Supramolecular structures and photoelectronic properties of the inclusion complex of a cyclic free-base porphyrin dimer and C60

Article abstract of DOI:10.1002/chem.201001815

A cyclic free-base porphyrin dimer H₄-CPD_Py (CPD = cyclic porphyrin dimer) linked by butadiyne moieties bearing 4-pyridyl groups self-assembles to form a novel porphyrin nanotube in the crystalline state. The cyclic molecules link together through nonclassical C-H···N hydrogen bonds and π-π interactions of the pyridyl groups along the crystallographic a axis. H₄-CPD_Py includes a C ₆₀ molecule in its cavity in solution. In the crystal structure of the inclusion complex (C₆₀?H₄-CPD_Py), the dimer bites a C₆₀ molecule by tilting the porphyrin rings with respect to each other, and there are strong π-π interactions between the porphyrin rings and C₆₀. The included C₆₀ molecules form a zigzag chain along the crystallographic b axis through van der Waals contacts with each other. Femtosecond laser flash photolysis of C ₆₀?H₄-CPD_Py in the solid state with photoexcitation at 420 nm shows the formation of a completely charge-separated state {H₄-CPD_Py^?+ + C₆₀ ^?-}, which decays with a lifetime of 470 ps to the ground state. The charge-carrier mobility of the single crystal of C₆₀?H ₄-CPD_Py was determined by flash photolysis time-resolved microwave conductivity (FP-TRMC) measurements. C₆₀cH ₄-CPD_Py has an anisotropic charge mobility (σμ = 0.16 and 0.13cm ²V^-1s^-1) along the zigzag chain of C₆₀ (which runs at 45° and parallel to the crystallographic b axis). To construct a photoelectrochemical cell, C₆₀?H ₄-CPD_Py was deposited onto nanostructured SnO₂ films on a transparent electrode. The solar cell exhibited photovoltaic activity with an incident photon to current conversion efficiency of 17 %.

Full text of DOI:10.1002/chem.201001815

FULL PAPER
DOI: 10.1002/chem.201001815
Supramolecular Structures and Photoelectronic Properties of the Inclusion
Complex of a Cyclic Free-Base Porphyrin Dimer and C60
Hirofumi Nobukuni,[a] Yuichi Shimazaki,[b] Hidemitsu Uno,[c] Yoshinori Naruta,[a]
Kei Ohkubo,[d] Takahiko Kojima,[e] Shunichi Fukuzumi,[d, f] Shu Seki,[g] Hayato Sakai,[h]
Taku Hasobe,[h] and Fumito Tani*[a]
Abstract: A cyclic free-base porphyrin
dimer H4-CPDPy (CPD=cyclic porphy-
rin dimer) linked by butadiyne moiet-
ies bearing 4-pyridyl groups self-assem-
bles to form a novel porphyrin nano-
tube in the crystalline state. The cyclic
molecules link together through non-
porphyrin rings and C60. The included
C60 molecules form zigzag chain
along the crystallographic axis
The charge-carrier mobility of the
single crystal of C60ꢁH4-CPDPy was de-
termined by flash photolysis time-re-
solved microwave conductivity (FP-
TRMC) measurements. C60ꢁH4-CPDPy
has an anisotropic charge mobility
(Sm=0.16 and 0.13 cm2 Vꢀ1 sꢀ1) along
the zigzag chain of C60 (which runs at
458 and parallel to the crystallographic
b axis). To construct a photoelectro-
chemical cell, C60ꢁH4-CPDPy was de-
posited onto nanostructured SnO2
films on a transparent electrode. The
solar cell exhibited photovoltaic activi-
ty with an incident photon to current
conversion efficiency of 17%.
a
b
through van der Waals contacts with
each other. Femtosecond laser flash
photolysis of C60ꢁH4-CPDPy in the
solid state with photoexcitation at
420 nm shows the formation of a com-
pletely charge-separated state {H4-
ꢀ
classical C H···N hydrogen bonds and
p–p interactions of the pyridyl groups
along the crystallographic a axis. H4-
CPDPy includes a C60 molecule in its
cavity in solution. In the crystal struc-
ture of the inclusion complex (C60ꢁH4-
CPDPy), the dimer “bites” a C60 mole-
cule by tilting the porphyrin rings with
respect to each other, and there are
strong p–p interactions between the
CPDPy + +C60 }, which decays with a
C
Cꢀ
lifetime of 470 ps to the ground state.
Keywords: charge
fullerenes
transfer
photoinduced
·
·
electron transfer · photovoltaics ·
porphyrinoids
[a] Dr. H. Nobukuni, Prof. Dr. Y. Naruta, Prof. Dr. F. Tani
Institute for Materials Chemistry and Engineering
Kyushu University, 6-10-1 Hakozaki
[f] Prof. Dr. S. Fukuzumi
Department of Bioinspired Science, Ewha Womans University
Seoul, 120-750 (Korea)
Higashi-ku, Fukuoka 812-8581 (Japan)
Fax : (+81)92-642-2715
E-mail: tanif@ms.ifoc.kyushu-u.ac.jp
[g] Prof. Dr. S. Seki
Department of Applied Chemistry
Graduate School of Engineering, Osaka University
PRESTO (Japan) Science and Technology Agency (JST)
Suita, Osaka 565-0871 (Japan)
[b] Prof. Dr. Y. Shimazaki
College of Science, Ibaraki University, Bunkyo
Mito 310-8512 (Japan)
[h] Dr. H. Sakai, Prof. Dr. T. Hasobe
[c] Prof. Dr. H. Uno
Department of Chemistry, Faculty of Science and Technology
Keio University
PRESTO (Japan) Science and Technology Agency (JST)
Yokohama, Kanagawa 223-8522 (Japan)
Graduate School of Science and Engineering
Ehime University, Bunkyo-cho, Matsuyama 790-8577 (Japan)
[d] Prof. Dr. K. Ohkubo, Prof. Dr. S. Fukuzumi
Department of Material and Life Science
Graduate School of Engineering, Osaka University
Suita, Osaka 565-0871 (Japan)
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201001815.
[e] Prof. Dr. T. Kojima
Graduate School of Pure and Applied Sciences
University of Tsukuba, Tsukuba, Ibaraki 305-8571 (Japan)
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Introduction
such an arrangement represents the most effective way to
achieve the three key processes.[16]
Fullerene derivatives (C60, C70, [6,6]-phenyl C61-butyric acid
methyl ester (PCBM), etc) are seen as the ultimate electron
acceptors because of their favorable reduction potentials
and small reorganization energies in electron-transfer reac-
tions.[1] Hence, they are good candidate materials for molec-
ular electronics devices.[2] Well-ordered arrangements of full-
erene derivatives in the solid state are indispensable for this
application. For example, a single crystal of C60 has a fairly
high electron mobility (Sm=0.50 cm2 Vꢀ1 sꢀ1) as an organic
semiconductor.[3] However, it is still difficult to rationally ar-
range C60 molecules in a deliberate manner, because C60 is
composed of only carbon atoms, and has no functional
groups. One approach is to chemically modify C60 by intro-
ducing functional groups.[4] But these modifications can
compromise the attractive characteristics of pristine C60, be-
cause they break the symmetry and original electronic prop-
erties of C60. Another solution is to use host–guest chemis-
try; that is, the arrangement of host molecules including
C60.[5] As host molecules, electron-rich aromatic compounds,
such as calixarenes, resorcinarenes, and cyclotriveratrylenes,
have generally been used in supramolecular chemistry.[6]
Porphyrin derivatives are particularly attractive components
in the design of host molecules for fullerenes.[7] Cyclic bis-
porphyrin hosts were first designed by Aida and Tashiro,[8]
while acyclic bisporphyrin hosts were reported by Boyd and
Reed.[9] These inclusion complexes of fullerenes with por-
phyrin derivatives are stable in solution and in the crystal-
line state due to the p–p interactions between the curved p
planes of the fullerenes and the flat p planes of the porphyr-
ins.
