Tetrathiafulvalene-fused porphyrins via quinoxaline linkers: Symmetric and asymmetric donor-acceptor systems

Article abstract of DOI:10.1002/cphc.201200350

A tetrathiafulvalene (TTF) donor is annulated to porphyrins (P) via quinoxaline linkers to form novel symmetric P-TTF-P triads 1 a-c and asymmetric P-TTF dyads 2 a,b in good yields. These planar and extended π-conjugated molecules absorb light over a wide region of the UV/Vis spectrum as a result of additional charge-transfer excitations within the donor-acceptor assemblies. Quantum-chemical calculations elucidate the nature of the electronically excited states. The compounds are electrochemically amphoteric and primarily exhibit low oxidation potentials. Cyclic voltammetric and spectroelectrochemical studies allow differentiation between the TTF and porphyrin sites with respect to the multiple redox processes occurring within these molecular assemblies. Transient absorption measurements give insight into the excited-state events and deliver corresponding kinetic data. Femtosecond transient absorption spectra in benzonitrile may suggest the occurrence of fast charge separation from TTF to porphyrin in dyads 2 a,b but not in triads 1 a-c. Clear evidence for a photoinduced and relatively long lived charge-separated state (385 ps lifetime) is obtained for a supramolecular coordination compound built from the ZnP-TTF dyad and a pyridine-functionalized C₆₀ acceptor unit. This specific excited state results in a (ZnP-TTF)^?+...(C ₆₀py)^?- state. The binding constant of Zn ^II...py is evaluated by constructing a Benesi-Hildebrand plot based on fluorescence data. This plot yields a binding constant K of 7.20×10⁴ M^-1, which is remarkably high for bonding of pyridine to ZnP.

Full text of DOI:10.1002/cphc.201200350

DOI: 10.1002/cphc.201200350
Tetrathiafulvalene-Fused Porphyrins via Quinoxaline
Linkers: Symmetric and Asymmetric Donor–Acceptor
Systems
Hongpeng 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] and
Silvio Decurtins[a]
A tetrathiafulvalene (TTF) donor is annulated to porphyrins (P)
via quinoxaline linkers to form novel symmetric P–TTF–P triads
1a–c and asymmetric P–TTF dyads 2a,b in good yields. These
planar and extended p-conjugated molecules absorb light
over a wide region of the UV/Vis spectrum as a result of addi-
tional charge-transfer excitations within the donor–acceptor
assemblies. Quantum-chemical calculations elucidate the
nature of the electronically excited states. The compounds are
electrochemically amphoteric and primarily exhibit low oxida-
tion potentials. Cyclic voltammetric and spectroelectrochemical
studies allow differentiation between the TTF and porphyrin
sites with respect to the multiple redox processes occurring
within these molecular assemblies. Transient absorption meas-
urements give insight into the excited-state events and deliver
corresponding kinetic data. Femtosecond transient absorption
spectra in benzonitrile may suggest the occurrence of fast
charge separation from TTF to porphyrin in dyads 2a,b but
not in triads 1a–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 from
the ZnP–TTF dyad and a pyridine-functionalized C60 acceptor
unit. This specific excited state results in a (ZnP–TTF)·+
···(C60py)·ꢀ state. The binding constant of ZnII···py is evaluated
by constructing a Benesi–Hildebrand plot based on fluores-
cence data. This plot yields a binding constant K of 7.20ꢀ
104 mꢀ1, 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. Decurtins
Departement fꢀr Chemie und Biochemie
Universitꢁt Bern, Freiestrasse 3
1. Introduction
There is considerable interest in developing multi-chromophor-
ic arrays as a way to gain insight into the fundamental aspects
of energy- and electron-transfer processes and to mimic multi-
step charge-separation processes in natural photosynthesis
and ultimately organic-based solar energy conversion technol-
ogies.[1] Porphyrins (P) are prominent molecular components of
such donor–acceptor (D–A) arrays and have found widespread
use 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 range
of electron acceptor- or donor-linked porphyrins have been in-
tensively studied.[1,7–10] Among them, however, only a few
papers on molecular systems that include the well-known elec-
tron donor tetrathiafulvalene (TTF) as an annulated moiety to
the porphyrin core have appeared in the literature,[10,11] per-
haps due to synthetic difficulties. In all cases, the TTF unit acts
as an electron donor and the porphyrin core as an electron ac-
ceptor leading to photoinduced intramolecular charge transfer
from the TTF donor to the porphyrin chromophore. However,
no TTF-fused porphyrin conjugates in which two porphyrin
rings are directly annulated to the central TTF core through p
linkers have been reported.
3012 Bern (Switzerland)
Fax: (+41)31-631-3995
E-mail: liu@iac.unibe.ch
[b] Dr. S. V. Bhosale,+ S. Rivadehi, Prof. S. J. Langford
School of Chemistry, Monash University
Clayton, VIC-3800 (Australia)
E-mail: bsheshanath@gmail.com
[c] Dr. L. Sanguinet, Dr. E. Levillain
Institut des Sciences et Technologies Molꢂculaires d’Angers
Universitꢂ d’Angers, CNRS UMR 6200
2 Bd Lavoisier, 49045 Angers Cedex (France)
[d] Dr. M. E. El-Khouly, Prof. S. Fukuzumi
Department of Material and Life Science
Graduate School of Engineering, Osaka University
Suita, Osaka 565-0871 (Japan)
E-mail: fukuzumi@chem.eng-osaka-u.ac.jp
[e] Prof. Y. Morita
Department of Chemistry
Graduate School of Science, Osaka University
1-1 Machikaneyama, Toyonaka, Osaka-560-0043 (Japan)
[f] Prof. S. Fukuzumi
Department of Bioinspired Science
Ewha Womans University
Seoul 120-750 (Korea)
[+] Current address: School of Applied Sciences, RMIT University
GPO Box 2476V, Melbourne, VIC-3100 (Australia)
Based on our experience in the functionalization of TTF[12]
and our keen interest in molecular (opto)electronic devices, we
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/cphc.201200350.
ChemPhysChem 0000, 00, 1 – 14
ꢁ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
1
&
ÞÞ
These are not the final page numbers!

S.-X. Liu, S. V. Bhosale, S. Fukuzumi et al.
aimed for the synthesis and electrochemical and spectroscopic
investigations of TTF-annulated free-base and metal(II) por-
phyrins 1 and 2, fused via quinoxaline linker(s), as shown in
Figure 1. Novel symmetric P–TTF–P triads 1a–c and asymmet-
ric P–TTF dyads 2a,b have been prepared, which exhibit
almost planar molecular geometries. The reference compound
quinoxalinoporphyrin R3 acts as an especially interesting build-
ing block for creating larger multiporphyrin arrays, proposed
either as molecular wires or as functional mimics of plant and
bacterial photosynthetic reaction centres.[13] Incorporation of
a 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 ground
and electronically excited states were studied by photophysical
methods (steady-state and transient), cyclic voltammetry and
spectroelectrochemical experiments as well as quantum-chemi-
cal calculations. In addition, a photoinduced charge-separated
state of a supramolecular assembly of asymmetric P–TTF dyad
2b with a functionalized C60 acceptor unit was investigated.
good yields by metallation of the corresponding 1a and 2a
with Zn(OAc)2.
All new compounds were purified by chromatographic sepa-
ration on silica gel and fully characterized. IR spectra of the
products showed no carbonyl stretches at about 1725 and
1738 cmꢀ1, indicative of the absence of any remaining carbonyl
groups 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 for
X-ray crystallography were grown by diffusion of hexane into
a solution of 2a in CHCl3. The molecular structure of 2a is
shown in Figure 2. The molecules are slightly corrugated along
the long axis of the p-conjugated skeleton. In the crystal struc-
ture, they stack in an almost perfect alignment along the
P–TTF axis in an alternating head-to-tail fashion with the TTF
group of one molecule overlying the porphyrin unit of another
one (Supporting Information Figure S1).
2.2. Electrochemistry
2. Results and Discussion
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 1a–c undergo several reversible multi-electron
oxidation 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 inspection
alone, a comprehensive interpretation of these oxidation pro-
cesses is not straightforward. Therefore, thin-layer cyclic vol-
2.1. Synthesis and Characterization
In brief, target compounds 1 and 2 were obtained by direct
condensation reaction of TTF precursors 3[14] and 4[15] with the
corresponding porphyrin-2,3-diones 5[16c] and 6[16] (Scheme 1).
Compounds 1a and 1c were produced in the presence of
acetic acid at reflux as brownish red powders in 74 and 77%
yield, respectively. Compound 2a was synthesized in CHCl3/
pyridine at 658C for 2 h as a greenish brown crystalline solid in
96% yield. Finally, zinc complexes 1b and 2b were obtained in
Figure 1. Structures of investigated compounds 1 and 2 and reference compounds R–R3.
&2
&
www.chemphyschem.org
ꢁ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ChemPhysChem 0000, 00, 1 – 14
ÝÝ
These are not the final page numbers!

