Supramolecular tetrad of subphthalocyanine-triphenylamine-zinc porphyrin coordinated to fullerene as an "antenna-reaction-center" mimic: formation of a long-lived charge-separated state in nonpolar solvent

Article abstract of DOI:10.1002/chem.201000045

We report here the formation of a long-lived charge-separated state of a self-assembled donor-acceptor tetrad, formed by axial coordination of a fulleropyrrolidine appended with an imidazole coordinating ligand (C ₆₀Im) to the zinc center of a subphthalocyanine-triphenylamine-zinc porphyrin (SubPc-TPA-ZnP), as a charge-stabilizing antenna reaction center mimic in toluene. The subphthalocyanine and triphenylamine entities, with their high-energy singlet states, act as an energy-transferring antenna unit to produce a singlet zinc porphyrin. The formation constant for the self-assembled tetrad was determined to be 1.0×10⁴M^-1, suggesting a moderately stable complex-formation. The geometric and electronic structures of the covalently linked SubPc-TPA-ZnP triad and self-assembled SubPc-TPA-ZnP:C₆₀Im tetrad were examined by using an ab initio B3LYP/6-31G method. The majority of the highest occupied frontier molecular orbital was found over the ZnP and TPA entities, whereas the lowest unoccupied molecular orbital was located over the fullerene entity, suggesting the formation of the radical-ion pair (SubPc-TPA-ZnP^·+:C ₆₀Im^·-). The redox measurements revealed that the energy level of the radical-ion pair in toluene is located lower than that of the singlet and triplet states of the zinc porphyrin and fullerene entities. The femtosecond transient absorption measurements revealed fast charge separation from the singlet porphyrin to the coordinated C₆₀Im with a life-time of 1.1 ns. Interestingly, slow charge recombination (1.6 × 10⁵ s^-1) and the long lifetime of the charge-separated state (6.6 μs) were obtained in toluene by utilizing the nanosecond transient measurements.

Full text of DOI:10.1002/chem.201000045

FULL PAPER
DOI: 10.1002/chem.201000045
Supramolecular Tetrad of Subphthalocyanine–Triphenylamine–Zinc
Porphyrin Coordinated to Fullerene as an “Antenna-Reaction-Center”
Mimic: Formation of a Long-Lived Charge-Separated State in Nonpolar
Solvent
Mohamed E. El-Khouly,[a] Dong Kyu Ju,[b] Kwang-Yol Kay,*[b] Francis DꢀSouza,*[c] and
Shunichi Fukuzumi*[a, d]
+
C
CÀ
Abstract: We report here the formation
of a long-lived charge-separated state
formation. The geometric and electron-
ic structures of the covalently linked
SubPc–TPA–ZnP triad and self-assem-
bled SubPc–TPA–ZnP:C60Im tetrad
were examined by using an ab initio
B3LYP/6-31G method. The majority of
the highest occupied frontier molecular
orbital was found over the ZnP and
TPA entities, whereas the lowest unoc-
cupied molecular orbital was located
over the fullerene entity, suggesting the
formation of the radical-ion pair
(SubPc–TPA–ZnP :C60Im ).
The
redox measurements revealed that the
energy level of the radical-ion pair in
toluene is located lower than that of
the singlet and triplet states of the zinc
porphyrin and fullerene entities. The
of
a self-assembled donor–acceptor
tetrad, formed by axial coordination of
a fulleropyrrolidine appended with an
imidazole coordinating ligand (C60Im)
to the zinc center of a subphthalocya-
femtosecond
transient
absorption
nine–triphenylamine–zinc
porphyrin
measurements revealed fast charge
separation from the singlet porphyrin
to the coordinated C60Im with a life-
time of 1.1 ns. Interestingly, slow
charge recombination (1.6ꢀ105 sÀ1) and
the long lifetime of the charge-separat-
ed state (6.6 ms) were obtained in tolu-
ene by utilizing the nanosecond transi-
ent measurements.
(SubPc–TPA–ZnP), as a charge-stabi-
lizing antenna reaction center mimic in
toluene. The subphthalocyanine and
triphenylamine entities, with their high-
energy singlet states, act as an energy-
transferring antenna unit to produce a
singlet zinc porphyrin. The formation
constant for the self-assembled tetrad
was determined to be 1.0ꢀ104 mÀ1, sug-
gesting a moderately stable complex
Keywords: artificial photosynthesis ·
electron transfer · fullerenes · por-
phyrinoids · subphthalocyanines ·
supramolecular chemistry
Introduction
entities are arranged through noncovalent incorporation
into a well-defined protein matrix.[1] The light-induced elec-
tron transfer and energy transfer events occur between
these well-organized pigments with a high quantum efficien-
The X-ray structures of the bacterial photosynthetic reaction
centers have revealed that the electron donor and acceptor
[a] Dr. M. E. El-Khouly, Prof. Dr. S. Fukuzumi
Department of Material and Life Science
Graduate School of Engineering
Osaka University
[c] Prof. Dr. F. DꢁSouza
Department of Chemistry
Wichita State University
1845 Fairmount, Wichita, KS, 67260-0051 (USA)
Fax : (+1)316-978-3431
E-mail: Francis.dsouza@wichita.edu
SORST, Science and Technology Agency (JST)
Suita, Osaka 565-0871 (Japan)
Fax : (+81)6-6879-7370
E-mail: fukuzumi@chem.eng.osaka-u.ac.jp
[d] Prof. Dr. S. Fukuzumi
Department of Bioinspired Science
Ewha Womans University
Seoul 120-750 (South Korea)
[b] D. K. Ju, Prof. Dr. K.-Y. Kay
Department of Molecular Science and Technology
Ajou University, Suwon 443-749 (South Korea)
Fax : (+82)31-219-1615
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201000045.
E-mail: kykay@ajou.ac.kr
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cy.[1] Owing to their importance in light-energy harvesting
and developing optoelectronic devices, development of rela-
tively simple donor–acceptor model systems designed to
mimic the events of the photosynthetic reaction center has
been one of the important goals of chemistry during the
past two decades.[2–15] More recently, researchers have begun
incorporating not only the ꢃreaction centerꢁ electron-transfer
functionality, but also the energy transfer ꢃantennaꢁ function-
ality into artificial photosynthetic constructs. In the devel-
oped artificial systems, energy-funneling antenna molecules
have been elegantly connected to the donor–acceptor sys-
tems to probe sequential energy- and electron-transfer pro-
cesses, thus mimicking the complex “antenna-reaction
center” functionality of photosynthesis.
Although a substantial amount of progress in terms of
charge stabilization has been accomplished in covalently
linked donor–acceptor systems, achieving similar results on
a self-assembled donor–acceptor has been challenging be-
cause of the occurrence of multiple equilibrium processes
and the inferior stability of the adopted self-assembly ap-
proaches.[15] In the hope of finding a long-lived charge-sepa-
rated state in the self-assembled systems, we report here a
novel example of a triad and tetrad comprising porphyrin,
triphenylamine, subphthalocyanine, and fullerene entities, as
antenna-reaction center mimics (Figure 1). The rationale for
choosing the different entities and the design concepts are
as follows: porphyrin, the pigment of life, is a suitable pri-
mary electron donor owing to its resemblance to the natural
photosynthetic chlorophyll pigment, easy synthetic manipu-
lations, extensive absorption, and favorable redox proper-
ties.[16] To increase the donor ability of zinc porphyrin (low-
ering the oxidation potential), the electron-rich triphenyla-
mine (TPA) entity is substituted at the meso position of the
zinc–porphyrin ring. Owing to the close proximity of the
TPA entity to the porphyrin p ring, delocalization of the
porphyrin p system over the triphenylamine entity is expect-
ed.[17] The comparatively electron-deficient, subphthalocya-
nine, SubPc, in 1 plays the role of the antenna unit. The
SubPc entity possesses i) strong absorption in the visible
region (l=500–700 nm), ii) higher energy of the singlet ex-
cited state (2.16 eV) and triplet excited state (1.40 eV) com-
pared with those of phthalocyanines, and iii) relatively low
reorganization energies.[13,14] The covalently linked sub-
phthalocyanine–triphenylamine–zinc porphyrin 1, owing to
the presence of three chromophores absorbing different por-
tions of the visible spectrum, guarantees an increased ab-
sorption cross-section and an efficient use of the solar
energy. Finally, fullerene,[18] the ultimate electron accept-
or,[8–15] has been utilized to construct the supramolecular
tetrad 2 by a self-assembly approach involving axial coordi-
nation.[15] Here, an imidazole-appended fullerene has been
chosen over the pyridine-appended fullerene because of its
increased ability to form stable coordination bonds with
metal ions in the porphyrin cavity.[15,20] The presence of full-
erene is expected to stabilize the charge-separated state,
owing to favorable energy states and low-reorganization
energy.[21]
The electron-transfer process from the electron-donating
ZnP and TPA entities to the electron-accepting subphthalo-
+
CÀ
C
cyanine to form SubPc –TPA–ZnP in 1 is confirmed in
this study by different photochemical techniques. To achieve
a long-lived charge-separate state in nonpolar toluene, the
self-assembled tetrad 2 is formed in toluene (Figure 1).