Imahori et al. have recently reported a novel approach for
constructing a vertical alignment of bicontinuous porphyrin–
fullerene arrays on a flat semiconducting electrode for a
photoelectrochemical device with high efficiency.[17]
Therefore, a linear arrangement of C60 inside porphyrin
derivative hosts is expected to provide photoinduced charge
separation and smooth vectorial charge transport, both of
which are the most fundamental prerequisites for efficient
photovoltaics.
Recently, we reported an inclusion complex composed of
a cyclic nickel porphyrin dimer (Ni2-CPDPy, Scheme 1) and
C60.[18] In this complex (C60ꢁNi2-CPDPy), C60 molecules are
On the other hand, many porphyrin–fullerene conjugates
have been extensively studied as functional models of the
reaction center for charge separation in natural photosyn-
thesis.[10] In these conjugates, fullerenes usually behave as
electron acceptors, whereas porphyrin derivatives tend to
act as electron donors. Long lifetimes of charge-separated
states with high quantum yields (e.g., 0.53 s and 83%, re-
spectively) have been reported[11] that are comparable to
those of the reaction center in natural photosynthesis. More-
over, fullerenes have been employed as n-type semiconduc-
tors, and porphyrin derivatives have been used as p-type
semiconductors of the active layers in organic photovoltaic
(OPV) devices.[12] OPV devices are expected to be inexpen-
sive, lightweight, flexible, and ubiquitous energy conversion
systems in the future.[13–15] The main advantages of OPV de-
vices lie in their cost and processability; one can easily fabri-
cate large-area devices, because organic materials are com-
patible with solution-processing techniques. But the power
conversion efficiency (h) in the OPV devices reported thus
far are still low. The mechanism of power conversion from
light to current is composed of three important processes;
light harvesting, charge separation, and carrier transport.
Thus, the enhancement of the power conversion efficiency,
in general, requires a highly ordered and bicontinuous
donor–acceptor arrangement in the active layers because
Scheme 1. Molecular structure of Ni2-CPDPy and synthetic route for H4-
CPDPy.
linearly arranged in the inner channel of the porphyrin
nanotube to form a supramolecular peapod. In addition, the
complex exhibits a high anisotropic electron mobility (Sm=
0.72 cm2 Vꢀ1 sꢀ1) along the linear arrangement of C60.[19]
However, the expected charge-separated state was not ob-
served in the time-resolved transient absorption spectra of
C60ꢁNi2-CPDPy because the singlet excited state of the
nickel porphyrin immediately gives rise to the triplet excited
state by intersystem crossing,[20] and the low-energy triplet
excited state of C60 (3C60*) is then formed by energy trans-
fer.[21] The estimated energy level of the charge-separated
3
state (1.98 eV) is higher than that of C60* (1.60 eV).[22]
Thus, the corresponding free-base porphyrin compound is
more likely to yield a charge-separated state for the follow-
ing reasons: 1) a free-base porphyrin generally has a lower
oxidation potential than that of the corresponding nickel
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Inclusion Complex of a Cyclic Free-Base Porphyrin Dimer and C60
FULL PAPER
complex, so the desired charge separation becomes more
feasible; and 2) an intersystem crossing from a singlet excit-
ed state to a triplet excited state for a free-base porphyrin
would be much slower than that of the corresponding nickel
complex. Herein, we report the supramolecular structures
and photoelectrochemical properties of the inclusion com-
plex of the free-base porphyrin dimer (H4-CPDPy, Scheme 1)
and C60. The structure of this complex (C60ꢁH4-CPDPy) was
characterized by X-ray crystallography. We investigated the
photodynamics of C60ꢁH4-CPDPy in the solid state by femto-
second laser flash photolysis. The charge-carrier mobility of
C60ꢁH4-CPDPy in the single crystal was determined by flash-
photolysis time-resolved microwave conductivity (FP-
TRMC) measurements.[23] Furthermore, the photovoltaic
properties of C60ꢁH4-CPDPy were also studied and com-
pared with those of C60ꢁNi2-CPDPy.
respectively. In comparison with the structure of the Ni2-
CPDPy molecule,[18] the H4-CPDPy molecule has two charac-
teristic features (Scheme 2): 1) The porphyrin rings show a
higher planarity. The displacements of the meso carbon
atoms from the four-nitrogen mean plane (ꢀ0.154, ꢀ0.055,
ꢀ0.216, 0.145 ꢁ, positive values meaning outward) are much
smaller than those of Ni2-CPDPy (ꢀ0.473, 0.553, ꢀ0.603,
0.503 ꢁ), and 2) the two porphyrin rings are in a “slipped”
Results and Discussion
Formation and structure of a porphyrin nanotube: H4-
CPDPy was synthesized from the corresponding zinc porphy-
ꢂ
rin monomer with two terminal C C triple bonds by Glaser
coupling catalyzed by copper(I) under air in 20% yield
(Scheme 1). The zinc monomer rather than the free-base
monomer was used to inhibit copper ion insertion to the
porphyrin.[24] The zinc ion was easily removed by acid treat-
ment.
Purple crystals of H4-CPDPy suitable for X-ray crystallog-
raphy were grown by slow evaporation of a solution in
CHCl3/o-dichlorobenzene. The H4-CPDPy molecule has a
rectangular shape (Figure 1a–c).[25] The distances between
the centers of the two porphyrin rings and the two mid-
points of the butadiyne moieties are 10.785 and 14.247 ꢁ,
Scheme 2. Schematic representations of structural features in the single
crystals of a)–d) Ni2-CPDPy and e)–h) H4-CPDPy. a), e) front view;
b), f) side view; c), g) top view; d), h) tubular assembly.
arrangement with respect to
each other, and are not rotated
around the center-to-center axis
from the top view (Figure 1c).
Also, the two butadiyne moiet-
ies are coplanar from the side
view (Figure 1b). Seven o-di-
chlorobenzene molecules of
crystallization per H4-CPDPy
molecule are incorporated into
the structure; five inside the
cavity, and two outside, but
they are severely disordered.
A novel porphyrin nanotube
can be observed in the crystal
packing of H4-CPDPy (Figure 2
and Figure S1 in the Supporting
Information).[26] The tubular
structure is formed along the
Figure 1. ORTEP drawings of a)–c) H4-CPDPy and d)–f) C60ꢁH4-CPDPy with 50% probability thermal ellip-
soids (solvent molecules and hydrogen atoms are omitted for clarity). a), d) front view; b), e) side view;
c), f) top view.
direction of the crystallographic
a axis by self-assembly through
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F. Tani et al.
with C···N distances of 3.373(6) and 3.473(5) ꢁ. The other
noncovalent interaction is a weak p–p interaction between
the pyridyl groups. For this interaction, the shortest carbon–
carbon distance is 3.645(8) ꢁ, and the dihedral angle is
7.458. In total, the adjacent dimers along the a axis are
linked by four hydrogen bonds and two p–p interactions.
These interactions are similar to those of the crystal struc-
ture of Ni2-CPDPy.[18] The center-to-center distance between
porphyrins along this tubular assembly is 14.895 ꢁ for H4-
CPDPy. In both Ni2-CPDPy and H4-CPDPy, each tube axis is
not parallel with the vector joining the pyridyl-substituted
meso carbon atoms; that is, each vector has a certain obli-
que angle to each tube axis. However, there is a clear differ-
ence between the arrangements of the porphyrin moieties in
Ni2-CPDPy and H4-CPDPy (Scheme 2). In the Ni2-CPDPy
tubes, the two vectors of the upper and lower porphyrins
show opposite oblique angles relative to the tube axis. On
the other hand, the vectors of the two porphyrins of H4-
CPDPy exhibit the same oblique angle relative to the tube
axis.
