrasse 33012 Bern (Switzerland)Fax: (+ 41) 31-631-3995E-mail : liu@iac.unibe.ch

[b] Dr. S. V. Bhosale ,+ S. Rivadehi, Prof. S. J. LangfordSchool of Chemistry, Monash UniversityClayton, VIC-3800 (Australia)E-mail : bsheshanath@gmail.com

[c] Dr. L. Sanguinet, Dr. E. LevillainInstitut des Sciences et Technologies Mol�culaires d’AngersUniversit� d’Angers, CNRS UMR 62002 Bd Lavoisier, 49045 Angers Cedex (France)

[d] Dr. M. E. El-Khouly, Prof. S. FukuzumiDepartment of Material and Life ScienceGraduate School of Engineering, Osaka UniversitySuita, Osaka 565-0871 (Japan)E-mail : fukuzumi@chem.eng-osaka-u.ac.jp

[e] Prof. Y. MoritaDepartment of ChemistryGraduate School of Science, Osaka University1-1 Machikaneyama, Toyonaka, Osaka-560-0043 (Japan)

[f] Prof. S. FukuzumiDepartment of Bioinspired ScienceEwha Womans UniversitySeoul 120-750 (Korea)

[+] Current address : School of Applied Sciences, RMIT UniversityGPO Box 2476V, Melbourne, VIC-3100 (Australia)

Supporting information for this article is available on the WWW underhttp://dx.doi.org/10.1002/cphc.201200350.

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aimed for the synthesis and electrochemical and spectroscopicinvestigations of TTF-annulated free-base and metal(II) por-phyrins 1 and 2, fused via quinoxaline linker(s), as shown inFigure 1. Novel symmetric P–TTF–P triads 1 a–c and asymmet-ric P–TTF dyads 2 a,b have been prepared, which exhibitalmost planar molecular geometries. The reference compoundquinoxalinoporphyrin R3 acts as an especially interesting build-ing block for creating larger multiporphyrin arrays, proposedeither as molecular wires or as functional mimics of plant andbacterial photosynthetic reaction centres.[13] Incorporation ofa strongly electron donating TTF substituent into porphyrin(s)would allow fine-tuning of electronic properties of these tar-gets. Herein, the electronic structures of 1 and 2 in the groundand electronically excited states were studied by photophysicalmethods (steady-state and transient), cyclic voltammetry andspectroelectrochemical experiments as well as quantum-chemi-cal calculations. In addition, a photoinduced charge-separatedstate of a supramolecular assembly of asymmetric P–TTF dyad2 b with a functionalized C60 acceptor unit was investigated.

2. Results and Discussion

2.1. Synthesis and Characterization

In brief, target compounds 1 and 2 were obtained by directcondensation reaction of TTF precursors 3[14] and 4[15] with thecorresponding porphyrin-2,3-diones 5[16c] and 6[16] (Scheme 1).Compounds 1 a and 1 c were produced in the presence ofacetic acid at reflux as brownish red powders in 74 and 77 %yield, respectively. Compound 2 a was synthesized in CHCl3/pyridine at 65 8C for 2 h as a greenish brown crystalline solid in96 % yield. Finally, zinc complexes 1 b and 2 b were obtained in

good yields by metallation of the corresponding 1 a and 2 awith Zn(OAc)2.

All new compounds were purified by chromatographic sepa-ration on silica gel and fully characterized. IR spectra of theproducts showed no carbonyl stretches at about 1725 and1738 cm�1, indicative of the absence of any remaining carbonylgroups of the a-dione groups of 5[17] and 6,[16c] respectively.1H NMR and mass spectra as well as elemental analyses unam-biguously indicate that the synthesized compounds are in ac-cordance with the predicted molecular structures.

In case of the asymmetric P–TTF dyad, crystals suitable forX-ray crystallography were grown by diffusion of hexane intoa solution of 2 a in CHCl3. The molecular structure of 2 a isshown in Figure 2. The molecules are slightly corrugated alongthe long axis of the p-conjugated skeleton. In the crystal struc-ture, they stack in an almost perfect alignment along theP–TTF axis in an alternating head-to-tail fashion with the TTFgroup of one molecule overlying the porphyrin unit of anotherone (Supporting Information Figure S1).

2.2. Electrochemistry

The electrochemical properties of compounds 1 and 2 were in-vestigated by cyclic voltammetry in CH2Cl2. Their electrochemi-cal data are collected in Table 1 together with those of the ref-erence compounds R–R3 for comparison.

Compounds 1 a–c undergo several reversible multi-electronoxidation processes for successive oxidation of both the cen-tral TTF core and two porphyrin rings. As shown in Figure 3,such complex and broad patterns of redox waves are indica-tive of sequential overlapping oxidations. By simple inspectionalone, a comprehensive interpretation of these oxidation pro-cesses is not straightforward. Therefore, thin-layer cyclic vol-

Figure 1. Structures of investigated compounds 1 and 2 and reference compounds R–R3.

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tammetry (TLCV) experiments were performed. However, onlythe TLCV of 1 c (Figure 4) provides clear evidence of the ratioof number of electrons involved in each oxidation step. Clearly,1 c exhibits two two-electron and one single-electron oxida-tions, which are assigned to the two stable successive oxida-tion states of the two porphyrin rings at 0.44 and 0.75 V andone oxidation state of the TTF core at 0.61 V, respectively, bycomparison with the redox data of reported porphyrin deriva-tives such as R2[18] and R3 as well as TTF reference compoundR1.[14] In the cases of 1 a and 1 b, the instability of the radicalsat low scan rates does not allow us to observe well-definedredox processes. Since insertion of metal(II) ions into the por-phyrin core leads to negative shifts of redox potentials,[18, 19]

the first oxidation process for 1 a and 1 b is anticipated for si-

multaneous oxidation of the two porphyrin rings to the radicalcation species. The broadness of the second waves suggeststhat the first oxidation of the central TTF core to generate theradical cation overlaps with the second simultaneous oxidationof two prophyrin radical cations to their dication states. Com-pared to reference compound R3, the first oxidation potentialof 1 a is shifted by �120 mV. This finding can be attributed tothe stabilizing effect of the extended p conjugation, whichoffers the possibility of delocalizing the free spin over theentire conjugated p system, and, importantly, also to the elec-

Scheme 1. Synthesis of TTF-annulated porphyrins 1 and 2.

