Photoinduced energy and electron transfer in phenylethynyl-bridged zinc porphyrin-oligothienylenevinylene-C60 ensembles

Article abstract of DOI:10.1002/chem.201102260

Donor-bridge-acceptor triad (Por-2TV-C₆₀) and tetrad molecules ((Por)₂-2TV-C₆₀), which incorporated C₆₀ and one or two porphyrin molecules that were covalently linked through a phenylethynyl-oligothienylenevinyl

Full text of DOI:10.1002/chem.201102260

FULL PAPER
DOI: 10.1002/chem.201102260
Photoinduced Energy and Electron Transfer in Phenylethynyl-Bridged Zinc
Porphyrin–Oligothienylenevinylene–C60 Ensembles
Maxence Urbani,[a] Kei Ohkubo,[b] D. M. Shafiqul Islam,[b] Shunichi Fukuzumi,*[b, c] and
Fernando Langa*[a]
Abstract: Donor–bridge–acceptor triad
(Por-2TV-C60) and tetrad molecules
((Por)2-2TV-C60), which incorporated
C60 and one or two porphyrin mole-
cules that were covalently linked
through a phenylethynyl-oligothienyle-
nevinylene bridge, were synthesized.
Their photodynamics were investigated
by fluorescence measurements, and by
femto- and nanosecond laser flash pho-
tolysis. First, photoinduced energy
transfer from the porphyrin to the C60
moiety occurred rather than electron
transfer, followed by electron transfer
from the oligothienylenevinylene to
the singlet excited state of the C60
moiety to produce the radical cation of
oligothienylenevinylene and the radical
anion of C60. Then, back-electron trans-
fer occurred to afford the triplet excit-
ed state of the oligothienylenevinylene
moiety rather than the ground state.
Thus, the porphyrin units in (Por)-2TV-
C60 and (Por)2-2TV-C60 acted as effi-
cient photosensitizers for the charge
separation between oligothienylenevi-
nylene and C60.
Keywords: electron transfer · ener-
gy transfer · fullerenes · oligothie-
nylenevinylene · porphyrins · zinc
Introduction
Porphyrins, which are characterized by their high molar
absorption coefficients and which give fast energy and/or
electron transfer to acceptor components in synthetic ana-
logues of natural chlorophyll molecules, have been widely
used as promising candidates for light-capturing chromo-
phores.[3,4,5] The structural complexity of light-harvesting an-
tenna complexes (LH1 and LH2) has prompted the design
and preparation of light-harvesting multiporphyrin sys-
tems.[4,5] Fullerenes have also been widely used as 3D elec-
tron acceptors, owing to their small reorganization energy in
electron-transfer reactions, which results from the p-electron
system being delocalized over the curved 3D surface, to-
gether with the rigid and confined structure of the aromatic
p-sphere.[3a–f, 6,7] The introduction of conjugated systems that
act as bridges (B) between the donor (D) and the acceptor
(A) mediates the energy-transfer and electron-transfer pro-
cesses.
The development of artificial photosynthetic systems that
use solar energy would be a major advance in energy pro-
duction and a critical breakthrough with respect to the
growing concern of environmental pollution caused by the
use of fossil fuels.[1] Typical designs of such systems have
tried to mimic natural photosynthesis, such as the efficient
capture of photons of visible light and electron/hole separa-
tion by electron transfer. In this respect, nanomaterials that
are composed of multiporphyrins and carbon-based p-elec-
tron acceptors (in particular C60) have been utilized to con-
struct efficient light-energy conversion systems, such as pho-
tovoltaic devices.[2]
[a] Dr. M. Urbani, Prof. Dr. F. Langa
Instituto de Nanociencia
Nanotecnologꢀa y Materiales Moleculares (INAMOL)
University of Castilla-La Mancha Campus
de la Fꢁbrica de Armas, Toledo 45072 (Spain)
E-mail: Fernando.Langa@uclm.es
Oligophenylenevinylenes, oligophenyleneethynylene, and
heterocyclic oligomers, such as oligothiophenes, oligofurans,
and oligopyrroles, have been widely used as wires to connect
D and A moieties.[8,9] However, the detailed role of oligo-
thienylenevinylenes[9] as bridges in terms of energy transfer
versus electron transfer has yet to be scrutinized.
[b] Dr. K. Ohkubo, Dr. D. M. S. Islam, Prof. Dr. S. Fukuzumi
Department of Material and Life Science
Graduate School of Engineering
Osaka University and ALCA
Herein, we report the synthesis, electrochemical, and pho-
todynamic studies of a porphyrin-2TV-C60 triad and a (por-
phyrin)2-2TV-C60 tetrad together with reference compounds.
Several factors were considered for designing this system:
1) an adequate gradient of the oxidation potentials, 2) thie-
nylvinylenes[9] and phenylethynyl linkers[10] have well-known
efficiency as molecular wires, and 3) the porphyrin core and
phenylene planes are orthogonal, thereby breaking the con-
jugation between them. Photoinduced energy transfer and
electron-transfer processes were investigated by using fem-
Japan Science and Technology Agency (JST)
2-1 Yamada-oka, Suita, Osaka 565-0871 (Japan)
Fax : (+81)6-6879-7370
E-mail: fukuzumi@chem.eng.osaka-u.ac.jp
[c] Prof. Dr. S. Fukuzumi
Department of Bioinspired Science
Ewha Womans University
Seoul, 120-750 (Korea)
Supporting information for this article, including the synthesis and
physical measurements, is available on the WWW under http://
dx.doi.org/10.1002/chem.201102260.
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tosecond and nanosecond laser flash photolysis measure-
ments tougher with their redox properties.
alytic iodine, which mainly led to degradation products, pre-
sumably owing to the presence of the aldehyde group. How-
ever, the ratios of the trans–trans isomers were significantly
increased (up to 96%) after purification by column chroma-
tography on silica gel and low-temperature recrystallization
in n-pentane. Compounds 4 and 7 were finally obtained in
83 and 66% yield, respectively. Activated bromophenyl
compounds 4 and 7 were then subjected to Sonogashira cou-
pling with TMSA, thereby affording the desired silyl-pro-
tected derivatives in good to acceptable yields. Full cleavage
of the terminal alkyne units was then achieved by treatment
with potassium carbonate in THF/MeOH (1:1). Compound
5 was isolated in excellent yield (99%) after column chro-
matography on silica gel. However, several recrystallizations
at low temperature were necessary to isolate the pure trans
isomer (E,E)-5 (E,E/Z,E, >98%)[13] thus leading to a signifi-
cant decrease in the yield (61%, 2 steps from compound 4).
In the case of compound 8, the trans isomer was isolated
more easily (E,E/Z,E, >99%).[13] However, many careful
and tedious purification steps were required to separate the
bis-alkyne precursor ((E,E)-8a) from the by-product ((E,E)-
8b), which we were unable to fully isolate. We were able to
improve the ratio of (E,E)-8a/8b up to 77:23[13] in the purest
sample. The overall yield of compound 8a was estimated to
be 47% in 2 steps from (E,E)-7 (based on the effective
amount of compound 8a in the 77:23 mixture). The intro-
duction of the terminal aldehyde functional group into com-
pounds 3 and 6 to obtain aldehydes 4 and 7, before coupling
the porphyrins, was crucial at this stage because unformylat-
ed (2TV) bromophenyl derivatives 3 and 6 were poorly re-
active toward Sonogashira coupling (with TMSA and por-
Results and Discussion
Synthesis: The synthesis of 2TV building blocks is shown in
Scheme 1. Phosphonates 1 and 2 were prepared from 3,5-di-
bromo benzaldehyde and 4-bromobenzyl bromide, respec-
tively, according to literature procedures.[11] The reaction of
phosphonate 1 with 2TV-aldehyde[12] in THF in the presence
of tBuOK under Wittig–Horner conditions stereoselectively
afforded the trans-trans isomer (E,E)-3 in good yield (69%).
