[60]Fullerene-perchlorotriphenylmethide anion triads. Synthesis and study of photoinduced intramolecular electron-transfer processes

Article abstract of DOI:10.1039/b514882k

For the first time an anionic donor, the perchlorotriphenylmethide anion (PTM^-), has been covalently bonded to C₆₀, generating the C₆₀-(PTM^-)₂ triad that is reversibly oxidized to the corresponding C<

Full text of DOI:10.1039/b514882k

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www.rsc.org/materials | Journal of Materials Chemistry
[60]Fullerene–perchlorotriphenylmethide anion triads. Synthesis and study
of photoinduced intramolecular electron-transfer processes{
Ste´phanie Chopin,a Jack Cousseau,*a Eric Levillain,a Concepcio´ Rovira,*b Jaume Veciana,*b
Atula S. D. Sandanayaka,c Yasuyuki Arakic and Osamu Ito*c
Received 20th October 2005, Accepted 7th November 2005
First published as an Advance Article on the web 17th November 2005
DOI: 10.1039/b514882k
For the first time an anionic donor, the perchlorotriphenylmethide anion (PTM2), has been
covalently bonded to C60, generating the C60–(PTM2)2 triad that is reversibly oxidized to the
?
corresponding C60–perchlorotriphenylmethyl radical triad C60–(PTM )2. For the triad
C60–(PTM2)2, photoinduced charge-separation can be confirmed to occur via the excited singlet
states of the C60 moiety and the PTM anion in polar and nonpolar solvents from quenching of
their fluorescence intensities in the region of 700–750 nm and 560–630 nm, respectively. The
charge-separation state was confirmed by the nanosecond transient absorption spectra in the
visible and near-IR spectral regions. After charge-separation, back electron transfer takes place
with a lifetime of about 80 ns. Steady-state concentration of the highly persistent PTM radical was
observed after repeated laser light irradiation.
charge-recombination processes enter the inverted region of
Introduction
the Marcus parabola.
Since C60 has been revealed as a very attractive electron
In the present study, for the first time an anionic donor, the
perchlorotriphenylmethide anion (PTM2), has been covalently
acceptor with unique photo-physical and electrochemical
properties,1–3 considerable efforts have been devoted in recent
bonded to a C60 derivative, generating the C60–perchloro-
years to develop systems in which C60 is covalently linked to
triphenylmethide anion triad 1 shown in Fig. 1.
electron donors,4–15 in addition to the blend systems consisting
Triphenylmethide anions have been reported to be quite
of C60 and donors.16–23 Donor–acceptor systems including C60
stable when the hydrogen atoms of the triphenyl groups are
are of particular interest, because they exhibit characteristic
substituted by chlorine atoms.25 The stability is not only due
electronic properties in the excited states with interesting
to the electron-withdrawing character of the substituents,
photo-physical properties attributed to the small reorganiza-
but also to an effective steric shielding of the central carbon
tion energy of C60 in electron transfer processes due to its
wrapped by the six bulky chlorine atoms in the ortho positions
spherical rigid molecular shape.24 Thus, a lot of research has
of the phenyl rings. In addition, PTM anions are reversibly
been conducted for a better understanding of photoinduced
oxidized to highly persistent perchlorotriphenylmethyl radicals
electron-transfer processes in dyads and triads including
+
?
(PTM ) at low potential (around 20.55 V, versus Fc/Fc )
C60.4–15 These phenomena open the potential applications
being therefore very good donors.26
in the realization of new artificial photosynthetic systems,
For the target triad C60–(PTM2)2 (1) we expected the
molecular electronic devices, and photovoltaic cells.4,6,7
occurrence of an electron transfer from the anionic part to the
Among the wide variety of donor molecules that have been
photoexcited C60 moiety, generating the neutral perchloro-
covalently linked to C60, most donors are neutral molecules
?
triphenylmethyl radical (PTM ) and the radical anion of the
such as aromatic amines, carotene, tetrathiafulvalenes, ferro-
cenes, porphyrins, phthalocyanines, oligothiophenes, p con-
jugated phenyl oligomers, etc. These dyads generated the
radical anion–radical cation pairs, some of them showing quite
persistent charge-separated state in polar solvents, since the
aLaboratoire CIMMA, UMR CNRS 6200, University of Angers,
2 Bd Lavoisier, 49045 Angers Cedex, France.
E-mail: jack.cousseau@univ-angers.fr
bInstitut de Ciencia de Materials de Barcelona, C.S.I.C., Campus de la
UAB, 08193 Bellaterra, Spain. E-mail: vecianaj@icmab.es;
cun@icmab.es
cInstitute of Multidisciplinary Research for Advanced Materials, Tohoku
University, Katahira 2-1-1, Aoba-ku, Sendai 980-8577, Japan.
E-mail: ito@tagen.tohoku.ac.jp
{ Electronic supplementary information (ESI) available: CV of
compounds 1 and 5, minimized geometry of compound 1, time-
resolved fluorescence spectra, transient spectrum and time profiles in
Fig. 1 Molecular structure of C60–(PTM2)2.
polar solvents. See DOI: 10.1039/b514882k
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C60 moiety. This represents a completely new situation in this
kind of donor–acceptor systems since the charge-recombination
takes place between the C60 radical anion and a neutral radical,
which may show quite different behavior from the usual charge-
separated states generating oppositely charged species.
salt by washing the dark purple precipitate with hexane
several times.
According to the donor characteristics of bisanion 1, when a
CH2Cl2 solution of this salt containing an excess of AgNO3 as
oxidant is shaken for a few minutes, the bistriphenylmethyl
radical 6 was obtained as a deep red solid in quantitative
yield after filtration (Scheme 2). The reaction was followed by
UV-Vis spectroscopy; Fig. 2 shows the evolution of the spectra
over time. The disappearance of the intense band centered
at 518 nm corresponding to the PTM2 anion26e was accom-
panied by the increasing of the characteristic bands of the
PTM radical at 364 and 384 nm.26 The presence of two iso-
sbestic points at 435 and 600 nm is clear evidence of the clean
Results and discussion
Synthesis of C60–(PTM2)2
The synthesis of the target triad 1 consisting of two donor
units, the perchlorinated triphenylmethide anions, and the C60
moiety as the acceptor unit, was achieved by a multi-step
synthetic procedure in which the bis-acylation of the C60-diol
427 using the PTM acid chloride 3 is the key step. The new acid
chloride derivative 3 was obtained in good yield (80%)
following the same procedure used in the synthesis of its
radical counterpart28 through refluxing 4-[bis(2,3,4,5,6-penta-
chlorophenyl)methyl]-2,3,5,6-tetrachlorobenzoic acid29 in an
excess of thionyl chloride. We carried out the esterification
reaction in refluxing CH2Cl2 under an argon atmosphere in the
presence of dimethylaminopyridine (DMAP). Note that this
reaction affords compound 5, the precursor of the target
compound 1, in quite good yield (y60%), although two bulky
groups are attached to the fullerene moiety through the
neighboring alcohol groups. In fact the yield is very similar to
that obtained in the esterification of C60-diol 4 with a TTF-
acid chloride with long alkyl chains that afford high flexibility
to the linkage.30 As shown in Scheme 1 the deprotonation of
the bis a-H precursor 5 yields quantitatively the target triad 1,
by converting the non electroactive a-H triphenylmethane
addends to electroactive carbanions that are very good donors.