Tetrathiafulvalene-Fused Porphyrins
Scheme 1. Synthesis of TTF-annulated porphyrins 1 and 2.
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] (2a with decyl in-
stead of propyl chains).
ox1
1=2
ox2
1=2
ox3
1=2
ox4
1=2
red1
1=2
red2
Compound
E
E
E
E
E
E
1=2
1a
1b
1c
2a
2b
R[d]
R1
R2a[e]
R2b[e]
R3
0.47[a]
0.34[a]
0.44[a]
0.15
0.19
0.11
0.75[b]
0.56[b]
0.61
ꢀ1.62
ꢀ1.71
ꢀ1.64
ꢀ1.58
ꢀ1.03
ꢀ1.44
ꢀ1.93
ꢀ1.59
ꢀ1.77
ꢀ1.61
ꢀ1.79
ꢀ2.06
ꢀ2.06
ꢀ1.77
ꢀ1.76[c]
ꢀ1.77
0.75[a]
0.85
0.64[a]
0.80
0.60[a]
0.48
0.50
0.89
1.04
0.57
0.53[a]
0.26
ꢀ1.79
ꢀ2.21
ꢀ1.81
0.64[c]
0.74
Figure 2. Molecular structure of 2a with 50% thermal ellipsoids and hydro-
gen atoms as spheres of arbitrary size.
0.59
[a] Two overlapping one-electron redox processes. [b] Broad peak. [c] Irre-
versible. [d] Reported potentials relative to Ag/AgCl in CH2Cl2, which are
converted to Fc/Fc+ scale by subtracting 0.51 V from values relative to
Ag/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]
tammetry (TLCV) experiments were performed. However, only
the TLCV of 1c (Figure 4) provides clear evidence of the ratio
of number of electrons involved in each oxidation step. Clearly,
1c 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 and
one oxidation state of the TTF core at 0.61 V, respectively, by
comparison with the redox data of reported porphyrin deriva-
tives such as R2[18] and R3 as well as TTF reference compound
R1.[14] In the cases of 1a and 1b, the instability of the radicals
at low scan rates does not allow us to observe well-defined
redox 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 1a and 1b is anticipated for si-
multaneous oxidation of the two porphyrin rings to the radical
cation species. The broadness of the second waves suggests
that the first oxidation of the central TTF core to generate the
radical cation overlaps with the second simultaneous oxidation
of two prophyrin radical cations to their dication states. Com-
pared to reference compound R3, the first oxidation potential
of 1a is shifted by ꢀ120 mV. This finding can be attributed to
the stabilizing effect of the extended p conjugation, which
offers the possibility of delocalizing the free spin over the
entire conjugated p system, and, importantly, also to the elec-
ChemPhysChem 0000, 00, 1 – 14
ꢁ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemphyschem.org
&
3
&
ÞÞ
These are not the final page numbers!

S.-X. Liu, S. V. Bhosale, S. Fukuzumi et al.
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 two
reduction 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 1a, which forms a red-
purple solution, exhibits intense electronic absorptions over
the whole visible part of the optical spectrum at all energies
higher than 16000 cmꢀ1 (below 625 nm, Figure 6a). This ab-
sorption pattern does not correspond solely to the sum of the
optical absorptions of the constituents of this molecule. In-
stead of the distinct and narrow Soret band of porphyrin sys-
tems, which typically appears around 24000 cmꢀ1 (400–
450 nm), multiple and extensively broadened absorption
bands show up. This observation is apparently an outcome of
the annulation of p-conjugated molecular units with different
electron donor and acceptor characteristics into the predomi-
nantly planar structure of 1a, which finally contributes to the
occurrence of additional electronic charge-transfer (CT) transi-
tions. As is discussed below, the electronic structure of 1a can
thus be represented as an A–A’–D–A’–A system, which is
a useful description for analysis of the different CT characteris-
tics. The electronic absorption spectrum of the structurally
asymmetric 2a (Figure 6b), now an electronic A–A’–D system,
exhibits an analogous pattern, but the dominant contributions
from 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 6c).
Figure 3. Cyclic voltammograms of 1a (solid line), 1b (dashed line) and 1c
(dotted line) in CH2Cl2 (0.1m Bu4NPF6; Pt working electrode; scan rate
100 mVsꢀ1).
Figure 4. TLCV of 1c (4.3ꢀ10ꢀ5 m) in CH2Cl2 (0.1m Bu4NPF6; Pt working elec-
trode; scan rate 10 mVsꢀ1).
tron-donating effect of the TTF moiety. Additional strong sup-
port for these assignments is given by spectroelectrochemical
data (see below).
In contrast, the first oxidation process of compounds 2a and
2b corresponds to oxidation of the TTF unit to the radical
cation species, by comparison with R and R3 (see Table 1). As
illustrated in Figure 5, differences clearly exist between metal-
free 2a and metallated 2b in the broadness of the subsequent
oxidations. For 2a, the overlapping oxidations of the TTF radi-
cal cation and the porphyrin core to its trication form give rise
to 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 2b, upon metallation, a negative shift in the
oxidation potential centred at the porphyrin core leads to
a one-electron oxidation at 0.48 V. The sequential oxidations of
both TTF and porphyrin radical cations are not separated in
Figure 6. Electronic absorption spectra of 1a (a), 2a (b) and R3 (c) in benzo-
nitrile solution, together with the calculated S0!Sn transitions (energies and
oscillator strengths) at the TD-B3LYP/TZVP level of theory.
2.4. Quantum-Chemical Calculations
Quantum-chemical calculations were carried out to determine
energies, intensities and type of electronic excitations of 1a,
2a and reference compound R3 for comparison. The molecular
structure of quinoxalino[2,3-b]tetraphenylporphyrin R3 was cal-
Figure 5. Cyclic voltammograms of 2a (solid line) and 2b (dashed line) in
CH2Cl2 (0.1m Bu4NPF6; Pt disc working electrode; scan rate 100 mVsꢀ1).
&4
&
www.chemphyschem.org
ꢁ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ChemPhysChem 0000, 00, 1 – 14
ÝÝ
These are not the final page numbers!