Owing to the varying redox and optical properties of the dif-
ferent entities of the tetrad, several interesting properties
are envisioned in the tetrad: i) the subphthalocyanine entity
with its higher singlet state (2.16 eV) is expected to act as an
energy-transferring antenna unit to the zinc porphyrin and
to promote electron transfer to the electron-accepting fuller-
ene entity, ii) the triphenylamine entity with its higher sin-
glet state (2.55 eV) is also expected to be an energy-transfer-
ring antenna unit to the zinc porphyrin in addition to stabi-
lizing the charge-separated state,[17] and iii) owing to the
+
C
lower energy level of the radical-ion pair SubPc–TPA–ZnP
CÀ
:C60Im compared to the lowest excited singlet and triplet
states of both porphyrin and fullerene entities in nonpolar
toluene, formation of a long-lived charge-separated state of
+
C
CÀ
SubPc–TPA–ZnP :C60Im is expected. The latter is not a
common feature in the case of ZnP–C60 dyads, owing to the
undesired charge recombination of the radical-ion pair to
the low-lying triplet states of porphyrin and fullerene.[15,20,21]
The photochemical processes were examined in nonpolar
toluene, keeping in consideration that the protein environ-
ment surrounding the photosynthetic reaction center is non-
polar with a low dielectric constant eꢀ2.25.
Figure 1. Structures of the presently developed and investigated SubPc–
TPA–ZnP triad 1 and the self-assembled SubPc–TPA–ZnP:C60Im tetrad
2.
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A Zinc Porphyrin Coordinated to Fullerene
FULL PAPER
Results and Discussion
ZnP 1 in 82% yield. Reference compounds ZnP-TPA 12
and ZnP 3 were also synthesized in a similar way, and
SubPc-TPA was prepared according to the method previous-
ly reported by our group.[13]
Synthesis and characterization: Subphthalocyanine–triphe-
nylamine–zinc porphyrin (1) and its reference compounds,
ZnP–TPA (12) and ZnP (3) were prepared, as depicted in
Scheme 1. Every step of the reaction sequence proceeded
smoothly to give a good or moderate yield of the product.
Briefly, commercially available diphenylamine was coupled
with 4-iodoanisole under Ullmann conditions[22] to give 4-
methoxytriphenylamine (4) in 86% yield, and subsequently
Vilsmeier formylation[23] was carried out to produce alde-
hyde 5 in 94% yield. Metal-free asymmetrical porphyrin 6
was prepared according to a typical method for porphyrin
synthesis[24] in a yield of 8%, and subsequent demethylation
of the methoxy group in 6 was performed by using BBr3 to
give porphyrin 7 in 69% yield. The hydroxy group in 7 re-
placed the axial chlorine atom of SubPc-Cl, which was syn-
thesized according to the literature procedures,[13,14] to pro-
duce SubPc–TPA–H2P 8 in 10% yield. Finally, metalation
was carried out using zinc acetate to afford SubPc–TPA–
Computational studies: To gain insight into the molecular
geometry and electronic structure, computational studies
were performed by using the ab initio B3LYP/6-31G
method. In the optimized structure of 1 (see Figure S1 in
the Supporting Information), the center-to-center distance
(dCC) between the Zn center and the B center of SubPc was
13.6 ꢄ. The electron cloud of the highest occupied frontier
molecular orbital (HOMO) was delocalized over the por-
phyrin macrocycle and the triphenylamine entities, while the
lowest unoccupied molecular orbital (LUMO) was fully lo-
calized over the SubPc entity. These results suggest that the
TPA–ZnP act as electron donors, whereas the SubPc acts as
+
CÀ
C
an electron acceptor, to afford SubPc –TPA–ZnP
.
When C60Im is axially coordinated with ZnP–TPA–SubPc
(Figure 2), the center-to-center distances between the C60Im
Scheme 1. Synthesis of compounds 1, 2, and 3. a) K2CO3, Cu, [18]crown-6, o-dichlorobenzene, 1808C, 36 h, 86%; b) POCl3, DMF, 1,2-dichloroethane,
reflux, 4 h, 94% for 5, 12 h, 85% for 9; c) 1) hexanal, pyrrole, BF3·O(C2H5)2, 2) DDQ, triethylamine, 2-propanol, dichloromethane, RT, 3 h, 8% for 6
and 10; d) BBr3, dichloromethane, RT, 12 h, 69%; e) SubPc-Cl, toluene, reflux, 6 days, 10%; f) zinc acetate, dichloromethane, methanol, RT, 1 h, 82%
for 1, 92% for 12, and 88% for 3; g) 1) pyrrole, BF3·O(C2H5)2, 2) DDQ, 2-propanol, dichloromethane, RT, 3 h, 11%.
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
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S. Fukuzumi, K.-Y. Kay, F. D’Souza et al.
Figure 3. Cyclic voltammograms of 1 and self-assembled 2 in CH2Cl2 con-
taining 0.1m (n-C4H9)4NClO4. Scan rate=100 mVsÀ1
.
chlorobenzene, and toluene, respectively.[25] Based on the
ÀDGCR value, the driving forces of the charge-separation
process (ÀDGCSS) through the singlet porphyrin (2.06 eV)
were estimated to be 0.49, 0.29, and 0.17 eV in benzonitrile,
o-dichlorobenzene, and toluene, respectively.[25]
Figure 2. Frontier HOMO and LUMO orbitals of self-assembled 2.
and ZnP and SubPc of the formed supramolecular system
were computed to be 11.7 and 22.7 ꢄ, respectively. The elec-
tron cloud of the HOMO and HOMOÀ1 were delocalized
over the porphyrin macrocycle and the substituted triphe-
nylamine entities, whereas the LUMO and LUMO+3 were
fully localized over the C60Im and SubPc entities, respective-
ly. These results suggest that the ZnP and TPA act as elec-
On the other hand, the redox measurements of self-as-
sembled 2 exhibited the first oxidation potential of ZnP and
the first reduction of C60Im and SubPc at 578, À689, and
À1078 mV versus SCE, respectively (Figure 3 and Figure S4
in the Supporting Information). From these findings, the
penta-coordinated ZnP formed by coordination of C60Im
with a Zn atom is found to be less positive than the ZnP of
1 by 88 mV (versus SCE), suggesting an increased electron-
donor ability of ZnP when photoinduced charge separation
takes place in 2.[26] From these values, the ÀDGCR and
tron donors, whereas the C60Im acts as an electron acceptor,
+
C
CÀ
to afford SubPc–TPA–ZnP :C60Im as the final charge-sep-
arated state. The orbital energies of the HOMO, HOMOÀ1,
LUMO, and LUMO+3 were found to be À4.41, À4.70,
À3.26, and À2.60 eV for the SubPc–TPA–ZnP:C60Im. The
calculated values of the HOMO–LUMO and HOMO–
LUMO+3 gaps (gas phase) were found to be 1.16 and
1.81 eV, respectively, which are in a good agreement with
the electrochemically measured (difference between the first
oxidation and first reduction potential) values, as discussed
below.
S
ÀDGCS values of the stabilized charge-separated SubPc–
+
C
CÀ
TPA–ZnP :C60Im were estimated as 1.36 and 0.70 eV, re-
spectively, in toluene. The finding that the energy level of
+
C
CÀ
SubPc–TPA–ZnP :C60Im is lower than the energy of both
the triplet porphyrin (1.55 eV) and C60 (1.53 eV) suggests
the exothermic electron transfer via the triplet porphyrin
(ÀDGCST =0.17 eV) and fullerene (ÀDGCST =0.15 eV) in tol-
uene.