Compound 1 was isolated as the pure tetrabutylammoniun
2
?
transformation of C60–(PTM )2 (1) into C60–(PTM )2 (6).
Bisradical 6 was characterized by EPR spectroscopy. The
X-band isotropic spectrum of 6 in toluene–CH2Cl2 at room
temperature consists of a signal with a central intense line and
small satellite overlapped lines corresponding to the coupling
of the unpaired electron with the naturally abundant 13C
?
isotope at the a and aromatic positions of the PTM addends.
The giso value, 2.0023, as well as the isotropic coupling
constant values, a1 (13Ca) = 30 G and a2 (13Carom) = 12 G, are
usual values for the monoradicals of the PTM family.26 The
spectrum of bisradical 6 in frozen toluene–CH2Cl2 solution
does not show the characteristic fine structure nor the
forbidden Dms = 2 transition characteristic of the triplet
species. All these features indicate that the two radical units in
?
the C60–(PTM )2 triad are not interacting.
Electrochemical measurements
The redox behavior of all new compounds was studied by
cyclic voltammetry and the PTM2[18-crown-6]+ salt and
Scheme 1 Synthesis of C60–(PTM2)2(NBu4+)2. Conditions: i) SOCl2, reflux; ii) DMAP, CH2Cl2, 35 uC; iii) NBu4OH, THF, room temperature.
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?
Scheme 2 Synthesis of C60–(PTM )2 (6).
Table 1 Redox potentials of C60–(PTM2)2 and references (E1/2 vs.
Fc/Fc+ in o-DCB–CH3CN (95 : 5))
Compound
Eox/V
E1red/V
E2red/V
E3red/V
C60
PTM2
C60–(PTMH)2
21.03
21.42
21.87
20.54
20.52
21.10
21.49
C60–(PTM2)2
21.12a
21.50a
a
Very weak signal.
electrode (platinum, gold and carbon vitreous), excluding a
phenomenon of adsorption to the electrode, and the solvent
(CH2Cl2 and o-dichlorobenzene (o-DCB)). The unexpected
behavior of compound 1 is not understood and new studies on
other negative charged compounds are underway in order to
know if the negative charges present in the addends of C60 can
be responsible for this.
In order to calculate, from the Weller equations,31 the free-
energy changes for charge-separation (DGCS) and charge-
recombination (DGCR) for C60–(PTM2)2 the first reduction
potential (Ered) value of the C60 moiety and the first oxidation
potential (Eox) of the PTM2 moiety are needed. From
these Eox and Ered values, the DGCS and DGCR values were
calculated using eqn (1)–(3):
Fig. 2 UV-Vis spectra obtained upon oxidation of bisanion 1 in
CH2Cl2.
pristine C60 were also studied under the same conditions as
the reference compounds. As expected, triad 5, in which only
the C60 moiety is electroactive, presents the characteristic
reversible reduction waves of the substituted C60 compounds.
By contrast, unexpected results were obtained in the cyclic
voltammogram of the triad C60–(PTM2)2, 1, which contains
two different electroactive moieties. In all conditions assayed,
only one reversible oxidation wave appears clearly (see ESI{
Fig. SI1 and SI2) whereas the waves expected for the C60
moiety are quite weak. The wave corresponding to the redox
characteristics of the anionic PTM moieties appears at the
same potential as the reference PTM2[18-crown-6]+, indicating
that there is no influence of one anionic moiety on the other
and that there is no interaction with the C60 moiety.
2DGCS = DE0-0 2 (2DGCR
)
(1)
(2)
2DGCR = Eox 2 Ered + DGS
{DGs~
ꢂꢀ
(3)
ꢁꢀ ꢁ
ꢀ
ꢁꢀ ꢁꢃ
e2
1
1
1
1
1
1
1
(3)
z
{
{
z
4pe0 2Rz 2R{ RCC
es
2Rz 2R{
er
where DE0-0 is the energy of the 0-0 transition of C60, R+ the
radius of the PTM radical,26 2 the radius of the radical anion
R
of C60 and Rcc the distance between the two electroactive
sites;32 e, e0, es, and er are the elementary charge, vacuum
permittivity, and static permittivities of the solvents used for
rate measurements and redox potential measurements, respec-
tively. The DGCS and DGCR values for C60–(PTM2)2 in
different solvents are summarized in Table 2. In polar solvent
such as PhCN, charge-separation processes via excited singlet
states of the C60 moiety (1C60*) and the PTM2 (1(PTM2)*) are
The reversibility observed in the cyclic voltammogram of
compound 1 is in accordance with the stability of the free
?
bisradical C60(PTM )2, 6. In Table 1, the E1/2 values for C60,
C60–(PTM2)2 1, PTM2[18-crown-6]+ and C60–(PTMH)2 5 are
summarized. Weak reduction peaks of the C60 unit in charged
triad 1 were always observed under different conditions,
the phenomenon being independent of the concentration,
excluding an intermolecular phenomenon, the nature of the
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Fig. 2. The absorption bands of the C60 moiety appear at
700 nm and in the shorter wavelength than 400 nm. Since
this spectrum is almost the same as the one resulting from
the summed spectrum of the components PTM2 and C60,
an appreciable interaction between moieties may not be
present in the ground state. For the transient absorption
measurements, a 355 nm laser light was used, which excites
the C60 moiety about 90% and 10% of to the PTM2 moiety.
For time-resolved fluorescence measurement, a 400 nm laser
light was used, which excites both the C60 moiety (75%) and
the PTM2 moiety (25%).
Table 2 Free-energy changes for charge separation (2DGCS) via the
excited states of C60 in C60–(PTM2)2 and charge recombination
2
(2DGCR) of C60 –(PTM )(PTM )
2
?