Figure 2. Molecular structure of 2 a with 50 % thermal ellipsoids and hydro-gen atoms as spheres of arbitrary size.

Table 1. Redox potentials [V vs. Fc/Fc+] of compounds 1 and 2 in CH2Cl2

and of reference compounds R1,[14] R2,[18a] R3 and R[11] (2 a with decyl in-stead of propyl chains).

Compound Eox11=2 Eox2

1=2 Eox31=2 Eox4

1=2 Ered11=2 Ered2

1=2

1 a 0.47[a] 0.75[b] �1.62 �1.791 b 0.34[a] 0.56[b] �1.71 �2.061 c 0.44[a] 0.61 0.75[a] �1.64 �2.062 a 0.15 0.60[a] 0.85 �1.58 �1.772 b 0.19 0.48 0.64[a] �1.03 �1.76[c]

R[d] 0.11 0.50 0.80 1.04 �1.44 �1.77R1 0.57 0.89 �1.93R2a[e] 0.53[a] �1.59 �1.79R2b[e] 0.26 0.64[c] �1.77 �2.21R3 0.59 0.74 �1.61 �1.81

[a] Two overlapping one-electron redox processes. [b] Broad peak. [c] Irre-versible. [d] Reported potentials relative to Ag/AgCl in CH2Cl2, which areconverted to Fc/Fc+ scale by subtracting 0.51 V from values relative toAg/AgCl. [e] Reported potentials relative to SCE in CH2Cl2, which are con-verted to Fc/Fc+ scale by subtracting 0.46 V from SCE values.[20]

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tron-donating effect of the TTF moiety. Additional strong sup-port for these assignments is given by spectroelectrochemicaldata (see below).

In contrast, the first oxidation process of compounds 2 a and2 b corresponds to oxidation of the TTF unit to the radicalcation species, by comparison with R and R3 (see Table 1). Asillustrated in Figure 5, differences clearly exist between metal-free 2 a and metallated 2 b in the broadness of the subsequentoxidations. For 2 a, the overlapping oxidations of the TTF radi-cal cation and the porphyrin core to its trication form give riseto a broad redox wave, followed by the third one-electron oxi-dation of the porphyrin radical to generate its tetracation spe-cies at 0.85 V. For 2 b, upon metallation, a negative shift in theoxidation potential centred at the porphyrin core leads toa one-electron oxidation at 0.48 V. The sequential oxidations ofboth TTF and porphyrin radical cations are not separated in

their potentials, and thus show an apparent one-step conver-sion of the dication to its tetracation species.

In the negative potential direction, all of them exhibit tworeduction processes, corresponding to reduction of the por-phyrin core(s) in analogy to reference compounds R–R3.

2.3. Steady-State Optical Absorption Measurements

Structurally symmetric compound 1 a, which forms a red-purple solution, exhibits intense electronic absorptions overthe whole visible part of the optical spectrum at all energieshigher than 16 000 cm�1 (below 625 nm, Figure 6 a). This ab-sorption pattern does not correspond solely to the sum of theoptical absorptions of the constituents of this molecule. In-stead of the distinct and narrow Soret band of porphyrin sys-tems, which typically appears around 24 000 cm�1 (400–450 nm), multiple and extensively broadened absorptionbands show up. This observation is apparently an outcome ofthe annulation of p-conjugated molecular units with differentelectron donor and acceptor characteristics into the predomi-nantly planar structure of 1 a, which finally contributes to theoccurrence of additional electronic charge-transfer (CT) transi-tions. As is discussed below, the electronic structure of 1 a canthus be represented as an A–A’–D–A’–A system, which isa useful description for analysis of the different CT characteris-tics. The electronic absorption spectrum of the structurallyasymmetric 2 a (Figure 6 b), now an electronic A–A’–D system,exhibits an analogous pattern, but the dominant contributionsfrom charge-transfer transitions do not show up all that much.The same trend holds also for the next even smaller fragment,namely, the quinoxalino[2,3-b]tetraphenylporphyrin R3 (Fig-ure 6 c).

2.4. Quantum-Chemical Calculations

Quantum-chemical calculations were carried out to determineenergies, intensities and type of electronic excitations of 1 a,2 a and reference compound R3 for comparison. The molecularstructure of quinoxalino[2,3-b]tetraphenylporphyrin R3 was cal-

Figure 3. Cyclic voltammograms of 1 a (solid line), 1 b (dashed line) and 1 c(dotted line) in CH2Cl2 (0.1 m Bu4NPF6 ; Pt working electrode; scan rate100 mV s�1).

Figure 4. TLCV of 1 c (4.3 � 10�5m) in CH2Cl2 (0.1 m Bu4NPF6 ; Pt working elec-

trode; scan rate 10 mV s�1).

Figure 5. Cyclic voltammograms of 2 a (solid line) and 2 b (dashed line) inCH2Cl2 (0.1 m Bu4NPF6 ; Pt disc working electrode; scan rate 100 mV s�1).

Figure 6. Electronic absorption spectra of 1 a (a), 2 a (b) and R3 (c) in benzo-nitrile solution, together with the calculated S0!Sn transitions (energies andoscillator strengths) at the TD-B3LYP/TZVP level of theory.