Inclusion properties of C60 with H4-CPDPy in solution: As
expected from the distance between the centers of the two
porphyrin rings (10.785 ꢁ), which is comparable to the
outer diameter of C60 (about 10.3 ꢁ), H4-CPDPy can include
C
60 inside its cavity in solution. The UV/Vis absorption spec-
tral change during the addition of C60 to the solution of H4-
CPDPy in CHCl3/toluene (1:1) is shown in Figure 4. The
Soret band was redshifted with a decrease in intensity,
whereas the Q band was also redshifted but increased in in-
tensity. The Job plot (415 nm) upon mixing H4-CPDPy and
C60 also displayed a signature pattern for the formation of a
1:1 host–guest complex (C60ꢁH4-CPDPy) (see Figure S2 in
the Supporting Information).[26] On the basis of the titration
of H4-CPDPy with C60, the association constant (Kassoc) was
determined to be 9.6ꢂ104 mꢀ1 (Figure S3 in the Supporting
Information).[26] This value is nearly half that of Ni2-
Figure 2. Crystal structures of tubular assemblies of H4-CPDPy. o-Dichlor-
obenzene molecules and hydrogen atoms are omitted for clarity. a) front
view; b) side view; c) top view. In a) and b), N=blue; C=gray.
[18]
two kinds of cooperative noncovalent interaction between
the cyclic molecules (Figure 3). One is a pair of complemen-
CPDPy and is smaller than that of the cyclic free-base por-
5
ꢀ1
ꢀ
ꢀ
phyrin dimer (7.5ꢂ10 m ) linked by
OACHTNGUTERNU(NG CH2)6O spacers
ꢀ
tary C H···N hydrogen-bonding interactions between the
rather than by butadiyne.[27]
pyrrole b-CH and the nitrogen atoms of the pyridyl groups,
Figure 3. Details of the noncovalent interactions linking the cyclic por-
phyrin dimers in the crystal of H4-CPDPy. Hydrogen atoms are omitted
Figure 4. Absorption spectral changes of H4-CPDPy upon titration with
C60 in CHCl3/toluene (1:1) at room temperature. The inset shows the Q-
band region. [H4-CPDPy]=4.0ꢂ10ꢀ6 m, [C60]=3.9ꢂ10ꢀ6–3.6ꢂ10ꢀ5 m.
ꢀ
except in the C H···N moieties. N=gray; C, H=black.
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Inclusion Complex of a Cyclic Free-Base Porphyrin Dimer and C60
FULL PAPER
ESIMS of a 1:1 mixture of H4-CPDPy and C60 in CH2Cl2/
methanol/CH3COOH (50:50:0.2) revealed two peak clusters
at m/z 2047.3 ([H4-CPDPy+C60]+) and 1023.7 ([H4-
CPDPy+C60]2+) with no peaks of free H4-CPDPy and C60
(Figure S4 in the Supporting Information).[26] These spectra
indicate that the 1:1 complex of H4-CPDPy with C60 is stable.
The 13C NMR spectrum of a 1:1 mixture of H4-CPDPy and
13C-enriched C60 in CDCl3/[D8]toluene (1:1) showed a singlet
signal arising from included C60 at d=141.1 ppm, which is
shifted upfield from that of free C60 (d=143.4 ppm) on ac-
count of the ring-current effect of the porphyrins (Figure S5
in the Supporting Information).[26]
moieties are also observed upon inclusion. On the other
hand, the porphyrin rings maintain planarity; the displace-
ments of the meso carbon atoms from the four-nitrogen
mean plane are ꢀ0.299, 0.190, ꢀ0.256, ꢀ0.106, ꢀ0.246,
ꢀ0.042, ꢀ0.151, ꢀ0.161 ꢁ (positive values meaning out-
ward). These results indicate that inclusion induces a drastic
structural change, presumably because the distance between
the two porphyrins is too short to accommodate C60 in the
parallel conformation. Although Ni2-CPDPy has the same
butadiynyl spacer groups, the porphyrin was saddle-distorted
to give a longer center-to-center distance (12.596 ꢁ for
C60ꢁNi2-CPDPy), and to accommodate C60 in the parallel
conformation. In most examples of inclusion complexes of
The redox potentials of H4-CPDPy, C60 and C60ꢁH4-CPDPy
were determined by voltammetry (Table 1) (Figure S6 in the
Supporting Information).[26] In the thin-film state on the
ꢀ
C60 with porphyrins, a 6:6 ring-juncture C C bond of the
fullerene is closest to the porphyrin.[7,8] In the present case,
however, the nearest bond of C60 is the 6:5 juncture. The
shortest separations between the carbon atoms of C60 and
the porphyrin centers are 2.850, 2.903, 3.025 and 3.065 ꢁ
(Figure 5). These values represent fairly strong p–p interac-
tions between the porphyrins and C60. There is one water
molecule and at least three toluene molecules per H4-CPDPy
molecule in the structure. Elemental analysis supports this
composition. The toluene molecules are highly disordered,
and are taken into account by the PLATON Squeeze tech-
nique.[31]
Table 1. Redox potentials (versus Fc+/Fc) of H4-CPDPy, C60, and C60ꢁH4-
CPDPy with 0.1m nBu4NClO4.
Compound
Oxidation[a]
E1
Reduction[b]
E1
P
1/2
H4-CPDPy
C60
C60ꢁH4-CPDPy
0.81
–
0.83
–
ꢀ0.97
ꢀ1.00
[a] The oxidation potentials were analyzed by DPV of film states of the
samples on platinum electrodes in acetonitrile with 0.1m nBu4NClO4.
[b] The reduction potentials were determined by cyclic voltammetry in o-
dichlorobenzene/pyridine (1:1) with 0.1m nBu4NClO4. Scan rate=
0.1 Vsꢀ1. The concentration was 0.2 mm.
electrode, the oxidation potential of the porphyrin unit in
C60ꢁH4-CPDPy (0.83 V versus Fc+/Fc by differential pulse
voltammetry (DPV)) showed a 0.02 V anodic shift compared
with that of H4-CPDPy (0.81 V). In comparison with that of
Ni2-CPDPy (0.88 V), these potentials are slightly lower. In
cyclic voltammograms of o-dichlorobenzene/pyridine (1:1),
the first cathodic process corresponding to the reduction of
the fullerene entity of C60ꢁH4-CPDPy was observed at
ꢀ1.00 V, which is cathodically shifted by 0.03 V in compari-
son with pristine C60 (ꢀ0.97 V). The small anodic shift of
the oxidation potential of the porphyrin and the small
cathodic shift of the reduction potential of C60 compared
with their reference compounds are indicative of the charge-
transfer interaction between the porphyrins and C60.[8,19,28–30]
Figure 5. Details of the noncovalent interactions between H4-CPDPy and
C60. Hydrogen atoms are omitted. N=gray; C=black.