Surprisingly, the reaction of phosphonate 2 under the same
conditions afforded compound 6, but as an E/Z isomeric
mixture; this result prompted us to perform the Z!E iso-
merization of compound 6, by treatment with a catalytic
amount of iodine in refluxing toluene, to yield isomer
(E,E)-6 in 79% yield.
Our first attempt to directly functionalize compound 6
with (trimethylsilyl)acetylene (TMSA) by Sonogashira cou-
pling failed, and mainly led to a mixture of the mono-
(major) and bis-ethynyl (minor) products, presumably owing
to the poor reactivity of m-bis-bromophenyl 6. To increase
their reactivities toward Sonogashira coupling, compounds 3
and 6 were first formylated by using a Vilsmeyer procedure
in the presence of POCl3 (1.3 equiv)/DMF (2–3 equiv) in re-
fluxing DCE overnight to afford isomers (E,E)-4 and (E,E)-
7, respectively, with high trans-stereoselectivity (E,E/Z,E,
about 90%).[13] However, in these cases, Z!E isomerization
of the mixtures could not be achieved by treatment with cat-
Scheme 1. Synthesis of 2TV building blocks, reagents and conditions: a) tBuOK, THF, 08C!RT 2 h ((E,E)-3: 69%); b) I2 (cat.), toluene, 6 h ((E,E)-6:
79%); c) POCl3 (1.3 equiv)/DMF (2–3 equiv), DCE, reflux, overnight ((E,E)-4: 83%; (E,E)-7: 66%); d) TMSA, [Pd(PPh3)4], CuI, Et3N, RT, 24–48 h;
AHCTUNGTRENNUNG
e) K2CO3, THF/MeOH (1:1), RT, 8 h ((E,E)-5: 62%; (E,E)-8a/8b: 82%, two steps). DCE=1,2-dichloroethane, DMF=N,N-dimethylformamide,
TMSA=trimethylsilylacetylene.
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Zinc-Porphyrin–Oligothienylenevinylene–C60 Ensembles
FULL PAPER
phyrins). Then, because porphyrins are reactive under Vils-
meyer conditions, their undesired formylation side-reactions
were avoided.
(E,E)-10 was isolated in 89% yield (with respect to (E,E)-
8a) after purification by size-exclusion chromatography and
column chromatography on silica gel. By following the same
procedure, pure (E,E)-9 was isolated in 66% yield.
The incorporation of C60 was achieved by the [3+2] dipo-
lar cycloaddition with azomethine ylides that were generat-
ed in situ from aldehydes 9/10 and sarcosine in refluxing
chlorobenzene, according to the procedure described by
Prato and Maggini;[16] triad 11 and tetrad 12 were formed in
81% and 49% yield, respectively (Scheme 3). The structures
of compounds 11 and 12 were confirmed by MS (MALDI-
TOF, see the Experimental Section and the Supporting In-
formation, Figures SI.11 and
Synthetic approaches to prepare triad 11 and tetrad 12, as
well as their respective porphyrin precursors 9 and 10, are
shown in Scheme 2 and Scheme 3. The preparation of por-
phyrins 9 and 10 involved the Cu-free Pd-catalyzed cross-
coupling of building blocks (E,E)-5 or (E,E)-8a/8b with
A3B-type zinc porphyrin PZnI [5-p-iodophenyl-10,15,20-tris-
(2,4,6-trimethylphenyl)zinc porphyrin][14] under the condi-
tions optimized by Lindsey for the synthesis of ethyne-
linked, multiporphyrin arrays.[15] Pure bis-adduct aldehyde
SI.12).
Characterization of these
compounds was achieved by
NMR and UV/Vis spectroscopy.
1H NMR spectra of compounds
11 and 12 are shown in Figure 1
(for compounds 3–10, see the
Supporting Information).
Derivatives 3–12 all displayed
simple, well-resolved average
NMR spectra at room tempera-
ture that were in agreement
with their structures. The pres-
ence of a stereogenic center in
the pyrrolidine rings of com-
pounds 11 and 12 induced an
asymmetric center (C1 symme-
try) and involved two enantio-
meric forms (R and S). Interest-
Scheme 2. Synthesis of Por-2TV (9) and (Por)2-2TV (10), reagents and conditions: a) AsPh3, [Pd2ACTHNUGRTNEUNG(dba)3], Et3N/
ingly, all of these compounds
showed much-simpler NMR
spectra than expected owing to
fast dynamic phenomena at
toluene (1:5), 3 days (from (E,E)-5, 9: 66%; from (E,E)-8a/8b, 10: 89% based on (E,E)-8a). dba=dibenzyli-
deneacetone.
room temperature. First, for all of the para derivatives (3, 4,
5, 9, and 11), an AB quartet was always clearly observed for
the para-substituted phenyl-ring protons (HX/Y). This obser-
vation indicated that exchange between the HX/HY and HX’/
HY’ protons was always fast at 298 K on the NMR timescale
(Scheme 4a) such that they appeared equivalent in the
1H NMR spectrum. In other words, the rotation around the
ꢀ
C C bond that linked the 2TV moiety to the central phenyl
core was faster than the NMR timescale at 298 K (fast rota-
tion 1, Scheme 4a). Next, an AB quartet (Ho/m) was ob-
served for the para-substituted bridging phenyl ring in the
1H NMR spectra of compounds 9 and 11, which indicated
fast exchange between the Ho/m and Ho’/m’ protons. Obvious-
ly, in this latter case, the fast exchange could also be ex-
ꢀ
plained by a fast rotation around the carbon carbon triple
bond (rotation 2, Scheme 4c). Although in principle the b-
pyrrolic protons in compound 11 should lose their equiva-
lency owing to the presence of the fulleropyrollidine moiety,
an “A3B-type porphyrin” pattern was observed for both de-
rivatives 9 and 11, as attested to by the signals from the por-
phyrin moiety: an AB quartet and a singlet were observed
Scheme 3. Synthesis of Por-2TV-C60 (11) and (Por)2-2TV-C60 (12), re-
agents and conditions: a) C60, sarcosine, PhCl, reflux, 12 h (from 9, 11:
81%; from 10, 12: 49%).
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S. Fukuzumi, F. Langa et al.
for the four sets of b-pyrrolic
protons (b1/b2 and b3/b4 respec-
tively).
Similar observations and con-
clusions were drawn for the cor-
responding meta derivatives (6,
7, 8, 10, and 12). First, an AX2
system for the 1,3,5-trisubstitut-
ed phenyl ring protons (HX/Y
)
was clearly observed in all
cases, which attested to a fast
exchange between the HY and
HY’ protons (Scheme 4b). Inter-
estingly, the para-substituted
(Ho/m) protons on the bridging
phenyl rings of compounds 10
and 12 also only displayed one
unique AB quartet. This obser-
vation attested to a fast ex-
change between the Ho/Hm and
Ho’/Hm’ protons on one hand,
and between the two phenyl
bridging phenyl rings on the
other hand. This result was also
evidenced by the signals of the
porphyrin moiety in compounds
Figure 1. 1H NMR spectra (CDCl3, 400 MHz) of Por-2TV-C60 (11) and (Por)2-2TV-C60 (12) (* denotes the re-
sidual CHCl3 solvent peak, # denotes CH2Cl2).