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culated in C2 symmetry, and the molecular structures of 1 aand 2 a were determined without symmetry constraints. Thecalculated geometry of 2 a is in good agreement with its X-raystructure (see Supporting Information). The molecular skele-tons of the p-conjugated systems were virtually planar (Sup-porting Information Figure S2), with the sole exception of thewell-known soft structural bending within the neutral TTF frag-ments (ca. 138) and, as expected, the out-of-plane rotations ofthe pendant phenyl groups (70–1118). However, calculations ofthe MOs were approximated while applying D2h or C2h pointgroup symmetries to the molecules. Some important frontierMOs and their calculated energies are shown in Figures 7 and8. The frontier MOs of 1 a basically result from linear combina-tions of orbitals from the central TTF core with the plus/minuslinear combinations of orbitals from the pendant quinoxalineand porphyrin units. In 1 a, the HOMO (au) electron density ismainly located on the central TTF unit with clear inclusion ofboth pendant quinoxaline units. This can be best compared

with the case of an analogous electronic pentad system show-ing the same core fragment.[14] Next, the energetically closelying HOMO�1 and HOMO�2 as well as HOMO�3 andHOMO�4 are essentially both pairs of plus/minus combina-tions (bg, au) of “left and right” of what would be HOMO andHOMO�1 of a single porphyrin molecule alone. Analogously,LUMO and LUMO + 1 of a single porphyrin now combine toLUMO and LUMO + 1 as well as LUMO + 2 and LUMO + 3 forthe symmetric molecule 1 a. The LUMO + 4 and LUMO + 5 fi-nally represent the quinoxaline LUMOs. The dividing line be-tween HOMO and HOMO�1/�2 is opposite to what is expect-ed from the experimental CV data; however, the calculationsare for isolated molecules with symmetry constraints and, evenmore importantly, the energies of their highest occupied MOsare in a quite narrow energy range anyway. The interpretationof the MO scheme of 2 a follows analogously, although corre-sponding linear combinations are no longer needed. For R3,since no TTF donor is built in, the HOMO is mainly localized on

the porphyrin core, but signifi-cantly decoupled from the fusedquinoxaline fragment. In all ofthese cases, the LUMO andLUMO + 1 extend across the qui-noxaline group(s), lowering theirenergies. These results are in ac-cordance with those of reportedanalogues.[19]

The calculated vertical elec-tronic transitions for 1 a, 2 a andR3 are shown by sticks in thespectra in Figure 6, and their cal-culated energies and oscillatorstrengths are given in Tables 2–4. For 1 a, the DT-DFT calculation(D2h constraint) predicts S0!S1

and S0!S2 excitations with onlyvery weak intensities, and theirelectronic character correspondsbasically to the Q-band-typetransitions of porphyrin systems.However, the energetically closelying S0!S3 transition describesthe expected symmetry-allowedHOMO (au)!LUMO (bg) promo-tion (93 %) and thus exhibits CTcharacter (A !!D!!A). Thecalculated energy and oscillatorstrength compare fairly well withthe first absorption band ap-pearing around 16 500 cm�1

(605 nm). The S0!S11 excitationreflects the A’ !D!A’ type ofcharge-transfer absorption, andthe S0!S20 excitation revealscontributions of the A!A’–D–A’ !A type of charge-transfertransition. The following S0!S29Figure 7. Frontier MOs of the p-conjugated skeleton of 1 a.

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excitation with the highest oscil-lator strength corresponds tothe Soret-band character of theporphyrins. Altogether, theselatter excitations lead to thebroad and intense absorptionprofile from 18 000 cm�1 up-wards in energy (below 555 nm);however, a specific assignmentof the calculated transitionswithin this broad profile can notbe made at this stage.

For 2 a, as expected, theHOMO!LUMO promotion(98 %) significantly shows upwith the excitation S0!S1 ata similar energy as in the case of1 a, and it matches the lowestenergy absorption band quitewell ; this transition describes anA !!D charge transfer. The pro-nounced S0!S5 excitation corre-sponds to the expected A’ !Dtype of charge transfer. Andlastly, the S0!S11 excitation re-flects again the correspondingporphyrin Soret band. Overall, itis clear that the Soret-type ab-sorption dominates the spec-trum, and the different charge-transfer transitions contribute tobroadening of the absorptionprofile towards lower energies.In the case of R3, the S0!S1 andS0!S2 excitations bear the Q-type character of the porphyrinunit, and the S0!S3 and partlythe S0!S5 excitations have a por-phyrin-to-quinoxaline charge-transfer character. Finally, thetransitions to the S7 and S8

states show mixtures of Soret-band and charge-transfer charac-ters. Compared to the corre-sponding meso-tetraphenylpor-phyrin, direct fusion of the qui-noxaline unit to the porphyrincore gives rise to broadeningand red shifts of the spectrumdue to the extended p conjuga-tion. Again, the calculated transi-tions show up at slightly higherenergies than the observedones. Furthermore, one can alsoconclude that for all three com-pounds the theoretical HOMO–LUMO gaps (HLG) compare fa-

Figure 8. Frontier MOs of the p-conjugated skeletons of 2 a (a) and R3 (b).

Table 2. Energies, oscillator strengths and dominant contributions of the respective molecular orbitals forS0!Sn of 1 a.

State Excitationenergy [cm�1]

Oscillatorstrength

Dominant contributions [%]

S1 17 122 0.0002 H�2!L + 1 (43), H�1!L (23), H�1!L + 2 (13)S2 17 170 0.0000 H�2!L + 3 (34), H�2!L + 2 (16), H�3!L + 1 (14)S3 17 274 0.6276 H! L(93)S11 20 748 1.3026 H!L + 4 (88)S20 22 233 0.2617 H�3!L + 4 (31), H�4!L + 5 (23), H�4!L + 1 (18)S29 24 991 3.8195 H�4!L + 3 (22), H�3!L + 2 (17)

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vourably with the experimental CV data and similarly well withthe optical HLG determined from the onset of the respectiveabsorption profiles; for example, these values are in the rangeof 2.0–2.4 eV for 1 a, and 2.0–2.3 eV for 2 a.

2.5. Spectroelectrochemical Studies

To gain insight into the potential evolution of the redox behav-iours of 1 and 2 and also to investigate in more detail the siteof electron transfer, systematic changes in the optical spectraupon oxidation of the neutral species were examined by spec-troelectrochemistry, as shown in Figures 9 and 10 (see also theSupporting Information, Figures S3–S5).

