Conformation effect of oligosilane linker on photoinduced electron transfer of tetrasilane-linked zinc porphyrin-[60]fullerene dyads

Article abstract of DOI:10.1016/j.jorganchem.2006.05.062

A series of zinc porphyrin-[60]fullerene dyads linked by conformation-constrained tetrasilanes and permethylated tetrasilane have been synthesized for the evaluation of the conformation effect of the tetrasilane linkers on the photoinduced electron transf

Full text of DOI:10.1016/j.jorganchem.2006.05.062

Journal of Organometallic Chemistry 692 (2007) 356–367
www.elsevier.com/locate/jorganchem
Conformation effect of oligosilane linker on photoinduced
electron transfer of tetrasilane-linked zinc porphyrin–[60]fullerene dyads
a
b
a,
b
Yuki Shibano , Mikio Sasaki , Hayato Tsuji *, Yasuyuki Araki ,
b,
a,c,
*
Osamu Ito *, Kohei Tamao
a
International Research Center for Elements Science (IRCELS), Institute for Chemical Research, Kyoto University, Uji, Kyoto 611-0011, Japan
b
Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Katahira, Aoba-ku, Sendai 980-8577, Japan
c
RIKEN Frontier Research System, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan
Received 2 March 2006; received in revised form 8 May 2006; accepted 12 May 2006
Available online 30 August 2006
Abstract
A series of zinc porphyrin–[60]fullerene dyads linked by conformation-constrained tetrasilanes and permethylated tetrasilane have
been synthesized for the evaluation of the conformation effect of the tetrasilane linkers on the photoinduced electron transfer. The
excited-state dynamics of these dyads have been studied using the time-resolved fluorescence and absorption measurements. The fluores-
cence of the zinc porphyrin moiety in each dyad was quenched by the electron transfer to the fullerene moiety. The transient absorption
measurements revealed that the final state of the excited-state process was a radical ion pair with a radical cation on the zinc porphyrin
moiety and a radical anion on the fullerene moiety as a result of the charge separation. The charge separation and charge recombination
rates were found to show only slight conformation dependence of the tetrasilane linkers, which is characteristic for the Si-linkages.
ꢀ 2006 Elsevier B.V. All rights reserved.
Keywords: Electron transfer; Porphyrin; Fullerene; Oligosilane; Conformation
1. Introduction
these dyads induces a fast ET from the porphyrin to the
fullerene moiety to generate long-lived charge-separated
(CS) states [2,3] which are essential for the further trans-
duction of the incident light energy [4]. Porphyrins are
some of the most ideal donors and photo-sensitizers
because of their low oxidation potentials as well as their
expanded p-electron system which are suitable for efficient
light-harvesting by covering the wide spectral range of the
solar irradiation [5]. Fullerenes, such as C60, have been
revealed as promising photo-sensitizers and electron-accep-
tors due to the following unique structural and electronic
properties [6–10]; the wide absorption range due to their
extremely expanded p-electron systems, the low-lying
LUMO, and the small reorganization energies which accel-
erate the forward ET process and decelerate the back ET
process as described by the Marcus parabola [11].
Electron transfer (ET) plays a key role in many essential
biological reactions, such as in natural photosynthesis, in
which an incident light causes a cascade of energy transfer
(EN) and subsequent ET. Recently, various types of cova-
lently linked donor–acceptor molecules have been synthe-
sized for understanding and mimicking the ET and EN
during the natural photosynthesis to develop an artificial
photosynthesis as a new energy source [1]. The most widely
investigated donor–acceptor systems are the porphyrin–
fullerene hybrid molecules since the photoexcitation of
*
Corresponding authors. Present address: Department of Chemistry,
The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.
Tel./fax: +81 3 5841 4368.
E-mail addresses: tsuji@chem.s.u-tokyo.ac.jp (H. Tsuji), ito@tagen.
tohoku.ac.jp (O. Ito), tamao@riken.jp (K. Tamao).
Another important factor of the Marcus theory is the
electronic coupling between the donor and acceptor, which
depends not only on the donor–acceptor distance, but also
0022-328X/$ - see front matter ꢀ 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2006.05.062

Y. Shibano et al. / Journal of Organometallic Chemistry 692 (2007) 356–367
357
on the electronic properties of the linkers. Thus, the donor–
acceptor hybrid molecules with a wide variety of linkers
including non-conjugated linkers, such as amides [6,12–
15], imides [16], and norbornylogous bridges [17], and
p-conjugated linkers, such as oligoynes [18] and oligothi-
ophenes [19], have been synthesized in order to elucidate
the influence of the electronic properties of the linkers on
the electronic coupling term. These studies have demon-
strated that the attenuation factors of the non-conjugated
linkers are large, while those of the p-conjugated linkers
are small. These cases dealt with mainly carbon-based link-
ers, and it is of great interest to study the ET through the
heavier element-based architecture.
Scheme 1.
Among the heavy main group element-catenated sys-
tems, polysilanes and oligosilanes have been extensively
studied because of their potential utilities as charge trans-
port materials and photoconductive materials derived from
the high degree of r-electron delocalization over the silicon
framework (r-conjugation) [20]. One of the most striking
features of the oligosilanes is the high sensitivity of their
properties to the conformation of the silicon framework.
Since the silicon backbones of the oligosilanes are highly
flexible due to a small rotational barrier of the Si–Si bond,
the elucidation of the structural dependence of their prop-
erties requires conformation control in an appropriate
manner [21,22]. Our approach for freezing the dynamic
behavior of the oligosilanes is based on the incorporation
of the disilane or trisilane into the bicyclic framework
[21], and these studies have provided clear-cut evidence
for the generally accepted idea that the anti conformation
with large SiSiSiSi dihedral angle (x) effectively extends
the r-conjugation while syn and cisoid conformations with
a small x insulate the r-conjugation.
an alternative synthetic route for the conformationally con-
strained tetrasilanes to the previously reported selective
synthesis based on the stereospecific nucleophilic substitu-
tion reaction on the silicon center [21a]. Thus, the mixture
of the conformation-constrained tetrasilanes Ph–Si4(anti)–
Ph and Ph–Si4(syn)–Ph having phenyl groups on each end
of the silicon chain was first prepared by the reaction of a
bicyclic dichlorodisilane Cl–Si2(syn)–Cl and dim-
ethylphenylsilyllithium [24]. The mixture of the isomers
was subjected to the reaction with trifluoromethanesulfonic
acid (TfOH) followed by the treatment with 2-propanol to
Very recently, we reported the synthesis of a zinc por-
phyrin–fullerene dyad linked by 1,2-dialkynyldisilane and
investigated their excited-state dynamics. The occurrence
of the effective intramolecular photoinduced ET and the
generation of the CS state indicates that the disilane moiety
works as a molecular wire [23]. The construction of the
porphyrin–fullerene dyads linked by conformation-con-
strained oligosilane chain is of interest for evaluating the
influence of the degree of r-conjugation and the dynamic
behavior of the silicon chain on the ET. In this paper, we
report the synthesis of the porphyrin–fullerene dyads
linked by the conformation-constrained tetrasilane, such
as ZnP–[Si4(anti)]–C60 and ZnP–[Si4(syn)]–C60, as well as
the permethylated tetrasilane-linked dyad ZnP–[Si4]–C60
(Chart 1) to study their excited-state dynamics on the basis
of
time-resolved
fluorescence
and
absorption
measurements.