Crystal structure of the inclusion complex of C60 with H4-
CPDPy: Black single crystals of C60ꢁH4-CPDPy were pre-
pared from a 1:1 mixture of H4-CPDPy in CHCl3 and C60 in
toluene. X-ray crystallography revealed a 1:1 inclusion com-
plex of C60 with H4-CPDPy (Figure 1d–f).[25] In the crystal
structure of C60ꢁH4-CPDPy, the dimer includes a C60 mole-
cule in a clamshell-like conformation, in which the porphy-
rin rings are tilted with respect to each other. The dihedral
angle of the two porphyrin planes is 52.388, which is in stark
contrast to the parallel conformation in the crystal structure
of H4-CPDPy. The increase of the distance (11.126 ꢁ) be-
tween the centers of the two porphyrins and the decrease of
that (13.915 ꢁ) between the midpoints of the butadiyne
In contrast, C60ꢁH4-CPDPy shows a highly symmetric
1H NMR spectrum in solution at room temperature. The in-
cluded C60 molecule would oscillate in the cavity much
faster than the NMR timescale and/or would be positioned
above the center of the porphyrin ring in solution.
To our surprise, the C60 molecules form a zigzag chain
along the crystallographic b axis in the crystal packing, and
a nanotube structure is no longer observed (Figure 6). The
distance between the centers of the adjacent C60 molecules
along the zigzag array (arrow A in Figure 6a) is 10.018 ꢁ.
This value is comparable to the outer diameter of C60 (ca.
10.3 ꢁ). In other words, the C60 molecules have van der
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F. Tani et al.
Figure 6. Zigzag arrays of C60ꢁH4-CPDPy in the crystal structures. Solvent
molecules and hydrogen atoms are omitted for clarity. The H4-CPDPy
units and the C60 molecules are depicted by wire frames and space-filling
models, respectively. a) Top view; b) side view.
Waals contacts with each other along the zigzag arrange-
ment. This zigzag array is derived from a partial covering of
H4-CPDPy. The uncovered p plane of the three-dimensional
and symmetrical C60 molecule (rather than two-dimensional
common aromatic compounds) enables these interesting in-
teractions. The distances between the centers of the C60 mol-
ecules along the parallel direction to b axis (arrow B) and in
the adjacent zigzag arrays (arrows C and D) are 15.059,
18.161, and 16.250 ꢁ, respectively. The two distances
marked by arrows B and E are equivalent. The two porphy-
rin rings facing each other along the a axis are very close,
with the shortest nitrogen–nitrogen distance 3.462 ꢁ.
Figure 7. Transient absorption spectra of a) H4-CPDPy and b) C60ꢁH4-
CPDPy recorded at 1, 300, and 3000 ps after photoexcitation at 420 nm in
KBr pellets.
Photochemical properties of the inclusion complex of C60
with H4-CPDPy: Time-resolved transient absorption spectra
in the solid state for H4-CPDPy and C60ꢁH4-CPDPy in KBr
pellets were obtained by femtosecond laser flash photolysis
after photoexcitation at 420 nm (Figure 7). A sharp peak at
[32]
Cꢀ
1070 nm assignable to the radical anion of C60 (C60
)
was
observed in the transient absorption spectra of C60ꢁH4-
CPDPy. This clearly differs from the results of C60ꢁNi2-
CPDPy. Thus, the formation of a completely charge-separat-
Figure 8. Decay–time profile of the absorption of C60ꢁH4-CPDPy in a
ed state {H4-CPDPy + +C60 } was confirmed, although the
C
Cꢀ
KBr pellet at 1070 nm.
absorbance due to the radical cation of the porphyrin (H4-
CPDPy +) in the 500–800 nm region is not clear because
C
there would be overlap with the bleaching of the porphyrin
Q-band absorption. The electron transfer from the porphy-
rin singlet excited state to C60 is also supported by the
quenching of the porphyrin fluorescence from 650 to 750 nm
in the spectrum of C60ꢁH4-CPDPy in comparison with that
of H4-CPDPy (Figure S7 in the Supporting Information). The
fluorescence of the free-base porphyrin is observed in this
region as a valley in the spectra of H4-CPDPy (Figure 7a).
The decay of the absorption band at 1070 nm of C60ꢁH4-
CPDPy has two steps, as shown in Figure 8. The first step has
a lifetime of 18 ps, which corresponds to the disappearance
of the singlet excited state of the porphyrin 1H4-CPDPy*.
The S1 of the porphyrin has a broad absorption from 800 to
1200 nm, as shown in Figure 7a. The second component co-
incides with the decay of {H4-CPDPy + +C60 }, which has a
lifetime of 470 ps.
C
Cꢀ
The photodynamics in the solid of C60ꢁH4-CPDPy is sum-
marized in Figure 9. Photoexcitation at 420 nm immediately
affords both the singlet excited state of porphyrin 1H4-
CPDPy* (1.90 eV)[33] and the singlet excited state of fullerene
1C60* (2.00 eV).[34] Both species undergo intrasupramolecular
electron transfer to give a charge-separated state {H4-
CPDPy + +C60 } (1.83 eV), the energy level of which can be
C
Cꢀ
estimated from the difference between the one-electron re-
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Chem. Eur. J. 2010, 16, 11611 – 11623

Inclusion Complex of a Cyclic Free-Base Porphyrin Dimer and C60
FULL PAPER
The transient conductivity in
the single crystal of C60ꢁH4-
CPDPy was measured by using
TRMC (Figure 11 shows the ki-
netic traces). The transient con-
ductivity can be expressed as
(fSm), in which
f and Sm
denote photocarrier generation
yield (quantum efficiency) and
the sum of mobilities for nega-
tive and positive carriers, re-
spectively. Upon irradiation
with a laser pulse of excitation
wavelength of 532 nm, the
single crystal of C60ꢁH4-CPDPy
Figure 9. Energy diagram for the photochemical events in C60ꢁH4-CPDPy.
duction potential of C60 and the oxidation potential of the
porphyrin moieties in C60ꢁH4-CPDPy (Table 1). However,
electron-transfer rates in the two pathways are different;
1
18 ps in 1H4-CPDPy*, whereas C60* decays within 1 ps.
Meanwhile, the charge-separated state has a lifetime of
470 ps, and it decays directly to the ground state.
A charge-separated state was clearly detected for C60ꢁH4-
CPDPy, but not for C60ꢁNi2-CPDPy.[19] This is probably be-
cause the energy level of the charge-separated state of
C60ꢁH4-CPDPy (1.83 eV) is lower than that of C60ꢁNi2-
CPDPy (1.98 eV). Also, the free-base porphyrin has a much
slower intersystem crossing to its triplet excited state, which
would undergo energy transfer to C60. This would result in
the lower-energy C60 triplet excited state instead of the
charge-separated state. Thus, it is possible to improve the ef-
ficiency of the charge separation by tuning the electronic
properties of the porphyrin moiety.
Charge mobility of the inclusion complex of C60 with H4-
CPDPy: The zigzag array of C60 molecules, formed through
van der Waals contacts with each other, and the clear forma-
Cꢀ
tion of the radical anion of C60 (C60 ) are expected to lead
to high electron mobility in the C60ꢁH4-CPDPy crystal. To
measure the charge mobility in C60ꢁNi2-CPDPy, a single
crystal was subjected to FP-TRMC measurements.[23] The
TRMC technique holds several advantages over time of
flight (TOF) and field-effect transistor (FET) methods:
1) there is no need for electrodes, 2) analysis of the aniso-
tropic charge transport can be made in the single crystal,
3) detection of charge carrier mobility can be made on the
nanometer scale, and 4) small effects arising through chemi-
cal or physical defects of the crystals can be detected.
We have determined the face indices of C60ꢁH4-CPDPy by
X-ray crystallographic analysis (Figure 10). The crystal ex-
hibits a platelike shape. The zigzag chain of C60 runs down
the longest axis of the crystal. The electric field of the reso-
nant microwave in the cavity was applied at various direc-
tions relative to the crystallographic b axis to investigate the
anisotropy of the charge mobility.