As illustrated in Figure 9 a, chemical oxidation of 2 a withless than 1 equiv of [Fe(bpy)3](PF6)3 (bpy = 2,2’-bipyridine) leadsto a gradual decrease of the absorption band around 600 nm(16 670 cm�1) and concomitant emergence of a new broad ab-sorption band peaking at 830 nm (12 050 cm�1), characteristicfor formation of the TTF radical cation species. However, theSoret band is intensified, sharpened and slightly moves tohigher frequency. All of these observations suggest minor par-ticipation of the porphyrin ring in the first oxidation process,which occurs mainly on the TTF moiety. Furthermore, beyond1.4 equiv of [Fe(bpy)3](PF6)3 (Figure 9 b), the TTF radical absorp-tion band decreases quickly, while new broad absorptionbands grow in the 600–1000 nm (16 670–10 000 cm�1) regionalong with a rapid decrease in the intensity of the Soret band,a spectral feature that is conceivably attributable to formationof a porphyrin radical cation during the second oxidation pro-cess. The sequential oxidations are also borne out by the simi-larity to the thin-layer UV/Vis/NIR spectra of 2 a and 2 b ob-tained in situ by successively applying oxidation potentials(Supporting Information Figures S3 and S4). All of these resultsare in good agreement with the previous discussion from

cyclic voltammetry, in that thefirst oxidation occurs at the TTFunit and the second at the por-phyrin core.

Figure 10 shows the variationof the absorbance spectra of 1 cas the voltage is stepped from�0.2 to + 0.5 V. As the potentialshifts positively, the intensities inthe higher energy range (withSoret-band character) significant-ly decrease and a new broad ab-sorption band grows in the 600–800 nm (16 670–12 500 cm�1)region. These spectral changessuggest that the electron-trans-fer site is porphyrin ring centredand leads to the formation ofporphyrin cation radicals duringthe first oxidation process. Thesame holds for the thin-layerUV/Vis/NIR spectral change of1 b (Supporting Information Fig-

Table 3. Energies, oscillator strengths and dominant contributions of the respective molecular orbitals forS0!Sn of 2 a.

State Excitationenergy [cm�1]

Oscillatorstrength

Dominant contributions [%]

S1 16 513 0.1524 H!L (98)S2 17 166 0.0000 H�2!L (48), H�1!L + 1 (47)S4 18 132 0.0023 H�1!L (63), H�2!L + 1 (35)S5 20 307 0.3757 H!L + 2 (96)S6 21 942 0.0563 H�1!L + 2 (83), H�2!L + 1 (11)S7 22 340 0.1600 H�2!L + 2 (58), H�2!L (23), H�1!L + 1 (16)S11 25 279 2.0773 H�2!L + 1 (43), H�1!L (23), H�1!L + 2 (13)

Table 4. Energies, oscillator strengths and dominant contributions of the respective molecular orbitals forS0!Sn of R3.

State Excitationenergy [cm�1]

Oscillatorstrength

Dominant contributions [%]

S1 17 230 0.0000 H!L + 1 (50), H�1!L (49)S2 18 169 0.0131 H!L (64), H�1!L + 1 (35)S3 22 541 0.0739 H!L + 2 (84), H�1!L + 1 (10)S5 22 897 0.2196 H�1!L + 2 (54), H�1!L (23), H!L + 1 (17)S7 25 817 1.7913 H�1!L + 1 (48), H!L (27), H!L + 2 (14)S8 25 818 0.5522 H�1!L + 2 (37), H�3!L + 1 (19), H!L + 1 (18)

Figure 9. Variation of the UV/Vis/NIR absorption spectra of 2 a (7.16 � 10�6m)

in CH2Cl2 upon successive addition of aliquots of [Fe(bpy)3](PF6)3.

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ure S5) upon the first oxidation. These observations are inqualitative agreement with the aforementioned interpretationof the electrochemical data.

2.6. Femtosecond and Nanosecond Absorption SpectralStudies

Femtosecond transient absorption spectroscopy was used toobtain insight into the excited-state events of triads 1, dyads2, and reference compound R3. The compounds were probedwith 400/430 nm excitation to selectively excite the porphyrinfluorophores. The femtosecond transient absorption spectra ofR3 in benzonitrile (Figure 11) reveal instantaneous formation ofthe singlet porphyrin features. Here, the transient absorptionspectra exhibit the absorption bands in the visible region witha maximum at 475 nm, which decayed slowly (1.00 � 108 s�1) topopulate the corresponding triplet manifold.

The spectral features in the visible region, which were seenimmediately upon excitation of triads 1 a–c in benzonitrile(Supporting Information Figures S6–S8), reveal transient ab-sorption bands of the singlet-excited state of porphyrin, withrate constants of 1.18 � 108, 1.80 � 108 and 2.23 � 109 s�1, respec-tively. Therefore, one can state clearly that electron transferfrom TTF to the excited state of porphyrin is not detected inthese triads. This observation is in a good agreement with theelectrochemical studies, which suggest that the electron trans-fer is thermodynamically not favoured.

Upon excitation of dyad 2 a in benzonitrile (Figure 12), thefemtosecond spectrum recorded at 7 ps showed formation of

the singlet excited state of porphyrin. A study on the kineticsof 2 a in the initial 200 ps suggests that the singlet excitedstate of porphyrin decays much faster (1.0 � 1010 s�1) than thatof 1 a. The transient spectra of 2 b (Supporting Information Fig-ure S9) exhibit the same features as 1 b with a rate constant of1ZnP* (7.0 � 1010 s�1). These results indicate electron transferfrom TTF to the singlet porphyrin, considering that energytransfer from the singlet-excited porphyrin to TTF is not feasi-ble. This observation is consistent with the electrochemicalstudies, which show that electron transfer is thermodynamical-ly favoured for 2 a and 2 b in polar benzonitrile. The differencein the rates of charge separation from TTF to the singlet excit-ed porphyrin of dyad 2 a (kCS = 9.80 � 109 s�1) and 2 b (kCS =

6.98 � 1010 s�1) can be explained by the difference in the free-energy changes of charge-separation processes (�DGCS) of 2 a(0.17 eV) and 2 b (0.86 eV).[21]

Upon exciting reference R3 with a 430 nm laser, the comple-mentary nanosecond transient absorption spectra of R3 inbenzonitrile showed the absorption bands of the triplet excit-ed porphyrin in the visible region with a maximum at 470 nm(Figure 13). The triplet excited state of porphyrin decays with

Figure 10. Variation of UV/Vis/NIR spectroelectrochemistry of 1 c(4.6 � 10�4

m) in CH2Cl2 (with 0.1 m Bu4NPF6) upon variation of the electric po-tential.