2. Results and discussion
2.1. Synthesis
Scheme 1 shows the preparation of the tetrasilane moi-
eties. As demonstrated in Scheme 1a, we have developed
Chart 1.

358
Y. Shibano et al. / Journal of Organometallic Chemistry 692 (2007) 356–367
give a mixture of i-PrO–Si4(anti)–Oi-Pr and i-PrO–
Si4(syn)–Oi-Pr with isopropoxy groups on each end. The
crystalline anti-isomer was obtained in pure form by crys-
tallization of the viscous reaction mixture from toluene/
acetonitrile, while the oily syn-isomer was obtained by sil-
ica gel column chromatography of the concentrated
mother liquor. The configuration of the anti-isomer was
confirmed by X-ray crystallography (Table 1, Fig. 1). The
current procedure is advantageous when both isomers
are needed at once and is applicable to the gram-scale prep-
aration of the conformationally constrained tetrasilane
units.
Scheme 1b shows the synthesis of the permethylated
tetrasilane Cl–Si4–Cl having chlorine on each end. Thus,
the reaction of 1,2-dichlorotetramethyldisilane with the
dimethylphenylsilylmagnesium reagent [25] produced Ph–
Si4–Ph, which was dephenylchlorinated with hydrogen
chloride in the presence of AlCl3 to give the target product.
Scheme 2 shows the preparation of the dyads from the
obtained tetrasilanes. The chlorine or isopropoxy groups
of the tetrasilanes were substituted with p-bromophenyl
groups using p-bromophenyllithium, followed by the trans-
formation of one bromine atom to a formyl group to give
Fig. 1. ORTEP drawing of i-PrO–Si4(anti)–Oi-Pr with thermal ellipsoid
˚
plot (50% probability). Selected bond lengths (A) and angles (ꢁ): Si(1)–
Si(2) 2.3597(12), Si(2)–Si(2*) 2.3588(18), Si(1)–Si(2)–Si(2*) 109.06(3),
Si(1)–Si(2)–Si(2*)–Si(1*) 180.
the unsymmetrical tetrasilanes Br–[Si4]–CHO having a p-
bromophenyl group on one end and a p-formylphenyl
group on the other end. Suzuki-Miyaura coupling between
the porphyrin boronic ester ZnP–Bpin and Br–[Si4]–CHO
produced the porphyrin-linked tetrasilanes containing a
formyl group ZnP–[Si4]–CHO. The Prato reaction [26]
using C60 and N-methylglycine gave the tetrasilane-linked
zinc porphyrin–fullerene dyads ZnP–[Si4]–C60. The prod-
Table 1
Crystal data and structure refinement for i-PrO–Si4(anti)–Oi-Pr
1
ucts were characterized on the basis of their H, 13C, 29Si
Formula
C20H46O2Si4
NMR, and FAB-mass spectra. The reference compounds
ZnP–[Si2] and [Si2]–C60 were synthesized in a similar
manner.
Formula weight
Temperature (K)
Wavelength (A)
Crystal system
Space group
430.93
173(2)
0.71070
Triclinic
˚
In the 1H NMR spectra of the dyads ZnP–[Si4]–C60 and
ZnP–[Si4(anti)]–C60, the signals of eight b protons of the
ZnP core are shifted upfield by 0.01–0.10 ppm relative to
ZnP–[Si4]–CHO and the porphyrin reference ZnP–[Si2].
These spectral perturbations can be understood by the
shielding effect of the C60 moiety, and we assumed the exis-
tence of a fast equilibrium between two conformers: a
folded conformer, in which the ZnP and C60 moieties are
proximate to each other, and an extended conformer, in
which the ZnP and C60 moieties are separated from each
other as shown in Fig. 2. Such an upfield shift of the por-
phyrin b protons of ZnP–[Si4(syn)]–C60 is small relative to
ZnP–[Si4(anti)]–C60 and ZnP–[Si4]–C60, suggesting that the
folded-extended equilibrium moves to the extended con-
former in ZnP–[Si4(syn)]–C60. These assumptions are sup-
ported by the semi-empirical calculations (Fig. 2) and
photophysical measurements described below.
ꢀ
P1 ð#2Þ
Unit cell dimensions
˚
a (A)
7.503(5)
8.992(6)
10.658(7)
91.205(7)
109.362(8)
106.988(8)
643.2(7)
˚
b (A)
˚
c (A)
a (ꢁ)
b (ꢁ)
c (ꢁ)
3
˚
Volume (A )
Z
1
Dcalc (g/cm3)
1.112
0.243
238
Absorption coefficient (mmꢀ1
F(000)
)
Crystal size (mm)
h Range for data collection (ꢁ)
Index ranges
0.50 · 0.30 · 0.20
3.37–27.52
ꢀ9 6 h 6 9,
ꢀ10 6 k 6 11,
ꢀ13 6 l 6 13
5092
2814 (0.0339)
95.0
0.9530 and 0.8881
Full-matrix least-squares
on F2
Reflections collected
Independent reflections (Rint
Completeness to h = 27.52ꢁ (%)
Maximum and minimum transmission
Refinement method
)
2.2. Electrochemistry
To estimate the energies of the CS states formed by the
photoexcitation, the first oxidation potential (Eox) of the
ZnP moiety and the first reduction potential (Ered) of
the C60 moiety were measured in benzonitrile (BN) using
the square-wave voltammetry method in the presence of
ferrocene (Fc) as the internal standard. The data are
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I > 2r(I)]
R indices (all data)
2814/0/202
1.037
R1 = 0.0318, wR2 = 0.0825
R1 = 0.0370, wR2 = 0.0846
0.346 and ꢀ0.208
Largest difference in peak
ꢀ3
˚
and hole (e A
)

Y. Shibano et al. / Journal of Organometallic Chemistry 692 (2007) 356–367
359
Scheme 2.
summarized in Table 2. The Eox values of the dyads ZnP–
[Si4(anti)]–C60, ZnP–[Si4(syn)]–C60, and ZnP–[Si4]–C60 are
almost the same, while the Ered values slightly vary from
ꢀ1.04 to ꢀ1.10 V versus Fc/Fc+. Thus, the DE values in
Table 2, which denote the energy of the CS states when
the distances between ZnP and C60 are the same, vary
among these three dyads, indicating the existence of the
slight interaction between the ZnP and C60 moieties in
the ground state. From these values, energy levels of the
CS states are found to be moderately low, thus the charge
separation from the singlet excited state of the ZnP and C60
moieties are exothermic paths and can occur.
the Soret and Q bands of porphyrins are broadened, and a
weak broad CT absorption band arises in the NIR region
when porphyrins are located close to fullerenes [27]. The
weaker perturbation in ZnP–[Si4(syn)]–C60 than those in
ZnP–[Si4(anti)]–C60 and ZnP–[Si4]–C60 is explained by the
hindrance of the approach of ZnP to C60 in ZnP–
[Si4(syn)]–C60.