Figure 10. A view of the single crystal of C60ꢁH4-CPDPy and the face indi-
ces determined by X-ray crystallographic analysis. a) Photograph of the
crystal of C60ꢁH4-CPDPy. b) Crystal shape with the indices for C60ꢁH4-
CPDPy. c) Molecular arrangement of C60ꢁH4-CPDPy corresponding to the
photograph.
revealed a strong transient conductivity fSm with peaks of
5.2ꢂ10ꢀ3 cm2 Vꢀ1 sꢀ1 at 458 to the b axis, 4.1ꢂ10ꢀ3 cm2 Vꢀ1 sꢀ1
along the b axis, and 9.8ꢂ10ꢀ4 cm2 Vꢀ1 sꢀ1 at 908 to the b
axis.
To determine the value of the charge-carrier mobility Sm,
the f value was obtained by the conventional direct-current
Chem. Eur. J. 2010, 16, 11611 – 11623
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F. Tani et al.
In contrast, the higher electron mobility of C60ꢁNi2-CPDPy
was ascribed to the continuous linear array of C60 molecules
with no intervening groups. The anisotropic mobility along
the b axis (0.13 cm2 Vꢀ1 sꢀ1) is comparable to that along the
458 direction, although the distance between the center of
C60 molecules along the b axis (15.059 ꢁ, arrow B) is longer
than between those (10.018 ꢁ) at 458 to the b axis. This may
result from the continuous arrangement of the C60 molecules
along the b axis with the intervening butadiynyl groups, the
steric hindrance of which is relatively small. Moreover, the
porphyrins along the b axis would also contribute to the
charge (hole) transport (arrow E). On the other hand, the
mobility (0.030 cm2 Vꢀ1 sꢀ1) along the direction vertical to
the b axis (arrow D) is much smaller, because the donor–ac-
ceptor (porphyrin–C60) alternating array is formed in this di-
rection. As a whole, these results show that charge trans-
port, mainly electron transport, along the well-ordered
zigzag array (at 458 and parallel to the b axis) is more feasi-
ble than along the other directions.
Figure 11. Conductivity transients for the single crystal of C60ꢁH4-CPDPy.
The red, blue, and green curves correspond to the conductivity at 458,
parallel, and 908 to the b axis, respectively.
current integration (DC-CI) method, in which thin films of
C60ꢁH4-CPDPy were spin-coated from a solution of C60ꢁH4-
CPDPy in CHCl3/toluene (1:1) on a brush-shaped electrode
with a 5 mm gap under excitation at 532 nm with a power
density ranging from 4.8 to 7.2 mJcmꢀ2.[26] The maximum
yield of photocarrier generation obtained under an applied
bias was f=0.032. Note that the current transients were ob-
tained under an applied bias with a range of 2.0ꢂ103 to 6.4ꢂ
104 Vcmꢀ1 between the electrodes. To identify the charge
carrier (electron or hole) we also made measurements by
using thin films of C60ꢁH4-CPDPy sandwiched between Al
and semitransparent Au electrodes. The transient current
was observed under both negative and positive biases of
ꢃ0.5–3.1ꢂ105 Vcmꢀ1 with an illumination of 16 mJcmꢀ2.
This indicates that both electron and hole act as charge car-
riers in C60ꢁH4-CPDPy. The current integration of electron
(25 mCcmꢀ2) is 20 times that of hole (1.2 mCcmꢀ2). Hence,
the main charge carrier is the electron transported by the
C60 molecules. Assuming that the f values in the single crys-
tal are the same as those in the film, the single crystal of
C60ꢁH4-CPDPy exhibits minimum charge mobilities of 0.16,
0.13, and 0.030 cm2 Vꢀ1 sꢀ1 at 458, parallel, and 908 to the b
axis, respectively.[35]
Photoelectrochemistry of the inclusion complexes of C60
with H4-CPDPy: Efficiencies of formation of the charge-sep-
arated state and carrier transport are key factors in the pho-
tovoltaic process. To evaluate the solar-energy conversion
properties, photoelectrochemical cells composed of C60ꢁH4-
CPDPy or C60ꢁNi2-CPDPy were fabricated. Figure 12 shows
Figure 12. Illustration of the photoelectrochemical cell.
The observed highest value (0.16 cm2 Vꢀ1 sꢀ1) for C60ꢁH4-
CPDPy
is
lower
than
that
of
C60ꢁNi2-CPDPy
(0.72 cm2 Vꢀ1 sꢀ1), in spite of the C60–C60 van der Waals con-
tacts in C60ꢁH4-CPDPy. This is probably because the C60
molecules are in a zigzag arrangement rather than in a
straight line. The pairs of C60 molecules are not continuous
along the 458 direction to the b axis (arrow A in Figure 6a);
that is, one pair is separated from the other pairs along this
direction. Electron transport between the pairs of the adja-
cent zigzag arrays seems to be retarded due to the distance
(18.161 ꢁ) between them (see arrow C in Figure 6a) and the
presence of the intervening groups such as the phenyl
groups. Effective electron transport would only occur in the
range of around 2 nm (the sum of the outer diameter of two
C60 molecules), although TRMC measurements suggest
charge carrier mobility on the scale of a few nanometers.[23]
an illustration of the photocurrent measurement system of
ꢀ
an optically transparent electrode (OTE) with an Iꢀ/I3
redox couple as an electrolyte system.[12f–h] For this measure-
ment, clusters of C60ꢁH4-CPDPy and C60ꢁNi2-CPDPy were
prepared by using the following procedure: First, the 1:1
mixture of H4-CPDPy or Ni2-CPDPy in CHCl3 (1 mm) and C60
in o-dichlorobenzene (1 mm) was prepared. Then, the mix-
ture (1 mL) was diluted with hexane (3 mL; final concentra-
tion: 125 mm in CHCl3/o-dichlorobenzene/hexane=1:1:6, de-
noted as (C60ꢁH4-CPDPy)n and (C60ꢁNi2-CPDPy)n). The “ref-
erence” clusters H4-CPDPy, Ni2-CPDPy, and C60 were also
prepared (denoted as (H4-CPDPy)n, (Ni2-CPDPy)n, and (C60)n,
respectively). Figure 13 shows the TEM images of all clus-
ters. Interestingly, clusters with diameters of the order of
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Inclusion Complex of a Cyclic Free-Base Porphyrin Dimer and C60
FULL PAPER
C60ꢁH4-CPDPy and C60ꢁNi2-CPDPy, the clusters were depos-
ited on the SnO2 nanocrystallites (denoted as OTE/SnO2/
(C60ꢁH4-CPDPy)n and OTE/SnO2/(C60ꢁNi2-CPDPy)n, respec-
tively). Figure 14 shows the absorption spectra of OTE/
SnO2/H4-CPDPy and OTE/SnO2/Ni2-CPDPy on OTE films
after deposition, which largely agrees with those of
(C60ꢁH4-CPDPy)n and (C60ꢁNi2-CPDPy)n (Figure S10 in the
Supporting Information). This suggests that an interpene-
trating structure is formed from (C60ꢁH4-CPDPy)n and
(C60ꢁNi2-CPDPy)n on OTE/SnO2.