Electrochemical studies and electron transfer driving forces:
The redox measurements were carried out by using cyclic
voltammogram (CV) and differential pulse voltammogram
(DPV) techniques in deaerated dichloromethane (CH2Cl2)
to estimate the driving forces for the electron-transfer pro-
cesses. The first oxidation potential (Eox) of 12 is located at
690 mV versus SCE that is less positive by 20 mV compared
to 3 (see Figures S2 and S3 in the Supporting Information),
suggesting that the triphenylamine unit slightly improves the
electron-donor ability of ZnP. The redox measurements of 1
show the first oxidation of the ZnP and the first reduction
potential (Ered) of SubPc at 666 and À1111 mV versus SCE,
respectively (Figure 3). Based on the first Eox and Ered
Steady-state UV/Vis spectral studies: As shown in Figure 4,
the absorption spectra of the reference SubPc consist of a
high-energy B-band (l=311 nm) and lower energy Q-bands
(l=518 and 565 nm) arising from p–p* transitions, which
are associated with 14 p-electron systems, analogous to
those of porphyrins and phthalocyanines. The absorption
spectra of the 3 exhibited a Soret band at l=423 nm and Q-
bands at l=557 and 599 nm, whereas the absorption band
of TPA was located at l=303 nm. In agreement with the
MO calculations and redox measurements, the ZnP Soret
band of 12 was red shifted by nearly 4 nm compared with
that of 3, suggesting interactions between the porphyrin p
system and the substituted triphenylamine entity. The elec-
tronic absorption spectra of 1 displayed common features of
values, the driving forces for the charge recombination
+
CÀ
C
(ÀDGCR) of SubPc –TPA–ZnP to the ground state were
calculated as 1.57, 1.77, and 1.89 eV in benzonitrile, o-di-
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A Zinc Porphyrin Coordinated to Fullerene
FULL PAPER
Emission studies: The photophysical behavior was first in-
vestigated using steady-state fluorescence. When the most
intense visible band at l=430 nm was excited, the fluores-
cence spectra of 12 revealed emission bands at l=605 and
653 nm. In the case of 1, the emission intensity of the ZnP
moiety was significantly quenched in benzonitrile, o-
dichloroACTHNUTRGNEbUNG enzene, and toluene (Figure 6). These observations
Figure 4. Steady-state absorption spectra of 1 and the reference com-
pounds in toluene.
the electron-donor ZnP–TPA and the electron-acceptor
SubPc subunits, suggesting the absence of electronic interac-
tions between them in the ground state. Changing the sol-
vent to benzonitrile shifted the absorption spectrum to red
by about 5 nm compared to that in toluene and dichloroben-
zene.
Figure 6. Fluorescence spectra of 12 in toluene and 1 in different sol-
vents; lex =430 nm.
Upon coordination of C60Im with 1, the formation of the
pentacoordinated zinc porphyrin complex was characterized
by a diminished Soret band intensity, a 4 nm red-shift, and
the appearance of an isosbestic point at l=430 nm. This ob-
servation suggests that the imidazole unit attached to the
C60 was involved in coordination with the Zn atom, forming
self-assembled 2 (Figure 5). No new absorption bands in the
together with the calculated negative DGCS values from
1ZnP*, suggest that the charge-separation process occurs
1
from the electron-donating ZnP* to the electron-accepting
+
CÀ
C
SubPc, generating SubPc –TPA–ZnP in both polar and
nonpolar solvents.
When the SubPc was selectively excited at l=470–
580 nm, the emission band of 1SubPc*–TPA–ZnP around
l=571 nm was significantly quenched compared to that of
the SubPc reference (see Figure S5 in the Supporting Infor-
mation). With the decrease in the fluorescence intensity of
SubPc, we could detect the emission bands of the ZnP
entity, which were not clearly observed for the ZnP refer-
ence within this range of excitation wavelengths under the
experimental conditions. This suggests that the observed
porphyrin emission is a result of energy transfer from the
singlet subphthalocyanine (2.16 eV) to the singlet porphyrin
(2.06 eV). Excitation spectra of 1, recorded by fixing the
emission monochromator to the porphyrin emission maxi-
mum in the range of l=580–670 nm, revealed a subphthalo-
cyanine absorption in addition to ZnP absorption bands (see
Figure S6 in the Supporting Information). This observation
confirms that the observed porphyrin emission is a result of
singlet energy transfer from the subphthalocyanine entity to
the porphyrin.
Figure 5. UV/Vis spectral changes observed during the complexation of 1
with C60Im in toluene. Inset: Benesi–Hildebrand plot for the change of
absorbance at l=426 nm constructed to obtain the binding constant.
The fluorescence lifetime measurements support the con-
siderations derived from the steady-state fluorescence spec-
tra in a more quantitative way (see Figure S7 in the Sup-
porting Information). The ZnP reference exhibited mono-
exponential decay with a lifetime (tf) of 2080 ps, which is in
a good agreement with the reported value. In the case of 1,
the fluorescence decay-time profile of ZnP was fitted satis-
factorily with mono-exponential decay with a lifetime of less
than 100 ps. Such a shortening of the fluorescence lifetime
near IR region were observed, suggesting the absence of p–
p type interactions between them. The Benesi–Hildebrand
plot[27] constructed from the absorbance data revealed a
straight line with K=1.1ꢀ104 mÀ1 (see Figure 5 inset), indi-
cating stable complex formation. The binding constant of
the self-assembled 2 is considerably high compared with
many-studied axial ligands.[28]
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S. Fukuzumi, K.-Y. Kay, F. D’Souza et al.
indicates the occurrence of charge separation via the singlet
+
CÀ
C
ZnP to the attached SubPc, generating SubPc –TPA–ZnP .
Based on the fluorescence lifetimes of the SubPc–
TPA–1ZnP* and ZnP reference, the rates of fluorescence
S
quenching (kq ) were evaluated to be as much as 1010 sÀ1 in
both polar benzonitrile and nonpolar toluene.
Upon addition of C60Im to a solution of 1 in toluene, the
fluorescence intensity of the singlet ZnP was significantly
quenched (see Figure S8 in the Supporting Information).
Scanning the emission wavelength to longer wavelength re-
gions (l=700–775 nm) revealed no emission of the fullero-
pyrrolidine moiety at l=720 nm. The ZnP emission intensi-
ty decreased as the concentration of the fulleropyrrolidine
increased, suggesting the occurrence of electron transfer
from the singlet ZnP to C60Im. The binding constant for the
supramolecular complex formation was evaluated by con-
structing a Benesi–Hildebrand plot of the quenching data.
As shown in the inset of Figure S8 in the Supporting Infor-
mation, the calculated binding constant was found to be
1.1ꢀ104 mÀ1, a value close to that calculated from the optical
data shown in Figure 5, suggesting a moderately stable com-
plex formation.
Femtosecond and nanosecond transient absorption measure-
ments: Spectroscopic evidence for the occurrence of elec-
tron transfer in 1 was obtained from femtosecond transient
absorption measurements in benzonitrile and toluene
(Figure 7) by using 430-nm laser light, with which the ZnP
moiety is selectively excited. In the time-resolved spectrum
at 1 ps, the absorption band at l=470 nm is assigned to
1ZnP*, whereas the spectra at >6 ps, which show absorption
peaks in the visible region, are ascribed to the formation of
Figure 7. Differential transient absorption spectra obtained upon femto-
second photoexcitation (l=430 nm) of 1 (upper) and self-assembled 2
(lower) in deaerated toluene. lex =430 nm.
CÀ
C
the radical-ion pair SubPc –TPA–ZnP +. The time-profile
+
C
of TPA–ZnP in the visible region (Figure 7, inset) shows a
fast rise, from which the rate of the charge-separation pro-
cess (kCSS) via ZnP* was calculated to be 8.9ꢀ1010 sÀ1. On
1
+
C
the other hand, the decay-profile of TPA–ZnP was ob-
served, as shown in inset of Figure 8, from which the rate
constant of the charge-recombination process (kCR) and the
lifetime of the radical-ion pair (tRIP =1/kCR) were evaluated
to be 3.9ꢀ109 sÀ1 and 256 ps, respectively. When changing
the solvent to toluene, the kCR and tRIP values were evaluat-
ed to be 7.1ꢀ109 sÀ1 and 140 ps, respectively. These results
are qualitatively in agreement with a charge-recombination
processes occurring in the normal region of the Marcus
plot.[29–31]
Figure 8. Nanosecond transient spectra of self-assembled 2 in deaerated
toluene. lex =430 nm.