Fig. 4 shows the steady-state fluorescence spectra of
ZnP–[Si4(anti)]–C60, ZnP–[Si4(syn)]–C60, ZnP–[Si4]–C60,
and ZnP–[Si2] measured in BN at room temperature with
excitation at 546 nm, which is one of the isosbestic points
of the absorption spectra. The fluorescence quantum yields
Dyad
FL
of the dyads ðU
Þ and ZnP–[Si2] ðURFLef Þ were evaluated
using zinc tetraphenylporphyrin as a reference as summa-
rized in Table 3 [28]. The shapes of the spectra of the dyads
are almost identical to that of the porphyrin reference ZnP–
[Si2]. The fluorescence of the C60 moiety, which is normally
expected to appear around 720 nm upon excitation, was
hardly recognized in Fig. 4 due to its low fluorescence quan-
tum yield. The fluorescence intensities of the ZnP moiety of
the dyads significantly decreased compared to that of ZnP–
[Si2], indicating the occurrence of the quenching of the low-
est singlet excited-state of the ZnP by connecting the C60
moiety. The order of the fluorescence intensities is ZnP–
[Si4(syn)]–C60 > ZnP–[Si4(anti)]–C60 > ZnP–[Si4]–C60. The
fact that the fluorescence intensities of the conformation
constrained dyads are higher than that of ZnP–[Si4]–C60
can be attributed the suppression effect of the vibrational
and rotational non-radiative decay of the excited state in
terms of the constraint of the molecular movement by the
cyclic structure [29]. The slightly higher fluorescence quan-
tum yield of ZnP–[Si4(syn)]–C60 than that of ZnP–
[Si4(anti)]–C60 is consistent with the NMR and the absorp-
tion spectral measurements that the ZnP–[Si4(syn)]–C60 has
a lower amount of the folded conformer than ZnP–
[Si4(anti)]–C60.
2.3. Steady-state photophysical measurements
The UV–Vis–NIR absorption spectra of the dyads and
the reference compounds measured in BN at room temper-
ature are shown in Fig. 3 and the data are summarized in
Table 3. The Soret bands of ZnP–[Si4(anti)]–C60 and
ABS
max
ZnP–[Si4]–C60 (k
¼ 437:5nm) show a 6.5 nm red-shift
and their extinction coefficients are about a half that of
ZnP–[Si2]. The spectra of ZnP–[Si4(anti)]–C60 and ZnP–
[Si4]–C60 show the broadened Q bands, as compared to that
of ZnP–[Si2], in addition to the weak broad absorption
bands close to near-IR region (800–900 nm) where the ref-
erence compounds show no or little absorption. On the
other hand, such spectral perturbations are somewhat smal-
ler in ZnP–[Si4(syn)]–C60 than the other dyads. Thus, the
Soret band of ZnP–[Si4(syn)]–C60 (kABS ¼ 433:5nm) is red-
max
shifted by only 2.5 nm relative to the reference compound
ZnP–[Si2], and the absorption band in the near-IR region
is slightly weaker than those of ZnP–[Si4(anti)]–C60 and
ZnP–[Si4]–C60. These spectral features can be understood
by considering the existence of the folded conformers in
equilibrium with extended conformers; it is well-known that

360
Y. Shibano et al. / Journal of Organometallic Chemistry 692 (2007) 356–367
Fig. 2. Extended and folded conformers of each dyad, together with the center-to-center distances between ZnP and C60 moiety (Rcc).
Table 2
First oxidation (Eox), reduction potentials (Ered), and differences
(DE = Eox ꢀ Ered) of the dyads measured in BN
Compound
Eox (V)a
Ered (V)a
DE (V)a
ZnP–[Si4(anti)]–C60
ZnP–[Si4(syn)]–C60
ZnP–[Si4]–C60
0.27
0.27
0.27
ꢀ1.04
ꢀ1.08
ꢀ1.10
1.31
1.35
1.37
vs. Fc/Fc+.
a
2.4. Time-resolved photophysical measurements
The time-resolved fluorescence measurements of the BN
solution of the dyads ZnP–[Si4(anti)]–C60, ZnP–[Si4(syn)]–
C60, and ZnP–[Si4]–C60, and the porphyrin reference ZnP–
[Si2] were performed using a time-correlated single-photon
Fig. 3. Steady-state UV–Vis–NIR absorption spectra of ZnP–[Si4(anti)]–
C60 (-----), ZnP–[Si4(syn)]–C60 (– – –), ZnP–[Si4]–C60 (——), ZnP–[Si2]
(– – –), and [Si ]–C (–ꢁ ꢁ ꢁ–) in BN. (a) Soret band region (350–500 nm)
Æ
Æ
2
60
and (b) longer wavelength region (500–1000 nm).

Y. Shibano et al. / Journal of Organometallic Chemistry 692 (2007) 356–367
361
Table 3
Steady-state UV–Vis–NIR absorption and fluorescence spectra of the
dyads ZnP–[Si4]–C60 and the reference compound ZnP–[Si2] in BN
Compound
Absorption
Fluorescence
Dyad
=U
FL
FL
ABS
max
a
kFmLax=nm ðUFL
Þ
U
Ref
k
ðeÞ=nm
ZnP–[Si4(anti)]–C60 437.5 (317000) 609, 660 (1.4 · 10ꢀ3
)
)
)
)
0.025
0.035
0.015
–
563.5 (16400)
604.5 (10900)
ZnP–[Si4(syn)]–C60 433.5 (303000) 608, 660 (2.0 · 10ꢀ3
563.0 (15900)
604.5 (10200)
ZnP–[Si4]–C60
437.5 (312000) 609, 659 (8.7 · 10ꢀ4
563.5 (16400)
604.5 (10800)
Fig. 5. Fluorescence time-profile of ZnP moiety of ZnP–[Si4(anti)]–C60
,
ZnP–[Si4(syn)]–C60,ZnP–[Si4]–C60
, and ZnP–[Si2] in BN excited by
ZnP–[Si2]
431.0 (572000) 609, 660 (5.8 · 10ꢀ2
561.0 (20200)
400 nm laser light.
602.5 (11500)
a
Fluorescence quantum yield relative to zinc tetraphenylporphyrin
Table 4
(UFL = 0.04).
Fluorescence lifetime (sFL) and charge-recombination rate (kCR) in BN
Dyad
FL
FL/ns (fraction/%)a
s
=s
kCR (sꢀ1
)
Ref
FL
Compound
s
ZnP–[Si4(anti)]–C60
ZnP–[Si4(syn)]–C60
ZnP–[Si4]–C60
ZnP–[Si2]
0.40 (77)
0.32 (70)
0.25 (65)
1.90 (100)
0.21
0.17
0.13
–
4.3 · 106
2.9 · 106
2.7 · 106
–
a
Fitted by bi-exponential function.
ZnP–[Si4(anti)]–C60 [30]. The relative sFL values of the
Dyad
FL
Ref
FL
dyads ðs
=s Þ are higher than the fluorescence quan-
tum yields estimated from the steady-state fluorescence
Dyad
FL
Ref
FL
measurements ðU
=U Þ in Table 3 [31]. This inconsis-
tency between these two parameters can be understood
by the assumption that the dyads contain a considerable
amount of the folded conformers, which immediately
transit to the non-fluorescent state, such as exciplex, which
is hardly observable in the steady-state fluorescence
measurements.
Fig. 4. Steady-state fluorescence spectra of ZnP–[Si4(anti)]–C60 (-----),
ZnP–[Si4(syn)]–C60 (– – –), and ZnP–[Si4]–C60 (——) excited by 546 nm
light. Inset: Full picture of the fluorescence spectra of the dyads and ZnP–
The nanosecond transient absorption spectra of ZnP–
[Si4(syn)]–C60 in BN are shown in Fig. 6. The other dyads
afforded similar spectra. An intense transient absorption
band of the C60-radical anion was clearly observed around
1000 nm. Although there was breach around 520 nm, the
transient absorption band of the ZnP-radical cation was
[Si ] (– – –).