10 and 12: an AB quartet and a singlet were observed for
the four sets of b-pyrrolic protons (b1/b2 and b3/b4, respec-
tively). This latter observation attested to a fast exchange
between the two inequivalent porphyrins PZn and PZn’ of
compound 12, which appeared to be magnetically equivalent
1
to each other in the H NMR spectra. We concluded from
these NMR spectra that both fast rotations 1 and 2 occurred
in meta derivatives 10 and 12 and one could reasonably sup-
pose that should also both take place for the corresponding
para derivatives (9 and 11). APT 13C NMR experiments (see
the Supporting Information) of compounds 11 and 12 re-
vealed two unique, characteristic signals for the sp ethynyl
carbons (d=90.7 and 90.6 ppm for compound 11; d=90.3
and 89.6 ppm for compound 12), which agreed with this hy-
pothesis.
Finally, the steric hindrance that arose from the bulky
ortho-hexyl chains on the thiophene that was directly linked
to the pyrrolidine ring should induce a restricted rotation
ꢀ
around the thiophene pyrrolidine bond. Such phenomena
are well-known and have been observed in the case of
phenyl-substituted pyrrolidinofullerene derivatives.[17] Never-
theless, to the best of our knowledge, such phenomena have
not been heavily investigated nor discussed in depth for
thiophene-based derivatives. In principle, compounds (R/S)-
11 and (R/S)-12 may exist as two sets of diastereoisomeric
conformers (a and b; Figure 2). However, NMR spectrosco-
py seemed to indicate that only one atropoisomer existed at
298 K. Indeed, the NMR spectra of fullerene derivatives 11
and 12 displayed sharp, well-defined signals at room temper-
ature. In particular, the signals of the vinylic protons of the
2TV moiety appeared as a unique AB quartet and a singlet
Scheme 4. Fast dynamic exchanges at 298 K and 1H nomenclature of the
phenyl bridging rings in a) the para series, b) the meta series, c) triad 11,
and d) tetrad 12.
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Zinc-Porphyrin–Oligothienylenevinylene–C60 Ensembles
FULL PAPER
lidine ring). However, the difference in energy was rather
too small to fully explain why only one isomer had been
formed under these experimental conditions (chloroben-
zene, 1208C). Apart from steric hindrance considerations,
other factors could also contribute to the high diastereose-
lectivities for compounds 11 and 12. Additional energetic
factors and/or dipolar-moment effects may also be heavily
involved in the stabilization of the in-situ-generated azome-
thine ylide intermediates in chlorobenzene. As we had pre-
viously suggested and observed for other [C60]pyrrolidine–
ꢀ
nTV derivatives, the stabilization of the intermediate by p
p stacking between the C60 curved cage and the p-aromatic
backbone of 2TV should play an important role.[18]
The redox behavior of compounds 11 and 12, as well as
their precursors (5 and 8a/8b–10) and reference compounds
(porphyrin PZnI and C60), were investigated by cyclic vol-
tammetry (CV) and by Osteryoung square-wave voltamme-
try (OSWV) in ODCB/MeCN (8:2) at room temperature
(for the CVs, see the Supporting Information, Figure SI.6;
for the OSWVs, see the Supporting Information, Figure
SI.7). The chemical reversibility (or irreversibility) of these
redox processes and the number of electrons engaged
(where possible) were deduced from CVs experiments.
Owing to irreversible oxidation processes of 2TV-based de-
rivatives, all redox potentials (versus Fc/Fc+) were systemat-
ically deduced from OSWV experiments (Table 1).
Figure 2. Energy-minimized equilibrium geometry of the C60–thiophene
fragment: theoretical structure of the two lowest-energy conformers (a
and b) in the ground state (298 K). Calculations were performed with
Spartan 10 by using the “conformer distribution” semiempirical PM3
method. The hexyl chains were replaced by propyl groups in the calcula-
tions (only the R enantiomer is shown).
for the two sets of trans-coupled vinylic protons Ha/b (JACTHNUTRGENUG(N a,b)
ꢁ16 Hz) and Hc/d, respectively. Moreover, one unique AB
quartet for protons Hf/f’ and a singlet for the He proton were
observed for the pyrrolidine ring. In addition, APT
13C NMR spectroscopy of compounds 11 and 12 revealed
two signals for the sp3 carbons of the C60 mono-adducts (d=
70.0 and 68.8 ppm for compound 11; d=70.0 and 68.9 ppm
for compound 12; see the Supporting Information). From
these experimental NMR observations, two hypotheses
Table 1. Redox potentials of compounds 5, 8–12, C60, and [5-p-iodophen-
yl-10,15,20-tris-(2,4,6-trimethylphenyl)porphyrin] measured by OSWV
(versus Fc/Fc+).[a]
ꢀ
could be raised: either the rotation around the thiophene
Ered2 [V]
Ered1 [V]
Eox1 [V]
Eox2 [V]
Eox3 [V]
pyrrolidine bond was faster than NMR timescale at room
temperature (i.e., fast equilibrium between the a and b atro-
poisomeric forms) or that the rotation was fully restricted
(based on NMR observations, this hypothesis would imply
that only one atropoisomer existed at 298 K). This latter hy-
pothesis was the most likely, as it is well-known that steric
hindrance that arises from any bulky group located at the
ortho position of the pyrrolidine ring induces a high rota-
tional energy barrier that is sufficient to prevent any rota-
tion around the pyrrolidine ring at 298 K.[17] Therefore, it
was reasonable to suggest that the cycloaddition reactions
on the fullerene core were highly diastereoselective, thereby
leading to only one atropoisomer, in agreement with other
examples previously reported in the literature.[17b,c] To deter-
mine which diastereoisomer was present, we performed
semi-empirical computational studies on a fulleropyrroli-
P
5
8
9
10
11
12
C60
ZnI
ꢀ2.33
ꢀ1.93
–
–
ꢀ1.33
ꢀ1.37
ꢀ1.10
ꢀ1.09
ꢀ0.99
0.35
0.73
–
–
–
0.74
0.90 (br)
0.90 (br)[b]
0.94 (br)[b]
–
–
0.52[b]
0.52[b]
0.33
0.77[b]
0.78[b]
0.53[b]
0.58[b]
0.71
–
–
–
0.31 (br)
0.36
0.35
ꢀ1.50
ꢀ1.37
ꢀ1.35
0.74
–
–
[a] 0.20m Bu4NClO4, solvent: ODCB/MeCN (8:2). [b] Irreversible ac-
cording to CV. ODCB=1,2-dichlorobenzene.
In the cathodic region, the first reduction wave of fullero-
pyrrolidine derivatives 11 (Ered1 =ꢀ1.10 V) and 12 (Ered1
=
ꢀ1.09 V) was assigned to the first reversible reduction of
the fullerene core through a one-electron process. The satu-
ration of one of their C60 double bonds resulted in a cathodic
shift of their reduction potentials (DVꢁꢀ0.10 V) in compar-
ison with unsubstituted C60 (Ered1 =ꢀ0.99 V). These values
were in agreement with those previously reported for other
similar fulleropyrrolidine–2TV derivatives, in particular
those reported by Roncali et al.[9a,19] for a C60-2TV system
(Ered1 =ꢀ1.08 V) and by ourselves for a C60-2TV-C70 dumb-
bell (Ered1 =ꢀ1.30 V).[18] At lower cathodic potentials, por-
ꢀ
dine thiophene fragment by using different alkyl groups
(methyl, ethyl, or propyl; Figure 2). The difference in
energy between the a and b isomeric forms was estimated
ACTHNUTRGNEUNG
to be 5.6 kJmolꢀ1(methyl), 7.3 kJmolꢀ1 (ethyl), and
7.6 kJmolꢀ1 (propyl). These results, together with computa-
tional studies of compounds 11 and 12 (semi-empirical PM3
method; see the Supporting Information, Figure SI.22–
SI.31), both agreed that the a-atropoisomeric forms were
the lowest-energy conformers (in which the hexyl chains
were located on the same side as the He proton of the pyrro-
phyrin macrocycle(s) showed
a second (irreversible) reduction that involved one-electron
processes for PZnI, Por-2TV-CHO (9), and Por-2TV-C60
a first (reversible) and
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S. Fukuzumi, F. Langa et al.