Tetrathiafulvalene-Fused Porphyrins
culated in C2 symmetry, and the molecular structures of 1a
and 2a were determined without symmetry constraints. The
calculated geometry of 2a is in good agreement with its X-ray
structure (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 the
well-known soft structural bending within the neutral TTF frag-
ments (ca. 138) and, as expected, the out-of-plane rotations of
the pendant phenyl groups (70–1118). However, calculations of
the MOs were approximated while applying D2h or C2h point
group symmetries to the molecules. Some important frontier
MOs and their calculated energies are shown in Figures 7 and
8. The frontier MOs of 1a basically result from linear combina-
tions of orbitals from the central TTF core with the plus/minus
linear combinations of orbitals from the pendant quinoxaline
and porphyrin units. In 1a, the HOMO (au) electron density is
mainly located on the central TTF unit with clear inclusion of
both 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 close
lying HOMOꢀ1 and HOMOꢀ2 as well as HOMOꢀ3 and
HOMOꢀ4 are essentially both pairs of plus/minus combina-
tions (bg, au) of “left and right” of what would be HOMO and
HOMOꢀ1 of a single porphyrin molecule alone. Analogously,
LUMO and LUMO+1 of a single porphyrin now combine to
LUMO and LUMO+1 as well as LUMO+2 and LUMO+3 for
the symmetric molecule 1a. The LUMO+4 and LUMO+5 fi-
nally represent the quinoxaline LUMOs. The dividing line be-
tween HOMO and HOMOꢀ1/ꢀ2 is opposite to what is expect-
ed from the experimental CV data; however, the calculations
are for isolated molecules with symmetry constraints and, even
more importantly, the energies of their highest occupied MOs
are in a quite narrow energy range anyway. The interpretation
of the MO scheme of 2a 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 fused
quinoxaline fragment. In all of
these cases, the LUMO and
LUMO+1 extend across the qui-
noxaline group(s), lowering their
energies. These results are in ac-
cordance with those of reported
analogues.[19]
The calculated vertical elec-
tronic transitions for 1a, 2a and
R3 are shown by sticks in the
spectra in Figure 6, and their cal-
culated energies and oscillator
strengths are given in Tables 2–
4. For 1a, the DT-DFT calculation
(D2h constraint) predicts S0!S1
and S0!S2 excitations with only
very weak intensities, and their
electronic character corresponds
basically to the Q-band-type
transitions of porphyrin systems.
However, the energetically close
lying S0!S3 transition describes
the expected symmetry-allowed
HOMO (au)!LUMO (bg) promo-
tion (93%) and thus exhibits CT
! !
character (A
D!!A). The
calculated energy and oscillator
strength compare fairly well with
the first absorption band ap-
pearing around 16500 cmꢀ1
(605 nm). The S0!S11 excitation
!
reflects the A’ D!A’ type of
charge-transfer absorption, and
the S0!S20 excitation reveals
contributions of the A!A’–D–
!
A’
A
type of charge-transfer
Figure 7. Frontier MOs of the p-conjugated skeleton of 1a.
transition. The following S0!S29
ChemPhysChem 0000, 00, 1 – 14
ꢁ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemphyschem.org
&
5
&
ÞÞ
These are not the final page numbers!

S.-X. Liu, S. V. Bhosale, S. Fukuzumi et al.
excitation with the highest oscil-
lator strength corresponds to
the Soret-band character of the
porphyrins. Altogether, these
latter excitations lead to the
broad and intense absorption
profile from 18000 cmꢀ1 up-
wards in energy (below 555 nm);
however, a specific assignment
of the calculated transitions
within this broad profile can not
be made at this stage.
For 2a, as expected, the
HOMO!LUMO
promotion
(98%) significantly shows up
with the excitation S0!S1 at
a similar energy as in the case of
1a, and it matches the lowest
energy absorption band quite
well; this transition describes an
! !
A
D charge transfer. The pro-
nounced S0!S5 excitation corre-
!
D
sponds to the expected A’
type of charge transfer. And
lastly, the S0!S11 excitation re-
flects again the corresponding
porphyrin Soret band. Overall, it
is clear that the Soret-type ab-
sorption dominates the spec-
trum, and the different charge-
transfer transitions contribute to
broadening of the absorption
profile towards lower energies.
In the case of R3, the S0!S1 and
S0!S2 excitations bear the Q-
type character of the porphyrin
unit, and the S0!S3 and partly
the S0!S5 excitations have a por-
phyrin-to-quinoxaline
charge-
transfer character. Finally, the
transitions 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 porphyrin
core gives rise to broadening
and red shifts of the spectrum
due to the extended p conjuga-
tion. Again, the calculated transi-
tions show up at slightly higher
energies than the observed
ones. Furthermore, one can also
conclude that for all three com-
pounds the theoretical HOMO–
LUMO gaps (HLG) compare fa-
Figure 8. Frontier MOs of the p-conjugated skeletons of 2a (a) and R3 (b).
Table 2. Energies, oscillator strengths and dominant contributions of the respective molecular orbitals for
S0!Sn of 1a.
State
Excitation
energy [cmꢀ1
Oscillator
strength
Dominant contributions [%]
]
S1
S2
S3
S11
S20
S29
17122
17170
17274
20748
22233
24991
0.0002
0.0000
0.6276
1.3026
0.2617
3.8195
Hꢀ2!L+1 (43), Hꢀ1!L (23), Hꢀ1!L+2 (13)
Hꢀ2!L+3 (34), Hꢀ2!L+2 (16), Hꢀ3!L+1 (14)
H! L(93)
H!L+4 (88)
Hꢀ3!L+4 (31), Hꢀ4!L+5 (23), Hꢀ4!L+1 (18)
Hꢀ4!L+3 (22), Hꢀ3!L+2 (17)
&6
&
www.chemphyschem.org
ꢁ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ChemPhysChem 0000, 00, 1 – 14
ÝÝ
These are not the final page numbers!

Tetrathiafulvalene-Fused Porphyrins
cyclic voltammetry, in that the
first oxidation occurs at the TTF
unit and the second at the por-
phyrin core.
Table 3. Energies, oscillator strengths and dominant contributions of the respective molecular orbitals for
S0!Sn of 2a.
State
Excitation
energy [cmꢀ1
Oscillator
strength
Dominant contributions [%]
]
Figure 10 shows the variation
of the absorbance spectra of 1c
as the voltage is stepped from
ꢀ0.2 to +0.5 V. As the potential
shifts positively, the intensities in
the higher energy range (with
Soret-band character) significant-
ly decrease and a new broad ab-
sorption band grows in the 600–
S1
S2
S4
S5
S6
S7
S11
16513
17166
18132
20307
21942
22340
25279
0.1524
0.0000
0.0023
0.3757
0.0563
0.1600
2.0773
H!L (98)
Hꢀ2!L (48), Hꢀ1!L+1 (47)
Hꢀ1!L (63), Hꢀ2!L+1 (35)
H!L+2 (96)
Hꢀ1!L+2 (83), Hꢀ2!L+1 (11)
Hꢀ2!L+2 (58), Hꢀ2!L (23), Hꢀ1!L+1 (16)
Hꢀ2!L+1 (43), Hꢀ1!L (23), Hꢀ1!L+2 (13)
Table 4. Energies, oscillator strengths and dominant contributions of the respective molecular orbitals for
S0!Sn of R3.
800 nm
(16670–12500 cmꢀ1)
region. These spectral changes
suggest that the electron-trans-
fer site is porphyrin ring centred
and leads to the formation of
porphyrin cation radicals during
the first oxidation process. The
same holds for the thin-layer
UV/Vis/NIR spectral change of
1b (Supporting Information Fig-
State
Excitation
Oscillator
strength
Dominant contributions [%]
energy [cmꢀ1
]
S1
S2
S3
S5
S7
S8
17230
18169
22541
22897
25817
25818
0.0000
0.0131
0.0739
0.2196
1.7913
0.5522
H!L+1 (50), Hꢀ1!L (49)
H!L (64), Hꢀ1!L+1 (35)
H!L+2 (84), Hꢀ1!L+1 (10)
Hꢀ1!L+2 (54), Hꢀ1!L (23), H!L+1 (17)
Hꢀ1!L+1 (48), H!L (27), H!L+2 (14)
Hꢀ1!L+2 (37), Hꢀ3!L+1 (19), H!L+1 (18)
vourably with the experimental CV data and similarly well with
the optical HLG determined from the onset of the respective
absorption profiles; for example, these values are in the range
of 2.0–2.4 eV for 1a, and 2.0–2.3 eV for 2a.
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 site
of electron transfer, systematic changes in the optical spectra
upon oxidation of the neutral species were examined by spec-
troelectrochemistry, as shown in Figures 9 and 10 (see also the
Supporting Information, Figures S3–S5).
As illustrated in Figure 9a, chemical oxidation of 2a with
less than 1 equiv of [Fe(bpy)3](PF6)3 (bpy=2,2’-bipyridine) leads
to a gradual decrease of the absorption band around 600 nm
(16670 cmꢀ1) and concomitant emergence of a new broad ab-
sorption band peaking at 830 nm (12050 cmꢀ1), characteristic
for formation of the TTF radical cation species. However, the
Soret band is intensified, sharpened and slightly moves to
higher 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, beyond
1.4 equiv of [Fe(bpy)3](PF6)3 (Figure 9b), the TTF radical absorp-
tion band decreases quickly, while new broad absorption
bands grow in the 600–1000 nm (16670–10000 cmꢀ1) region
along with a rapid decrease in the intensity of the Soret band,
a spectral feature that is conceivably attributable to formation
of 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 2a and 2b ob-
tained in situ by successively applying oxidation potentials
(Supporting Information Figures S3 and S4). All of these results
are in good agreement with the previous discussion from
Figure 9. Variation of the UV/Vis/NIR absorption spectra of 2a (7.16ꢀ10ꢀ6 m)
in CH2Cl2 upon successive addition of aliquots of [Fe(bpy)3](PF6)3.
ChemPhysChem 0000, 00, 1 – 14
ꢁ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemphyschem.org
&
7
&
ÞÞ
These are not the final page numbers!