Æ
Æ
2
counting technique. The fluorescence time-profiles of the
ZnP moiety are shown in Fig. 5, and the major components
Dyad
FL
Ref
FL
of the lifetimes (s
for the dyads and s for ZnP–[Si2])
fitted by bi-exponential functions are summarized in Table
4. The remarkable shortening of the fluorescence lifetimes
of the dyads compared with ZnP–[Si2] indicates the occur-
rence of the ET and EN from the lowest singlet excited-
states of ZnP to C60 of the dyads although the involvement
of the direct EN is not appreciable in the present case [14].
The multi-component fluorescence decay can be attributed
to the fluctuations of the conformers. The order of the fluo-
rescence lifetimes of the dyads is as follows: ZnP–
[Si4(anti)]–C60 > ZnP–[Si4(syn)]–C60 > ZnP–[Si4]–C60. The
shortest lifetime of ZnP–[Si4]–C60 is due to the dynamic
behavior of the silicon chain [29], as already discussed.
Such a dynamic molecular motion would be also the origin
of the shorter lifetime of ZnP–[Si4(syn)]–C60 than that of
Fig. 6. Nanosecond transient absorption spectra of ZnP–[Si4(syn)]–C60 in
BN at 0.1 and 1.0 ls. Inset: absorption time-profile at 1000 nm.

362
Y. Shibano et al. / Journal of Organometallic Chemistry 692 (2007) 356–367
also observed at a wavelength shorter than 700 nm. These
absorptions indicate the formation of the radical ion-pair
Kieselgel 60 (70-230 mesh, Merck) unless otherwise stated.
All reactions were carried out under nitrogen unless other-
wise stated. All dry solvents were freshly distilled under N2
before use. THF, Et2O, and DME were distilled from
sodium/benzophenone. Benzene and toluene were distilled
from sodium. CH2Cl2 was distilled from CaH2. Acetone
was distilled from anhydrous K2CO3. Hexane was distilled
from sodium/benzophenone/triglym. 1,7-Dichloro-1,7-disi-
labicyclo[5.5.0]dodecane [21a], 1,2-dichloro-1,1,2,2-tetram-
ethyldisilane [32], 1-(4-bromophenyl)-1,1,2,2-tetramethyl-
2-phenyldisilane [33], [5-(4,4,5,5-tetramethyl-1,3,2-dioxa-
borolan-2-yl)-10,15,20-tris[30,50-(di-tert-butyl)phen-yl]por-
phinato]zinc(II) (ZnP–Bpin) [34], and [Si2]–C60 [23] were
synthesized as described before.
ZnPꢀþ–½Si4ðsynÞꢂ–Cꢀꢀ by the intramolecular charge separa-
60
tion. The charge-recombination rates (kCR) of the dyads
estimated by the decay rate of the transient absorption at
1000 nm are summarized in Table 4. The kCR of the dyads
slightly depend on the linkage conformation: ZnP–[Si4-
(anti)]–C60 > ZnP–[Si4(syn)]–C60 > ZnP–[Si4]–C60, which
Dyad
FL
shows an opposite tendency to that of the 1=s
values.
Although the mechanism of the charge-recombination pro-
cess is not clear at the present stage, this result is suggestive
of the existence of the superexchange mechanism in the
back ET through the Si-linkage and a competitive charge-
recombination path, such as a direct back ET by the intra-
molecular collision of the radical ion centers based on the
molecular motion.
4.2. anti- and syn-1,7-Isopropoxydimethylsilyl-1,7-
disilabicyclo[5.5.0]dodecane (i-PrO–Si4(anti)–O-i-Pr
and i-PrO–Si4(syn)–Oi-Pr)
3. Conclusion
Zinc porphyrin–fullerene dyads linked by the conforma-
tion-constrained tetrasilanes were synthesized together with
the permethylated tetrasilane-linked dyad. Time-resolved
fluorescence measurements revealed that the ET occur on
a sub-nanosecond to nanosecond timescale. The transient
absorption spectra in polar solvents are mainly composed
of the C60-radical anion and the ZnP-radical cation, indicat-
ing the generation of the CS state with a sub-microsecond
lifetime. The lifetimes of the CS states hardly depend on
the conformation of the tetrasilane linkers. These observa-
tions imply that the CR rate show little dependence on
the degree of r-conjugation. This is in sharp contrast to
the p-conjugated linkers, which show the unambiguous
linkage dependence of the ET rates [13]. Such a difference
would be one of the characteristics of the silicon linkage.
The clarification of the dependence of the ET rates on the
number of silicon atoms in the oligosilane linkers are cur-
rently being performed in our laboratories.
To a solution of 1,7-dichloro-1,7-disilabicyclo[5.5.0]
dodecane (Cl–Si2(syn)–Cl; 2.35 g, 8.78 mmol) in THF
(10 mL) was added a solution of dimethylphenylsilylli-
thium, which was prepared from lithium (granular,
512 mg, 73.7 mmol) and chlorodimethylphenylsilane (3.0
mL, 18.1 mmol) in THF (20 mL), dropwise over 10 min
at 0 ꢁC. Upon completion of the addition, the reaction mix-
ture was allowed to warm to room temperature. After
being stirred for 2 h, the resulting mixture was quenched
with H2O (20 mL) and evaporated to remove THF. To
the residue was added Et2O (20 mL). The resulting biphasic
mixture was separated and the aqueous layer was extracted
with Et2O (3 · 20 mL). The combined organic layer was
washed with brine (40 mL) and dried over MgSO4. After
filtration and evaporation, the residue was subjected to
silica gel column chromatography (hexane, Rf = 0.32) to
give 3.09 g (6.62 mmol, 75% yield) of a mixture of anti-
and syn-1,7-dimethylphenylsilyl-1,7-disilabicyclo[5.5.0]do-
decanes (Ph–Si4(anti)–Ph and Ph–Si4(syn)–Ph) as white
solids (syn/anti = 1.7/1). This mixture was used for the next
reaction without separating the isomers.
4. Experimental
4.1. General
To a solution of the mixture of Ph–Si4(anti)–Ph and Ph–
Si4(syn)–Ph (3.09 g, 6.62 mmol) in CH2Cl2 (16 mL) was
added TfOH (1.2 mL, 13.6 mmol) dropwise over 5 min at
0 ꢁC. Upon completion of the addition, the reaction mix-
ture was stirred for 1 h. To this mixture was added 2,6-luti-
dine (3.1 mL, 26.7 mmol) in one portion and added a
solution of isopropyl alcohol (1.5 mL, 19.6 mmol) in
CH2Cl2 (5 mL) dropwise over 5 min at 0 ꢁC. Upon comple-
tion of the addition, the reaction mixture was allowed to
warm to room temperature and stirred for 2 h. To this
mixture was added H2O (20 mL). The resulting biphasic
mixture was separated and the aqueous layer was extracted
with Et2O (3 · 20 mL). The combined organic layer was
washed with brine (30 mL) and dried over MgSO4. After
filtration and evaporation, the residue was subjected to sil-
ica gel column chromatography (Silica Gel 60 N (spherical,
neutral), Kanto Chemical Co., Inc, hexane/Et3N = 100/1,
Melting points (mp) were determined with a Yanaco
MP-S3 instrument and are uncorrected. H and 13C NMR
1
spectra were recorded on a Varian Mercury (300 MHz for
1H) and JEOL EX-270 (67.94 MHz for 13C) spectrometer
in C6D6 unless otherwise stated and chemical shifts are
reported in d ppm with reference to internal solvent peak
for 1H (C6HD5: 7.20 ppm) and 13C (C6D6: 128.0 ppm),
respectively. 29Si NMR spectra were recorded with JEOL
EX-270 (59.62 MHz for 29Si) spectrometer in C6D6 with
the use of the proton-decoupled INEPT technique using tet-
ramethylsilane (0.0 ppm) as an external standard. Recycle
preparative gel permeation chromatography (GPC) was
performed using polystyrene gel columns (JAIGEL 1H
and 2H, LC-908, Japan Analytical Industry) with toluene
as an eluent. Column chromatography was performed using

Y. Shibano et al. / Journal of Organometallic Chemistry 692 (2007) 356–367
363
Rf = 0.07–0.15) to give 2.50 g (5.80 mmol, 88% yield) of a
mixture of anti- and syn-1,7-isopropoxydimethylsilyl-1,7-
disilabicyclo[5.5.0]dodecane (i-PrO–Si4(anti)–Oi-Pr and
i-PrO–Si4(syn)–Oi-Pr) as a colorless oil (syn/anti = 1.6/1).