Figure 11. Differential absorption spectra obtained upon femtosecond flashphotolysis (430 nm) of reference R3 in benzonitrile at the indicated time in-tervals. Inset : Decay profile of the singlet porphyrin at 475 nm.

Figure 12. Differential absorption spectra obtained upon femtosecond flashphotolysis (400 nm) of 2 a in benzonitrile at the indicated time intervals.Inset : Decay profile of the singlet porphyrin at 480 nm.

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a rate constant of 6.4 � 103 s�1. Similar spectra were observedfor 1 a and 2 a in benzonitrile (Supporting Information Figur-es S10 and S11). These observations suggest the absence ofelectron transfer via the triplet state of porphyrin, which isthermodynamically not favoured. The short-lived triplet stateof triad 1 c was not observed in the transient spectra (Support-ing Information Figure S12).

2.7. Complex Formation and Photochemical Studies ofSupramolecular Triad 2b:C60py

Dyad 2 b was utilized to build, by an axial-coordination ap-proach, a novel supramolecular architecture with fullerenefunctionalized by a pyridine entity (Figure 14). The optical ab-sorption changes observed during increasing addition of N-pyridyl-3,4-fulleropyrrolidine (C60py)[22] to a solution of 2 b in o-dichlorobenzene, a non-coordinating solvent, are shown inFigure 15. During the titration, the ZnP-type absorption bandof 2 b located at 422 nm diminished in intensity with red shiftsof the absorption band to 432 nm, characteristic of axial coor-dination of the ZnII ion.

Formation of the supramolecular triad 2 b :C60py was alsoconfirmed by steady-state emission studies. As shown inFigure 16, the fluorescence spectrum of dyad 2 b in o-dichloro-benzene reveals an emission band at 640 nm corresponding tothe singlet (ZnP–TTF)*. An increasing concentration of C60py inthe solution results in a decrease in emission intensity. Thissuggests the occurrence of a photochemical processes; anelectron transfer from the singlet state of 2 b to C60 could beenvisioned. The ZnII···py binding constant was evaluated byconstructing a Benesi–Hildebrand plot, as shown in Figure 16(inset), which yields a binding constant K of 7.20 � 104

m�1,

nearly two orders of magnitude higher than that reported forC60py binding to ZnP.[23]

To probe the redox properties of the 2 b :C60py, cyclic voltam-metric studies were performed in o-dichlorobenzene contain-ing 0.10 m Bu4N(PF6) as supporting electrolyte (Supporting In-formation Figure S13). The first reduction potential of the

Figure 13. Nanosecond transient absorption spectra of reference R3 in ben-zonitrile at the indicated time intervals. Inset : Decay profile of the tripletporphyrin at 470 nm.

Figure 14. Molecular structure of supramolecular triad 2 b :C60py.

Figure 15. UV/Vis spectral changes observed upon increasing addition ofC60py to dyad 2 b in o-dichlorobenzene.

Figure 16. Fluorescence spectral changes observed upon increasing additionof C60py to 2 b in o-dichlorobenzene; lex = 420 nm. Inset : Benesi–Hildebrandplot.

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C60py entity was located at �0.67 V versus SCE, while the oxi-dation potentials of 2 b were located at 0.64, 0.86 and 1.10 Vversus SCE. The energetics for a photoinduced electron trans-fer from 1ZnP*–TTF to C60 were evaluated by using the redoxand spectral data discussed above. The driving forces forcharge separation (DGCS) and charge recombination (DGCR) aregiven via the excited singlet state ZnP*–TTF and were found tobe 1.31 and 0.77 eV, respectively. These results suggest thatthe electron transfer from the singlet ZnP*–TTF to C60 is ther-modynamically possible.

To unravel the electron-transfer route and obtain kinetic in-formation, further transient spectral studies on a femtosecondtimescale were performed. The 2 b :C60py supramolecular triadwas probed with 430 nm laser excitation to selectively excitethe porphyrin fluorophore in toluene solution (Figure 17). The

transient absorption spectrum measured 5 ps after femtosec-ond laser excitation exhibits the transient absorption of theZnP–TTF singlet excited state (1ZnP*–TTF). With time, the1ZnP*–TTF absorption peak at 540 nm diminishes in intensitywhile a concomitant increase in absorbance at 1000 nm, dueto the C60 radical anion (C60·�), and similarly at 620–700 nmdue to the ZnP radical cation (ZnP· +), is observed. These spec-tra provide direct evidence for electron transfer from the pho-toexcited ZnP*–TTF unit to C60. The kinetics of this electrontransfer from 1ZnP*–TTF to C60 was analyzed by exponential fit-ting of the rise profile of the radical C60

·� (at 1000 nm; kCS =

2.84 � 1012 s�1 and kCR = 2.60 � 109 s�1). Based on the kCR value,the lifetime of the (ZnP–TTF)·+ ···(C60py)·� charge-separatedstate was determined to be 385 ps.