(11), and two-electron processes for (Por)2-2TV-CHO (10)
and (Por)2-2TV-C60 (12). In these latter cases, both porphy-
rin moieties appeared to be reduced simultaneously. Inter-
estingly, the first reduction of the porphyrin(s) in reference
compounds 9 (E1red =ꢀ1.33 V) and 10 (E1red =ꢀ1.37 V) were
positive-shifted by about +0.4 V compared to model por-
phyrin PZnI (E1red =ꢀ1.93 V), which could be due to the
presence of the ethynyl-2TV-CHO bridge. The second re-
duction potential peak in compounds 11 (Ered2=ꢀ1.50 V)
and 12 (Ered2 =ꢀ1.37 V) was more difficult to assign because
both the reduction of the porphyrin(s) and other reductions
of C60 may overlap. However, we could clearly conclude
that the reductions of porphyrin(s) in compounds 11 and 12
occurred at lower potentials than the first reduction of the
and 10 (E=+0.58 V) were reasonably assigned to the first
oxidation of 2TV by comparison with their respective 2TV
models (5: E=+0.52 V and 8a/8b: E=+0.52 V). Interest-
ingly, in OSWV, the intensity of the first oxidation peak of
2TV was roughly half of the expected value compared to
those of the porphyrin (reversible) in compound 9, owing to
an average value for the irreversible half-wave in OSWV. In
compounds 11 and 12, the first oxidation of 2TV was more
difficult to ascribe. The OSWVs and CVs seemed to show
a third irreversible oxidation peak as a small shoulder at
around +0.9 V. By comparison with the values obtained for
compounds 5–10, it was reasonable to suppose that they
should belong to the second irreversible oxidation (assigned
to the 2TV unit) with positive shifts of about 0.13–0.16 V.
Based on this hypothesis, the first oxidation potential should
also be shifted at much higher potential (around +0.7 V)
than compounds 5–10 (0.53–0.58 V). As the second oxida-
tion of the porphyrin moiety in compounds 11 and 12 oc-
curred at +0.71 V and +0.74 V, respectively, we suggested
that the first irreversible oxidation of the 2TV bridge in
compounds 11 and 12 must be overlapped by the second re-
versible oxidation of the porphyrin(s). These positive shifts
in the oxidation of the 2TV bridge (DVꢁ+0.15 V) in C60-
based derivatives 11 and 12, compared to their reference
compounds without C60, were coherent with similar observa-
tions for other fulleropyrrolidine–nTV derivatives reported
by ourselves[18] and others.[9a,19] Indeed, it has previously
been well-established that the introduction of a fulleropyrro-
lidine moiety at one tip of nTVs causes important positive-
shifts of its oxidation potentials when compared to unsubsti-
tuted nTV. This behavior has been explained by two main
reasons: First, the presence of bulky groups, such as fullero-
pyrrolidine (and porphyrins in our cases), hinders the ap-
proach of 2TV onto the electrode surface, thus leading to
higher oxidation potentials for the 2TV moiety; and second,
the lower coefficient diffusion in solution of the fullerene
derivatives. Finally, we also suggest, as we had previously re-
ported for other similar derivatives,[18] that the relative close
contact between the 2TV moiety and the C60 cage should
C
60 moiety.
In the anodic region, two reversible oxidations at around
+0.35 V and +0.73 V were clearly observed for the porphy-
rin moieties of PZnI and compounds 9–12 without any sig-
nificant changes. Only small negative shifts (30–40 mV)
were observed for compounds 9 and 10, which could be due
to the weak effect of the terminal aldehyde group. These re-
sults suggested that the electron transfer from the porphyrin
moiety must be located on the macrocycle ring. For (Por)2-
2TV-CHO (10) and (Por)2-2TV-C60 (12), only two oxidation
processes were observed for the porphyrins. These results
suggested that both porphyrin moieties in compounds 10
and 12 were equivalent from an electrochemical point of
view, thus involving two-electrons for each of the two-elec-
tron-oxidation processes. This result was also evidenced in
the cathodic region, where the reductions of both porphyrins
also occurred simultaneously in two-electron processes (al-
though in the case of compound 12, they were more difficult
to distinguish, owing to the overlap with the reductions
waves that arose from the fullerene moiety). CVs of 2TV-
based derivatives 5 and 8a/8b showed two irreversible one-
electron-transfer oxidation processes. In particular, two
well-defined oxidation waves were clearly observed in the
forward scan but became poorly defined when the potential
was inverted (backward scan). It has been previously report-
ed that the oxidation of short oligothienylenevinylene deriv-
atives (n<4) leads to the formation of nTV radical cation
species, usually followed by fast electropolymerization on
the electrode surface. However, the absence of any free
a positions on the thiophene moieties, together with the
presence of pendant hexyl chains, tended to avoid, or at
least slow down, these electropolymerization processes.[12]
OSWV clearly revealed two half-wave oxidations peaks for
compounds 5 (Eox1 =+0.52 V; Eox2 =+0.77 V) and 8a/8b
(Eox1 =+0.52 V; Eox2 =+0.78 V), which was in agreement
with previously reported values for unsubstituted 2TV
(Eox1 =+0.54 V; Eox2 =+0.87 V).12,19 The chemically irrever-
sible oxidation of 2TV precluded a clear evaluation of the
electron-exchange processes for compounds 9, 10, 11, and
12. Moreover, the second reversible oxidation of the por-
phyrin(s) was close to those of the 2TVs, which also helped
to make their assignments difficult. Nevertheless, the second
half-wave oxidation peaks of compound 9 (E=+0.53 V)
ꢀ
allow for p p stacking interactions. Therefore, the with-
drawing effect of the directly linked fulleropyrrolidine
toward the 2TV bridge should also contribute to the in-
crease in its oxidation potentials in compounds 11 and 12.
These potentials suggested that the radical cation (in photo-
induced-electron-transfer processes) must be located in the
porphyrins with the TV acting as a bridge. The experimen-
tally determined HOMO–LUMO gap for compound 12 was
1.44 eV.
The UV/Vis absorption properties of compounds 11 and
12 were studied in toluene, CH2Cl2, and benzonitrile. The
absorption spectra of compounds 11 and 12 in CH2Cl2 are
shown in Figure 3. These spectra showed the characteristic
ZnII–porphyrin absorption bands: a Soret band at 430 nm
and two Q bands at around 550 and 590 nm. Furthermore,
the typical absorption of the fulleropyrrolidine in the UV
region was also distinguishable. However, the absorption
bands of the 2TV moiety were more difficult to distinguish
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Zinc-Porphyrin–Oligothienylenevinylene–C60 Ensembles
FULL PAPER
CH2Cl2 (see the Supporting Information, Figure SI.15). Such
solvatochromism effects in polar solvents have been previ-
ously explained by the higher polarization of the ground
electronic state for systems with covalently bridged spacers
and strong electron-acceptors.[20]
The fluorescence spectra of (Por)2-2TV-C60 (12) in toluene
and in benzonitrile (lex =420 nm), along with those of refer-
ence compound (Por)2-2TV (10), are shown in Figure 4. The
fluorescence intensity of the porphyrin moiety (1Por*;
maxima at 600 and 650 nm in toluene) was markedly re-
duced (by a factor of at least 98%) compared with that of
compound 10 by the fullerene group on the opposite side of
2TV in compound 12. In toluene, the appearances of the
peaks at 715 nm owing to the fluorescence of fullerene indi-
cated energy transfer from the 1Por* moiety to the C60
moiety. In PhCN, a significant decrease in the fluorescence
Figure 3. UV/Vis spectra of Por-2TV-C60 (11) and (Por)2-2TV-C60 (12) in
CH2Cl2.