The femtosecond transient absorption measurements of
the self-assembled tetrad 2 in nonpolar toluene showed the
+
C
absorption of TPA–ZnP in the visible region between 650
CÀ
and 800 nm, together with the near-IR absorption of C60Im
with a maximum at l=1000 nm, confirming the formation
Nanosecond transient absorption measurements: The nano-
second transient spectra of the reference 12 in toluene, by
employing 430-nm laser light, exhibited the absorption of
triplet ZnP at l=450 nm. The triplet-state decayed to the
ground state with a rate of 1.0ꢀ104 sÀ1. In the case of 1, the
recorded absorption spectra in both benzonitrile and tolu-
ene are similar to that of ZnP, suggesting the absence of
of the radical ion pair SubPc–TPA–ZnP +:C60 . The time-
C
CÀ
CÀ
profile of C60Im in the NIR region (Figure 7, inset) shows
a fast rise, from which the rate of the charge-separation pro-
cess (kCSS) from the singlet ZnP to C60Im was calculated as
8.0ꢀ1011 sÀ1. The kCR and tRIP values were evaluated to be
6.3ꢀ108 sÀ1 and 1.1 ns, respectively.
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A Zinc Porphyrin Coordinated to Fullerene
FULL PAPER
electron transfer via triplet ZnP (see Figure S9 in the Sup-
porting Information). The absorption intensity of SubPc–
TPA–3ZnP* was significantly decreased compared with the
3
triplet ZnP* and decayed with a rate of 1.0ꢀ104 sÀ1.
In the case of self-assembled 2, it was interesting to detect
+
C
the transient absorption bands of TPA–ZnP in the visible
region (see Figure S10 in the Supporting Information) and
CÀ
C60Im in the NIR region in the microseconds region
(Figure 8). This observation demonstrates the generation of
the radical-ion pair in toluene. From the energetic point of
view, the electron transfer from the triplet porphyrin to the
attached C60Im in toluene is exothermic. The decay of
CÀ
C60Im was fit by first-order kinetics, suggesting the absence
of the bimolecular electron-transfer process. The kCR and
+
C
CÀ
tRIP values of SubPc–TPA–ZnP :C60Im were estimated to
be 1.6ꢀ106 sÀ1 and 6.6 ms, respectively. We believe that this
long-lived charge-separated state is a consequence of the
persistence of the triplet-correlated radical-ion pair charac-
ter, which results in the corresponding forbidden character
of the charge recombination back to the singlet ground
state. In other words, the triplet multiplicity of the radical
ion-pair, which is populated from the electron transfer from
the triplet porphyrin to the attached C60Im, plays an impor-
tant role in determining its long lifetime. The quick decay of
the radical species in oxygen-saturated toluene confirms the
+
C
CÀ
triplet-spin character of the SubPc–TPA–ZnP :C60Im .
The energy-level diagrams, shown in Figure 9, summarize
the observed intramolecular events of 1 and the self-assem-
bled 2. The energy level of the radical-ion pair, SubPc–
+
C
CÀ
TPA–ZnP :C60Im , which was calculated by using Eox, Ered
,
Figure 9. Energy level diagrams of 1 in different solvents and self-assem-
bled 2 in toluene. lex =430 nm.
and the center-to-center distance (RCC), is found to be lower
than the level of the excited singlet and triplet states of both
ZnP and C60Im. The electron transfer via the singlet ZnP
was observed by the femtosecond laser spectral measure-
gests that the charge recombination is occurring in the
normal region of the Marcus plot.
ments in the order of picoseconds. Interestingly, the unusual
+
C
long-lived charge-separated state of SubPc–TPA–ZnP
Interestingly, in the supramolecular tetrad 2, obtained by
axial coordination of C60Im to ZnP–TPA–SubPc, we ach-
ieved the anticipated charge stabilization in nonpolar sol-
vents. The formation constant for the self-assembled tetrad
was determined to be 1.0ꢀ104 mÀ1, suggesting a moderately
stable complex formation. The electrochemical measure-
CÀ
:C60 in the order of microseconds was clearly observed in
toluene. From a point of view of mechanistic information,
the advantage of supramolecular 1:C60Im is that both the
+
C
lifetimes of the singlet and triplet SubPc–TPA–ZnP
:C60Im could be determined.
CÀ
ments revealed that the energy level of the radical-ion pair
+
C
CÀ
(SubPc–TPA–ZnP :C60Im ) is located lower than that of
the singlet and triplet states of the zinc porphyrin and the
fullerene entities. The geometric and electronic structures of
the tetrad, examined by ab initio B3LYP/6-31G methods, re-
vealed the HOMO to be over the ZnP and TPA entities,
Conclusion
The synthesis, characterization, and photochemical events in
the molecular triad, SubPc–TPA–ZnP, comprising a sub-
phthalocyanine, triphenylamine, and a zinc porphyrin, is de-
scribed. Excitation of SubPc in the triad resulted in efficient
energy transfer to the ZnP entity. By utilizing femtosecond
laser photolysis, the electron transfer from the singlet ZnP,
which is generated either by energy transfer from SubPc or
whereas the LUMO to be over the fullerene entity, suggest-
+
C
CÀ
ing that the formation of SubPc–TPA–ZnP -C60Im as the
charge-separation products. The main quenching pathway
involved electron transfer from the singlet excited ZnP to
the C60Im moiety. The rate constant of the forward electron
transfer, kCS, was determined to be 8ꢀ1011 sÀ1. Interestingly,
a slow charge recombination (1.6ꢀ105 sÀ1) and the long life-
time of the charge-separated state (6.6 ms) were obtained in
toluene by utilizing nanosecond transient measurements.
The formation of a long-lived charge-separated state in the
through direct excitation, to the electron-accepting SubPc
CÀ
C
+
was observed, forming SubPc –TPA–ZnP with lifetimes
of 256 and 140 ps in benzonitrile and toluene, respectively.
The finding that the lifetime of SubPc –TPA–ZnP is
longer in polar benzonitrile than in nonpolar toluene sug-
CÀ
C
+
Chem. Eur. J. 2010, 16, 6193 – 6202
ꢂ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
6199

S. Fukuzumi, K.-Y. Kay, F. D’Souza et al.
and the extract was dried over MgSO4, and evaporated. The residue was
chromatographed on silica gel with dichloromethane/n-hexane (3:1) to
give compound 5 (2.15 g, 94%) in a yellow solid. M.p. 86–878C; 1H NMR
(400 MHz, CDCl3): d=9.74 (s, 1H), 7.64 (d, J=4.8 Hz, 2H), 7.31 (m,
2H), 7.14 (d, J=4.8 Hz, 2H), 7.10 (m, 3H), 6.93 (d, J=4.8 Hz, 2H), 6.88
(d, J=4.4 Hz, 2H), 3.80 ppm (s, 3H); elemental analysis (%) calcd for
C20H17NO2: C 79.19, H 5.65, N 4.62; found: C 79.02, H 5.84, N 4.34.
tetrad was interpreted as a consequence of the persistence
of the triplet-correlated radical-ion pair character that is for-
bidden for charge recombination back to the singlet ground
state.
5-[4-{N-(4-Methoxyphenyl)-N-phenylamino}phenyl]-10,15,20-trisACHTUNGTRENNUNG(pentyl)-
Experimental Section
21H,23H-porphine (6): Boron trifluoride diethyl etherate (1.34 mL,
10.56 mmol) was added to a solution of compound 5 (2 g, 6.6 mmol),
hexanal (2.4 mL, 19.8 mmol), and pyrrole (1.8 mL, 26.4 mmol) in a mix-
ture of dichloromethane (2.6 L) and 2-propanol (17 mL). The mixture
was stirred at room temperature for 90 min. 2,3-Dichloro-5,6-dicyano-1,4-
benzoquinone (DDQ, 6 g, 26.4 mmol) was added and the mixture was
stirred at room temperature for 70 min. Finally triethylamine (3.7 mL,
26.4 mmol) was added and the mixture was stirred for 30 min. The sol-
vent was removed under reduced pressure and the product was chroma-
tographed on silica gel with chloroform/n-hexane (3:2) to give compound
Materials and instruments: Reagents and solvents were purchased as re-
agent grade and used without further purification. All reactions were per-
formed by using dry glassware under a nitrogen atmosphere. Analytical
TLC was carried out on Merck 60 F254 silica gel plates, and column
chromatography was performed on Merck 60 silica gel (230–400 mesh).