3. Conclusions

Novel symmetric porphyrin–tetrathiafulvalene–porphyrin triadsannulated through quinoxaline linkers into planar and largely

extended p-conjugated molecules have been synthesized. Sim-ilarly, asymmetric porphyrin–tetrathiafulvalene dyads havebeen prepared as well. These electrochemically amphotericcompounds have been investigated by cyclic voltammetry,thin-layer cyclic voltammetry and spectroelectrochemicalmethods in order to elucidate the sites of the redox processes.The data suggest that in the triads initial oxidation occurs atthe peripheral porphyrin sites, and is directly followed withina narrow potential range by formation of the TTF radicals. Thisorder is reversed for the dyad systems and other reported TTF-annulated porphyrins. Ab initio calculations demonstrate thatthe TTF-type and porphyrin-type HOMOs show up at quitesimilar energies. Photophysical experiments reveal electronicexcitations which can be traced back to the specific type of in-tramolecular charge-transfer character ; these additional elec-tronic transitions are a direct consequence of the synthetic ap-proach to annulate donor and acceptor chromophores intorigid and planar p-conjugated molecular systems. The poten-tial to build up further supramolecular assemblies was demon-strated by using a fullerene acceptor unit.

Experimental Section

General : Air- and/or water-sensitive reactions were conductedunder argon in dry, freshly distilled solvents. Elemental analyseswere performed on an EA 1110 Elemental Analyzer CHN Carlo ErbaInstruments. FTIR spectra were recorded on a PerkinElmer OneFTIR spectrometer. 1H and 13C NMR spectra were measured ona Bruker spectrometer with tetramethylsilane as internal standard.Mass spectra were recorded on an FTMS 4.7T BioAPEX II with theMALDI ionization method.

Materials : Unless otherwise stated, all reagents were purchasedfrom commercial sources and used without additional purification.2-[5,6-Diamino-4,7-bis(4-pentylphenoxy)-1,3-benzodithiol-2-yli-dene]-4,7-bis(4-pentylphenoxy)-1,3-benzodithiole-5,6-diamine (3),[14]

5,6-diamino-2-(4,5-bis(propylthio)-1,3-dithio-2-ylidene)-benzo[d]-[1,3]dithiole (4),[15] 2,3-dioxo-5,10,15,20-tetrakis(3’,5’-di-tert-butyl-phenyl)chlorin (5),[16c] 2,3-dioxo-5,10,15,20-tetrakisphenylchlorin(6)[16] and N-pyridyl-3,4-fulleropyrrolidine (C60py)[22] were preparedaccording to literature procedures.

Cyclic Voltammetry: Cyclic voltammetry (CV) was performed for1 a–c in a three-electrode cell equipped with a platinum millielec-trode, a platinum wire counter-electrode and a silver wire as quasi-reference electrode. The electrochemical experiments were carriedout under dry and oxygen-free atmosphere (H2O<1 ppm, O2<

1 ppm) in CH2Cl2 (0.8 mm) with 0.1 m Bu4NPF6 as supporting elec-trolyte at 100 mV s�1. The voltammograms were recorded on anEGG PAR 273A potentiostat with positive feedback compensation.Based on repetitive measurements, absolute errors on potentialswere estimated to be around �5 mV. The number of electrons wasdetermined by recording the voltammograms under thin-layerconditions (TLCV), and dichloronaphthoquinone was used as an in-ternal reference for the number of exchanged electrons. The exper-imental voltammograms were deconvoluted with the Condeconsoftware.Cyclic voltammetry (CV) was carried out for 2 a, 2 b and R1 ina three-electrode cell equipped with a Pt disc working electrode,a glassy carbon counter-electrode and Ag/AgCl reference elec-trode. The electrochemical experiments were carried out under dryand an oxygen-free atmosphere in CH2Cl2 with 0.1 m Bu4NPF6 as

Figure 17. Differential absorption spectra obtained upon femtosecond flashphotolysis (430 nm) of 2 b :C60py at the indicated time intervals in toluene.Inset : Rise–decay profile of the C60 radical anion monitored at 1000 nm toevaluate the charge-separation and charge-recombination kinetics.

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Tetrathiafulvalene-Fused Porphyrins

supporting electrolyte. The voltammograms were recorded ona PGSTAT 101 potentiostat.

Cyclic voltammograms of supramolecular triad 2 b :C60py were re-corded on a BAS CV-50W Voltammetric Analyzer. A platinum discelectrode was used as working electrode, while a platinum wireserved as a counter-electrode. An SCE electrode was used as refer-ence electrode. All measurements were carried out in o-dichloro-benzene containing Bu4NPF6 (0.1 m) as supporting electrolyte. Thescan rate was 50 mV s�1.

Spectroelectrochemistry: The setup used for the UV/Vis spectro-electrochemical experiments has been described previously.[24] Theevolution of UV/Vis/NIR spectra after successive additions of [Fe-(bpy)3](PF6)3 aliquots was followed on a PerkinElmer Lambda 10spectrophotometer in a 1 cm quartz cell with a solution of 2 a(7.16 � 10�6

m) in CH2Cl2 and a solution of [Fe(bpy)3](PF6)3 (1.43 �10�3

m) in CH3CN.

Photophysical Measurements: Steady-state absorption spectrawere recorded on a Shimadzu UV-3100PC spectrometer or a Hew-lett Packard 8453 diode-array spectrophotometer at room temper-ature. Fluorescence measurements were carried out on a Shimadzuspectrofluorophotometer (RF-5300PC). Fluorescence spectra of the2 b :C60py supramolecular triad were monitored by using a VarianEclipse spectrometer. A right-angle detection method was used.

Femtosecond transient absorption spectroscopic experiments wereconducted by using an Integra-C ultrafast source (QuantronixCorp.), a TOPAS optical parametric amplifier (Light Conversion Ltd.)and a commercially available optical detection system (Helios) pro-vided by Ultrafast Systems LLC. The sources for the pump andprobe pulses were derived from the fundamental output of Inte-gra-C (780 nm, 2 mJ pulse�1 and fwhm = 130 fs) at a repetition rateof 1 kHz. 75 % of the fundamental output of the laser was intro-duced into TOPAS, which has optical frequency mixers resulting intuneable range from 285 to 1660 nm, while the rest of the outputwas used for white light generation. Typically, 2500 excitationpulses were averaged for 5 s to obtain the transient spectrum ata set delay time. Kinetic traces at appropriate wavelengths were as-sembled from the time-resolved spectral data. All measurementswere conducted at 298 K. The transient spectra were recorded byusing fresh solutions in each laser excitation.