S.-X. Liu, S. V. Bhosale, S. Fukuzumi et al.
The spectral features in the visible region, which were seen
immediately upon excitation of triads 1a–c in benzonitrile
(Supporting Information Figures S6–S8), reveal transient ab-
sorption bands of the singlet-excited state of porphyrin, with
rate constants of 1.18ꢀ108, 1.80ꢀ108 and 2.23ꢀ109 sꢀ1, respec-
tively. Therefore, one can state clearly that electron transfer
from TTF to the excited state of porphyrin is not detected in
these triads. This observation is in a good agreement with the
electrochemical studies, which suggest that the electron trans-
fer is thermodynamically not favoured.
Upon excitation of dyad 2a in benzonitrile (Figure 12), the
femtosecond spectrum recorded at 7 ps showed formation of
Figure 10. Variation of UV/Vis/NIR spectroelectrochemistry of 1c
(4.6ꢀ10ꢀ4 m) in CH2Cl2 (with 0.1m Bu4NPF6) upon variation of the electric po-
tential.
ure S5) upon the first oxidation. These observations are in
qualitative agreement with the aforementioned interpretation
of the electrochemical data.
2.6. Femtosecond and Nanosecond Absorption Spectral
Studies
Femtosecond transient absorption spectroscopy was used to
obtain insight into the excited-state events of triads 1, dyads
2, and reference compound R3. The compounds were probed
with 400/430 nm excitation to selectively excite the porphyrin
fluorophores. The femtosecond transient absorption spectra of
R3 in benzonitrile (Figure 11) reveal instantaneous formation of
the singlet porphyrin features. Here, the transient absorption
spectra exhibit the absorption bands in the visible region with
a maximum at 475 nm, which decayed slowly (1.00ꢀ108 sꢀ1) to
populate the corresponding triplet manifold.
Figure 12. Differential absorption spectra obtained upon femtosecond flash
photolysis (400 nm) of 2a in benzonitrile at the indicated time intervals.
Inset: Decay profile of the singlet porphyrin at 480 nm.
the singlet excited state of porphyrin. A study on the kinetics
of 2a in the initial 200 ps suggests that the singlet excited
s
state of porphyrin decays much faster (1.0ꢀ1010 ꢀ1) than that
of 1a. The transient spectra of 2b (Supporting Information Fig-
ure S9) exhibit the same features as 1b with a rate constant of
1ZnP* (7.0ꢀ1010 sꢀ1). These results indicate electron transfer
from TTF to the singlet porphyrin, considering that energy
transfer from the singlet-excited porphyrin to TTF is not feasi-
ble. This observation is consistent with the electrochemical
studies, which show that electron transfer is thermodynamical-
ly favoured for 2a and 2b in polar benzonitrile. The difference
in the rates of charge separation from TTF to the singlet excit-
ed porphyrin of dyad 2a (kCS =9.80ꢀ109 sꢀ1) and 2b (kCS =
6.98ꢀ1010 ꢀ1) can be explained by the difference in the free-
s
energy changes of charge-separation processes (ꢀDGCS) of 2a
(0.17 eV) and 2b (0.86 eV).[21]
Upon exciting reference R3 with a 430 nm laser, the comple-
mentary nanosecond transient absorption spectra of R3 in
benzonitrile 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 11. Differential absorption spectra obtained upon femtosecond flash
photolysis (430 nm) of reference R3 in benzonitrile at the indicated time in-
tervals. Inset: Decay profile of the singlet porphyrin at 475 nm.
&8
&
www.chemphyschem.org
ꢁ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ChemPhysChem 0000, 00, 1 – 14
ÝÝ
These are not the final page numbers!

Tetrathiafulvalene-Fused Porphyrins
Figure 15. UV/Vis spectral changes observed upon increasing addition of
C60py to dyad 2b in o-dichlorobenzene.
Figure 13. Nanosecond transient absorption spectra of reference R3 in ben-
zonitrile at the indicated time intervals. Inset: Decay profile of the triplet
porphyrin at 470 nm.
Formation of the supramolecular triad 2b:C60py was also
confirmed by steady-state emission studies. As shown in
Figure 16, the fluorescence spectrum of dyad 2b in o-dichloro-
benzene reveals an emission band at 640 nm corresponding to
the singlet (ZnP–TTF)*. An increasing concentration of C60py in
the solution results in a decrease in emission intensity. This
suggests the occurrence of a photochemical processes; an
electron transfer from the singlet state of 2b to C60 could be
envisioned. The ZnII···py binding constant was evaluated by
constructing a Benesi–Hildebrand plot, as shown in Figure 16
(inset), which yields a binding constant K of 7.20ꢀ104 mꢀ1,
nearly two orders of magnitude higher than that reported for
C60py binding to ZnP.[23]
a rate constant of 6.4ꢀ103 sꢀ1. Similar spectra were observed
for 1a and 2a in benzonitrile (Supporting Information Figur-
es S10 and S11). These observations suggest the absence of
electron transfer via the triplet state of porphyrin, which is
thermodynamically not favoured. The short-lived triplet state
of triad 1c was not observed in the transient spectra (Support-
ing Information Figure S12).
2.7. Complex Formation and Photochemical Studies of
Supramolecular Triad 2b:C60py
Dyad 2b was utilized to build, by an axial-coordination ap-
proach, a novel supramolecular architecture with fullerene
functionalized 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 2b in o-
dichlorobenzene, a non-coordinating solvent, are shown in
Figure 15. During the titration, the ZnP-type absorption band
of 2b located at 422 nm diminished in intensity with red shifts
of the absorption band to 432 nm, characteristic of axial coor-
dination of the ZnII ion.
To probe the redox properties of the 2b:C60py, cyclic voltam-
metric studies were performed in o-dichlorobenzene contain-
ing 0.10m Bu4N(PF6) as supporting electrolyte (Supporting In-
formation Figure S13). The first reduction potential of the
Figure 16. Fluorescence spectral changes observed upon increasing addition
of C60py to 2b in o-dichlorobenzene; lex =420 nm. Inset: Benesi–Hildebrand
plot.
Figure 14. Molecular structure of supramolecular triad 2b:C60py.
ChemPhysChem 0000, 00, 1 – 14
ꢁ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemphyschem.org
&
9
&
ÞÞ
These are not the final page numbers!