Melting points were determined by using an Electrothermal IA 9000
series melting point apparatus and are uncorrected. NMR spectra were
recorded by using a Varian Mercury-400 (400 MHz) spectrometer with a
TMS peak as reference. UV/Vis spectra were recorded by using a Jasco
V-550 spectrometer. MALDI-TOF MS spectra were recorded by using
an Applied Biosystems Voyager-DE-STR. Elemental analyses were per-
formed with a Perkin–Elmer 2400 analyzer. Steady-state fluorescence
spectra were measured by using a Shimadzu RF-5300 PC spectrofluoro-
photometer equipped with a photomultiplier tube having high sensitivity
in the l=700–800 nm region. Cyclic voltammograms were carried by
using a BAS CV-50W Voltammetric Analyzer. A platinum disk electrode
was used as working electrode, whereas a platinum wire served as a
counter electrode. SCE electrode was used as a reference electrode. All
measurements were carried out in CH2Cl2 containing 0.1m (n-
1
6 (0.42 g, 8%) as a purple solid. M.p. 868C; H NMR (400 MHz, CDCl3):
d=9.48 (m, 4H), 9.37 (d, J=4.4 Hz, 2H), 8.92 (d, J=4.8 Hz, 2H), 7.96
(d, J=4.4 Hz, 2H), 7.36 (m, 8H), 7.05 (m, 1H), 6.98 (d, J=8.8 Hz, 2H),
4.94 (m, 6H), 3.87 (s, 3H), 2.53 (m, 6H), 1.77 (m, 6H), 1.55 (m, 6H),
0.98 (m, 9H), À2.64 ppm (s, 2H); elemental analysis (%) calcd for
C54H59N5O: C 81.68, H 7.49, N 8.82; found: C 81.43, H 7.64, N 8.64.
5-[4-{N-(4-Hydroxyphenyl)-N-phenylamino}phenyl]-10,15,20-trisACHTUNGTRENNUNG(pentyl)-
21H,23H-porphine (7): Boron tribromide (1.0m solution in dichlorome-
thane) (0.56 mL, 0.56 mmol) was added to a solution of compound 6
(200 mg, 0.38 mmol) in dichloromethane (7 mL) at 08C and stirred for
30 min. The reaction mixture was stirred at room temperature for 12 h,
poured into water, and then extracted with dichloromethane (3ꢀ50 mL).
The extract was dried over Na2SO4, and evaporated. The residue was
chromatographed on silica gel with dichloromethane/methanol (100:1) to
C4H9)4NClO4 as the supporting electrolyte. The scan rate=100 mVsÀ1
.
Laser flash photolysis: The studied compounds were excited by using a
Panther OPO pumped by Nd:YAG laser (Continuum, SLII-10, 4–6 ns
fwhm) at l=430 nm with the powers of 1.5 and 3.0 mJ per pulse. The
transient absorption measurements were performed using a continuous
xenon lamp (150 W) and an InGaAs-PIN photodiode (Hamamatsu 2949)
as a probe light and a detector, respectively. The output from the photo-
diodes and a photomultiplier tube was recorded with a digitizing oscillo-
scope (Tektronix, TDS3032, 300 MHz). Femtosecond transient absorption
spectroscopy experiments were conducted using an ultrafast source: Inte-
gra-C (Quantronix Corp.), an optical parametric amplifier: TOPAS
(Light Conversion Ltd.) and a commercially available optical detection
system: Helios provided by Ultrafast Systems LLC. The source for the
pump and probe pulses were derived from the fundamental output of In-
tegra-C (780 nm, 2 mJ/pulse and fwhm=130 fs) at a repetition rate of
1 kHz. 75% of the fundamental output of the laser was introduced into
TOPAS which has optical frequency mixers resulting in tunable range
from l=285 to 1660 nm, whereas 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 assembled from the time-resolved spec-
tral data. All measurements were conducted at 298 K. The transient spec-
tra were recorded by using fresh solutions in each laser excitation.
1
give compound 7 (204 mg, 69%) as a purple solid. M.p. 1078C; H NMR
(400 MHz, CDCl3): d=9.48 (m, 4H), 9.37 (d, J=4.8 Hz, 2H), 8.92 (d, J=
4.8 Hz, 2H), 7.96 (d, J=4.0 Hz, 2H), 7.35 (m, 8H), 7.06 (m, 1H), 6.91 (d,
J=8.4 Hz, 2H), 4.94 (m, 6H), 4.65 (s, 1H), 2.53 (m, 6H), 1.77 (m, 6H),
1.54 (m, 6H), 0.98 (m, 9H), À2.64 ppm (s, 2H); elemental analysis (%)
calcd for C53H57N5O: C 81.61, H 7.37, N 8.98; found: C 81.41, H 7.60, N
8.75.
SubPc-TPA-H2P (8): Compound 7 (100 mg, 0.128 mmol) was added to a
solution of SubPc-Cl (110 mg, 0.256 mmol) in toluene (4 mL), and the re-
action solution was refluxed for six days. The reaction mixture was
cooled to room temperature and the solvent was evaporated. The prod-
uct was chromatographed on silica gel with dichloromethane to give com-
pound
8 (15 mg, 10%) as a
purple solid. M.p. 1228C; 1H NMR
(400 MHz, CDCl3): d=9.52 (m, 4H), 9.46 (d, J=4.8 Hz, 2H), 8.97 (d, J=
4.8 Hz, 2H), 8.85 (m, 6H), 7.88 (m, 8H), 7.25 (m, 2H), 7.16 (m, 4H),
6.98 (m, 1H), 6.83 (d, J=8.4 Hz, 2H), 5.46 (d, J=4.0 Hz, 2H), 4.94 (m,
6H), 2.53 (m, 6H), 1.77 (m, 6H), 1.54 (m, 6H), 0.98 (m, 9H), À2.65 ppm
(s, 2H); elemental analysis (%) calcd for C77H68N11BO: C 78.76, H 5.84,
N 13.12; found: C 78.61, H 6.11, N 12.98.
4-(Diphenylamino)anisole (4): Copper powder (1.50 g, 23.6 mmol),
K2CO3 (6.55 g, 54.4 mmol), [18]crown-6 (0.31 g, 1.17 mmol), and diphe-
nylamine (2.00 g, 11.8 mmol) were added to a solution of 4-iodoanisole
(4.15 g, 17.7 mmol) in o-dichlorobenzene (20 mL). After refluxing the re-
action mixture for 48 h, it was cooled to room temperature and filtered
off. The filtrate was evaporated and the residue was washed with ethanol
and recrystallized from ethanol to give compound 4 (1.43 g, 86%) as a
brown solid. M.p. 108–1098C; 1H NMR (400 MHz, CDCl3): d =7.18 (m,
4H), 7.05 (d, J=4.4 Hz, 2H), 7.01 (d, J=4.8 Hz, 4H), 6.92 (m, 2H), 6.82
(d, J=4.4 Hz, 2H), 3.78 ppm (s, 3H); elemental analysis (%) calcd for
C19H17NO: C 82.88, H 6.22, N 2.84; found: C 82.87, H 6.25, N 2.93.
SubPc-TPA-ZnP (1): After blocking light, compound
8 (15 mg,
0.012 mmol) was added to a solution of zinc acetate (23 mg, 0.12 mmol)
in dichloromethane/methanol (10:1, 5 mL), and stirred for 30 min. The
solvent was removed under reduced pressure and then the product was
chromatographed on silica gel with dichloromethane to give compound 1
(13 mg, 82%) as a red solid. M.p. 1468C; 1H NMR (400 MHz, CDCl3):
d=9.53 (m, 4H), 9.47 (d, J=4.8 Hz, 2H), 8.98 (d, J=4.8 Hz, 2H), 8.86
(m, 6H), 7.89 (m, 8H), 7.20 (m, 6H), 6.99 (m, 1H), 6.83 (d, J=8.8 Hz,
2H), 5.45 (d, J=8.8 Hz, 2H), 4.95 (m, 6H), 2.55 (m, 6H), 1.82 (m, 6H),
1.56 (m, 6H), 1.02 ppm (m, 9H); 13C NMR (CDCl3): d = 151.45, 149.77,
149.70, 149.46, 149.21, 148.97, 148.11, 147.25, 141.43, 136.28, 135.16,
132.14, 131.15, 130.01, 129.33, 128.92, 128.77, 128.63, 126.82, 123.79,
122.39, 120.39, 120.05, 120.00, 119.33, 38.96, 35.96, 33.28, 30.11, 23.23,
14.67, 1.63, 0.48 ppm; UV/Vis (toluene): lmax =308, 432, 523, 562 nm; MS
(MALDI-TOF); m/z: C77H66BN11OZn calcd: 1235.48; found 1235.75; ele-
mental analysis (%) calcd for C77H66BN11OZn: C 74.73, H 5.38, N 12.48;
found: C 74.61, H 5.51, N 12.38.