?
Solvent
2DGSCS/eVa
2DGTCS/eVa
2DGCR/eVa
Toluene
o-DCB
PhCN
CH3CN
a
0.92
1.26
1.33
1.34
0.70
1.06
1.13
1.14
0.82
0.46
0.39
0.38
1
Calculated from eqns (1)–(3) employing DE0-0 = 1.72 eV for C60*,
DE0-0 = 1.52 eV for C60*, Eox = 20.52 V for PTM2, and Ered
=
˚
32
3
21.12 V for C60 vs. Fc/Fc+ in o-DCB–CH3CN 95 : 5. R+ = 7.4 A
for PTM2, and R2
˚ ˚
= 4.7 A for C60, and RCC = 10 A.
Permittivities of toluene, o-DCB, and PhCN are 2.38, 9.93, 25.2, and
37.5 respectively.
Fluorescence measurements
Steady-state fluorescence spectra of PTM2, C60–(PTMH)2,
C60–(PTM2)2 in toluene and o-DCB are shown in Fig. 4. The
fluorescence peak (lf) for C60–(PTM2)2 appeared at 600 nm
(Fig. 4b), which is almost the same as that of PTM2 (Fig. 4a).
Therefore, the origin of the observed fluorescence at 600 nm of
C60–(PTM2)2 is attributed to the PTM2 moiety. From the
cross point of the fluorescence band and absorption band after
normalizing both intensities, the lowest excited singlet energy
(E0-0) of the PTM2 moiety was estimated to be 2.1 eV.
exothermic and predicted to occur easily. In toluene, the
charge-separation process is also exothermic and can occur.
The charge-separation process via the excited triplet state of
C60 (3C60*) is also exothermic in polar and nonpolar solvents.
Steady-state absorption measurements
Steady-state absorption spectra of C60–(PTMH)2 5, C60–
(PTM2)2 1, and PTM2 in PhCN are shown in Fig. 3. For
C60–(PTMH)2, the peaks at 700 and 430 nm bands are
attributed to the characteristic bands of the functionalized C60.
In the case of C60–(PTM2)2, the broad absorption band at
518 nm is characteristic of the PTM2 moiety, as shown in
The fluorescence of the C60 moiety would be expected to
appear at 720 nm as shown for C60–(PTMH)2 (Fig. 4a). In the
case of C60–(PTM2)2, however, the fluorescence of the C60
Fig. 4 Steady-state fluorescence spectra of (a) PTM2 (0.05 mM) and
Fig. 3 Steady-state absorption spectra of (a) C60–(PTMH)2 (0.1 mM)
in PhCN and (b) C60–(PTM2)2 and PTM2 (0.025 mM) in PhCN.
C
60–(PTMH)2 (0.05 mM), and (b) C60–(PTM2)2 (0.05 mM) in toluene
and o-DCB; lex = 550 nm.
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Fig. 5 Fluorescence time profiles at 560–630 nm in o-DCB and
PhCN; lex = 400 nm.
moiety may be hidden by the huge fluorescence tail of
1(PTM2)*. Further quantitative analyses on the fluorescence
properties were carried out based on fluorescence lifetime
measurements.
Time-resolved fluorescence spectra and fluorescence lifetimes
The peak position and shape of time-resolved fluorescence
1
spectra of (PTM2)* (see ESI{) are quite similar to those of
the steady-state spectra. Within the fluorescence lifetime, the
spectral shape is almost the same. The time profiles of
the fluorescence peak position are shown in Fig. 5. The
fluorescence time profile of 1(PTM2)* showed slow fluores-
cence decay obeying a single exponential function, yielding a
fluorescence lifetime of 4100 ps in toluene and o-DCB.20a In
PhCN, a shorter lifetime (1000 ps) was evaluated, suggesting
differences in the excited state of 1(PTM2)* in this polar
solvent from that in nonpolar and less polar solvents.
Fig. 7 Fluorescence time profiles at (a) 560–630 nm and (b) 710–
750 nm, respectively, in toluene and o-DCB; lex = 400 nm.
that in non-polar toluene within experimental errors, in which
both decays are the same as that of pristine 1C60*, as expected
for a compound with no donor moieties that can not present
charge-separation.
Also for C60–(PTMH)2, the time-resolved fluorescence
spectra (see ESI{) are in good agreement with the steady-state
fluorescence spectrum. Within the fluorescence lifetime of
C60–(PTMH)2 the spectral shape is unchanged. Time profiles
of the fluorescence intensity at the peak position in toluene
and o-DCB are shown in Fig. 6. In slightly polar o-DCB, the
fluorescence lifetime of the 1C60* moiety is almost the same to
Time profiles of the fluorescence peak position of C60–
(PTM2)2 in toluene and o-DCB are shown in Fig. 7. Slight
blue shift of the florescence peak was observed in the time-
resolved fluorescence spectra of C60–(PTM2)2 (see ESI{) on
going from toluene to o-DCB, which is the same trend as
observed in steady-state measurements. The fluorescence
lifetimes of the 1(PTM2)* moiety in C60–(PTM2)2 at 560–
1
630 nm (Fig. 7) are quite shorter than that of (PTM2)* in all
studied solvents (Fig. 5). This finding indicates that a quench-
ing process from the 1(PTM2)* moiety to the C60 moiety takes
place for C60–1(PTM2)*(PTM2). Even in nonpolar solvents
like toluene, the fluorescence decay rate of the 1(PTM2)*
moiety in C60–1(PTM2)*(PTM2) was faster than that of the
1
isolated (PTM2)*, it is possible to consider that both energy
1
transfer and charge separation occur via (PTM2)*.
From the (tf)sample value of the 1(PTM2)* moiety in C60–
(PTM2)2, the intramolecular quenching rate-constant (kS
)
q
was evaluated using eqn (4):
kS = (1/tf)sample 2 (1/tf)ref
(4)
q
where (tf)ref is the fluorescence lifetime of PTM2 in toluene.20e
Fig. 6 Fluorescence decays of C60–(PTMH)2 at 700–750 nm in
toluene and o-DCB; lex = 410 nm.