1
intensity was observed without the appearance of C60* fluo-
rescence. The fluorescence quantum yields (F) and lifetimes
of compounds 9–12 are shown in Table 2, together with their
fluorescence lifetimes (tf).
because they were mostly overlapped by the intense Soret
band of the porphyrin(s) (15–30 times more-intense). For
2TV reference derivatives 5 and 8a/8b, two absorption
bands were observed at around 340 and 390 nm. These
bands appeared to be red-shifted in compounds 9, 10, 11,
and 12 in all of the solvents tested (Dlꢁ20–60 nm); in par-
ticular, the 2TV band at around 460 nm was observed as
a broad shoulder. The absorption coefficients of compounds
11 and 12 in CH2Cl2 were consistent with porphyrin/2TV/
fullerene ratios of 1:1:1 and 2:1:1, respectively.
Table 2. Fluorescence quantum yields (F) and fluorescence lifetimes (tf)
in PhCN and toluene.
Compound
PhCN
Toluene
tf [ns]
F
tf [ns]
F
Por-2TV (9)
AHCTUNGTRENNUNG
0.031
0.033
0.006
0.006
1.7
1.5
0.038
0.035
0.004
0.005
1.8
1.5
[a]
[a]
–
–
[a]
[a]
G
–
–
[a] Too fast to determine accurately.
The fluorescence emission of (Por)2-2TV-C60 (12) as well
as its model compound (10) were studied in toluene and
benzonitrile (Figure 4). Red-shifts of the Soret and Q bands
of about 10 nm were observed in the emission/absorption
spectra in benzonitrile compared to those in toluene or
Photodynamics: First, the photodynamics of reference com-
pound Ph-2TV (5) was examined by femtosecond laser flash
photolysis. A transient absorption band at 755 nm, which
was due to the singlet excited state of Ph-2TV (1Ph-2TV*),
was observed upon photoexcitation at 430 nm (Figure 5).
The decay of the absorption band at 755 nm was accompa-
nied by the generation of an absorption band at 600 nm,
which was assigned to the triplet excited state of Ph-2TV
(3Ph-2TV*). The rate constant of intersystem crossing from
3
1Ph-2TV* to Ph-2TV* was determined from the decay of
absorbance at 755 nm to be 3.9ꢃ109 sꢀ1 ((260 ps)ꢀ1) in
PhCN at 298 K (Figure 5).
Next, the photodynamics of Por-2TV (9) was examined by
femtosecond laser flash photolysis. Upon photoexcitation at
430 nm, a transient absorption band at 470 nm was ob-
served, owing to the singlet excited state of the porphyrin
moiety, together with a transient absorption band at 755 nm,
which was due to the singlet excited state of the 2TV moiety
(Figure 6a). The transient absorption band at 755 nm de-
cayed much-more-rapidly than the reference compound
(Ph-2TV) because of fast energy transfer from the singlet
excited state of 2TV to the Por moiety (Figure 6a). The
decay of the absorbance at 470 nm coincided with the ap-
pearance of an absorption band at 620 nm, which was due to
the triplet excited state of the 2TV moiety (Figure 6a). This
Figure 4. Room-temperature fluorescence spectra of Por2-2TV (10) and
(Por)2-2TV-C60 (12) in photoexcited toluene (a and b, respectively) and
benzonitrile (c and d, respectively) at 420 nm, with matching absorption
at lex =420 nm.
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S. Fukuzumi, F. Langa et al.
Scheme 5. Energy diagram for the photoinduced-energy-transfer process-
es of Por-2TV (9).
time profiles (Figure 6b,c) to be 1.5ꢃ1012 sꢀ1 and 7.0ꢃ
108 sꢀ1, respectively.
When C60 was attached to the Por-2TV moiety (9) in Por-
2TV-C60 (11), transient absorption bands at 740 and 1130 nm
+
C
owing to 2TV were observed, together with a transient ab-
Cꢀ
sorption band at 1000 nm, which was due to C60 , upon fem-
Figure 5. a) Transient absorption spectra of Ph-2TV (5) taken at 2, 250,
and 1500 ps after femtosecond laser excitation at 430 nm in Ar-saturated
PhCN; b) decay profile of the absorbance at 755 nm owing to 1Ph-2TV*.
tosecond laser excitation at 430 nm (Figure 7a). This assign-
ment of the absorption bands at 740 and 1130 nm was con-
firmed by the absorption spectrum of 2TV , which was pro-
+
C
duced by the one-electron oxi-
dation of Ph-2TV (5) with
[RuACHTNUTGRNEUNG
(bpy)3]3+ (Figure 8), al-
though both absorption maxima
were slightly blue-shifted. The
time profiles of the absorbances
at 1130 nm (Figure 7b) and
740 nm (Figure 7c) showed the
formation and decay of the
charge-separate state (Por-
+
C
Cꢀ
2TV -C60 ). The rate constant
+
C
of formation of 2TV (2.0ꢃ
1012 sꢀ1 ((0.5 ps)ꢀ1), as deter-
mined from the decay profile of
the absorbance at 740 nm (Fig-
ure 7c), was much faster than
the rate constant of formation
of 3TV* from the intersystem
crossing of 1Por* and the
energy transfer from 3Por* to
Figure 6. a) Transient absorption spectra of Por-2TV (9) taken at 1, 800, and 3000 ps after femtosecond laser
excitation at 430 nm in Ar-saturated PhCN; b) decay profile of the absorbance at 755 nm; c) rise profile at
620 nm.
2TV in Figure 5b ((260 ps)ꢀ1).
1
result indicated that the intersystem crossing from the sin-
glet excited state to the triplet excited state of the porphyrin
moiety was followed by rapid energy transfer from the por-
phyrin to the 2TV moiety to produce the triplet excited
state of the 2TV moiety (Scheme 5). The rate constant of
This result indicated that energy transfer from Por* to C60
1
was much faster than electron transfer from Por* to C60 and
the intersystem crossing. As a result, the electron transfer
1
+
C
Cꢀ
.
from 2TV to C60* occurred to produce 2TV and C60
+
C
Cꢀ
Thus, the CS state of Por-2TV -C60 was produced, rather
1
+
C
Cꢀ
than Por -2TV-C60 , despite the higher energy of Por-
the energy transfer from 2TV* to Por and the intersystem
+
C
Cꢀ
2TV -C60 (1.61 eV versus 1.42 eV). The decay time profile
crossing of Por were determined from the decay and rise-
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Zinc-Porphyrin–Oligothienylenevinylene–C60 Ensembles
FULL PAPER
excited state was also much
faster than electron transfer
+
C
from Por to 2TV to produce
+
C
Cꢀ
Por -2TV-C60 . The decay of
the absorbance at 600 nm,
3
which was due to 2TV* in Por-
2TV-C60 (11), was significantly
3
faster than the decay of 2TV*
in Por-2TV (9; Figure 10). The
acceleration of the decay of
32TV* with C60, with a rate con-
stant of 7.2ꢃ105 sꢀ1 ((1.3 ms)ꢀ1),
as compared to the rate con-
stant without C60 ((5.9 ms)ꢀ1),
suggested that electron transfer
3
from Por to 2TV* occurred but
that the back-electron transfer
+
Cꢀ
C
Figure 7. a) Transient absorption spectra of Por-2TV-C60 (11) taken at 1, 10, and 3000 ps after femtosecond
laser excitation at 430 nm in Ar-saturated PhCN; time profiles of absorbance at b) 1130 and c) 740 nm.
from C60 to Por was much
3
faster than the decay of 2TV*
to the ground state. This result
was in sharp contrast to that of triad Por-2TV-C60 without
a phenylethynyl bridge (Scheme 6), which afforded a rela-
+
C
Cꢀ [9d]
tively long-lived CT state of Por -2TV-C60
. Thus, the in-
troduction of the phenylethynyl bridge resulted in the accel-
eration of the energy transfer from Por to C60, but retarded
+
C
Figure 8. Absorption spectra of Ph-2TV (5; solid line) and Ph-2TV
(dashed line) from the one-electron oxidation of Ph-2TV (2.7ꢃ10ꢀ5 m)
with [Ru(bpy)3]
(PF6)3 (2.7ꢃ10ꢀ5 m) in CH2Cl2.