Figure 13. TEM images of a) (C60ꢁH4-CPDPy)n, b) (H4-CPDPy)n,
c) (C60ꢁNi2-CPDPy)n, d) (Ni2-CPDPy)n, and e) (C60)n.
hundreds of nm were formed in the cases of (C60ꢁH4-
CPDPy)n, (H4-CPDPy)n, (C60ꢁNi2-CPDPy)n, and (C60)n, but not
in the case of (Ni2-CPDPy)n. (C60ꢁH4-CPDPy)n gave rise to
especially large clusters; even greater than the sum of the
sizes of (H4-CPDPy)n and (C60)n. In contrast, the clusters of
(C60ꢁNi2-CPDPy)n were similar to the summation of (Ni2-
CPDPy)n and (C60)n. Dynamic light scattering (DLS) meas-
urements support the TEM results. Figure S9 in the Support-
ing Information shows the DLS results of (C60ꢁH4-CPDPy)n,
(H4-CPDPy)n, (C60ꢁNi2-CPDPy)n, (Ni2-CPDPy)n, and (C60)n
prepared under the same conditions. The average diameter
of (C60ꢁH4-CPDPy)n (1300 nm) was larger than that of (H4-
CPDPy)n (220 nm), (C60ꢁNi2-CPDPy)n (530 nm), or (C60)n
(190 nm). On the other hand, the average diameter of (Ni2-
CPDPy)n (44 nm) was small. The absorption spectra of these
composite clusters also show the broadened aggregated fea-
tures (Figure S10 in the Supporting Information).
The clusters composed of C60ꢁH4-CPDPy and C60ꢁNi2-
CPDPy were assembled on a nanostructured SnO2 electrode
(denoted as OTE/SnO2). An electrophoretic deposition pro-
cedure was applied to deposit these clusters from a CHCl3/
o-dichlorobenzene/hexane suspension. Upon application of
a DC electric field of 200 Vcmꢀ1 for 1 min between the
OTE/SnO2 and OTE electrodes, which were kept parallel in
a CHCl3/o-dichlorobenzene/hexane suspension containing
Figure 14. Absorption spectra of a) OTE/SnO2/(C60ꢁH4-CPDPy
) (solid
n
line) and OTE/SnO /
(H4-CPDPy
)
(dotted line), and b) OTE/SnO2/
(dotted line).
n
(C60ꢁNi2-CPDPy (solid line) and OTE/SnO2/(Ni2-CPDPy
)
)
n
n
To evaluate the photoelectrochemical performance of the
(C60ꢁH4-CPDPy)n and (C60ꢁNi2-CPDPy)n films, we used the
OTE/SnO2 as a photoanode in a photoelectrochemical cell.
Photocurrent measurements were performed in acetonitrile
containing LiI (0.5m) and I2 (0.05m) as a redox electrolyte
with a Pt gauge counter electrode.[12i] The photocurrent and
photovoltage responses following the excitation of the OTE/
SnO2/(C60ꢁH4-CPDPy)n and OTE/SnO2/(C60ꢁNi2-CPDPy)n
electrodes in the visible-light region (AM (air mass) = 1.5)
are shown in Figure S11 in the Supporting Information. The
photocurrent response is prompt, steady, and reproducible
during repeated on/off cycles of visible-light illumination.
The short-circuit photocurrent density (Isc) of 1.10 mAcmꢀ2
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11619

F. Tani et al.
and open-circuit voltage (Voc) of 300 mV were reproducibly
obtained during these measurements. These experiments
confirmed the potential of (C60ꢁH4-CPDPy)n and (C60ꢁNi2-
CPDPy)n for harvesting light energy and generating photo-
current during the operation of a photoelectrochemical cell.
To evaluate the spectral photoresponses of (C60ꢁH4-
CPDPy)n, (C60ꢁNi2-CPDPy)n, (H4-CPDPy)n, and (Ni2-CPDPy)n
on OTE/SnO2, photocurrent action spectra were also mea-
sured by using a standard two-electrode system in photo-
electrochemical cells (Figure 15).[12f–h] The incident photon
to current efficiency (IPCE) values were calculated by nor-
malizing the photocurrent values for the incident-light
energy and intensity in Equation (1):[12j]
volvement of (C60ꢁH4-CPDPy)n and (C60ꢁNi2-CPDPy)n in
photocurrent generation. OTE/SnO2/(C60ꢁH4-CPDPy)n gives
rise to an especially broad photoresponse in the longer
wavelength region (700–800 nm) because of the extended
absorption of highly ordered clusters of C60ꢁH4-CPDPy. The
maximum IPCE value for (C60ꢁH4-CPDPy)n (17%) is much
larger than that of (C60ꢁNi2-CPDPy)n (4%). This clearly in-
dicates that the organized donor and acceptor alignment in
(C60ꢁNi2-CPDPy)n enhances the IPCE.
We also evaluated the power characteristics of the OTE/
SnO2/(C60ꢁH4-CPDPy)n and OTE/SnO2/(C60ꢁNi2-CPDPy)n
electrodes (Figure S12 in the Supporting Information). The
power conversion efficiency, h, is calculated by using Equa-
tion (2):[12i]
IPCE ð%Þ ¼ 100 ꢄ 1240 ꢄ Isc=ðWin ꢄ lÞ
ð1Þ
h ¼ FF ꢄ Isc ꢄ Voc=Win
ð2Þ
in which the fill factor (FF) is defined as FF=[IV]max/IscVoc,
in which Voc is the open-circuit photovoltage, and Isc is the
short-circuit photocurrent. OTE/SnO2/(C60ꢁH4-CPDPy)n has
a fill factor of 0.40, an open-circuit voltage of 300 mV, a
short-circuit current density of 1.10 mAcmꢀ2, and an overall
power conversion efficiency (h) of 0.33% at an input power
(Win) of 40 mWcmꢀ2, whereas FF=0.34, Voc =160 mV, and
Isc =0.148 mAcmꢀ2 in the OTE/SnO2/(C60ꢁNi2-CPDPy)n. The
h value of OTE/SnO2/(C60ꢁH4-CPDPy)n (0.33%) is more
than 16 times that of OTE/SnO2/(C60ꢁNi2-CPDPy)n (0.02%).
Such a significant enhancement of the h value demonstrates
that the strong ordering in the clusters and the efficient
charge separation in (C60ꢁH4-CPDPy)n improve the light-
energy conversion properties.
Conclusion
We have reported the synthesis and crystal structure of a
new porphyrin nanotube derived from the cyclic free-base
porphyrin dimer H4-CPDPy with pyridyl substituents as self-
assembling moieties. The tube is constructed through the
ꢀ
stacking of the cyclic molecules through unique C H···N hy-
drogen bonds and p–p interactions between the pyridyl
groups in the crystal. The formation of the 1:1 inclusion
complex of C60 with H4-CPDPy (C60ꢁH4-CPDPy) was con-
firmed both in solution and in the crystal. Electrochemistry
reveals that H4-CPDPy and C60ꢁH4-CPDPy have lower por-
phyrin oxidation potentials than those of Ni2-CPDPy and
C60ꢁNi2-CPDPy, which results in the lower energy level of
the expected charge-separated state. The zigzag array of C60
molecules is formed with van der Waals contacts between
C60 molecules inside the spaces surrounded by the porphyrin
moieties in the crystal structure of C60ꢁH4-CPDPy. The for-
mation of a charge-separated state of C60ꢁH4-CPDPy in the
solid of C60ꢁH4-CPDPy was observed by using femtosecond
laser flash photolysis. This result is different from that ob-
tained with C60ꢁNi2-CPDPy, and shows that it is possible to
improve the efficiency of the charge separation by tuning
Figure 15. Photocurrent action spectra of a) the OTE/SnO2/(C60ꢁH4-
CPDPy
)
electrode (line with circles) and the OTE/SnO /
(H4-CPDPy
)
)
n
n
n
)
electrode
n
(line with squares). Electrolyte: 0.5m LiI and 0.05m I2 in acetonitrile.
in which Isc is the short-circuit photocurrent (Acmꢀ2), Win is
the incident-light intensity (Wcmꢀ2), and l is the wavelength
(nm). The overall response of (C60ꢁNi2-CPDPy)n and
(C60ꢁH4-CPDPy)n on OTE/SnO2 parallels the broad absorp-
tion spectral features (Figure 15), which indicates the in-
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Inclusion Complex of a Cyclic Free-Base Porphyrin Dimer and C60
FULL PAPER
8.36 (d, J=7.6, 2H; Ar-H), 8.66 (s, 2H; Ar-H), 9.07 (d, J=4.6 Hz, 4H;
pyrrole b-H), 9.11 (d, J=4.6 Hz, 4H; pyrrole b-H), 9.17 ppm (d, J=4.4,
4H; Ar-H); HR-FAB-MS (NBA): m/z calcd for C46H26N6Zn: 726.1510;
found: 726.1506; IR (KBr): n˜ =3280, 1599, 1340, 1203, 1076, 997, 924,
the electronic properties of the porphyrin moiety. An aniso-
tropic charge mobility along the crystallographic b axis for
the single crystal of C60ꢁH4-CPDPy was measured by FP-
TRMC. The highest charge mobility was Sm=0.16 and
0.13 cm2 Vꢀ1 sꢀ1 along the zigzag array of C60.