4-{N-(4-Methoxyphenyl)-N-phenylamino}benzaldehyde (5): Compound 4
(2.0 g, 7.26 mmol), and carefully poured POCl3 (2.77 mL, 30.28 mmol)
were added to a solution of DMF (2.35 mL, 30.28 mmol) in 1,2-dichloro-
ethane (20 mL). The mixture was refluxed for 4 h, cooled to room tem-
perature, and poured into saturated aqueous sodium acetate solution
(50 mL). The product was extracted with dichloromethane (3ꢀ50 mL),
6200
www.chemeurj.org
ꢂ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2010, 16, 6193 – 6202

A Zinc Porphyrin Coordinated to Fullerene
FULL PAPER
4-(Diphenylamino)benzaldehyde (9): Triphenylamine (1.8 g, 7.57 mmol)
and carefully poured POCl3 (2.77 mL, 30.28 mmol) was added to a solu-
tion of DMF (2.35 mL, 30.28 mmol) in 1,2-dichloroethane (20 mL). The
mixture was refluxed for 12 h, cooled to room temperature, and then
poured into saturated aqueous sodium acetate solution (300 mL). The
product was extracted with dichloromethane (3ꢀ50 mL) and the extract
was dried over MgSO4, and evaporated. The residue was chromatograph-
ed on silica gel with dichloromethane to give compound 9 (1.85 g, 85%)
as a yellow solid. M.p. 1328C; 1H NMR (400 MHz, CDCl3): d=9.78 (s,
1H), 7.64 (d, J=4.8 Hz, 2H), 7.31 (t, J=7.6 Hz, 4H), 7.14 (m, 6H),
6.98 ppm (d, J=8.0 Hz, 2H); elemental analysis (%) calcd for C19H15NO:
C 83.49, H 5.53, N 5.12; found: C 83.22, H 5.71, N 5.01.
Acknowledgements
This work was supported by a Grant-in-Aid (No. 20108010) and the
Global COE (center of excellence) program “Global Education and Re-
search Center for Bio-Environmental Chemistry” of Osaka University
from Ministry of Education, Culture, Sports, Science and Technology,
Japan, KOSEF/MEST through WCU project (R31-2008-000-10010-0), the
National Science Foundation (Grant Nos. 0804015 and EPS-0903806) and
matching support from the State of Kansas through Kansas Technology
Enterprise Corporation. K.-Y. Kay also acknowledges the financial sup-
port from Brain Korea 21 Program in 2008.
5-{4-(N,N-Diphenylamino)phenyl}-10,15,20-tris
phine (10): Boron trifluoride diethyl etherate (0.85 mL, 6.7 mmol) was
added to solution of compound (1.14 g, 4.17 mmol), hexanal
ACHTUNGERTN(NUNG pentyl)-21H,23H-por-
a
9
[1] a) The Photosynthetic Reaction Center (Eds.: J. Deisenhofer, J. R.
Norris), Academic Press, San Diego, 1993; b) J. Deisenhofer, O.
Epp, K. Miki, R. Huber, H. Michel, J. Mol. Biol. 1984, 180, 385;
c) R. A. Wheeler, Introduction to the Molecular Bioenergetics of
Electron, Proton, and Energy Transfer, ACS, Washington, 2004,
pp. 1–6; d) “Electron Transfer in Photosynthesis”: W. Leibl, P.
Mathis in Molecular to Global Photosynthesis (Eds.: M. D. Archer,
J. Barber), Imperial College Press, London, 2004, p. 117.
[2] a) G. McLendon, R. Hake, Chem. Rev. 1992, 92, 481; b) F. D. Lewis,
R. L. Letsinger, M. R. Wasielewski, Acc. Chem. Res. 2001, 34, 159;
c) J. S. Connolly, J. R. Bolton, Photoinduced Electron Transfer,
Part D (Eds.: M. A. Fox, M. Chanon), Elsevier, Amsterdam, 1988,
pp. 303–393.
[3] a) J. R. Miller, L. T. Calcaterra, G. L. Closs, J. Am. Chem. Soc. 1984,
106, 3047; b) G. L. Closs, J. R. Miller, Science 1988, 240, 440.
[4] a) M. R. Wasielewski, Acc. Chem. Res. 2009, 42, 1910; b) D. Gust,
T. A. Moore, A. L. Moore, Acc. Chem. Res. 2009, 42, 1890; c) H. A.
Kurreck, A. L. Moore, Acc. Chem. Res. 2001, 34, 40.
[5] a) M.-J. Blanco, M. C. Jimenez, J.-C. Chambron, V. Heitz, M. Linke,
J.-P. Sauvage, Chem. Soc. Rev. 1999, 28, 293; b) V. Balzani, A. Juris,
M. Venturi, S. Campagna, S. Serroni, Chem. Rev. 1996, 96, 759; c) V.
Balzani, A. Credi, M. Venturi, ChemSusChem 2008, 1, 26.
[6] a) M. N. Paddon-Row, Acc. Chem. Res. 1994, 27, 18; b) J. W. Verho-
even, Adv. Chem. Phys. 1999, 106, 603; c) K. Maruyama, A. Osuka,
N. Mataga, Pure Appl. Chem. 1994, 66, 867; d) A. Osuka, N.
Mataga, T. Okada, Pure Appl. Chem. 1997, 69, 797; e) L. Sun, L.
Hammarstrçm, B. ꢄkermark, S. Styring, Chem. Soc. Rev. 2001, 30,
36.
[7] a) J. S. Sessler, B. Wang, S. L. Springs, C. T. Brown in Comprehensive
Supramolecular Chemistry (Eds.: J. L. Atwood, J. E. D. Davies, D. D.
MacNicol, F. Vogtle), Pergamon, New York, 1996, Chapter 9; b) T.
Hayashi, H. Ogoshi, Chem. Soc. Rev. 1997, 26, 355; c) M. W. Ward,
Chem. Soc. Rev. 1997, 26, 365; d) P. Piotrowiak, Chem. Soc. Rev.
1999, 28, 143.
[8] a) S. Fukuzumi, Pure Appl. Chem. 2007, 79, 981; b) S. Fukuzumi,
Org. Biomol. Chem. 2003, 1, 609; c) S. Fukuzumi, Bull. Chem. Soc.
Jpn. 2006, 79, 177; d) S. Fukuzumi, T. Kojima, J. Mater. Chem. 2008,
18, 1427; e) S. Fukuzumi, Phys. Chem. Chem. Phys. 2008, 10, 2283;
f) D. L. Feldheim, C. D. Keating, Chem. Soc. Rev. 1998, 27, 1; g) In-
troduction of Molecular Electronics (Eds.: M. C. Petty, M. R. Bryce),
Oxford University Press, New York, 1995; h) M. Emmelius, G. Paw-
lowski, H. W. Vollmann, Angew. Chem. 1989, 101, 1475; Angew.
Chem. Int. Ed. Engl. 1989, 28, 1445. 18; i) S. Fukuzumi, T. Honda,
K. Ohkubo, T. Kojima, Dalton Trans. 2009, 3880.
[9] a) G. Kodis, P. A. Liddell, L. de La Garza, P. C. Clausen, J. S. Lind-
sey, A. L. Moore, T. A. Moore, D. Gust, J. Phys. Chem. A 2002, 106,
2036; b) D. Kuciauskas, P. A. Liddell, S. Lin, T. E. Johnson, S. J.
Weghorn, J. S. Lindsey, A. L. Moore, T. A. Moore, D. Gust, J. Am.