A
ACHTUNGTRENNUNG
of the absorbance at 740 nm (Figure 7c) afforded the rate
+
Cꢀ
C
constant of back-electron transfer from C60 to 2TV (6.4ꢃ
1010 sꢀ1 ((16 ps)ꢀ1).
The back-electron transfer mainly afforded 32TV*, as con-
firmed by the transient absorption band at 600 nm that was
observed upon nanosecond laser excitation at 355 nm
+
C
(Figure 9). No observation of the CS state of Por -2TV-
Cꢀ
C60 indicated that the back-electron transfer to the triplet
Figure 10. Decay profiles of absorbance at 600 nm owing to 32TV* in
Por-2TV-C60 (11; gray) and Por-2TV (9; black) upon nanosecond laser ex-
citation in Ar-saturated PhCN.
Figure 9. Transient absorption spectra of Por-2TV-C60 (11) upon nanosec-
ond laser excitation at 490 nm in Ar-saturated PhCN.
Scheme 6. The Por-2TV–C60 triad without a phenylethynyl bridge.
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S. Fukuzumi, F. Langa et al.
the electron transfer from Por to C60. Moreover, the back-
+
Cꢀ
C
electron transfer from C60 to Por was also enhanced by
the phenylethynyl bridge. The increased distance between
Por and C60 with the phenylethynyl bridge resulted in an in-
crease in the solvent-reorganization energy of electron
transfer, which led to an increase in the back-electron trans-
fer in the Marcus-inverted region.[6a,21]
Similar photodynamics was observed for (Por)2-2TV-C60
+
C
Cꢀ
tetrad (12; Figure 11). The formation of 2TV and C60
1
through electron transfer from 2TV to C60*, following
energy transfer from Por* to C60, was clearly seen in the
1
transient absorption spectra upon femtosecond laser excita-
tion (Figure 11), as was the case with the Por-2TV-C60 triad
+
Cꢀ
C
(Figure 7). The back-electron transfer from C60 to 2TV
also afforded 32TV* (lmax =600 nm; see the transient ab-
sorption at 3 ns, Figure 5) and C60* (lmax =700 nm), with
3
a rate constant of (17 ps)ꢀ1 (Figure 11b), which was the
same order as that of Por-2TV-C60 because the geometry be-
tween 2TV and C60 was the same as that between the (Por)2-
2TV-C60 tetrad and the Por-2TV-C60 triad. The light-harvest-
ing efficiency of the (Por)2-2TV-C60 tetrad was higher than
that of Por-2TV-C60 because of the higher extinction coeffi-
cient (Figure 3).
Scheme 7. Energy diagram for the photoinduced processes of Por-2TV-
C60 (11) and (Por)2-2TV-C60 (12).
1
C60, energy transfer from Por* to C60 occurred (rather than
electron transfer from 1Por* to C60), followed by electron
1
transfer from 2TV to C60* to produce the CS state of Por-
+
+
C
Cꢀ
C
2TV -C60 . Although the energy of the CS state of Por -
Cꢀ
2TV-C60 was lower than that of Por-2TV -C60 , back-elec-
tron transfer from C60 to 2TV occurred to produce 2TV*
rather than electron transfer from Por to 2TV , because of
C
Cꢀ
+
+
3
Cꢀ
C
+
C
the longer distance between Por and 2TV owing to the phe-
nylethynyl bridge. Energy transfer from 32TV* to C60 oc-
3
curred to afford C60*, followed by electron transfer from
3
+
C
Cꢀ
Por to C60* to produce Por -2TV-C60 , in which back-elec-
+
Cꢀ
C
tron transfer from C60 to Por occurred much-more-rapid-
ly than the triplet decay to the ground state (Scheme 7).
Conclusion
We have synthesized new electron donor–acceptor triad (11:
Por-2TV-C60) and tetrad molecules (12: (Por)2-2TV-C60).
(Por)2-2TV-C60 had strong absorption bands owing to the
two independent porphyrin moieties. The introduction of
the phenylethynyl bridge in Por-2TV-C60 and (Por)2-2TV-C60
resulted in drastic changes in their photodynamics, owing to
1
a switch from electron transfer from Por* to C60 in the com-
pound without the phenylethynyl bridge (Scheme 6) to
1
energy transfer from Por* to C60, thereby leading to the for-
+
C
Cꢀ
mation of the CS state of Por-2TV -C60 , which had higher
Figure 11. Transient absorption spectra of (Por)2-2TV-C60 (12) in Ar-satu-
rated PhCN after femtosecond laser excitation at 430 nm; b) time profile
at 705 nm.
+
C
Cꢀ
energy than the CS state of Por -2TV-C60 . Thus, the por-
phyrin units in (Por)2-2TV-C60 acted as a more-efficient pho-
tosensitizer than that in Por-2TV-C60 for the charge separa-
tion between 2TV and C60. This study provides a new photo-
The energy diagram is summarized in Scheme 7. The
sensitization strategy to afford the charge-separated state of
1
1
+
C
Cꢀ
energy levels of the singlet excited states of C60*, 2TV*,
2TV and C60 , which was higher in energy than the
1
+
C
Cꢀ
.