S.-X. Liu, S. V. Bhosale, S. Fukuzumi et al.
C60py entity was located at ꢀ0.67 V versus SCE, while the oxi-
dation potentials of 2b were located at 0.64, 0.86 and 1.10 V
versus SCE. The energetics for a photoinduced electron trans-
extended p-conjugated molecules have been synthesized. Sim-
ilarly, asymmetric porphyrin–tetrathiafulvalene dyads have
been prepared as well. These electrochemically amphoteric
compounds have been investigated by cyclic voltammetry,
thin-layer cyclic voltammetry and spectroelectrochemical
methods in order to elucidate the sites of the redox processes.
The data suggest that in the triads initial oxidation occurs at
the peripheral porphyrin sites, and is directly followed within
a narrow potential range by formation of the TTF radicals. This
order is reversed for the dyad systems and other reported TTF-
annulated porphyrins. Ab initio calculations demonstrate that
the TTF-type and porphyrin-type HOMOs show up at quite
similar energies. Photophysical experiments reveal electronic
excitations 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 into
rigid and planar p-conjugated molecular systems. The poten-
tial to build up further supramolecular assemblies was demon-
strated by using a fullerene acceptor unit.
1
fer from ZnP*–TTF to C60 were evaluated by using the redox
and spectral data discussed above. The driving forces for
charge separation (DGCS) and charge recombination (DGCR) are
given via the excited singlet state ZnP*–TTF and were found to
be 1.31 and 0.77 eV, respectively. These results suggest that
the 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 femtosecond
timescale were performed. The 2b:C60py supramolecular triad
was probed with 430 nm laser excitation to selectively excite
the porphyrin fluorophore in toluene solution (Figure 17). The
Experimental Section
General: Air- and/or water-sensitive reactions were conducted
under argon in dry, freshly distilled solvents. Elemental analyses
were performed on an EA 1110 Elemental Analyzer CHN Carlo Erba
Instruments. FTIR spectra were recorded on a PerkinElmer One
FTIR spectrometer. 1H and 13C NMR spectra were measured on
a Bruker spectrometer with tetramethylsilane as internal standard.
Mass spectra were recorded on an FTMS 4.7T BioAPEX II with the
MALDI ionization method.
Materials: Unless otherwise stated, all reagents were purchased
from 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 prepared
according to literature procedures.
Figure 17. Differential absorption spectra obtained upon femtosecond flash
photolysis (430 nm) of 2b:C60py at the indicated time intervals in toluene.
Inset: Rise–decay profile of the C60 radical anion monitored at 1000 nm to
evaluate the charge-separation and charge-recombination kinetics.
transient absorption spectrum measured 5 ps after femtosec-
ond laser excitation exhibits the transient absorption of the
ZnP–TTF singlet excited state (1ZnP*–TTF). With time, the
1ZnP*–TTF absorption peak at 540 nm diminishes in intensity
while a concomitant increase in absorbance at 1000 nm, due
to the C60 radical anion (C60·ꢀ), and similarly at 620–700 nm
due 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 electron
Cyclic Voltammetry: Cyclic voltammetry (CV) was performed for
1a–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 carried
out under dry and oxygen-free atmosphere (H2O<1 ppm, O2 <
1 ppm) in CH2Cl2 (0.8 mm) with 0.1m Bu4NPF6 as supporting elec-
trolyte at 100 mVsꢀ1. The voltammograms were recorded on an
EGG PAR 273A potentiostat with positive feedback compensation.
Based on repetitive measurements, absolute errors on potentials
were estimated to be around ꢁ5 mV. The number of electrons was
determined by recording the voltammograms under thin-layer
conditions (TLCV), and dichloronaphthoquinone was used as an in-
ternal reference for the number of exchanged electrons. The exper-
imental voltammograms were deconvoluted with the Condecon
software.
1
transfer from ZnP*–TTF to C60 was analyzed by exponential fit-
·ꢀ
ting of the rise profile of the radical C60 (at 1000 nm; kCS =
2.84ꢀ1012 sꢀ1 and kCR =2.60ꢀ109 sꢀ1). Based on the kCR value,
the lifetime of the (ZnP–TTF)·+···(C60py)·ꢀ charge-separated
state was determined to be 385 ps.
Cyclic voltammetry (CV) was carried out for 2a, 2b and R1 in
a 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 dry
and an oxygen-free atmosphere in CH2Cl2 with 0.1m Bu4NPF6 as
3. Conclusions
Novel symmetric porphyrin–tetrathiafulvalene–porphyrin triads
annulated through quinoxaline linkers into planar and largely
&10
&
www.chemphyschem.org
ꢁ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ChemPhysChem 0000, 00, 1 – 14
ÝÝ
These are not the final page numbers!