Chem. Soc. 1999, 121, 8604; c) P. A. Liddell, G. Kodis, L. de La Gar-
za, A. L. Moore, T. A. Moore, D. Gust, J. Phys. Chem. B 2004, 108,
10256; d) G. Kodis, Y. Terazono, P. A. Liddell, J. Andreasson, V.
Garg, M. Hambourger, A. L. Moore, T. A. Moore, D. Gust, J. Am.
Chem. Soc. 2006, 128, 1818; e) M. Wolffs, F. J. M. Hoeben, E. H. A.
Beckers, A. P. H. J. Schenning, E. W. Meijer, J. Am. Chem. Soc.
2005, 127, 13484.
(1.54 mL, 12.5 mmol), and pyrrole (1.16 mL, 16.67 mmol) in a mixture of
dichloromethane (1.65 L) and 2-propanol (17 mL). The mixture was
stirred at room temperature for 90 min. DDQ (3.78 g, 16.6 mmol) was
added and the mixture was stirred at room temperature for 70 min. Final-
ly, triethylamine (3.7 mL, 26.4 mmol) was added and the mixture was
stirred for 30 min. The product was chromatographed on silica gel with
chloroform/n-hexane (3:2) to give compound 10 (253 mg, 8%) as a
purple solid. M.p. 928C; 1H NMR (400 MHz, CDCl3): d=9.47 (m, 4H),
9.38 (d, J=4.8 Hz, 2H), 8.92 (d, J=4.8 Hz, 2H), 7.99 (d, J=4.0 Hz, 2H),
7.40 (m, 10H), 7.12 (m, 2H), 4.95 (m, 6H), 2.53 (m, 6H), 1.78 (m, 6H),
1.55 (m, 6H), 0.98 (m, 9H), À2.65 ppm (s, 2H); elemental analysis (%)
calcd for C53H57N5: C 83.31, H 7.52, N 9.17; found: C 83.09, H 7.76, N
9.01.
[5-{4-(N,N-Diphenylamino)phenyl}-10,15,20-trisACTHNUTRGNE(NUG pentyl)-21H,23H-por-
phinato]zinc, ZnP-TPA (12): After blocking light, compound 10 (210 mg,
0.28 mmol) was added to a solution of zinc acetate (504 mg, 2.75 mmol)
in dichloromethane/methanol (10:1, 20 mL), and stirred for 1 h. The sol-
vent was evaporated and then the product was chromatographed on
silica gel with dichloromethane to give compound 2 (210 mg, 92%) as a
purple solid. M.p. 1128C; 1H NMR (400 MHz, CDCl3): d=9.54 (m, 4H),
9.48 (d, J=4.8 Hz, 2H), 9.02 (d, J=4.8 Hz, 2H), 8.01 (d, J=7.6 Hz, 2H),
7.41 (m, 10H), 7.13 (m, 2H), 4.94 (m, 6H), 2.55 (m, 6H), 1.82 (m, 6H),
1.56 (m, 6H), 1.01 ppm (m, 9H); UV/Vis (toluene): lmax =305, 471, 558,
598 nm; elemental analysis (%) calcd for C53H55N5Zn: C 76.93, H 6.70, N
8.46; found: C 76.81, H 6.91, N 8.28.
5,10,15,20-TetrakisACHTUNGTRENNUNG(pentyl)-21H,23H-porphine (11): Boron trifluoride di-
ethyl etherate (0.85 mL, 6.7 mmol) was added to a solution of hexanal
(2.05 mL, 16.67 mmol) and pyrrole (1.16 mL, 16.67 mmol) in a mixture of
dichloromethane (1.65 L) and 2-propanol (17 mL). The mixture was
stirred at room temperature for 90 min. DDQ (3.78 g, 16.6 mmol) was
added and the mixture was stirred at room temperature for 70 min. Final-
ly, triethylamine (2.35 mL, 16.7 mmol) was added and the mixture was
stirred for 30 min. The solvent was evaporated and then the product was
chromatographed on silica gel with chloroform/n-hexane (3:2) to give
compound 11 (350 mg, 11%) as a purple solid. M.p. 1128C; 1H NMR
(400 MHz, CDCl3): d=9.42 (s, 8H), 4.92 (m, 8H), 2.50 (m, 8H), 1.78 (m,
8H), 1.55 (m, 8H), 0.99 (m, 12H), À2.63 ppm (s, 2H); elemental analysis
(%) calcd for C40H54N4: C 81.31, H 9.21, N 9.48; found: C 81.03, H 9.33,
N 9.08.
[5,10,15,20-TetrakisACHTUNGTRENNUNG(pentyl)-21H,23H-porphinato]zinc; ZnP (3): After
blocking light, compound 11 (200 mg, 0.33 mmol) was added to a solution
of zinc acetate (605 mg, 3.3 mmol) in dichloromethane/methanol (10:1,
20 mL), and stirred for 1 h. The solvent was removed under reduced
pressure and then the product was chromatographed on silica gel with di-
chloromethane to give compound 3 (189 mg, 88%) as a purple solid.
M.p. 1038C; 1H NMR (400 MHz, CDCl3): d=9.12 (s, 8H), 4.56 (m, 8H),
2.40 (m, 8H), 1.77 (m, 8H), 1.54 (m, 8H), 1.01 ppm (m, 12H). UV/Vis
(toluene): lmax =310, 471, 559, 598 nm; elemental analysis (%) calcd for
C40H52N4Zn: C 73.43, H 8.01, N 8.56; found: C 73.21, H 8.13, N 8.33.
Chem. Eur. J. 2010, 16, 6193 – 6202
ꢂ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
6201

S. Fukuzumi, K.-Y. Kay, F. D’Souza et al.
[10] a) H. Imahori, Y. Sakata, Adv. Mater. 1997, 9, 537; b) M. Prato, J.
Mater. Chem. 1997, 7, 1097; c) N. Martꢅn, L. Sanchez, B. Illescas, I.
Perez, Chem. Rev. 1998, 98, 2527; d) F. Diederich, M. Gomez-Lopez,
Chem. Soc. Rev. 1999, 28, 263; e) H. Imahori, Y. Sakata, Eur. J. Org.
Chem. 1999, 2445; f) D. M. Guldi, Chem. Commun. 2000, 321;
g) D. M. Guldi, M. Prato, Acc. Chem. Res. 2000, 33, 695; h) D. M.
Guldi, P. V. Kamat in Fullerenes (Eds.: K. M. Kadish, R. S. Ruoff),
Wiley, New York, 2000, Chapter 5, pp. 225–281; i) D. M. Guldi,
Chem. Soc. Rev. 2002, 31, 22; j) M. D. Meijer, G. P. M. van Klink, G.
van Koten, Coord. Chem. Rev. 2002, 230, 140; k) H. Imahori, S. Fu-
kuzumi, Adv. Funct. Mater. 2004, 14, 525.
[11] a) M. R. Wasielewski, Chem. Rev. 1992, 92, 435; b) H. Kurreck, M.
Huber, Angew. Chem. 1995, 107, 929; Angew. Chem. Int. Ed. Engl.
1995, 34, 849; c) P. D. W. Boyd, C. A Reed, Acc. Chem. Res. 2005,
38, 235; d) I. Bouamaied, T. Coskun, E. Stulz, Struct. Bonding
(Berlin) 2006, 121, 1.
[12] a) S. Fukuzumi, K. Ohkubo, H. Imahori, J. Shao, Z. Ou, G. Zheng,
Y. Chen, R. K. Pandey, M. Fujitsuka, O. Ito, K. M. Kadish, J. Am.
Chem. Soc. 2001, 123, 10676; b) K. Ohkubo, H. Kotani, J. Shao, Z.
Ou, K. M. Kadish, G. Li, R. K. Pandey, M. Fujitsuka, O. Ito, H. Ima-
hori, S. Fukuzumi, Angew. Chem. 2004, 116, 871; Angew. Chem. Int.
Ed. 2004, 43, 853; c) E. Maligaspe, N. V. Tkachenko, N. K. Subbaiy-
an, R. Chitta, M. E. Zandler, H. Lemmetyinen, F. D’Souza, J. Phys.
Chem. A 2009, 113, 8478.
[13] a) M. E. El-Khouly, S. H. Shim, Y. Araki, O. Ito, K.-Y. Kay, J. Phys.