The kinetic data are summarized in Table 3, which indicates
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Table 3 Fluorescence lifetimes (tf) at 710–730 nm, quenching rate-constants (kS
)
and quenching quantum yields (WS
)
q
via
q
1
C60–1(PTM2)*(PTM2), and rate constants (kSCS) and quantum yields (WSCS) for charge separation via C60*–(PTM2)2 at room temperature
a
q
1
1
a
1
Solvent
tfb/ps via 1(PTM2)*
kS a/s21 via 1(PTM2)*
WS via 1(PTM2)*
tfb/ps via C60
*
kS a/s21 via C60
*
WS
via C60*
CS
q
CS
Toluene
o-DCB
PhCN
a
150 (70%)
79 (85%)
6.4 6 109
0.96
0.98
100 (85%)
83 (94%)
95 (88%)
9.3 6 109
1.1 6 1010
9.8 6 109
b
0.93
0.94
0.93
1.3 6 1010
257 (70%)c
(3.7 6 109)c
(0.94)c
Calculated by using eqn (4) and (5). The values of (tf)ref were employed to be 4130 ps for PTM2 and 1390 for C60
.
Fluorescence decays of
1(PTM2)* and 1(C60)* were fitted with biexponential functions and the kqS, WqS, kS and WS values were calculated from the shorter
lifetimes with the major fraction. Effect of impurity in PhCN may be included.
CS
CS
c
efficient energy/electron transfer quenching processes of the
S
Nanosecond transient absorption measurements
PTM2 moiety in C60–(PTM2)2; thus, in the evaluated kq
Transient absorption spectra observed upon nanosecond laser
excitation (355 nm) of C60–(PTMH)2 in toluene are shown in
Fig. 8. The 355 nm laser light excites the C60 and PTMH
moieties. The broad absorption bands were observed in the
region of 600–850 nm, which is the absorption region of 3C60*
(peak = 700 nm).20e The decay time profile is quite slow on the
time scale of 1.5 ms. Even the PTMH moiety was excited,
values, both energy transfer rate constant (kENS) and charge-
separation rate constant (kCSS) may be included. For clear
evidence of the energy transfer process,
a rise of the
fluorescence of the 1C60* moiety at 720 nm would be expected,
but this was difficult to observe due to the quick decay of 1C60*
even in toluene (Fig. 7b).
The fluorescence quenching quantum yields of (WSq) via the
1(PTM2)* moiety in C60–(PTM2)2 in polar and nonpolar
solvents were evaluated from eqn (5):
1
the energy transfer gives the C60* moiety, which is finally
3
converted to C60* by ISC.
Transient absorption spectra observed by the nanosecond
laser excitation (355 nm) of C60–(PTM2)2 in toluene are shown
in Fig. 9. Broad absorption bands were observed in the region
WS = [(1/tf)sample 2 (1/tf)ref]/(1/t)sample
(5)
q
of 600–1200 nm, which can be attributed to the absorption
of the C60 moiety,20e although the absorption bands are
Thus,
WS
=
0.96–0.98
was
calculated
for
2
?
q
S
C60–1(PTM2)*(PTM2). Similarly, Wq may contain both
quantum yields of energy transfer (WENS) and quantum yields
of charge separation (WCSS).
2
2
?
broader compared with the pristine C60 and other C60
?
derivatives. This broadening may be caused by the interaction
2
2
?
?
between the C60 moiety and the (PTM )(PTM ) moiety, in
which anion, radical and halogen atoms may be the candidate
of the interactions. From the decay time-profile at 1020 nm,
In PhCN, the fluorescence decay rate was slower than those
in toluene and o-DCB, probably because of the presence of
some impurity in PhCN, which was quite difficult to eliminate.
By contrast with the fluorescence decay of the C60–(PTMH)2
moiety yielding the fluorescence lifetime (tf) of 1390 ps in
toluene (Fig. 6),20 the time profiles of the fluorescence at
720 nm of the C60 moiety in C60–(PTM2)2 (Fig. 7b) show
biexponential decay in o-DCB and toluene. The major com-
ponent decayed with the tf values in the 83 ps (94%)–100 ps
(85%) region, whereas the minor slow-decay components gave
tf values of 1300 ps. The tf values of the major components are
summarized in Table 3.
2
?
the charge-recombination rate constant (kCR) between C60
2
2
?
?
?
and PTM of C60 –(PTM )(PTM ) was evaluated to be
1.23 6 107 s21, from which the lifetime (tRIP) of the charge-
separated state was calculated to be 81 ns at room tem-
perature. Since the 355 nm laser light predominantly excites
the C60 moiety, the process photoinduced by the excitation of
PTM2 can be neglected.
Similarly, transient absorption–time profiles at 1020 nm
were observed in o-DCB and PhCN (see ESI{), although the
The difference between the tf values evaluated from the
main fluorescence decays in 710–750 nm in polar and nonpolar
solvents can be attributed predominantly to charge separation
1
via the C60* moiety in C60–(PTM2)2 generating the radical
2
ion-pair states (C60 –(PTM )(PTM )). From the tf value of
2
?
?
1
the C60* moiety in C60–(PTM2)2, the intramolecular charge-
separation rate constants (kSCS) in polar and nonpolar solvents
were evaluated from eqn (4) as summarized in Table 3. Thus,
the kS values for the C60–(PTM2)2 were evaluated to be
CS
(9.3–11.0) 6 109 s21 which indicate that charge separation via
the C60* moiety is an effective process in polar and nonpolar
1
solvents. The quantum yields of charge separation (WSCS) via
the 1C60* moiety in C60–(PTM2)2 were evaluated from eqn (5).
Thus, WS = 0.93–0.94 were calculated for the C60–(PTM2)2
CS
(Table 3) in polar and nonpolar solvents, respectively, which
indicates that the charge separation via the 1C60* moiety is the
main process, overwhelming the intersystem crossing (ISC)
Fig. 8 Nanosecond transient absorption spectra of 0.1 mM
C
60-(PTMH)2 observed by 532 nm laser irradiation at 100 ns ($)
3
and 1000 ns (#) in PhCN. Inset: Absorption–time profiles at 720 nm.
process to the C60* moiety even in toluene.
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Fig. 10 Steady-state absorption spectra of 0.10 mM C60–(PTM2)2 in
Fig. 9 Nanosecond transient absorption spectra of 0.05 mM C60
–
PhCN before and after 355 nm laser light (LS) irradiation.
(PTM2)2 observed by 355 nm laser irradiation at 100 ns ($) and
1000 ns (#) in toluene. Inset: Absorption–time profiles at 1020 nm.
transient absorption spectra were distorted in o-DCB and
PhCN by laser irradiation (see ESI{ Fig. SI-8). From the
decay time-profiles at 1020 nm, the charge-recombination rate
constants (kCR) were evaluated to be 1.30 6 107 and 1.72 6
107 s21 for o-DCB and PhCN, from which the tRIP values of
the charge-separated states were calculated to be 77 and 58 ns,
respectively, at room temperature as listed in Table 4.