798 cmꢀ1
; UV/Vis (THF): lmax (e)=403 (48400), 423 (559600), 555
(22000), 595 nm (5400 cmꢀ1 mꢀ1).
The photovoltaic activity of C60ꢁNi2-CPDPy and C60ꢁH4-
Synthesis of H4-CPDPy: This compound was synthesized according to the
literature[36] with modification as follows. CuICl (1.188 g, 12 mmol) was
added to a solution of 3 (73 mg, 0.1 mmol) in pyridine (200 mL). The re-
action mixture was stirred at 808C for 24 h under air after which time it
was diluted with CHCl3 (200 mL), washed with aqueous ammonia
(200 mL ꢂ 3), dried over Na2SO4, and the solvent was evaporated. The
purple residue was dissolved in pyridine (3 mL) again, and carefully
acidified with a 6n aqueous solution of HCl (aqueous, 40 mL). The green
suspension was carefully poured into a saturated aqueous solution of
NaHCO3 (200 mL), and extracted with CHCl3 (150 mL). The organic
layer was dried over Na2SO4 and the solvent was evaporated. The residue
was purified by flash column chromatography (CHCl3/MeOH=150:1).
After washing with methanol and drying in vacuo, the desired dimer
(13 mg, 20%) together with the corresponding trimer (12 mg, 18%) were
obtained as a reddish purple powder. 1H NMR (CDCl3, 400 MHz): d=
ꢀ3.01 (brs, 4H; -NH) 7.32 (s, 4H; Ar-H) 7.72 (d, J=8.1 Hz, 4H; Ar-H),
7.80 (t, J=7.8, 4H; Ar-H), 7.95 (brs, 4H; Ar-H), 8.61 (d, J=7.6, 8H; Ar-
H), 8.64 (d, J=4.9 Hz, 8H; pyrrole b-H), 8.67 (d, J=4.4 Hz, 8H; pyrrole
b-H), 8.96 ppm (brs, 8H; Ar-H); HR-FAB-MS (NBA): m/z calcd for
C92H52N12: 1324.4438; found: 1324.4419; IR (KBr): n˜ =1593, 1473, 1402,
974, 881, 798, 727, 660 cmꢀ1; UV/Vis (CHCl3): lmax (e)=417 (742800),
515 (34000), 549 (10400), 588 (10800), 645 nm (4400 cmꢀ1 mꢀ1); elemental
analysis calcd (%) for C92H52N12·1.5C6H4Cl2: C 78.47, H 3.78, N 10.87;
found: C 78.84, H 3.95, N 10.89.
CPDPy was evaluated by constructing photoelectrochemical
cells composed of modified electrodes and Iꢀ/I3 solution.
ꢀ
C60ꢁH4-CPDPy-modified electrodes exhibited light-energy
conversion properties, as represented by the IPCE value of
17% and the power conversion efficiency (h) of 0.33%.
This indicates that the inclusion complexes of the self-as-
sembling cyclic porphyrin dimers and fullerene C60 are valid
candidates for photovoltaic applications.
Experimental Section
Materials: All reagents and solvents were purchased from commercial
suppliers as the best grade available, and were used without further pu-
rification unless otherwise noted. o-Dichlorobenzene was purified by dis-
tillation under reduced pressure after stirring over CaCl2 for several
days.
Instruments: 1H and 13C NMR spectra were recorded on a JEOL JMX-
GX400 (400 MHz) spectrometer. Chemical shifts were reported as d
values in ppm relative to tetramethylsilane. High-resolution fast atom
bombardment MS (HR-FAB-MS) was performed on a JEOL LMS-HX-
110 spectrometer with 3-nitrobenzyl alcohol (NBA) as the matrix. UV/
Vis absorption and IR spectra were recorded on Shimadzu UV-3100PC
and BIO RAD FTS6000 spectrophotometers, respectively. ESIMS was
carried out on a Perkin–Elmer Sciex API 300 mass spectrometer. DPV
and cyclic voltammetry were performed on a BAS 100B and ALS 630C
potentiostat in a deaerated acetonitrile or o-dichlorobenzene/pyridine so-
lution containing 0.10m nBu4NPF6 as the supporting electrolyte. The typi-
cal scan rate was 100 mVsꢀ1. A 6 mm diameter platinum electrode was
used as the working electrode, while a platinum wire served as the coun-
ter electrode. An Ag/AgNO3 electrode in acetonitrile or o-dichloroben-
zene/pyridine, separated by a Vycor tip, was used as a reference. Redox
potentials were determined with respect to that of the Fc+/Fc redox
couple. All electrochemical measurements were carried out under an at-
mospheric pressure of argon.
1
C60ꢁH4-CPDPy: H NMR (CDCl3/[D6]benzene (1:1), 400 MHz): d=ꢀ2.86
(brs, 4H; -NH) 7.18 (s, 4H; Ar-H), 7.47–7.54 (m, 8H; Ar-H), 7.72–7.90
(brm, 8H; Ar-H), 8.47 (d, J=7.1 Hz, 4H; Ar-H), 8.58 (d, J=4.6 Hz, 8H;
pyrrole b-H), 8.65 (d, J=4.9 Hz, 8H; pyrrole b-H), 8.84–8.99 ppm (brm,
8H; Ar-H); IR (KBr): n˜ =1591, 1473, 1400, 1082, 974, 796, 725, 577,
528 cmꢀ1; elemental analysis calcd (%) for C92H52N12·C60·3C7H8.H2O: C
88.78, H 3.36, N 7.18; found: C 88.98, H 3.33, N 7.23.