Tetrathiafulvalene-Fused Porphyrins
supporting electrolyte. The voltammograms were recorded on
a PGSTAT 101 potentiostat.
matography (SiO2, petroleum ether (b.p. 40–608C)/CH2Cl2 3/2) to
afford a crude product. Subsequent reprecipitation from a solution
in CH2Cl2 with methanol gave 1a (19 mg, 74%) as a brownish red
Cyclic voltammograms of supramolecular triad 2b:C60py were re-
corded on a BAS CV-50W Voltammetric Analyzer. A platinum disc
electrode was used as working electrode, while a platinum wire
served as a counter-electrode. An SCE electrode was used as refer-
ence electrode. All measurements were carried out in o-dichloro-
benzene containing Bu4NPF6 (0.1m) as supporting electrolyte. The
1
powder. H NMR (300 MHz, CDCl3): d=8.90 (d, J=5.1 Hz, 4H), 8.78
(d, J=5.1 Hz, 4H), 8.75 (s, 4H), 8.06 (d, J=1.7 Hz, 8H), 7.92 (d, J=
1.7 Hz, 8H), 7.78–7.77 (dd, J=1.7 Hz, J=1.9 Hz, 4H), 7.66–7.65 (dd,
J=1.7 Hz, 4H), 7.04 (d, J=8.6 Hz, 8H), 6.73 (d, J=8.6 Hz, 8H), 2.57
(t, J=7.5 Hz, 8H), 1.53, 1.50 (2 s, 152H, tert-butyl protons and
CH2CH2 (CH2)2CH3 are overlapped), 1.35 (m, 16H), 0.88 (t, J=6.8 Hz,
12H), ꢀ2.52 ppm (brs, 4H); FTIR (KBr pellet): n˜ =3437, 2960, 2923,
2856, 1626, 1593, 1504, 1475, 1384, 1362, 1208, 1167, 1154, 1109,
922, 800, 720 cmꢀ1; MALDI-TOF MS: m/z 3125.91 [M]+; calcd for
C210H244N12O4S4 3125.81; elemental analysis calcd (%) for
scan rate was 50 mVsꢀ1
.
Spectroelectrochemistry: The setup used for the UV/Vis spectro-
electrochemical experiments has been described previously.[24] The
evolution of UV/Vis/NIR spectra after successive additions of [Fe-
(bpy)3](PF6)3 aliquots was followed on a PerkinElmer Lambda 10
spectrophotometer in a 1 cm quartz cell with a solution of 2a
(7.16ꢀ10ꢀ6 m) in CH2Cl2 and a solution of [Fe(bpy)3](PF6)3 (1.43ꢀ
10ꢀ3 m) in CH3CN.
C
210H244N12O4S4·2CH3OH: C 79.76, H 7.96, N 5.26; found: C 80.16, H
8.30, N 4.78.
Synthesis of Triad 1b:
A solution of Zn(OAc)2·2H2O (9 mg,
0.041 mmol) in CH3OH (5 mL) was added to a solution of com-
pound 1a (19 mg, 6 mmol) in CH2Cl2 (15 mL). The resulting mixture
was heated to 508C and stirred for 3.5 h. After cooling to room
temperature, the solvent was evaporated. The residue was purified
by column chromatography (SiO2, petroleum ether (b.p. 40–608C)/
CH2Cl2 3/2) to afford a crude product. Subsequent reprecipitation
from a solution in CH2Cl2 with methanol gave 1b (13.7 mg, 70%)
as a brownish red powder. 1H NMR (300 MHz, CDCl3): d=8.87 (d,
J=4.7 Hz, 4H), 8.82 (s, 4H), 8.68 (d, J=4.7 Hz, 4H), 8.02 (d, J=
1.7 Hz, 8H), 7.86 (d, J=1.9 Hz, 8H), 7.75–7.74 (dd, J=1.7 Hz, J=
1.9 Hz, 4H), 7.62–7.60 (dd, J=1.7 Hz, 4H), 7.05 (d, J=8.7 Hz, 8H),
6.75 (d, J=8.7 Hz, 8H), 2.58 (t, J=7.5 Hz, 8H), 1.49, 1.53 (2s, 152H,
tert-butyl protons and CH2CH2(CH2)2CH3 are overlapped), 1.36 (m,
16H), 0.91 ppm (t, J=7.2 Hz, 12H); FTIR (KBr pellet): n˜ =3437,
2958, 2923, 2854, 1625, 1592, 1504, 1464, 1384, 1361, 1218, 1170,
1112, 939, 812, 798, 711 cmꢀ1; MALDI-TOF MS: m/z: 3250.76
[M+H]+; calcd for C210H241N12O4S4Zn2: 3250.65; elemental analysis
calcd (%) for C210H240N12O4S4Zn2: C 77.48, H 7.43, N 5.16; found: C
77.15, H 7.83, N 4.63.
Photophysical Measurements: Steady-state absorption spectra
were 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 Shimadzu
spectrofluorophotometer (RF-5300PC). Fluorescence spectra of the
2b:C60py supramolecular triad were monitored by using a Varian
Eclipse spectrometer. A right-angle detection method was used.
Femtosecond transient absorption spectroscopic experiments were
conducted by using an Integra-C ultrafast source (Quantronix
Corp.), 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 and
probe pulses were derived from the fundamental output of Inte-
gra-C (780 nm, 2 mJpulseꢀ1 and fwhm=130 fs) at a repetition rate
of 1 kHz. 75% of the fundamental output of the laser was intro-
duced into TOPAS, which has optical frequency mixers resulting in
tuneable range from 285 to 1660 nm, while the rest of the output
was used for white light generation. Typically, 2500 excitation
pulses were averaged for 5 s to obtain the transient spectrum at
a set delay time. Kinetic traces at appropriate wavelengths were as-
sembled from the time-resolved spectral data. All measurements
were conducted at 298 K. The transient spectra were recorded by
using fresh solutions in each laser excitation.
Synthesis of Triad 1c: A suspension of 5b (19 mg, 0.016 mmol)
and 3 (8.3 mg, 0.008 mmol) in glacial acetic acid (4 mL) was heated
to reflux for 3 h under Ar. After cooling to room temperature, the
solvent was evaporated. The residue was purified by column chro-
matography (SiO2, petroleum ether (b.p. 40–608C)/CH2Cl2 1/1) to
afford a crude product. Subsequent reprecipitation from a solution
in CH2Cl2 with methanol gave 1c (20 mg, 77%) as a brownish red
powder. FTIR (KBr pellet): n˜ =3435, 2960, 2924, 2856, 1593, 1504,
1460, 1393, 1362, 1217, 1173, 1009, 939, 815, 799 cmꢀ1; MALDI-TOF
MS: 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.
For nanosecond transient absorption measurements deaerated sol-
utions of the compounds were excited by
a Panther OPO
equipped with a Nd:YAG laser (Continuum, SLII-10, 4–6 ns fwhm)
with a power of 10–15 mJpulseꢀ1. The photochemical reactions
were monitored by continuous exposure to an Xe lamp (150 W) as
probe light and a photomultiplier tube (Hamamatsu 2949) as de-
tector. Solutions were deoxygenated by argon purging for 15 min
prior to the measurements.
Synthesis of Dyad 2a: A mixture of porphyrin dione 6 (100 mg,
1.55ꢀ10ꢀ4 mol) and 4 (0.0735 mg, 1.70ꢀ10ꢀ4 mol) in CHCl3/pyri-
dine (10/1 v/v) was heated at 658C 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 by
flash column chromatography on silica with CH2Cl2/CH3OH (100/1)
as eluent to afford 2a (154.9 mg, 96%) as a dark greenish brown
crystalline solid. 1H NMR (400 MHz, CDCl3): d=8.92 (d, J=8.2 Hz,
4H), 8.71 (s, 2H), 8.23–8.21 (d, J=8.0 Hz, 4H), 8.13–8.12 (d, J=
8.0 Hz, 4H), 7.79–7.75 (m, 10H), 7.63 (s, 2H), 7.62 (s, 2H), 2.86–2.82
(t, J=6.4 Hz, 4H), 1.76–1.66 (m, 4H), 1.07–1.03 (t, J=7.2 Hz, 6H),
ꢀ2.75 ppm (s, 2H); 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,
Ab Initio Calculations: DFT and time-dependent DFT calculations of
porphyrin–quinoxaline, TTF–porphyrin and TTF–diporphyrin were
performed 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 was
calculated in C2 symmetry and the other two without symmetry re-
strictions. The electronic excitation spectra were calculated with
the SVP basis set.
Synthesis of Triad 1a: A suspension of 5a (19 mg, 0.017 mmol)
and 3 (8.3 mg, 0.008 mmol) in glacial acetic acid (6 mL) was heated
to reflux for 5 h under Ar. After cooling to room temperature, the
solvent was evaporated. The residue was purified by column chro-
ChemPhysChem 0000, 00, 1 – 14
ꢁ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemphyschem.org
&
11
&
ÞÞ
These are not the final page numbers!