Chem. B 2008, 112, 3910; b) J.-H. Kim, M. E. El-Khouly, Y. Araki,
O. Ito, K.-Y. Kay, Chem. Lett. 2008, 37, 544; c) M. E. El-Khouly,
J. B. Ryu, K.-Y. Kay, O. Ito, S. Fukuzumi, J. Phys. Chem. C 2009,
113, 15444.
[14] a) B. del Rey, T. Torres, Tetrahedron Lett. 1997, 38, 5351; b) C. G.
Claessens, T. Torres, J. Am. Chem. Soc. 2002, 124, 14522; c) C. G.
Claessens, D. Gonzꢆlez-Rodrꢅguez, T. Torres, Chem. Rev. 2002, 102,
835; d) D. Gonzꢆlez-Rodrꢅguez, T. Torres, D. M. Guldi, J. Rivera, L.
Echegoyen, Org. Lett. 2002, 4, 335; e) D. Gonzꢆlez-Rodrꢅguez, T.
Torres, M. M. Olmstead, J. Rivera, M. A. Herranz, L. Echegoyen, C.
Atienza Castellanos, D. M. Guldi, J. Am. Chem. Soc. 2006, 128,
10680; f) A. Medina, C. G. Glassens, G. M. Aminur Rahman, A.
Lamsabhi, O. Mo, M. Yanez, D. M. Guldi, T. Torres, Chem.
Commun. 2008, 1759.
[15] a) M. E. El-Khouly, O. Ito, P. M. Smith, F. D’Souza, J. Photochem.
Photobiol. C 2004, 5, 79; b) F. D’Souza, O. Ito, Coord. Chem. Rev.
2005, 249, 1410; c) R. Chitta, F. D’Souza, J. Mater. Chem. 2008, 18,
1440; d) F. D’Souza, O. Ito in Handbook of Organic Electronics and
Photonics, Vol. 1 (Ed.: H. S. Nalwa), American Scientific Publishers,
Stevenson Ranch, 2008, Chapter 13, pp. 485–521; e) Y. Araki, O. Ito
in Handbook of Organic Electronics and Photonics, Vol. 2 (Ed.:
H. S. Nalwa), American Scientific Publishers: California, 2008,
Chapter 12, pp. 473–513; f) Y. Araki, O. Ito, J. Photochem. Photo-
biol. C 2008, 9, 93; g) F. D’Souza, O. Ito, Chem. Commun. 2009,
4913; h) F. D’Souza, P. M. Smith, M. E. Zandler, A. L. McCarty, M.
Itou, Y. Araki, O. Ito, J. Am. Chem. Soc. 2004, 126, 7898.
b) H. Imahori, M. E. El-Khouly, M. Fujitsuka, O. Ito, Y. Sakata, S.
Fukuzumi, J. Phys. Chem. A 2001, 105, 325.
[20] a) F. D’Souza, G. R. Deviprasad, M. E. Zandler, V. T. Hoang, A.
Klykov, M. VanStipdonk, A. Perera, M. E. El-Khouly, M. Fujitsuka,
O. Ito, J. Phys. Chem. A 2002, 106, 3243; b) M. E. El-Khouly, L. M.
Rogers, M. E. Zandler, G. Suresh, M. Fujitsuka, O. Ito, F. D’Souza,
ChemPhysChem 2003, 4, 474.
[21] a) F. D’Souza, R. Chitta, K. Ohkubo, M. Tasior, N. K. Subbaiyan,
M. E. Zandler, M. K. Rogachi, D. T. Gryko, S. Fukuzumi, J. Am.
Chem. Soc. 2008, 130, 14263; b) F. D’Souza, E. Maligaspe, P. A.
Karr, A. L. Schumacher, M. E. Ojaimi, C. P. Gros, J.-M. Barbe, K.
Okubo, S. Fukuzumi, Chem. Eur. J. 2008, 14, 674.
[22] a) F. Ullmann, J. Bierlecki, Ber. Dtsch. Chem. Ges. 1901, 34, 2174;
b) S. Gauthier, J. M. J. Frechet, Synthesis 1987, 383.
[23] a) A. Vilsmeier, A. Haack, Ber. Dtsch. Chem. Ges. 1927, 60, 119;
b) X.-C. Li, Y. Liu, M. S. Liu, A. K.-Y. Jen, Chem. Mater. 1999, 11,
1568.
[24] a) J. S. Lindsey, R. W. Wagner, J. Org. Chem. 1989, 54, 828; b) M.
Gardner, A. J. Guerin, C. A. Hunter, U. Michelsen, C. Rotger, New
J. Chem. 1999, 23, 309.
[25] The driving forces for charge recombination (ÀDGCR) and charge
separation (ÀDGCS) were calculated according to the equations,
ÀDGCR =EoxÀEredÀDGS and ÀDGCS =E0,0À(ÀDGCR); where Eox is
R
the first oxidation potential of the porphyrin, Ered is the first reduc-
tion potential of the fullerene and subphthalocyanine, DE0,0 is the
energy of the 0–0 transition between the lowest excited state and
the ground state of the porphyrin as evaluated from the fluorescence
peaks. DGS refers to the static energy, calculated by using the “di-
electric continuum model” DGS =e2/(4pe0eSRCt-Ct). The symbols e0
and eS represent vacuum permittivity and dielectric constant of the
solvent, respectively.
[26] a) F. D’Souza, S. Gadde, M. E. Zandler, K. Arkady, M. E. El-
Khouly, M. Fujitusuka, O. Ito, J. Phys. Chem. A 2002, 106, 12393;
b) F. D’Souza, M. E. El-Khouly, S. Gadde, A. L. McCarty, P. A.
Karr, M. E. Zandler, Y. Araki, O. Ito, J. Phys. Chem. B 2005, 109,
10107.
[27] H. A. Benesi, J. H. Hildebrand, J. Am. Chem. Soc. 1949, 71, 2703.
[28] a) J. R. Miller, G. D. Dorough, J. Am. Chem. Soc. 1952, 74, 3977;
b) K. M. Kadish, L. R. Shiue, Inorg. Chem. 1982, 21, 1112.
[29] a) R. A. Marcus, J. Chem. Educ. 1968, 45, 356; b) R. A. Marcus, N.
Sutin, Biochim. Biophys. Acta Rev. Bioenerg. 1985, 811, 265;
c) R. A. Marcus, Angew. Chem. 1993, 105, 1161; Angew. Chem. Int.
Ed. Engl. 1993, 32, 1111; d) R. A. Marcus, Rev. Mod. Phys. 1993, 65,
599.
[30] S. Fukuzumi, K. Ohkubo, W. E, Z. Ou, J. Shao, K. M. Kadish, J. A.
Hutchison, K. P. Ghiggino, P. J. Sintic, M. J. Crossley, J. Am. Chem.
Soc. 2003, 125, 14984.
[31] a) I. R. Gould, J. E. Moser, B. Armitage, S. Farid, J. L. Goodman,
M. S. Herman, J. Am. Chem. Soc. 1989, 111, 1917; b) C. C. Moser,
J. M. Keske, K. Warncke, R. S. Farid, P. L. Dutton, Nature 1992, 355,
796; c) S. I. Khan, A. M. Oliver, M. N. Paddon-Row, Y. Rubin, J.
Am. Chem. Soc. 1993, 115, 4919; d) R. M. Williams, J. M. Zwier,
J. W. Verhoeven, J. Am. Chem. Soc. 1995, 117, 4093; e) R. D.
Cannon, Electron Transfer Reactions, Butterworth, London, 1980;
f) W. Adam, A. Schçnberger, Chem. Ber. 2006, 139, 2149.
[16] The Porphyrin Handbook (Eds.: K. M. Kadish, K. M. Smith, R. Gui-
lard), Academic Press, San Diego, 2000, pp. 1–20.
[17] F. D’Souza, S. Gadde, D.-M. S. Islam, C. A. Wijesinghe, A. L. Schu-
macher, M. E. Zandler, Y. Araki, O. Ito, J. Phys. Chem. A 2007, 111,
8552.
[18] H. W. Kroto, J. R. Heath, S. C. OꢁBrien, R. F. Curl, R. E. Smalley,
Nature 1985, 318, 162.
[19] a) H. Imahori, K. Hagiwara, T. Akiyama, M. Akoi, S. Taniguchi, T.
Okada, M. Shirakawa, Y. Sakata, Chem. Phys. Lett. 1996, 263, 545;
Received: January 8, 2010
Published online: April 21, 2010
6202
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ꢂ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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