and Por* in Por-2TV-C60 were evaluated from the absorp-
charge-separated state of Por and C60
tion and fluorescence peaks. The triplet states of C60, 2TV,
and Por have been evaluated previously from their weak
phosphorescence peaks.[9] Upon photoexcitation of Por-2TV-
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Zinc-Porphyrin–Oligothienylenevinylene–C60 Ensembles
FULL PAPER
dissolved in a minimum amount of CS2 and purified by column chroma-
tography on silica gel, first eluting with CS2 to remove any unreacted C60,
then with toluene to recover a mixture of products. After evaporation of
solvents, the crude product was purified by gel permeation chromatogra-
phy (toluene) and twice by column chromatography on silica gel (CS2/
CH2Cl2, 10:1). Compound 11 was obtained as a glassy dark-purple solid
in 81% yield (37.0 mg, 16.6 mmol). 1H NMR (CDCl3, 400 MHz) d=8.91
(d, 2H, 3J=4.6 Hz), 8.80 (d, 2H, 3J=4.6 Hz), 8.74 (s, 4H), 8.25 (d, 2H,
3J=8 Hz), 7.95 (d, 2H, 3J=8 Hz), 7.67 (d, 2H, 3J=8.3 Hz), 7.54 (d, 2H,
3J=8.3 Hz), 7.34 (d, 1H, 3Jtrans =15.8 Hz), 7.30 (br s, 6H), 7.06 (s, 2H),
6.92 (d, 1H, 3Jtrans =15.8 Hz), 5.33 (s, 1H), 4.97 (d, 1H, 2J=9.5 Hz), 4.22
(d, 1H, 2J=9.5 Hz), 2.95 (s, 3H), 2.81 (t, 2H, 3J=7.5 Hz), 2.64 (br s,
15H), 1.88 (s, 18H), 1.65–1.26 (m, 32H), 0.99–0.87 ppm (m, 12H);
13C NMR (APT, CDCl3, 100 MHz) d=155.8, 153.9, 153.2, 153.1, 150.0,
149.9, 149.8, 149.6, 147.0, 146.5, 146.2, 146.1, 146.0, 145.9, 145.81, 145.75,
145.6, 145.3, 145.2, 145.1, 145.0, 144.9, 144.39, 144.36, 144.0, 143.2, 143.1,
142.9, 142.7, 142.6, 142.35, 142.28, 142.1, 141.9, 141.81, 141.76, 141.7,
141.4, 140.3, 140.0, 139.9, 139.6, 139.30, 139.28, 139.02, 138.95, 137.9,
137.7, 137.4, 137.1, 136.5, 135.9, 135.3, 134.6, 134.5, 132.8, 132.1, 131.9,
131.2, 131.1, 130.7, 129.8, 127.6, 126.7, 126.2, 122.4, 121.9, 121.3, 120.0,
119.5, 119.3, 119.0, 118.8, 90.7, 90.6, 77.8, 70.0, 68.9, 40.6, 31.8, 31.8, 31.7,
31.6, 31.41, 31.36, 29.6, 29.5, 29.4, 29.1, 27.9, 27.2, 26.9, 22.71, 22.70, 22.65,
21.82, 21.77, 21.5, 14.23, 14.20, 14.1; IR (KBr): n˜ =2949, 2918, 2850, 2777,
1460, 1333, 997, 799, 523 cmꢀ1; UV/Vis (CH2Cl2): lmax (e)=254 (149000),
308.5 (81600), 422 (532000), 550 (31100), 590 nm (7570 dm3 molꢀ1 cmꢀ1);
MS (MALDI-TOF): m/z calcd (%) for C160H112N5OS2: 2232.77 (100),
2233.77 (98); found: 2233.04 [M+H]+.
Experimental Section
Synthesis of (E,E)-9: Compound (E,E)-5 (47.6 mg, 69.7 mmol, 1 equiv),
(A3B) iodo–zinc porphyrin[14] (89 mg, 95.7 mmol, 1.4 equiv), AsPh3
(30 mg, 90.0 mmol, 1.4 equiv), and [Pd2ACTHNUTRGNEUNG(dba)3] (11 mg, 12.0 mmol,
0.2 equiv) were successively added into a Schlenk tube. Three cycles of
argon/vacuum were then performed. Toluene (40 mL) and Et3N (8 mL)
were successively introduced via a cannula and the mixture was vigorous-
ly stirred at room temperature for three days. After evaporation of sol-
vents, the crude mixture was filtrated through a small amount of SiO2 gel
(toluene). The volume of the solution was reduced to 1 mL under re-
duced pressure and the mixture was purified by gel-permeation chroma-
tography (toluene), followed by two successive purifications by column
chromatography on silica gel (n-hexane/CH2Cl2/Et3N, 7:3:0.01) to afford
compound (E,E)-9 as
a dark-purple solid in 66% yield (68.6 mg,
46.2 mmol). 1H NMR (CDCl3, 400 MHz) d=9.81 (s, 1H), 8.92 (d, 2H,
3J=4.4 Hz), 8.82 (d, 2H, 3J=4.4 Hz), 8.75 (s, 4H), 8.29 (d, 2H, 3J=
7.6 Hz), 7.98 (d, 2H, 3J=7.6 Hz), 7.72 (d, 2H, 3J=7.9 Hz), 7.59 (d, 2H,
3J=7.9 Hz), 7.39 (d, 1H, 3Jtrans =15.9 Hz), 7.33 (m, 6H), 7.30 (d, 1H,
3Jtrans =15.8 Hz), 7.07 (d, 1H, 3Jtrans =15.8 Hz), 7.02 (d, 1H, Jtrans
=
3
3
15.9 Hz), 2.88 (t, 2H, J=7.5 Hz), 2.68 (br s, 15H), 1.92 (s, 18H), 1.62 (m,
8H), 1.56–1.35 (m, 24H), 1.06–0.86 ppm (m, 12H); 13C NMR (APT,
CDCl3, 100 MHz) d=181.7, 153.0, 150.0, 149.8, 149.6, 147.1, 143.9, 143.2,
142.6, 141.6, 139.3, 139.04, 138.95, 137.41, 137.35, 136.5, 134.73, 134.67,
134.5, 132.1, 131.8, 131.2, 131.1, 130.8, 129.8, 127.8, 127.6, 126.3, 123.7,
122.3, 121.1, 119.2, 118.9, 118.8, 118.6, 90.8, 90.6, 32.3, 31.7, 31.61, 31.55,
31.50, 31.4, 31.1, 29.7, 29.43, 29.36, 29.33, 27.23, 27.16, 27.1, 26.4, 22.65,
22.57, 21.8, 21.7, 21.5, 14.18, 14.11, 14.05 ppm; UV/Vis (CH2Cl2): lmax
(e)=300.5 (40800), 357.5 (26500), 422 (464300), 465.5 (76400), 549.5
(26800), 590 nm (5480 dm3 molꢀ1 cmꢀ1); MS (MALDI-TOF): m/z calcd.
(%) for C98H106N4S2OZn: 1483.71 (87), 1484.71 (100), 1485.73 (82);
found: 1483.95 (93), 1484.92 (100), 1485.89 (95) [M]+.