Isomers were separated by neutralized silica gel column
chromatography (PSQ 100B, Fuji Silysia, hexane/
AcOEt = 100/1) and recrystallization from toluene/acetoni-
trile. i-PrO–Si4(anti)–Oi-Pr: colorless crystals. Mp 72–
(190–195 ꢁC/13 mmHg) gave 4.44 g (14.6 mmol, 89% yield)
of 1,4-dichloro-1,1,2,2,3,3,4,4-octamethyltetrasilane [36]
1
(Cl–Si4–Cl) as colorless oil. H NMR (C6D6): d = 0.44 (s,
12H), 0.24 (s, 12H).
4.4. Conversion from X–Si4–X (X = Cl or i-PrO) to
Br–[Si4]–Br
1
73 ꢁC. H NMR (C6D6): d = 3.94 (sept, J = 6.0 Hz, 2H),
4.4.1. A typical procedure: 1,4-bis(4-bromophenyl)-
1,1,2,2,3,3,4,4-octamethyltetrasilane (Br–[Si4]–Br)
1.82–2.04 (m, 8H), 1.62–1.69 (m, 4H), 1.26 (ddd, J = 13.9,
8.5, 5.2 Hz, 4H), 1.16 (d, J = 6.0 Hz, 12H), 1.02 (ddd,
J = 13.9, 8.5, 5.2 Hz, 4H), 0.47 (s, 12H). 13C NMR (C6D6):
d = 65.57, 31.05, 28.05, 26.36, 12.90, 2.60. 29Si NMR
(C6D6): d = 14.48, ꢀ30.43. HRMS(EI): Calc. for
C20H46O2Si4: 430.2575. Found: 430.2594. i-PrO–Si4(syn)–
Oi-Pr: colorless oil. 1H NMR (C6D6): d = 3.97 (sept,
J = 6.0 Hz, 2H), 1.79–1.87 (m, 8H), 1.64–1.71 (m, 4H),
1.19 (d, J = 6.0 Hz, 12H), 0.95–1.14 (m, 8H), 0.49 (s, 12H).
13C NMR (C6D6): d = 65.70, 33.09, 26.42, 23.95, 11.53,
1.87. 29Si NMR (C6D6): d = 14.08, ꢀ38.70. HRMS(EI):
Calc. for C20H46O2Si4: 430.2575. Found: 430.2589.
To a suspension of p-dibromobenzene (4.79 g, 20.3
mmol) in Et2O (20 mL) was added 12.8 mL (20.0 mmol)
of a 1.56 M solution of n-butyllithium in hexane dropwise
over 10 min at ꢀ78 ꢁC. Upon completion of addition, the
reaction mixture was allowed to warm to room tempera-
ture and stirred for 2.5 h to give a suspension of p-
bromophenyllithium in Et2O.
To a suspension of p-bromophenyllithium in Et2O was
added a solution of Cl–Si4–Cl (1.54 g, 5.07 mmol) in Et2O
(15 mL) dropwise over 10 min at ꢀ78 ꢁC. Upon completion
of addition, the reaction mixture was allowed to warm to
room temperature and stirred for 1.5 h. To the resulting mix-
ture was added 5% aq. NH4Cl (40 mL). The resulting bipha-
sic mixture was separated and the aqueous layer was
extracted with Et2O (3 · 40 mL). The combined organic
layer was washed with brine (40 mL) and dried over MgSO4.
After filtration and evaporation, the residue was subjected to
silica gel column chromatography (hexane, Rf = 0.43) to
give 2.26 g (4.15 mmol, 82% yield) of Br–[Si4]–Br as pale yel-
low oil. The product contained some impurities but was used
for the next reaction without further purification. 1H NMR
(C6D6): d = 7.40 (d, J = 8.1 Hz, 4 H), 7.10 (d, J = 8.1 Hz,
4H), 0.28 (s, 12H), 0.06 (s, 12H). 13C NMR (C6D6):
d = ꢀ5.34, ꢀ2.82, 123.71, 131.28, 135.55, 138.52. 29Si
NMR (C6D6): d = ꢀ44.28, ꢀ17.31. HRMS(EI): Calc. for
C20H32Br2Si4: 541.9948. Found: 541.9955.
4.3. 1,4-Dichloro-1,1,2,2,3,3,4,4-octamethyltetrasilane
(Cl–Si4–Cl)
To a suspension of lithium (granular, 1.66 g, 239 mmol)
and THF (50 mL) was added a solution of chlorodimethyl-
phenylsilane (10.0 mL, 60.5 mmol) in THF (10 mL) drop-
wise over 20 min at 0 ꢁC. After being stirred for 4 h, the
resulting mixture was filtered to remove excess lithium.
To this silyllithium solution was added 60 mL (60.6 mmol)
of a 1.01 M solution of isopropylmagnesium bromide in
Et2O dropwise over 20 min at 0 ꢁC to give a silylmagne-
sium reagent.
To a solution of 1,2-dichloro-1,1,2,2-tetramethyldisilane
(5.65 g, 30.2 mmol) in THF (30 mL) was added the solu-
tion of thus prepared silylmagnesium reagent dropwise
over 20 min at 0 ꢁC. Upon completion of the addition,
the reaction mixture was allowed to warm to room temper-
ature. After being stirred for 8 h, the reaction mixture was
quenched with saturated aq. NH4Cl (20 mL) and H2O
(40 mL). The resulting biphasic mixture was separated
and the aqueous layer was extracted with Et2O
(3 · 50 mL). The combined organic layer was washed with
brine and dried over MgSO4. After filtration and evapora-
tion, the residue was subjected to silica gel column chroma-
tography (hexane, Rf = 0.33) to give 7.19 g (18.6 mmol,
62% yield) of 1,1,2,2,3,3,4,4-octamethyl-1,4-diphenyltetr-
4.4.2. anti-1,7-Bis(4-bromophenyl)-1,7-
disilabicyclo[5.5.0]dodecane (Br–[Si4(anti)]–Br)
Yield: 91% (white solids). Mp 97.5–98 ꢁC. 1H NMR
(C6D6): d = 7.41 (d, J = 8.1 Hz, 4H), 7.16 (d, J = 8.1 Hz,
4H), 1.42–1.51 (m, 8H), 1.21–1.27 (m, 4H), 0.95 (dt,
J = 14.4, 6.9 Hz, 4H), 0.64 (dt, J = 14.4, 6.9 Hz, 4H),
0.44 (s, 12H). 13C NMR (C6D6): d = 139.50, 135.82,
131.16, 123.56, 30.78, 27.72, 13.32, ꢀ0.88. 29Si NMR
(C6D6): d = ꢀ16.68, ꢀ28.43. HRMS(EI): Calc. for
C26H40Br2Si4: 622.0574. Found: 622.0562.