S.-X. Liu, S. V. Bhosale, S. Fukuzumi et al.
2664; c) T. S. Balaban, Acc. Chem. Res. 2005, 38, 612; d) N. Aratani, D.
Kim, A. Osuka, Acc. Chem. Res. 2009, 42, 1922.
[3] a) D. Kim, A. Osuka, Acc. Chem. Res. 2004, 37, 735; b) D. Holten, D. F.
Bocian, J. S. Lindsey, Acc. Chem. Res. 2002, 35, 57.
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 cmꢀ1; elemental analysis calcd
(%) for C60H44N6S6: C 69.20, H 4.26, N 8.07; found: C 69.18, H 4.26,
N 8.09.
[4] a) M. P. O’Neil, M. P. Niemczy, W. A. Svec, D. Gosztola, G. L. Gaines, M. R.
Wasielewski, Science 1992, 257, 63; b) X. Xiao, W. Xu, D. Zhang, H. Xu, H.
Lu, D. Zhu, J. Mater. Chem. 2005, 15, 2557; c) Y. Liu, C. Wang, M. Li, S. Lv,
G. Lai, Y. Shen, J. Porphyrins Phthalocyanines 2007, 11, 729; d) C. Liu, W.
Guan, P. Song, L.-K. Yan, Z.-M. Su, Inorg. Chem. 2009, 48, 6548.
[5] a) H. Imahori, T. Umeyama, S. Ito, Acc. Chem. Res. 2009, 42, 1809; b) A.
Yella, H.-W. Lee, H. N. Tsao, C. Yi, A. K. Chandiran, M. K. Nazeeruddin,
E. W.-G. Diau, C.-Y. Yeh, S. M. Zakeeruddin, M. Grꢃtzel, Science 2011, 334,
629; c) Y. Liu, H. Lin, J. T. Dy, K. Tamaki, J. Nakazaki, D. Nakayama, S.
Uchida, T. Kubo, H. Segawa, Chem. Commun. 2011, 47, 4010.
[6] a) P. L. Anelli, M. Asakawa, P. R. Ashton, R. A. Bissell, G. Clavier, R. Gçrski,
A. Kaifer, S. J. Langford, G. Mattersteig, D. Philp, N. Spencer, J. F. Stod-
dart, M. Tolley, D. J. Williams, Chem. Eur. J. 1997, 3, 1113; b) S. Saha, A. H.
Flood, J. F. Stoddart, S. Impellizzeri, S. Silvi, M. Venturi, A. Credi, J. Am.
Chem. Soc. 2007, 129, 12159.
[7] a) A. Osuka, H. Yamada, K. Maruyama, N. Mataga, T. Asahi, M. Ohkouchi,
T. Okada, I. Yamazaki, Y. Nishimura, J. Am. Chem. Soc. 1993, 115, 9439;
b) D. Wrꢄbel, A. Graja, Coord. Chem. Rev. 2011, 255, 2555; c) M. S. Voll-
mer, F. Wꢅrthner, F. Effenberger, P. Emele, D. U. Meyer, T. Stꢅmpfig, H.
Port, H. C. Wolf, Chem. Eur. J. 1998, 4, 260; d) F. D’Souza, O. Ito, Chem.
Commun. 2009, 4913; e) S.-H. Lee, A. G. Larsen, K. Ohkubo, Z.-L. Cai,
J. R. Reimers, S. Fukuzumi, M. J. Crossley, Chem. Sci. 2012, 3, 257; f) S. V.
Bhosale, S. Hackbarth, S. J. Langford, S. V. Bhosale, Chem. Asian J. 2012,
7, 176; g) G. de Miguel, M. Wielopolski, D. I. Schuster, M. A. Fazio, O. P.
Lee, C. K. Haley, A. L. Ortiz, L. Echegoyen, T. Clark, D. M. Guldi, J. Am.
Chem. Soc. 2011, 133, 13036.
[8] a) K. A. Jolliffe, T. D. M. Bell, K. P. Ghiggino, S. J. Langford, M. N. Paddon-
Row, Angew. Chem. 1998, 110, 959; Angew. Chem. Int. Ed. 1998, 37, 915;
b) M. Jaggi, B. Schmid, S.-X. Liu, S. V. Bhosale, S. Rivadehi, S. J. Langford,
S. Decurtins, Tetrahedron 2011, 67, 7231; c) K. A. Jolliffe, S. J. Langford,
A. M. Oliver, M. J. Shephard, M. N. Paddon-Row, Chem. Eur. J. 1999, 5,
2518; d) T. D. M. Bell, K. A. Jolliffe, K. P. Ghiggino, A. M. Oliver, M. J. Shep-
hard, S. J. Langford, M. N. Paddon-Row, J. Am. Chem. Soc. 2000, 122,
10661; e) K. A. Jolliffe, S. J. Langford, M. G. Ranasinghe, M. J. Shephard,
M. N. Paddon-Row, J. Org. Chem. 1999, 64, 1238.
[9] a) D. V. Konarev, R. N. Lyubovskaya, N. V. Drichko, E. I. Yudanova, Y. M.
Shul’ga, A. L. Litvinov, V. N. Semkin, B. P. Tarasov, J. Mater. Chem. 2000,
10, 803; b) P. A. Liddell, G. Kodis, L. De La Garza, J. L. Bahr, A. L. Moore,
T. A. Moore, D. Gust, Helv. Chim. Acta 2001, 84, 2765; c) G. Kodis, P. A.
Liddell, L. de La Garza, A. L. Moore, T. A. Moore, D. Gust, J. Mater. Chem.
2002, 12, 2100; d) S. Saha, L. E. Johansson, A. H. Flood, H.-R. Tseng, J. I.
Zink, J. F. Stoddart, Small 2005, 1, 87; e) S. Saha, E. Johansson, A. H.
Flood, H.-R. Tseng, J. I. Zink, J. F. Stoddart, Chem. Eur. J. 2005, 11, 6846;
f) K. Ogawa, Y. Nagatsuka, J. Porphyrins Phthalocyanines 2009, 13, 114.
[10] a) K. A. Nielsen, E. Levillain, V. M. Lynch, J. L. Sessler, J. O. Jeppesen,
Chem. Eur. J. 2009, 15, 506; b) H. Li, J. O. Jeppesen, E. Levillain, J.
Becher, Chem. Commun. 2003, 846; c) J. Becher, T. Brimert, J. O. Jeppe-
sen, J. Z. Pedersen, R. Zubarev, T. Bjørnholm, N. Reitzel, T. R. Jensen, K.
Kjaer, E. Levillain, Angew. Chem. 2001, 113, 2565; Angew. Chem. Int. Ed.
2001, 40, 2497.
Synthesis of Dyad 2b: A solution of Zn(OAc)2·2H2O (30 mg, excess)
in MeOH (1 mL) was added to a solution of 2a (25 mg, 2.15ꢀ
10ꢀ5 mol) in CHCl3 (5 mL). The resulting solution was heated at
658C 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 2b (22 mg, 93%) as a purple solid. 1H NMR
(300 MHz, CDCl3): d=8.64 (d, J=8.2 Hz, 4H), 7.99 (s, 2H), 7.98–7.97
(d, J=8.0 Hz, 4H), 7.88–7.86 (d, J=8.0 Hz, 4H), 7.77–7.76 (m, 10H),
7.70 (s, 2H), 7.63 (s, 2H), 2.87–2.85 (t, J=6.4 Hz, 4H), 1.74–1.69 (m,
4H), 1.07–1.03 ppm (t, J=7.2 Hz, 6H); 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, 127.67
126.89, 121.76, 121.31, 117.43, 38.37, 23.36, 13.20 ppm; FTIR (KBr
pellet): n˜ =3389, 3318, 2965, 2969, 1716, 1669, 1509, 1478, 1432,
1384, 1287, 1169, 1174, 1072, 1002, 917, 908, 793, 865 cmꢀ1; 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 2a: C60H44N6S6, M=
1040.20,
107.918(4)8, monoclinic P21/n, Z=4, V=4965.5(13) ꢂ3, 1calcd
1.393 gcmꢀ3
000 =2168, l=0.71073 ꢂ, T=123(2) K, m=
a=15.833(2),
b=19.591(3),
c=16.824(2) ꢂ,
b=
=
,
F
0.232 mmꢀ1, Bruker X8 Apex II CCD diffractometer, f scan, 28599
data collected, corrected for Lorenz and polarization effects, 8733
unique (Rint =0.0569) and 8733 observed [I>2s(I)], 694 refined pa-
rameters, R=0.0985, Rw =0.2265, w=[s2(F)]ꢀ1. CCDC 869800 (2a)
contains the supplementary crystallographic data for this paper.
These data can be obtained free of charge from The Cambridge
Crystallographic 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 Fellowship
award (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.
[11] Z. Wan, C. Jia, J. Zhang, X. Yao, Y. Shi, Dyes Pigm. 2012, 93, 1456.
[12] a) S.-X. Liu, S. Dolder, E. B. Rusanov, H. Stoeckli-Evans, S. Decurtins, C. R.
Chim. 2003, 6, 657; b) S.-X. Liu, C. Ambrus, S. Dolder, A. Neels, S. Decur-
tins, Inorg. Chem. 2006, 45, 9622; c) S. Delahaye, C. Loosli, S.-X. Liu, S.
Decurtins, G. Labat, A. Neels, A. Loosli, T. R. Ward, A. Hauser, Adv. Funct.
Mater. 2006, 16, 286; d) J.-C. Wu, S.-X. Liu, T. D. Keene, A. Neels, V. Mer-
eacre, A. K. Powell, S. Decurtins, Inorg. Chem. 2008, 47, 3452.
Keywords: density functional calculations · donor–acceptor
systems · photophysics · porphyrinoids · redox chemistry
[13] a) K. Sendt, L. A. Johnston, W. A. Hough, M. J. Crossley, N. S. Hush, J. R.
Reimers, J. Am. Chem. Soc. 2002, 124, 9299; b) M. J. Crossley, P. J. Sintic,
J. A. Hutchison, K. P. Ghiggino, Org. Biomol. Chem. 2005, 3, 852.
[14] H.-P. Jia, J. Ding, Y.-F. Ran, S.-X. Liu, C. Blum, I. Petkova, A. Hauser, S. De-
curtins, Chem. Asian J. 2011, 6, 3312.
[15] a) C. Jia, S.-X. Liu, C. Tanner, C. Leiggener, A. Neels, L. Sanguinet, E. Levil-
lain, S. Leutwyler, A. Hauser, S. Decurtins, Chem. Eur. J. 2007, 13, 3804.
[16] a) N. Banerji, S. V. Bhosale, I. Petkova, S. J. Langford, E. Vauthey, Phys.
Chem. Chem. Phys. 2011, 13, 1019; b) M. J. Crossley, C. S. Sheehan, T.
Khoury, J. R. Reimers, P. J. Sintic, New J. Chem. 2008, 32, 340; c) V. Pro-
[1] a) S. Fukuzumi, Phys. Chem. Chem. Phys. 2008, 10, 2283; b) V. Balzani, A.
Credi, M. Venturi, ChemSusChem 2008, 1, 26; c) D. Gust, T. A. Moore,
A. L. Moore, Acc. Chem. Res. 2001, 34, 40; d) M. R. Wasielewski, Chem.
Rev. 1992, 92, 435; e) M. E. El-Khouly, D. K. Ju, K.-Y. Kay, F. D’Souza, S. Fu-
kuzumi, Chem. Eur. J. 2010, 16, 6193; f) A. Harriman, F. Odobel, J.-P.
Sauvage, J. Am. Chem. Soc. 1995, 117, 9461.
[2] a) J. Yu, S. Mathew, B. S. Flavel, M. R. Johnston, J. G. Shapter, J. Am.
Chem. Soc. 2008, 130, 8788; b) I. V. Sazanovich, C. Kirmaier, E. Hindin, L.
Yu, D. F. Docian, J. S. Lindsey, D. Holten, J. Am. Chem. Soc. 2004, 126,
&12
&
www.chemphyschem.org
ꢁ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ChemPhysChem 0000, 00, 1 – 14
ÝÝ
These are not the final page numbers!