The solvent polarity effect on the tRIP values was small; for
polar and nonpolar solvents, almost similar lifetimes (tRIP) are
2
2
?
?
found. However, C60 –(PTM )(PTM ) in toluene gives a
long lifetime.
Repeated laser irradiation
By excitation of C60–(PTM2)2 with the 355 nm light, the
absorption band of PTM2 decreased; instead,
a sharp
peak appeared at 390 nm (Fig. 10), which is attributed to
?
the PTM moiety (see Fig. 2). This observation indicates
that after the photoinduced charge-separation the stable
2
C60–(PTM )(PTM ) species was generated, probably because
?
2
the C60 moiety may be quenched by some reactions such as
?
donation of an electron to the impurity in the solution.
Energy diagram
Fig. 11 shows an energy diagram of C60–(PTM2)2 when
PTM2 and C60 are excited. Energy levels of the radical ion-
Fig. 11 Schematic energy diagram for electron-transfer processes of
60–(PTM2)2.
2
pairs C60 –(PTM )(PTM ) are deduced from Table 2. In
2
?
?
C
toluene, o-DCB and PhCN, the charge-separation takes place
1
via C60–1(PTM2)*(PTM2) and C60*–(PTM2)2 as indicated
lower than these excited singlet states even in toluene. Thus,
3
the generation of C60*–(PTM2)2 through the ISC process
by the weak fluorescence intensity and the short fluorescence
2
2
lifetime, since the energy levels of C60 –(PTM )(PTM ) are
?
?
1
from C60*–(PTM2)2 is not possible, because the WS values
CS
are almost unity in all solvents. Furthermore, with excitation
of PTM2, an energy-transfer process is also possible from the
2
?
Table 4 Charge-recombination rate constant (kCR
2
(PTM )(PTM ) at room temperature
)
of C60
–
1
1(PTM2)* moiety to generate the C60* moiety.
?
Solvent
kCR/s21
tRIP/ns
Summary
Toluene
o-DCB
PhCN
1.23 6 107
1.30 6 107
1.72 6 107
81
77
58
We have succeeded, for the first time, in synthesizing a C60
based triad which bears an anionic donor as addend, the
118 | J. Mater. Chem., 2006, 16, 112–121
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perchlorotriphenylmethide anion (PTM2), thus generating
the C60–(PTM2)2 triad 1. For this triad, photoinduced
charge separation via both C60–1(PTM2)*(PTM2) and
1C60*–(PTM2)2 were observed in polar and nonpolar
solvents through photoexcitation at room temperature.
The efficiency and rate of the charge-separation process are
Synthesis of 4-[bis(2,3,4,5,6-pentachlorophenyl)methyl]-2,3,5,6-
tetrachlorobenzoyl chloride (3)
A
solution of 4-[bis(2,3,4,5,6-pentachlorophenyl)methyl]-
2,3,5,6-tetrachlorobenzoic acid (2)29 (149.7 mg; 0.194 mol) in
thionyl chloride (3 mL) was refluxed for 24 h. Excess SOCl2
was removed under reduced pressure. The resulting solid
was purified by chromatography (silica gel, chloroform).
Compound 3 was obtained in 80% yield as a beige solid.
IR (KBr): 675, 764, 810, 1780 (COCl) cm21. Anal. Calc. for
C20HCl15O2: C, 29.84; H, 0.12; Cl, 66.06. Found: C, 29.67; H,
0.14; Cl, 66.36%.
2
2
?
?
quite high. The longest lifetime for C60 –(PTM )(PTM )
was 81 ns in toluene at room temperature, which is quite
long and comparable with other C60 based dyads and
triads such as C60–fluorene–diphenylamine,33 C60–bridge–
dimethylaniline,5 C60–extended TTF34 or C60–long flexible
bridge-TTF.30 Even though the properties of C60 perchloro-
triphenylmethide anion based triads are not so good like the
best ones found in some C60–porphyrins and C60–chlorines
based dyads,36 the present study provides a new possibility
for functional fullerenes based on the perchlorotriphenyl-
methide anion, which can be added to other known functional
materials based on the parent perchlorotriphenylmethyl
radical that works as an acceptor and has permitted the
development of multifunctional switchable molecular sys-
tems.26e,35 We believe that the present study gives valuable
information not only about the photo-induced electron-
transfer chemistry of fullerene-triad systems, but also about
the materials science of perchlorotriphenylmethide anion
functional compounds.
Synthesis of 2,2-bis{4-[bis(2,3,4,5,6-pentachlorophenyl)methyl]-
2,3,5,6-tetrachlorobenzoyloxymethyl}-1,2-propano-1,2-
dihydro[60]fullerene (5)
A mixture of compound 427 (68.3 mg; 0.083 mmol), compound
3 (150 mg; 0.190 mmol) and dimethylaminopyridine (35.5 mg;
0.290 mmol) in freshly distilled dichloromethane (10 mL)
was stirred under argon atmosphere at 38 uC for 5 days.
The solvent was evaporated and the residue was purified by
column chromatography (silica gel, hexane then hexane–
CH2Cl2 2 : 1). Compound 5 was obtained in 59% yield as a
1
brown solid. H NMR (250 MHz, CDCl3): 3.97 (s, 4H, CH2–
C60), 5.41 (s, 4H, CH2–O–CO–), 7.06 (s, 2H, CH). IR (KBr):
527(C60), 810 (C–Cl), 1749 (CLO) cm21. UV-Vis (CH2Cl2):
lmax (e) = 430 (4625), 326 (32800), 305 (38900), 255 nm
(167000 L mol21 cm21). MS (MALDI-TOF): m/z calcd for
the maximum peak of C105H10O4Cl28 = 2327.17, observed
maximum [M]+ = 2327.25.