X-ray structure determination: X-ray crystallography was carried out on
single crystals of H4-CPDPy and C60ꢁH4-CPDPy by using
a Rigaku
RAXIS imaging plate area detector with graphite monochromated CuKa
radiation (l=1.54178 ꢁ). The crystals were mounted on a glass fiber. To
determine the cell constants and orientation matrix, three oscillation pho-
tographs were taken for each frame, with an oscillation angle of 38 and
an exposure time of 3 min. Reflection data were corrected for both Lor-
entz and polarization effects. The structures were solved by direct meth-
ods (SIR-2004)[37] with the Crystal Structure[38] crystallographic software
package, and refined by full-matrix least-squares procedures on F2 for all
reflections (SHELXL-97). Non-hydrogen atoms were refined anisotropi-
cally. Hydrogen atoms were refined by using the rigid model. The final
structures were validated by using PLATON cif check. Summaries of the
fundamental crystal data and experimental parameters for structure de-
termination are given below.[25]
Synthesis of 2: A solution of ZnACHTNUGTRNEUNG(OAc)2·2H2O (excess) in methanol
(120 mL) was added to a solution of 1[18] (150 mg, 0.19 mmol) in CHCl3
(300 mL) and heated at 658C under N2 overnight. The reaction mixture
was diluted with CHCl3 and washed with water (200 mL) twice. The or-
ganic layer was dried over Na2SO4 and the solvent was evaporated. The
solid obtained was washed with hexane and dried in vacuo to give 2 as a
purple powder (150 mg, 93%). 1H NMR ([D5]pyridine, 400 MHz): d=
0.31 (s, 18H; -SiACHTUNGTRENNUNG(CH3)3), 7.73 (t, J=7.7 Hz, 2H; Ar-H), 8.07 (d, J=
Time-resolved transient absorption measurements: Femtosecond transi-
ent absorption spectroscopy was conducted by using an ultrafast source
(Integra-C (Quantronix Corp.)), an optical parametric amplifier, TOPAS
7.8 Hz, 2H; Ar-H), 8.30 (d, J=4.4 Hz, 4H; Ar-H), 8.35 (d, J=7.6 Hz,
2H; Ar-H), 8.68 (s, 2H; Ar-H), 9.05 (d, J=4.6 Hz, 4H; pyrrole b-H),
9.11 (d, J=4.6 Hz, 4H; pyrrole b-H), 9.18 ppm (d, J=4.2 Hz, 4H; Ar-H);
HR-FAB-MS (NBA): m/z calcd for C52H42N6ZnSi2: 870.2301; found:
870.2285; IR (KBr): n˜ =2958, 2156, 1593, 1404, 1340, 1250, 1072, 997,
931, 860, 795, 717 cmꢀ1; UV/Vis (CHCl3): lmax (e)=424 (477200), 553
(19600) 594 nm (4200 cmꢀ1 mꢀ1).
(Light Conversion), and
a commercially available optical detection
system, Helios, provided by Ultrafast Systems LLC. The source for the
pump and probe pulses was derived from the fundamental output of Inte-
gra-C (780 nm, 2 mJ/pulse, and full-width at half-maximum (fwhm))
130 fs) at a repetition rate of 1 kHz. 75% of the fundamental output of
the laser was introduced into the TOPAS, which has optical frequency
mixers that provide a tunable range from 285 to 1660 nm, while the rest
of the output was used for white-light generation. Prior to generating the
probe continuum, a variable neutral density filter was inserted in the
path to generate a stable continuum. The laser pulse was then fed to a
delay line that provides an experimental time window of 3.2 ns with a
maximum step resolution of 7 fs. In our experiments, a wavelength at
420 nm of TOPAS output, which is the fourth harmonic of signal or idler
Synthesis of 3: A solution of potassium fluoride dehydrate (41 mg,
0.44 mmol) in DMF (4 mL) was added to 2 (87 mg, 0.1 mmol) under N2
at room temperature. The solution was stirred overnight at room temper-
ature. The reaction mixture was poured into water (40 mL) and filtered.
The residue was washed with water and then methanol before being
dried in vacuo to give 3 as a purple powder (61 mg, 85%). 1H NMR
ꢂ
([D5]pyridine, 400 MHz): d=4.25 (s, 2H; -C CH), 7.73 (t, J=7.7 Hz,
2H; Ar-H), 8.05 (d, J=8.1 Hz, 2H; Ar-H), 8.30 (d, J=4.2, 2H; Ar-H),
Chem. Eur. J. 2010, 16, 11611 – 11623
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
11621

F. Tani et al.
pulses, was chosen as the pump beam. As this TOPAS output consists of
not only the desired wavelength but also unnecessary wavelengths, the
latter (unwanted) output was deviated by using a wedge prism with a
wedge angle of 188. The desired beam was used to irradiate the sample
with a spot size of 1 mm diameter, where it was merged with the white
probe pulse in a close angle (<108). The probe beam, after passing
through the sample, was focused through a fiber-optic cable connected to
CPDPy, H4-CPDPy, C60ꢁNi2-CPDPy, Ni2-CPDPy and C60 are denoted as
OTE/SnO2/(C60ꢁH4-CPDPy)n,
OTE/SnO /
(H4-CPDPy)n,
OTE/SnO2/
2 A(C60)n, re-
(C60ꢁNi2-CPDPy)n, OTE/SnO2/(Ni2-CPDPy)n, and OTE/SnO /
CHTUNGTRENNUNG
spectively.
Measurement of photoelectrochemical solar cells: Photoelectrochemical
measurements were carried out in a standard two-compartment cell that
consisted of a working electrode and a Pt wire gauze counter electrode in
the electrolyte. The electrolyte was 0.5m LiI and 0.05m I2 in acetonitrile.
Keithley 2400 was used for recording photocurrent and photovoltage re-
sponses under an AM1.5 simulated light source (Otento-Sun II, Bunkoh-
Keiki). For IPCE measurements, a monochromator (SM-25, Bunkoh-
Keiki) was introduced into the path of the excitation beam (300 W xenon
lamp, Bunkoh-Keiki) for the selected wavelength. The lamp intensity at
each wavelength was determined by a Si photodiode (Hamamatsu Pho-
tonics S1337-1010BQ) and corrected.
a
CCD spectrograph for recording the time-resolved spectra (420–
1300 nm). Typically, 2500 excitation pulses were averaged over 5 s to
obtain the transient spectrum at a set delay time. Kinetic traces at appro-
priate wavelengths were assembled from the time-resolved spectral data.
All measurements were performed by using potassium bromide pellets
that contained the ground powders of H4-CPDPy or C60ꢁH4-CPDPy at
298 K.
FP-TRMC measurements: Nanosecond laser pulses from a Nd/yttrium +
aluminum + garnet laser (second harmonic generation) (532 nm) from
Spectra Physics, INDY-HG, full width at half maximum (5–8 ns)) were
used as excitation sources. The power density of the laser was set at 4.3–
110 mJcmꢀ2 (1.1–30ꢂ1016 photonscmꢀ2). For time-resolved microwave
conductivity (TRMC) measurements, the microwave frequency and
power were set at approximately 9.1 GHz and 3 mW, respectively, so that
the motion of the charge carriers was not disturbed by the low electric
field of the microwaves. A Rohde & Schwarz SMA-100 A signal genera-
tor was used as a microwave continuum source. A crystal was mounted
on a quartz rod with poly(vinylalcohol) binder, and set in the microwave
cavity resonator (TE012 mode). The mounted crystal was back excited
with a quartz rod, and rotated relative to the vector of the electric field
in the cavity. The TRMC signal picked up by a diode (rise time <1 ns)
was monitored by digital oscilloscope. All of the above experiments were
carried out at room temperature. The transient photoconductivity (Ds)
of the samples is related to the reflected microwave power (DPr/Pr) and
sum of the mobilities of charge carriers as given in Equations (3) and (4):
Acknowledgements
This work was supported by Grants-in-Aid (Scientific Research on Inno-
vative Areas No. 20108009 to F.T., “pi-Space”, and the Global COE Pro-
gram, “Science for Future Molecular Systems”) from the Ministry of
Education, Culture, Sports, Science and Technology of Japan, KOSEF/
MEST through WCU project (R31-2008-000-10010-0), and by a Research
Grant to F.T. from Tokuyama Science Foundation. H.N. acknowledges
the Japan Society for the Promotion of Science (JSPS) for a Research
Fellowship for Young Scientists.
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11622
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ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2010, 16, 11611 – 11623

Inclusion Complex of a Cyclic Free-Base Porphyrin Dimer and C60
FULL PAPER
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¯
group P1; a=14.8950(10), b=14.9173(10), c=15.5995(10) ꢁ; a=
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Received: June 28, 2010
Published online: August 30, 2010
Chem. Eur. J. 2010, 16, 11611 – 11623
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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11623