Synthesis of 12: Compound 12 was prepared according to the same pro-
cedure as described for compound 11, from a solution of (E,E)-10
(50.4 mg, 21.8 mmol, 1 equiv), sarcosine (59.0 mg, 662 mmol, 30 equiv),
and C60 (58.9 mg, 81.8 mmol, 4 equiv) in chlorobenzene (50 mL). After
evaporation of chlorobenzene under reduced pressure, the crude mixture
was dissolved in a minimum amount of CS2 and purified by column chro-
matography on silica gel, first eluting with CS2 to remove any unreacted
C60, then with toluene to recover a mixture of products. After evapora-
tion of the solvents, the crude material was purified twice by gel permea-
tion chromatography (toluene) and twice by column chromatography on
silica gel (CS2/CH2Cl2, 8:2). Compound (E,E)-12 was obtained as a glassy
dark-purple product in 49% yield (32.5 mg, 10.6 mmol). 1H NMR
Synthesis of (E,E)-10: Compound (E,E)-10 was prepared according to
the same procedure as compound 9, from a mixture of (E,E)-8a/8b
(150 mg; 77 mol%, 160 mmol bis-alkyne (E,E)-8a and 23 mol%,
47.9 mmol mono-alkyne (E,E)-8b), [5-p-iodophenyl-10,15,20-tris-(2,4,6-
trimethylphenyl) zinc porphyrin][14] (500 mg, 537 mmol), AsPh3 (30 mg,
212 mmol), [Pd2ACHTUNGTRENNUNG(dba)3] (60 mg, 65.5 mmol), in toluene (80 mL) and Et3N
3
3
(16 mL). After evaporation of the solvents, the crude product was filtered
through a small plug of silica gel (toluene). The volume of the solution
was reduced to 1 mL and the mixture was purified by gel permeation
chromatography. The first major band that contained (E,E)-10 was puri-
fied twice more by gel permeation chromatography and three times by
column chromatography on silica gel (n-hexane/CHCl3/Et3N, 5:5:0.01) to
afford (E,E)-10 (329 mg, 142 mmol) as a dark-purple solid in 89% yield
(based on the effective amount of starting (E,E)-8a). 1H NMR (CDCl3,
400 MHz) d= 9.66 (s, 1H), 8.98 (d, 4H, 3J=4.6 Hz), 8.87 (d, 4H, 3J=
4.6 Hz), 8.80 (s, 8H), 8.35 (d, 4H, 3J=7.8 Hz), 8.06 (d, 4H, 3J=7.8 Hz),
(CDCl3, 400 MHz) d=8.94 (d, 4H, J=4.6 Hz), 8.82 (d, 4H, J=4.6 Hz),
8.75 (s, 8H), 8.31 (d, 4H, 3J=7.8 Hz), 8.02 (d, 4H, 3J=7.8 Hz), 7.91 (s,
1H), 7.83 (s, 2H), 7.45 (d, 1H, 3Jtrans =15.8 Hz), 7.31 (s, 12H), 7.10 (s,
2H), 6.98 (d, 1H, 3Jtrans =15.8 Hz), 5.31 (s, 1H), 4.93 (d, 1H, 2J=9.7 Hz),
4.20 (d, 1H, 2J=9.7 Hz), 2.95 (s, 3H), 2.85–2.53 (m, 26H), 1.88 (s, 36H),
1.67–1.26 (m, 32H), 1.04–0.88 ppm (m, 12H); 13C NMR (APT, CDCl3,
100 MHz) d=155.7, 153.8, 153.15, 153.10, 150.0, 149.9, 149.8, 149.6,
146.89, 146.86, 146.4, 146.1, 146.0, 145.9, 145.8, 145.73, 145.72, 145.6,
145.5, 145.24, 145.19, 145.14, 144.99, 144.97, 144.91, 144.8, 144.3, 144.2,
144.0, 143.9, 143.4, 143.2, 142.9, 142.8, 142.6, 142.3, 142.23, 142.20, 142.1,
141.96, 141.85, 141.77, 141.74, 141.72, 141.69, 141.62, 141.3, 141.2, 140.4,
139.8, 139.7, 139.58, 139.56, 139.3, 139.0, 138.9, 138.4, 137.9, 137.4, 137.1,
136.4, 136.0, 135.4, 135.2, 134.6, 134.3, 133.3, 132.9, 131.9, 131.2, 131.1,
130.8, 129.9, 129.2, 127.7, 125.8, 124.2, 122.1, 122.0, 120.1, 119.5, 119.2,
119.0, 118.8, 90.3, 89.6, 77.8, 70.0, 68.8, 40.6, 31.8, 31.74, 31.69, 31.59,
31.44, 31.39, 29.7, 29.6, 29.49, 29.46, 29.1, 27.9, 27.2, 27.0, 22.72, 22.69,
22.66, 21.8, 21.7, 21.5, 14.23, 14.22, 14.20 ppm; FTIR (KBr): n˜ =2951,
2921, 2853, 1459, 1204, 999, 798, 723, 527 cmꢀ1; UV/Vis (CH2Cl2): lmax
(e)=255 (163000), 301 (109000), 422.5 (978000), 550 (48000), 590 nm
(9930 dm3 molꢀ1 cmꢀ1); MS (MALDI-TOF): m/z calcd (%) for
C215H156N9S2Zn2: 3059.05 (94), 3060.05 (100), 3061.05 (95); found: 3059.12
(94), 3060.08 (100), 3061.10 (96) [M+H]+.
7.98 (s, 1H), 7.90 (s, 2H), 7.52 (d, 1H, 3Jtrans =15.8 Hz), 7.34 (d, 1H,
3
3Jtrans =15.8 Hz), 7.35 (s, 8H), 7.34 (s, 4H), 7.10 (2ꢃd, 2H, Jtrans
=
15.8 Hz), 2.84 (2ꢃqt, 4H, 3J=7.5 Hz), 2.69 (br s, 22H), 1.93 (s, 36H),
1.75–1.30 (m, 32H), 1.09–0.91 ppm (m, 12H); 13C NMR (APT, CDCl3,
100 MHz) d=181.6, 153.02, 152.97, 150.03, 150.01, 149.8, 149.6, 147.1,
143.9, 143.6, 143.0, 141.7, 139.3, 139.1, 139.0, 138.1, 137.4, 136.2, 135.0,
134.65, 134.56, 133.6, 131.9, 131.25, 131.17, 130.8, 129.9, 129.3, 127.7,
126.9, 124.4, 123.7, 122.1, 121.9, 119.1, 119.0, 118.85, 118.77, 90.5, 89.5,
32.2, 31.74, 31.69, 31.65, 31.55, 31.4, 31.2, 29.7, 29.48, 29.46, 29.36, 27.29,
27.17, 26.5, 22.72, 22.67, 22.6, 21.8, 21.7, 21.5, 14.2, 14.11, 14.05 ppm; UV/
Vis (CH2Cl2): lmax (e)=279 (50500), 422.5 (683000), 456.5 (40750), 550
(33100), 590 nm (6 290 dm3 molꢀ1 cmꢀ1); MS (MALDI-TOF): m/z calcd
(%) for C153H150N8OS2Zn2: 2312.00 (100), 2313.00 (97.8); found: 2312.44
[M]+.
Synthesis of 11: A solution of (E,E)-9 (30.5 mg, 20.5 mmol, 1 equiv), sar-
cosine (45.5 mg, 511 mmol, 25 equiv), and C60 (45.5 mg, 63.2 mmol,
3 equiv) in chlorobenzene (40 mL) was thoroughly degassed by bubbling
through argon for 30 min. The solution was then heated to reflux for 12 h
under an argon atmosphere. After cooling to room temperature, chloro-
benzene was removed under reduced pressure and the crude mixture was
Acknowledgements
Financial support from the Ministerio de Ciencia y Tecnologꢀa of Spain,
FEDER funds (Project CTQ2010–17498), the Consolider Project HOPE,
Chem. Eur. J. 2012, 00, 0 – 0
ꢂ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
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S. Fukuzumi, F. Langa et al.
and the JJCC de Castilla-La Mancha (Project PEII11–0195–1214),
a Grant-in-Aid (Nos. 20108010 and 23750014) and the Global COE pro-
gram “Global Education and Research Center for Bio-Environmental
Chemistry” of Osaka University from the Ministry of Education, Culture,
Sports, Science and Technology, Japan, and from the KOSEF/MEST
through the WCU project (R31–2008–000–10010–0) are gratefully ac-
knowledged.
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1
[13] The ratio was estimated by H NMR spectroscopy.
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Zinc-Porphyrin–Oligothienylenevinylene–C60 Ensembles
FULL PAPER
[20] D. Laage, W. H. Thompson, M. Blanchard-Desce, J. T. Hynes, J.
Phys. Chem. A 2003, 107, 6032–6046.
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Received: July 22, 2011
Revised: February 17, 2012
Published online: && &&, 2012
Chem. Eur. J. 2012, 00, 0 – 0
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S. Fukuzumi, F. Langa et al.
Bridge over troubled waters: Photoin-
duced charge separation occurred in
an electron donor–bridge–acceptor
tetrad, which incorporated C60 and two
porphyrin groups that were covalently
linked through a phenylethynyl oligo-
thienylenevinylene bridge, by ultrafast
energy transfer from the photoexcited
porphyrin to C60 (EnT).
Energy Transfer
M. Urbani, K. Ohkubo, D. M. S. Islam,
S. Fukuzumi,* F. Langa* . . . &&&& — &&&&
Photoinduced Energy and Electron
Transfer in Phenylethynyl-Bridged
Zinc Porphyrin–Oligothienyleneviny-
lene–C60 Ensembles
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These are not the final page numbers!