Experimental
General information
Reagents were purchased from commercial suppliers
and used without further purification. Compounds 2,
PTM2[18-crown-6]+, and 4 were synthesized as previously
described.25,27,28 All solvents were spectrophotometric grade
and were distilled before use. Column chromatography was
performed using Merck silica gel 60. The NMR spectra
were recorded on a Bruker Avance DRX 500 spectrometer
(500 MHz for 1H, 125.5 MHz for 13C). IR spectra were run on
a FT-IR spectrometer BIO-RAD FTS 155, the solid com-
pounds being studied in KBr pellets. UV-Vis spectra were
recorded on a Cary 5 E Varian Spectrometer. MALDI-TOF
mass spectra were obtained on a Bruker Biflex III spectro-
meter, equipped with a N2 laser (337 nm) using dithranol as a
matrix. The ESI-MS spectra were obtained with a JEOL, JMS
700 B/E mass spectrometer.
Synthesis of C60–(PTM2)2(NBu4)2 (1)
Tetrabutylammonium hydroxide, 40 wt% solution in water,
y1.5 M (31.5 ml; 47.25 mmol) was added to a solution of
compound 5 (20 mg; 8.59 mmol) dissolved in freshly distilled
THF (2.5 mL). This mixture immediately became garnet-red
and was stirred for 2 hours in a light protected place. The
compound precipitates after addition of deoxygenated distilled
hexane. The resulting solid was purified by centrifugation, and
washed several times with deoxygenated distilled hexane. The
garnet-red compound 1 was obtained quantitatively. IR (KBr):
518 (C60), 810 (C–Cl), 1738 (CLO) cm21. UV (THF), lmax (e) =
518 nm (75000 L mol21 cm21). MS (ESI2): m/z calcd for
the maximum peak of C105H8O4Cl28 = 1163.58, observed
maximum 1162.45.
Electrochemical measurements
Steady-state measurements
Oxidation potentials (Eox) and reduction potentials (Ered
)
were measured by a voltammetric analyzer (EGG PAR 273A)
in a conventional three-electrode cell equipped with Pt
working electrodes and counter electrodes. A silver wire
served as a quasi-reference electrode; its potential was checked
against the ferrocene/ferrocenium couple (Fc/Fc+) before
and after each experiment, at a scan rate of 100 mV s21. In
each case, the solution contained y0.5 mM sample and 0.1 M
tetra n-butylammonium hexafluorophosphate (Bu4NPF6)
Steady-state absorption spectra in the visible and near-IR
regions were measured on a Jasco V570 DS spectrophoto-
meter. Steady-state fluorescence spectra were measured on a
Shimadzu RF-5300 PC spectrofluorophotometer equipped
with a photomultiplier tube having high sensitivity in the
700–800 nm region.
Time-resolved fluorescence measurements
dissolved in
a mixture of o-dichlorobenzene–acetonitrile
95 : 5 or other solvents. The experiments were performed in
a glove box.
The time-resolved fluorescence spectra were measured by single
photon counting method using a streakscope (Hamamatsu
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8 (a) A. Samanta and P. V. Kamat, Chem. Phys. Lett., 1992, 199,
635; (b) D. M. Guldi, M. Maggini, G. Scorrano and M. Prato,
J. Am. Chem. Soc., 1997, 119, 974; (c) K. G. Thomas, V. Biju,
M. V. George, D. M. Guldi and P. V. Kamat, J. Phys. Chem. A,
1998, 102, 5341; (d) D. M. Guldi, G. T. Garscia and J. Mattay,
J. Phys. Chem. A, 1998, 102, 9679; (e) M. Maggini, D. M. Guldi,
S. Mondini, G. Scorrano, F. Paolucci, P. Ceroni and S. Roffia,
Chem. Eur. J., 1998, 4, 1992; (f) A. Polese, S. Mondini, A. Bianco,
C. Toniolo, G. Scorrano, D. M. Guldi and M. Maggini, J. Am.
Chem. Soc., 1999, 121, 3446; (g) D. M. Guldi and M. Prato, Acc.
Chem. Res., 2000, 33, 695.
9 (a) J. Llacay, C. Rovira, J. Veciana, M. Mas and E. Molins, Chem.
Commun., 1997, 659; (b) J. Llacay, J. Veciana, J. Vidal-Gancedo,
J. L. Bourdelande, R. Gonzalez-Moreno and C. Rovira, J. Org.
Chem., 1998, 63, 5201.
10 (a) C. Boulle, J. M. Rabreau, P. Hudhomme, M. Cariou,
M. Jubault, A. Gorgues, J. Orduna and J. Gar´ın, Tetrahedron
Lett., 1997, 38, 3909; (b) P. Hudhomme, C. Boulle, J. M. Rabreau,
M. Cariou, M. Jubault and A. Gorgues, Synth. Met., 1998, 94, 73;
(c) D. Kreher, D. P. Hudhomme, A. Gorgues, H. Luo, Y. Araki
and O. Ito, Phys. Chem. Chem. Phys., 2003, 5, 4583.
Photonics, C4334-01) as a detector and the laser light (second
harmonic generation (SHG), 400 nm) of a Ti : sapphire laser
(Spectra-Physics, Tsunami 3950-L2S, 150 fs fwhm) as an
excitation source.36 Lifetimes were evaluated with software
attached to the equipment.
Nanosecond transient absorption measurements
Nanosecond transient absorption measurements were carried
out using THG (355 nm) of a Nd : YAG laser (Spectra-
Physics, Quanta-Ray GCR-130, 5 ns fwhm) as an excitation
source. For transient absorption spectra in the near-IR region
(600–1200 nm) and the time-profiles, monitoring light from a
pulsed Xe lamp was detected with a Ge-APD (Hamamatsu
Photonics, B2834). For the measurements in the visible region
(400–1000 nm), a Si-PIN photodiode (Hamamatsu Photonics,
S1722-02) was used as a detector.20,36
11 (a) E. Allard, J. Delaunay, F. Cheng, J. Cousseau, J. Orduna and
J. Gar´ın, Org. Lett., 2001, 3, 3503; (b) E. Allard, J. Cousseau,
J. Orduna, J. Gar´ın, H. Luo, Y. Araki and O. Ito, Phys. Chem.
Chem. Phys., 2002, 4, 5944.
Acknowledgements
The present work was supported by a Grant-in-Aid on
Scientific Research on Priority Areas (417) from the Ministry
of Education, Culture, Sports, Science and Technology of
Japan, Direccio´n General de Investigacio´n, Spain (Project
BQU2003-00760), DGR, Generalitat de Catalunya (Centre de
Referencia CeRMAE and Project 2001SG00362), EU COST
D14 and CNRS (France).
12 N. V. Tkachenko, L. Rantala, A. Y. Tauber, J. Helaja,
P. V. Hynninen and H. Lemmetyinen, J. Am. Chem. Soc., 1999,
121, 9378.