Tetrathiafulvalene-Fused Porphyrins
marak, P. L. Burn, J. Chem. Soc. Perkin Trans. 1 2001, 14; d) M. J. Crossley,
P. L. Burn, S. J. Langford, J. K. Prashar, J. Chem. Soc. Chem. Commun.
1995, 1921; e) P. T. Gulyas, S. J. Langford, N. R. Lokan, M. G. Ranasinghe,
M. N. Paddon-Row, J. Org. Chem. 1997, 62, 3038.
[22] a) M. Ohta, M. Masaki, Bull. Chem. Soc. Jpn. 1960, 33, 1150; b) F. T. Tat, Z.
Zhou, S. MacMahon, F. Song, A. L. Rheingold, L. Echegoyen, D. I. Schus-
ter, S. R. Wilson, J. Org. Chem. 2004, 69, 4602; c) A. Kahnt, L.-P. Heiniger,
S.-X. Liu, X. Tu, Z. Zheng, A. Hauser, S. Decurtins, D. M. Guldi, ChemPhys-
Chem 2010, 11, 651.
[23] F. D’Souza, G. R. Deviprasad, M. E. Zandler, V. T. Hoang, A. Klykov, M. Van
Stipdonk, A. Perera, M. E. El-Khouly, M. Fujitsuka, O. Ito, J. Phys. Chem. A
2002, 106, 3243.
[24] a) H. Laurent, A. Said, E. Levillain, J. Roncali, A. Emge, P. Baeuerle, J.
Phys. Chem. B 1998, 102, 7776; b) H. Spanggaard, J. Prehn, M. B. Nielsen,
E. Levillain, M. Allain, J. Becher, J. Am. Chem. Soc. 2000, 122, 9486.
[25] a) O. Treutler, R. Ahlrichs, J. Chem. Phys. 1995, 102, 346; b) C. Hꢃttig, F.
Weigend, J. Chem. Phys. 2000, 113, 5154; c) C. Hꢃttig, A. Kçhn, J. Chem.
Phys. 2002, 117, 6939.
[17] H. W. Daniell, S. C. Williams, H. A. Jenkins, C. Brꢅckner, Tetrahedron Lett.
2003, 44, 4045.
[18] a) K. M. Kadish, W. E. P. J. Sintic, Z. Ou, J. Shao, K. Ohkubo, S. Fukuzumi,
L. J. Govenlock, J. A. McDonald, A. C. Try, Z.-L. Cai, J. R. Reimers, M. J.
Crossley, J. Phys. Chem. B 2007, 111, 8762; b) P. J. Sintic, W. E. Z. Ou, J.
Shao, J. A. McDonald, Z.-L. Cai, K. M. Kadish, M. J. Crossley, J. R. Reimers,
Phys. Chem. Chem. Phys. 2008, 10, 268; c) W. E. K. M. Kadish, P. J. Sintic,
T. Khoury, L. J. Govenlock, Z. Ou, J. Shao, K. Ohkubo, J. R. Reimers, S. Fu-
kuzumi, M. J. Crossley, J. Phys. Chem. A 2008, 112, 556.
[19] J.-F. Lefebvre, D. Leclercq, J.-P. Gisselbrecht, S. Richeter, Eur. J. Org.
Chem. 2010, 1912.
[20] N. G. Connelly, W. E. Geiger, Chem. Rev. 1996, 96, 877.
[21] DGCR =e(EoxꢀEred) and ꢀDGCS =DE0-0ꢀe(EoxꢀEred), in which DE0-0 is the
energy of the singlet excited state of H2P (1.90 eV) and ZnP (2.08 eV),
Eox is the first oxidation potential of TTF, and Ered is the first reduction
potential of porphyrin and C60.
Received: April 23, 2012
Revised: June 1, 2012
Published online on && &&, 2012
ChemPhysChem 0000, 00, 1 – 14
ꢁ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemphyschem.org
&13
&
ÞÞ
These are not the final page numbers!

ARTICLES
H. Jia, B. Schmid, S.-X. Liu,* M. Jaggi,
P. Monbaron, S. V. Bhosale,* S. Rivadehi,
S. J. Langford, L. Sanguinet, E. Levillain,
M. E. El-Khouly, Y. Morita, S. Fukuzumi,*
S. Decurtins
&& – &&
Multi-chromophoric arrays: A tetrathia-
fulvalene donor is fused to one or two
porphyrins via quinoxaline linkers form-
ing asymmetric dyads or triads (e.g. see
picture), the redox and optical proper-
ties of which are studied. A supramolec-
ular complex of a dyad with a pyridine-
functionalized C60 acceptor undergoes
photoinduced electron transfer leading
to a relatively long-lived charge-separat-
ed state.
Tetrathiafulvalene-Fused Porphyrins
via Quinoxaline Linkers: Symmetric
and Asymmetric Donor–Acceptor
Systems
&14
&
www.chemphyschem.org
ꢁ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ChemPhysChem 0000, 00, 1 – 14
ÝÝ
These are not the final page numbers!