1
asilane [35] as white solids. H NMR (C6D6): d = 7.46–
7.49 (m, 4H), 7.2–7.3 (m, 6H), 0.39 (s, 12H), 0.16 (s, 12H).
To a solution of 1,1,2,2,3,3,4,4-octamethyl-1,4-diphenyl-
tetrasilane (6.39 g, 16.5 mmol) in benzene (20 mL) was
added AlCl3 (66.2 mg, 0.497 mmol), and then HCl gas
was blown on this mixture for 3 h at room temperature.
Hexane (20 mL) and acetone (1 mL) were added and the
resulting acetone/AlCl3 complex was filtered off.
Evaporation followed by distillation at reduced pressure
4.4.3. syn-1,7-Bis(4-bromophenyl)-1,7-
disilabicyclo[5.5.0]dodecane (Br–[Si4(syn)]–Br)
Yield: 69% (white solids). 1H NMR (C6D6): d = 7.42 (d,
J = 8.1 Hz, 4H), 7.16 (d, J = 8.1 Hz, 4H), 1.40–1.60 (m,
12H), 0.75–0.80 (m, 8H), 0.35 (s, 12H). 13C NMR (C6D6):
d = 138.75, 135.73, 131.28, 123.76, 32.84, 23.51, 11.51,
ꢀ1.85. 29Si NMR (C6D6): d = ꢀ17.93, ꢀ35.57. HRMS(EI):
Calc. for C26H40Br2Si4: 622.0574. Found: 622.0573.

364
Y. Shibano et al. / Journal of Organometallic Chemistry 692 (2007) 356–367
4.5. Conversion from Br–[Si4]–Br to Br–[Si4]–CHO
(s, 6H), 0.35 (s, 6H). 13C NMR (C6D6): d = 191.37,
148.37, 138.65, 136.95, 135.72, 134.45, 131.29, 128.64,
123.79, 32.81, 23.46, 11.45, ꢀ1.85, ꢀ2.06 (two peaks are
overlapped). 29Si NMR (C6D6): d = ꢀ17.61, ꢀ17.96,
ꢀ35.29, ꢀ35.49. HRMS(EI): Calc. for C27H41BrOSi4:
572.1418. Found: 572.1408.
4.5.1. A typical procedure: 1-(4-bromophenyl)-4-(4-
formylphenyl)-1,1,2,2,3,3,4,4-octamethyltetrasilane
(Br–[Si4]–CHO)
To a solution of Br–[Si4]–Br (2.13 g, 3.91 mmol) in THF
(16 mL) was added 2.5 mL (4.00 mmol) of a 1.56 M solu-
tion of n-butyllithium in hexane dropwise over 5 min at
ꢀ78 ꢁC. Upon completion of addition, the reaction mixture
was stirred for 1 h at this temperature to give a white sus-
pension. To this suspension was added a solution of N-
formylpiperidine (0.65 mL, 5.64 mmol) in THF (8 mL)
dropwise over 5 min at ꢀ78 ꢁC. After being stirred for
20 min, the reaction mixture was allowed to warm to room
temperature and stirred for 45 min. To the resulting clear
solution was added 1 N aq. HCl (30 mL). The resulting
biphasic mixture was evaporated to remove THF. To the
residue was added Et2O (60 mL). The resulting biphasic
mixture was separated and the aqueous layer was extracted
with Et2O (3 · 30 mL). The combined organic layer was
washed with brine (50 mL) and dried over MgSO4. After
filtration and evaporation, the residue was subjected to sil-
ica gel column chromatography (hexane/toluene = 1/1 to
toluene, then toluene/AcOEt = 10/1, Rf = 0.58 (toluene))
to give 781 mg (1.58 mmol, 40% yield (containing small
amount of impurities)) of Br–[Si4]–CHO as a pale yellow
paste. 1H NMR (C6D6): d = 9.76 (s, 1H), 7.65 (d,
J = 8.1 Hz, 2H), 7.40 (d, J = 8.1 Hz, 2H), 7.38 (d,
J = 8.1 Hz, 2H), 7.10 (d, J = 8.1 Hz, 2H), 0.30 (s, 6H),
0.28 (s, 6H), 0.06 (s, 6H), 0.05 (s, 6H). 13C NMR (C6D6):
d = 191.32, 148.11, 138.42, 136.99, 135.54, 134.29, 131.31,
128.68, 123.76, ꢀ2.87, ꢀ3.05, ꢀ5.37 (one peak is over-
lapped). 29Si NMR (C6D6): d = ꢀ17.01, ꢀ17.31, ꢀ43.91,
ꢀ44.08. HRMS(EI): Calc. for C21H33BrOSi4: 492.0792.
Found: 492.0793.
4.6. Preparation of ZnP–[Si4]–CHO
4.6.1. A typical procedure: ZnP–[Si4]–CHO
A mixture of Br–[Si4]–CHO (781 mg, 1.58 mmol) and
ZnP–Bpin (151 mg, 0.142 mmol) in DME (40 mL) and
H2O (0.8 mL) was deoxgenized by bubbling with nitrogen
for 30 min. To this mixture were added tetrakis(triphenyl-
phosphine)palladium(0) (45.5 mg, 0.0394 mmol) and Ba(O-
H)2 Æ 8H2O (501 mg, 1.59 mmol). The resulting mixture was
warmed to 80 ꢁC and stirred for 20 min. After cooling, the
resulting mixture was filtered through a pad of silica gel
and washed with CH2Cl2. After evaporation, the residue
was subjected to silica gel column chromatography (hex-
ane/toluene = 2/1 to 1/3, Rf = 0.70 (hexane/toluene =
1/4)) and subjected to GPC (toluene as an eluent,
tR = 72 min) to give 96.2 mg (0.0712 mmol, 50% yield) of
ZnP–[Si4]–CHO as purple solids. 1H NMR (C6D6):
d = 9.72 (s, 1H), 9.33–9.36 (m, 6H), 9.24 (d, J = 4.8 Hz,
2H), 8.46–8.47 (m, 6H), 8.41 (d, J = 7.8 Hz, 2H), 8.03–
8.04 (m, 3H), 7.85 (d, J = 8.1 Hz, 2H), 7.67 (d,
J = 8.1 Hz, 2H), 7.49 (d, J = 7.8 Hz, 2H), 1.55 (m, 54H),
0.65 (s, 6H), 0.43 (s, 6H), 0.33 (s, 6H), 0.27 (s, 6H). 13C
NMR (C6D6): d = 191.39, 151.05, 150.99, 150.94, 150.53,
149.03, 144.27, 143.12, 138.38, 136.84, 134.53, 134.35,
132.62, 132.53, 132.31, 132.16, 130.39, 130.32, 128.72,
122.78, 122.73, 121.06, 35.32, 32.03, ꢀ2.51, ꢀ2.82, ꢀ5.01,
ꢀ5.17. 29Si NMR (C6D6): d = ꢀ16.88, ꢀ17.53, ꢀ43.58
(one peak is overlapped). FAB-MS: 1350 ([M+H]+).