For nanosecond transient absorption measurements deaerated sol-utions of the compounds were excited by a Panther OPOequipped with a Nd:YAG laser (Continuum, SLII-10, 4–6 ns fwhm)with a power of 10–15 mJ pulse�1. The photochemical reactionswere monitored by continuous exposure to an Xe lamp (150 W) asprobe light and a photomultiplier tube (Hamamatsu 2949) as de-tector. Solutions were deoxygenated by argon purging for 15 minprior to the measurements.

Ab Initio Calculations: DFT and time-dependent DFT calculations ofporphyrin–quinoxaline, TTF–porphyrin and TTF–diporphyrin wereperformed with the B3LYP hybrid functional and the SVP basis set.All calculations were carried out with the TURBOMOLE V6.0 pro-gram package.[25] The molecular ground-state geometries of por-phyrin–quinoxaline, TTF–porphyrin and TTF–diporphyrin were opti-mized at the B3LYP/SVP level of theory. Porphyrin–quinoxaline wascalculated in C2 symmetry and the other two without symmetry re-strictions. The electronic excitation spectra were calculated withthe SVP basis set.

Synthesis of Triad 1 a : A suspension of 5 a (19 mg, 0.017 mmol)and 3 (8.3 mg, 0.008 mmol) in glacial acetic acid (6 mL) was heatedto reflux for 5 h under Ar. After cooling to room temperature, thesolvent was evaporated. The residue was purified by column chro-

matography (SiO2, petroleum ether (b.p. 40–60 8C)/CH2Cl2 3/2) toafford a crude product. Subsequent reprecipitation from a solutionin CH2Cl2 with methanol gave 1 a (19 mg, 74 %) as a brownish redpowder. 1H NMR (300 MHz, CDCl3): d= 8.90 (d, J = 5.1 Hz, 4 H), 8.78(d, J = 5.1 Hz, 4 H), 8.75 (s, 4 H), 8.06 (d, J = 1.7 Hz, 8 H), 7.92 (d, J =

1.7 Hz, 8 H), 7.78–7.77 (dd, J = 1.7 Hz, J = 1.9 Hz, 4 H), 7.66–7.65 (dd,J = 1.7 Hz, 4 H), 7.04 (d, J = 8.6 Hz, 8 H), 6.73 (d, J = 8.6 Hz, 8 H), 2.57(t, J = 7.5 Hz, 8 H), 1.53, 1.50 (2 s, 152 H, tert-butyl protons andCH2CH2 (CH2)2CH3 are overlapped), 1.35 (m, 16 H), 0.88 (t, J = 6.8 Hz,12 H), �2.52 ppm (br s, 4 H); FTIR (KBr pellet): n= 3437, 2960, 2923,2856, 1626, 1593, 1504, 1475, 1384, 1362, 1208, 1167, 1154, 1109,922, 800, 720 cm�1; MALDI-TOF MS: m/z 3125.91 [M]+ ; calcd forC210H244N12O4S4 3125.81; elemental analysis calcd (%) forC210H244N12O4S4·2 CH3OH: C 79.76, H 7.96, N 5.26; found: C 80.16, H8.30, N 4.78.

Synthesis of Triad 1 b : A solution of Zn(OAc)2·2 H2O (9 mg,0.041 mmol) in CH3OH (5 mL) was added to a solution of com-pound 1 a (19 mg, 6 mmol) in CH2Cl2 (15 mL). The resulting mixturewas heated to 50 8C and stirred for 3.5 h. After cooling to roomtemperature, the solvent was evaporated. The residue was purifiedby column chromatography (SiO2, petroleum ether (b.p. 40–60 8C)/CH2Cl2 3/2) to afford a crude product. Subsequent reprecipitationfrom a solution in CH2Cl2 with methanol gave 1 b (13.7 mg, 70 %)as a brownish red powder. 1H NMR (300 MHz, CDCl3): d= 8.87 (d,J = 4.7 Hz, 4 H), 8.82 (s, 4 H), 8.68 (d, J = 4.7 Hz, 4 H), 8.02 (d, J =1.7 Hz, 8 H), 7.86 (d, J = 1.9 Hz, 8 H), 7.75–7.74 (dd, J = 1.7 Hz, J =1.9 Hz, 4 H), 7.62–7.60 (dd, J = 1.7 Hz, 4 H), 7.05 (d, J = 8.7 Hz, 8 H),6.75 (d, J = 8.7 Hz, 8 H), 2.58 (t, J = 7.5 Hz, 8 H), 1.49, 1.53 (2 s, 152 H,tert-butyl protons and CH2CH2(CH2)2CH3 are overlapped), 1.36 (m,16 H), 0.91 ppm (t, J = 7.2 Hz, 12 H); FTIR (KBr pellet): n= 3437,2958, 2923, 2854, 1625, 1592, 1504, 1464, 1384, 1361, 1218, 1170,1112, 939, 812, 798, 711 cm�1; MALDI-TOF MS: m/z : 3250.76[M+H]+ ; calcd for C210H241N12O4S4Zn2: 3250.65; elemental analysiscalcd (%) for C210H240N12O4S4Zn2: C 77.48, H 7.43, N 5.16; found: C77.15, H 7.83, N 4.63.

Synthesis of Triad 1 c : A suspension of 5 b (19 mg, 0.016 mmol)and 3 (8.3 mg, 0.008 mmol) in glacial acetic acid (4 mL) was heatedto reflux for 3 h under Ar. After cooling to room temperature, thesolvent was evaporated. The residue was purified by column chro-matography (SiO2, petroleum ether (b.p. 40–60 8C)/CH2Cl2 1/1) toafford a crude product. Subsequent reprecipitation from a solutionin CH2Cl2 with methanol gave 1 c (20 mg, 77 %) as a brownish redpowder. FTIR (KBr pellet): n= 3435, 2960, 2924, 2856, 1593, 1504,1460, 1393, 1362, 1217, 1173, 1009, 939, 815, 799 cm�1; MALDI-TOFMS: m/z 3248.69 [M+H]+ ; calcd for C210H241N12O4S4Cu2 : 3248.65; el-emental analysis calcd (%) for C210H240N12O4S4Cu2 : C 77.57, H 7.44,N 5.17; found: C 77.97, H 8.15, N 4.55.