13 D. I. Schuster, P. Cheng, S. R. Wilson, V. Prokhorenko,
M. Katterle, A. R. Holzwarth, S. E. Braslavsky, G. Klihm,
R. M. Williams and C. Luo, J. Am. Chem. Soc., 1999, 21, 1599.
14 (a) T. Yamashiro, Y. Aso, T. Otsubo, H. Tang, T. Harima and
K. Yamashita, Chem. Lett., 1999, 443; (b) M. Fujitsuka, O. Ito,
T. Yamashiro, Y. Aso and T. Otsubo, J. Phys. Chem. A, 2000, 104,
4876; (c) P. A. van Hal, J. Knol, B. M. W. Langeveld-Voss,
S. C. J. Meskers, J. C. Hummelen and R. A. J. Janssen, J. Phys.
Chem. A, 2000, 104, 5974; (d) J. J. Apperloo, B. M. W. Langeveld-
Voss, J. Knol, J. C. Hummelen and R. A. J. Janssen, Adv. Mater.,
2000, 12, 908; (e) M. Fujitsuka, K. Matsumoto, O. Ito,
T. Yamashiro, Y. Aso and T. Otsubo, Res. Chem. Intermed.,
2001, 27, 73; (f) M. Fujitsuka, A. Masuhara, H. Kasai, H. Oikawa,
H. Nakanishi, O. Ito, T. Yamashiro, Y. Aso and T. Otsubo,
J. Phys. Chem. B, 2001, 105, 9930; (g) P. A. van Hal,
E. H. A. Beckers, S. C. J. Meskers, R. A. J. Janssen,
B. Jousselme, P. Blanchard and J. Roncali, Chem. Eur. J., 2002,
8, 5415; (h) E. H. A. Beckers, P. A. van Hal, A. Dhanabalan,
S. C. J. Meskers, J. Knol, J. C. Hummelen and R. A. J. Janssen,
J. Phys. Chem. A, 2003, 107, 6218.
15 (a) N. Mart´ın, L. Sa´nchez, B. Illescas and I. Pe´rez, Chem. Rev.,
1998, 98, 2527; (b) N. Mart´ın, L. Sa´nchez and D. M. Guldi, Chem.
Commun., 2000, 113; (c) M. A. Herranz and N. Mart´ın, Org. Lett.,
1999, 1, 2005; (d) N. Mart´ın, L. Sanchez, M. A. Herranz and
D. M. Guldi, J. Phys. Chem. A, 2000, 104, 4648; (e) M. A. Herranz,
N. Mart´ın, L. Sa´nchez, C. Seoane and D. M. Guldi, J. Organomet.
Chem., 2000, 599, 2; (f) D. M. Guldi, S. Gonza´lez, N. Mart´ın,
A. Anto´n, J. Mar´ın and J. Orduna, J. Org. Chem., 2000, 65, 1978;
(g) M. A. Herranz, B. Illescas, N. Mart´ın, C. Luo and D. M. Guldi,
J. Org. Chem., 2000, 65, 5728; (h) S. Gonza´lez, N. Mart´ın,
A. Swartz and D. M. Guldi, Org. Lett., 2003, 5, 557; (i) L. Sa´nchez,
M. A. Herranz and N. Mart´ın, J. Mater. Chem., 2005, 15, 1409.
16 (a) J. W. Arbogast, C. S. Foote and M. Kao, J. Am. Chem. Soc.,
1992, 114, 2277; (b) C. S. Foote, Top. Curr. Chem., 1994, 169, 347.
17 Y. Wang, J. Phys. Chem., 1992, 96, 764.
References
1 C. S. Foote, Top. Curr. Chem., 1994, 169, 347.
2 Fullerene, Chemistry, Physics and Technology, ed. K. M. Kadish
and R. S. Ruoff, Wiley-Interscience, New York, 2000.
3 Fullerene and Related Structures, ed. A. Hirsch, Springer, Berlin,
1999.
4 (a) P. A. Liddell, J. P. Sumida, A. N. Macpherson, L. Noss,
G. R. Seely, K. N. Clark, A. L. Moore, T. A. Moore and D. Gust,
Photochem. Photobiol., 1994, 60, 537; (b) H. Imahori, S. Cardoso,
D. Tatman, S. Lin, L. Noss, G. R. Seely, L. Sereno, C. Silber,
T. A. Moore, A. L. Moore and D. Gust, Photochem. Photobiol.,
1995, 62, 1009; (c) D. D. Kuciauskas, S. Lin, G. R. Seely,
A. L. Moore, T. A. Moore, D. Gust, T. Drovetskaya, C. A. Reed
and P. D. W. Boyd, J. Phys. Chem., 1996, 100, 15926.
5 (a) R. M. Williams, M. N. Zwier and J. W. Verhoeven, J. Am.
Chem. Soc., 1995, 117, 4093; (b) R. M. Williams, M. Koeberg,
J. M. Lawson, Y.-Z. An, Y. Rubin, M. N. Paddon-Row and
J. W. Verhoeven, J. Org. Chem., 1996, 61, 5055; (c) K. G. Thomas,
V. Biju, M. V. George, D. M. Guldi and P. V. Kamat, J. Phys.
Chem. A, 1998, 102, 5341; (d) K. G. Thomas, V. Biju, D. M. Guldi,
P. V. Kamat and M. V. George, J. Phys. Chem. B, 1999, 103, 8864;
(e) K. G. Thomas, V. Biju, D. M. Guldi, P. V. Kamat and
M. V. George, J. Phys. Chem. A, 1999, 103, 10755.
6 (a) N. S. Sariciftci, F. Wudl, A. J. Heeger, M. Maggini,
G. Scorrano, M. Prato, J. Bourassa and P. C. Ford, Chem. Phys.
Lett., 1995, 247, 510; (b) A. S. D. Sandanayaka, K. Matsukawa,
T. Ishi-I, S. Mataka, Y. Araki and O. Ito, J. Phys. Chem. B,
2004, 108, 19995; (c) A. S. D. Sandanayaka, K.-i. Ikeshita,
G. A. Rajkumar, Y. Furusho, Y. Araki, T. Takata and O. Ito,
J. Phys. Chem. A, 2005, 109, 8088; (d) A. S. D. Sandanayaka,
K. Ikeshita, Y. Araki, N. Kihara, Y. Furusho, T. Takata and
O. Ito, J. Mater. Chem., 2005, 15, 2276.
7 (a) H. Imahori, K. Hagiwara, M. Aoki, T. Akiyama, S. Taniguchi,
T. Okada, M. Shirakawa and Y. Sakata, J. Am. Chem. Soc., 1996,
118, 11771; (b) H. Imahori, S. Ozawa, K. Uchida, M. Takahashi,
T. Azuma, A. Ajavakom, T. Akiyama, M. Hasegawa, S. Taniguchi,
T. Okada and Y. Sakata, Bull. Chem. Soc. Jpn., 1999, 72, 485; (c)
H. Imahori, K. Tamaki, D. M. Guldi, C. Luo, M. Fujitsuka, O. Ito,
Y. Sakata and K. Fukuzumi, J. Am. Chem. Soc., 2001, 123, 2607.
18 (a) R. Seshadri, C. N. R. Rao, H. Pal, T. Mukherjee and
J. P. Mittal, Chem. Phys. Lett., 1993, 205, 395; (b) H. N. Ghosh,
H. Pal, A. V. Saper and J. P. Mittal, J. Am. Chem. Soc., 1993, 115,
11722.