4.5.2. anti-1-(4-Bromophenyl)-7-(4-formylphenyl)-1,7-
disilabicyclo[5.5.0]dodecane (Br–[Si4(anti)]–CHO)
4.6.2. ZnP–[Si4(anti)]–CHO
Yield: 30% (purple solids). 1H NMR (C6D6): d = 9.78 (s,
1H), 9.38 (d, J = 4.8 Hz, 2H), 9.32–9.35 (m, 4H), 9.26 (d,
J = 4.8 Hz, 2H), 8.46–8.47 (m, 6H), 8.40 (d, J = 8.1 Hz,
2H), 8.03–8.04 (m, 3H), 7.89 (d, J = 8.1 Hz, 2H), 7.70 (d,
J = 8.1 Hz, 2H), 7.53 (d, J = 8.1 Hz, 2H), 1.6–1.8 (m, 8H),
1.55 (s, 54H), 1.22–1.40 (m, 4H), 1.05–1.17 (m, 4H), 0.80–
0.96 (m, 4H), 0.80 (s, 6H), 0.56 (s, 6H). 13C NMR (CS2):
d = 189.87, 150.86, 150.41, 149.72, 148.68, 143.73, 142.61,
139.24, 136.95, 134.94, 134.76, 132.85, 132.74, 132.33,
131.87, 130.53, 129.58, 128.94, 127.38, 122.77, 121.42,
121.14, 35.56, 32.66, 31.69, 28.73, 28.66, 14.43, 14.26, 0.06,
ꢀ0.12. 29Si NMR (C6D6): d = ꢀ15.98, ꢀ16.66, ꢀ27.38
(one peak is overlapped). FAB-MS: 1430 ([M+H]+).
1
Yield: 39% (white solids). Mp 125–127 ꢁC. H NMR
(C6D6): d = 9.75 (s, 1H), 7.65 (d, J = 8.1 Hz, 2H), 7.44
(d, J = 8.1 Hz, 2H), 7.41 (d, J = 8.1 Hz, 2H), 7.15 (d,
J = 8.1 Hz, 2H), 1.41–1.48 (m, 8H), 1.20–1.27 (m, 4H),
0.90–1.01 (m, 4H), 0.60–0.69 (m, 4H), 0.46 (s, 6H), 0.44
(s, 6H). 13C NMR (C6D6): d = 191.34, 149.19, 139.40,
136.82, 135.80, 134.55, 131.19, 128.58, 123.59, 30.78,
27.72, 27.69, 13.31, ꢀ0.89, ꢀ1.06 (one peak is overlapped).
29Si NMR (C6D6): d = ꢀ16.38, ꢀ16.66, ꢀ28.03, ꢀ28.30.
HRMS(EI): Calc. for C27H41BrOSi4: 572.1418. Found:
572.1408.
4.5.3. syn-1-(4-Bromophenyl)-7-(4-formylphenyl)-1,7-
disilabicyclo[5.5.0]dodecane (Br–[Si4(syn)]–CHO)
Yield: 36% (white waxy solids). 1H NMR (C6D6):
d = 9.79 (s, 1H), 7.66 (d, J = 8.1 Hz, 2H), 7.44 (d,
J = 8.1 Hz, 2H), 7.42 (d, J = 8.1 Hz, 2H), 7.17 (d,
J = 8.1 Hz, 2H), 1.4–1.7 (m, 12H), 0.7–0.8 (m, 8H), 0.37
4.6.3. ZnP–[Si4(syn)]–CHO
Yield: 33% (purple solids). 1H NMR (C6D6): d = 9.69 (s,
1H), 9.34–9.38 (m, 6H), 9.27 (d, J = 4.8 Hz, 2H), 8.47–8.48
(m, 6H), 8.43 (d, J = 8.1 Hz, 2H), 8.03–8.04 (m, 3H), 7.92 (d,
J = 8.1 Hz, 2H), 7.69 (d, J = 8.1 Hz, 2H), 7.55 (d,

Y. Shibano et al. / Journal of Organometallic Chemistry 692 (2007) 356–367
365
J = 8.1 Hz, 2H), 1.6–1.9 (m, 12H), 1.55 (s, 54H), 1.0–1.2 (m,
4H), 0.84–0.92 (m, 4H), 0.71 (s, 6H), 0.56 (s, 6H). 13C NMR
(C6D6): d = 191.45, 151.04, 150.97, 150.91, 150.51, 148.98,
148.73, 144.29, 143.14, 138.47, 136.80, 134.52, 132.61,
132.53, 132.20, 130.39, 130.34, 128.69, 127.84, 122.75,
122.70, 121.02, 35.31, 32.96, 32.00, 23.72, 23.64, 11.93,
11.60, ꢀ1.47, ꢀ1.80. 29Si NMR (C6D6): d = ꢀ17.41,
ꢀ18.01, ꢀ34.97, ꢀ35.19. FAB-MS: 1430 ([M+H]+).
(s, 3H), 0.63 (s, 3H) (two aromatic protons are overlapped
with the solvent peak). 13C NMR (C6D6): d = 155.76,
153.04, 152.78, 151.07, 150.94, 150.86, 150.48, 149.03,
146.18, 145.94, 145.54, 145.44, 145.41, 145.23, 144.87,
144.60, 144.55, 144.50, 144.42, 144.37, 143.98, 143.73,
143.62, 143.53, 143.50, 143.45, 143.19, 143.04, 142.78,
142.68, 141.90, 141.67, 141.48, 141.43, 141.26, 141.16,
141.11, 141.08, 140.98, 140.84, 140.57, 140.51, 140.41,
140.24, 140.18, 140.03, 139.27, 139.01, 138.93, 137.41,
136.13, 135.90, 135.44, 134.91, 134.70, 132.84, 132.74,
132.41, 130.48, 130.40, 130.30, 128.36, 128.00, 127.64,
122.90, 121.65, 121.09, 83.18, 77.02, 69.34, 68.58, 39.64,
35.39, 32.15, 31.03, 30.91, 28.13, 28.00, 27.90, 13.85,
13.19, ꢀ0.50, ꢀ0.61, ꢀ0.98, ꢀ1.01. 29Si NMR (C6D6):
d = ꢀ16.61, ꢀ27.28, ꢀ28.35 (one peak is overlapped).
FAB-MS: 2177 ([M+H]+).
4.7. Preparation of ZnP–[Si4]–C60
4.7.1. A typical procedure: ZnP–[Si4]–C60
A solution of ZnP–[Si4]–CHO (81.7 mg, 0.0605 mmol),
C60 (216 mg, 0.300 mmol), and N-methylglycine (275 mg,
3.06 mmol) in toluene (300 mL) was deoxygenized by bub-
bling with nitrogen for 30 min and heated under reflux.