Synthesis of Dyad 2 a : A mixture of porphyrin dione 6 (100 mg,1.55 � 10�4 mol) and 4 (0.0735 mg, 1.70 � 10�4 mol) in CHCl3/pyri-dine (10/1 v/v) was heated at 65 8C for 2 h. Colour change was ob-served from yellowish to dark green and completion of the reac-tion was monitored by TLC. After completion pyridine was re-moved on a rotary evaporator, and the residue was purified byflash column chromatography on silica with CH2Cl2/CH3OH (100/1)as eluent to afford 2 a (154.9 mg, 96 %) as a dark greenish browncrystalline solid. 1H NMR (400 MHz, CDCl3): d= 8.92 (d, J = 8.2 Hz,4 H), 8.71 (s, 2 H), 8.23–8.21 (d, J = 8.0 Hz, 4 H), 8.13–8.12 (d, J =8.0 Hz, 4 H), 7.79–7.75 (m, 10 H), 7.63 (s, 2 H), 7.62 (s, 2 H), 2.86–2.82(t, J = 6.4 Hz, 4 H), 1.76–1.66 (m, 4 H), 1.07–1.03 (t, J = 7.2 Hz, 6 H),�2.75 ppm (s, 2 H); 13C NMR (125 MHz, CDCl3): d= 161.76, 155.01,152.53, 145.40, 144.93, 141.86, 141.78, 140.74, 139.58, 139.55,138.02, 134.46, 133.84, 128.14, 127.99, 127.63, 126.91, 121.70,

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S.-X. Liu, S. V. Bhosale, S. Fukuzumi et al.

121.29, 117.13, 38.38, 23.20, 13.18 ppm; FTIR (KBr pellet): n= 3389,3318, 2965, 2969, 1716, 1669, 1509, 1478, 1432, 1384, 1287, 1169,1174, 1072, 1002, 917, 908, 793, 865 cm�1; elemental analysis calcd(%) for C60H44N6S6 : C 69.20, H 4.26, N 8.07; found: C 69.18, H 4.26,N 8.09.

Synthesis of Dyad 2 b : A solution of Zn(OAc)2·2 H2O (30 mg, excess)in MeOH (1 mL) was added to a solution of 2 a (25 mg, 2.15 �10�5 mol) in CHCl3 (5 mL). The resulting solution was heated at65 8C for 2 h. After total conversion (confirmed by TLC), the solu-tion was washed with water and dried over anhydrous sodium sul-fate. The compound was purified on a silica gel column with CHCl3

as eluent to obtain 2 b (22 mg, 93 %) as a purple solid. 1H NMR(300 MHz, CDCl3): d= 8.64 (d, J = 8.2 Hz, 4 H), 7.99 (s, 2 H), 7.98–7.97(d, J = 8.0 Hz, 4 H), 7.88–7.86 (d, J = 8.0 Hz, 4 H), 7.77–7.76 (m, 10 H),7.70 (s, 2 H), 7.63 (s, 2 H), 2.87–2.85 (t, J = 6.4 Hz, 4 H), 1.74–1.69 (m,4 H), 1.07–1.03 ppm (t, J = 7.2 Hz, 6 H); 13C NMR (125 MHz, CDCl3)d= 160.05, 155.03, 148.45, 144.10, 142.93, 140.90, 140.23, 140.13,139.75, 139.45, 138.12, 133.986, 131.94, 130.24, 127.94, 127.67126.89, 121.76, 121.31, 117.43, 38.37, 23.36, 13.20 ppm; FTIR (KBrpellet): n= 3389, 3318, 2965, 2969, 1716, 1669, 1509, 1478, 1432,1384, 1287, 1169, 1174, 1072, 1002, 917, 908, 793, 865 cm�1; ele-mental analysis calcd (%) for C60H42N6S6Zn: C 65.23, H 3.83, N 7.61;found: C 65.21, H 3.85, N, 7.59.

X-Ray Structure Determination: Crystal data for 2 a : C60H44N6S6, M =1040.20, a = 15.833(2), b = 19.591(3), c = 16.824(2) �, b=107.918(4)8, monoclinic P21/n, Z = 4, V = 4965.5(13) �3, 1calcd =1.393 g cm�3, F000 = 2168, l= 0.71073 �, T = 123(2) K, m=0.232 mm�1, Bruker X8 Apex II CCD diffractometer, f scan, 28 599data collected, corrected for Lorenz and polarization effects, 8733unique (Rint = 0.0569) and 8733 observed [I>2 s(I)] , 694 refined pa-rameters, R = 0.0985, Rw = 0.2265, w = [s2(F)]�1. CCDC 869800 (2 a)contains the supplementary crystallographic data for this paper.These data can be obtained free of charge from The CambridgeCrystallographic Data Centre via www.ccdc.cam.ac.uk/data_re-quest/cif.

Acknowledgements

This work was supported by the Swiss National Science Founda-tion (grant No. 200020-130266/1), the EU-project (FUNMOLS FP7-212942-1), the Australian Research Council for Future Fellowshipaward (FT110100152) and the ARC Discovery Grant Program(DP1093337) as well as by the Global COE (center of excellence)program “Global Education and Research Center for Bio-Environ-mental Chemistry” of Osaka University from Ministry of Educa-tion, Culture, Sports, Science and Technology, Japan, and KOSEF/MEST through WCU project (R31-2008-000–10010-0) from Korea.

Keywords: density functional calculations · donor–acceptorsystems · photophysics · porphyrinoids · redox chemistry

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Received: April 23, 2012

Revised: June 1, 2012

Published online on June 29, 2012

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