19 E. Schaffner and H. Fischer, J. Phys. Chem., 1993, 97, 13149.
20 (a) A. Watanabe and O. Ito, J. Phys. Chem., 1994, 98, 7736; (b)
O. Ito, Y. Sasaki, Y. Yoshikawa and A. Watanabe, J. Phys. Chem.,
1995, 99, 9838; (c) Y. Sasaki, Y. Yoshikawa, A. Watanabe and
O. Ito, J. Chem. Soc., Faraday Trans., 1995, 91, 2287; (d) M. Alam,
A. Watanabe and O. Ito, J. Photochem. Photobiol. A, 1997, 104, 59;
(e) C. Luo, M. Fujitsuka, A. Watanabe, O. Ito, L. Gan, Y. Huang
and C. H. Huang, J. Chem. Soc., Faraday Trans., 1998, 94, 527.
120 | J. Mater. Chem., 2006, 16, 112–121
This journal is ß The Royal Society of Chemistry 2006

View Article Online
21 (a) M. Bennati, A. Grupp, P. Ba¨uerle and M. Mehring, Chem.
Phys., 1994, 185, 221; (b) M. Bennati, A. Grupp, P. Ba¨uerle and
M. Mehring, Mol. Cryst. Liq. Cryst., 1994, 256, 751.
28 M. Ballester, J. Riera, J. Castan˜er, C. Rovira, J. Veciana and
C. Onrubia, J. Org. Chem., 1983, 48, 3716.
29 M. Ballester, J. Castan˜er, J. Riera, A. Iban˜ez and J. Pujadas, J. Org.
Chem., 1982, 47, 259.
30 S. Chopin, Z. Gan, J. Cousseau, Y. Araki and O. Ito, J. Mater.
Chem., 2005, 15, 2288.
22 (a) B. Ma, G. E. Laeson, C. E. Bunker, A. Kitaygorodskiy and
Y.-P. Sun, Chem. Phys. Lett., 1995, 247, 51; (b) Y.-P. Sun,
B. Ma and G. E. Lawson, Chem. Phys. Lett., 1995, 233, 57; (c)
G. E. Lawson, A. Kitaygorodskiy, B. Ma, C. E. Bunker and
Y.-P. Sun, J. Chem. Soc., Chem. Commun., 1995, 2225.
23 S. Fukuzumi, T. Suenobu, M. Patz, T. Hirasaka, S. Itoh,
M. Fujitsuka and O. Ito, J. Am. Chem. Soc., 1998, 120, 8060.
24 (a) H. Imahori, K. Hagiwara, T. Akiyama, M. Akoi, S. Taniguchi,
T. Okada, M. Shirakawa and Y. Sakata, Chem. Phys. Lett., 1996,
263, 545; (b) H. Imahori, K. Tamaki, D. M. Guldi, C. Luo,
M. Fujitsuka, O. Ito, Y. Sakata and K. Fukuzumi, J. Am. Chem.
Soc., 2001, 123, 2607.
31 A. Weller, Z. Phys. Chem. Neue Folge, 1982, 133, 93.
32 The distance was evaluated from the minimized structure of
the triad 1 obtained using semiempirical AM1 calculations (see
ESI{ Fig. SI-3). Three resulting minimized geometries were
obtained in which the distance between the PTM unit and C60
are different. The geometry used was the conformation with
the lower formation enthalpy (DHf). Distances between the center
of C60 and PTM2 were evaluated to be 10 A from this optimized
˚
structure.
25 J. Veciana, J. Riera, J. Castan˜ar and N. Ferrer, J. Organomet.
Chem., 1985, 297, 131.
33 H. Luo, M. Fujitsuka, Y. Araki, O. Ito, P. Padmawar and
L. Y. Chiang, J. Phys. Chem. B, 2003, 107, 9312.
34 M. A. Herranz, N. Martin, J. Ramey and M. D. Guldi, Chem.
Commun., 2002, 2968.
35 (a) I. Ratera, D. Ruiz-Molina, J. Vidal-Gancedo, J. J. Novoa,
K. Wurst, J.-F. Letard, C. Rovira and J. Veciana, Chem. Eur. J.,
2004, 10, 603; (b) I. Ratera, D. Ruiz-Molina, F. Renz, J. Ensling,
K. Wurst, C. Rovira, G. Philipp and J. Veciana, J. Am. Chem.
Soc., 2003, 125, 1462.
36 (a) M. Yamazaki, Y. Araki, M. Fujitsuka and O. Ito, J. Phys.
Chem. A, 2001, 105, 8615; (b) F. D’Souza, G. R. Deviprasad,
M. E. Zandler, V. T. Hoang, A. Klykov, M. E. El-Khouly,
M. Fujitsuka and O. Ito, J. Phys. Chem. B, 2002, 106,
4952.
26 (a) M. Basllester, Adv. Phys. Org. Chem., 1989, 25, 267; (b)
J. Veciana, C. Rovira, N. Ventosa, M. I. Crespo and F. Palacio,
J. Am. Chem. Soc., 1993, 115, 57; (c) N. Ventosa, D. Ruiz, J. Sedo´,
C. Rovira, X. Toma´s, J.-J. Andre´, A. Bieber and J. Veciana, Chem.
Eur. J., 1999, 5, 3533; (d) D. Maspoch, D. Ruiz-Molina, K. Wurst,
N. Domingo, M. Cavallini, F. Biscarini, J. Tejada, C. Rovira and
J. Veciana, Nat. Mater., 2003, 2, 190; (e) C. Sporer, I. Ratera,
D. Ruiz-Molina, Y. Zhao, J. Vidal-Gancedo, K. Wurst, P. Jaitner,
K. Clays, A. Persoons, C. Rovira and J. Veciana, Angew. Chem.,
Int. Ed., 2004, 43, 5266.
27 S. Chopin, J. Delaunay and J. Cousseau, Tetrahedron Lett., 2005,
46, 373.
This journal is ß The Royal Society of Chemistry 2006
J. Mater. Chem., 2006, 16, 112–121 | 121