After being stirred for 10 h in the dark at this temperature,
the reaction mixture was allowed to cool to room temper-
ature and filtered through a pad of silica gel. After evapo-
ration, the residue was subjected to silica gel column
chromatography (hexane/toluene = 4/1 to 2/3, Rf = 0.65
(hexane/toluene = 1/1)) followed by preparative GPC (tol-
uene as an eluent, tR = 73 min). After evaporation, the res-
idue was washed with MeOH to give 100 mg (0.0477 mmol,
79% yield) of ZnP–[Si4]–C60 as dark purple solids. 1H
NMR (C6D6): d = 9.33 (m, 4H), 9.27 (d, J = 4.8 Hz, 2H),
9.16 (d, J = 4.8 Hz, 2H), 8.59 (d, J = 1.8 Hz, 2H), 8.53
(d, J = 1.8 Hz, 4H), 8.35 (d, J = 8.1 Hz, 2H), 8.07 (t,
J = 1.8 Hz, 1H), 8.04 (t, J = 1.8 Hz, 2H), 7.77 (d,
J = 8.1 Hz, 2H), 7.42 (d, J = 8.1 Hz, 2H), 4.33 (s, 1H),
4.19 (d, J = 9.3 Hz, 1H), 3.45 (d, J = 9.3 Hz, 1H), 2.46 (s,
3H), 1.63 (s, 18H), 1.61 (s, 18H), 1.60 (s, 18H), 0.65 (s,
3H), 0.64 (s, 3H), 0.46 (s, 3H), 0.46 (s, 3H), 0.38 (s, 6H),
ꢀ0.13 (s, 3H), ꢀ0.16 (s, 3H) (two aromatic protons are
overlapped with the solvent peak). 13C NMR (C6D6):
d = 155.66, 153.03, 152.70, 151.05, 150.94, 150.82, 150.44,
149.03, 148.98, 146.07, 145.72, 145.44, 145.25, 144.85,
144.60, 144.55, 144.49, 144.46, 144.36, 144.24, 143.90,
143.83, 143.67, 143.58, 143.47, 143.17, 142.97, 142.81,
142.60, 141.90, 141.69, 141.39, 141.28, 141.18, 141.03,
140.85, 140.82, 140.46, 140.39, 140.26, 140.23, 140.14,
139.96, 139.93, 139.27, 139.24, 138.94, 138.78, 138.22,
137.48, 135.98, 135.83, 135.49, 134.85, 134.70, 134.04,
132.69, 132.54, 132.48, 132.36, 130.44, 130.29, 128.79,
122.93, 122.85, 121.50, 121.02, 83.11, 77.01, 69.40, 68.53,
39.65, 35.39, 32.15, ꢀ2.77, ꢀ2.82, ꢀ2.85, ꢀ4.89, ꢀ5.40,
ꢀ5.58. 29Si NMR (C6D6): d = ꢀ16.61, ꢀ17.41, ꢀ43.23,
ꢀ44.48. FAB-MS: 2097 ([M+H]+).
4.7.3. ZnP–[Si4(syn)]–C60
Yield: 77% (dark purple solids). 1H NMR (C6D6):
d = 9.31 (d, J = 4.5 Hz, 2H), 9.25–9.28 (m, 6H), 8.48–8.50
(m, 2H), 8.45 (d, J = 1.5 Hz, 4H), 8.37 (d, J = 7.8 Hz,
2H), 8.02–8.05 (m, 3H), 7.95 (d, J = 7.8 Hz, 2H), 7.59–
7.64 (m, 2H), 4.05–4.08 (m, 2H), 3.27 (d, J = 9.0 Hz, 1H),
2.50 (s, 3H), 1.62–1.88 (m, 12H), 1.60 (s, 36H), 1.57 (s,
18H), 1.04–1.16 (m, 4H), 0.8–1.0 (m, 4H), 0.74 (s, 3H),
0.73 (s, 3H), 0.58 (s, 3H), 0.54 (s, 3H) (two aromatic protons
are overlapped with the solvent peak). 13C NMR (C6D6):
d = 155.35, 152.98, 152.42, 150.91, 150.87, 150.74, 150.43,
149.01, 146.36, 145.97, 145.67, 145.31, 145.20, 145.11,
145.02, 144.92, 144.65, 144.49, 144.36, 144.26, 144.16,
144.11, 144.01, 143.85, 143.73, 143.48, 143.37, 143.12,
143.06, 141.99, 141.76, 141.72, 141.64, 141.38, 141.26,
141.20, 141.10, 141.03, 140.98, 140.92, 140.84, 140.75,
140.59, 140.42, 140.24, 139.01, 138.96, 138.93, 138.86,
138.60, 137.56, 136.21, 135.47, 134.93, 134.60, 134.29,
132.92, 132.72, 132.64, 132.41, 130.47, 130.39, 130.24,
128.94, 122.88, 122.75, 121.32, 121.07, 83.09, 76.71, 69.34,
68.38, 39.78, 35.39, 32.91, 32.17, 30.34, 13.89, 12.25,
12.12, 12.01, ꢀ1.11, ꢀ1.19, ꢀ1.42, ꢀ1.57. 29Si NMR
(C6D6): d = ꢀ17.33, ꢀ17.88, ꢀ35.34 (one peak is over-
lapped). FAB-MS: 2177 ([M+H]+).
4.8. Synthesis of ZnP–[Si2]
A solution of 1-(4-bromophenyl)-1,1,2,2-tetramethyl-2-
phenyldisilane (61.2 mg, 0.175 mmol) and ZnP–Bpin
(20.4 mg, 0.0192 mmol) in DME (5 mL) and H2O
(0.1 mL) was deoxygenized by bubbling with nitrogen for
30 min. To this mixture were added dichlorobis(triphenyl-
phosphine)palladium(II) (4.7 mg, 0.00670 mmol) and
Ba(OH)2 Æ 8H2O (58.2 mg, 0.184 mmol). The resulting
mixture was heated to 80 ꢁC and stirred for 0.5 h at this
temperature. After cooling, the resulting mixture was fil-
tered through a pad of silica gel and washed with CH2Cl2.
After evaporation, the residue was subjected to silica gel
column chromatography (hexane/toluene = 4/1 to 2/1,
Rf = 0.18 (hexane/toluene = 4/1)) followed by preparative
4.7.2. ZnP–[Si4(anti)]–C60
Yield: 67% (dark purple solids). 1H NMR (C6D6):
d = 9.30–9.34 (m, 6H), 9.16 (d, J = 4.8 Hz, 2H), 8.52–
8.56 (m, 6H), 8.34 (d, J = 8.1 Hz, 2H), 8.03–8.06 (m,
3H), 7.81 (d, J = 8.1 Hz, 2H), 7.52 (d, J = 8.1 Hz, 2H),
4.19 (s, 1H), 4.09 (d, J = 9.3 Hz, 1H), 3.28 (d, J = 9.3 Hz,
1H), 2.45 (s, 3H), 1.63–1.82 (m, 8H), 1.63 (s, 18H), 1.62
(s, 36H), 1.2–1.6 (m, 12H), 0.76 (s, 3H), 0.74 (s, 3H), 0.65

366
Y. Shibano et al. / Journal of Organometallic Chemistry 692 (2007) 356–367
GPC (toluene as an eluent, tR = 74 min) to give 11.2 mg
(0.00928 mmol, 48% yield) of ZnP–[Si2] as purple solids.
1H NMR (C6D6): d = 9.33–9.35 (m, 6H), 9.21 (d,
J = 4.5 Hz, 2H), 8.47–8.48 (m, 6H), 8.35 (d, J = 8.1 Hz,
2H), 8.04 (t, J = 1.7 Hz, 3H), 7.79 (d, J = 8.1 Hz, 2H),
7.61–7.64 (m, 2H), 7.27–7.39 (m, 3H), 1.56 (s, 36 H), 1.54
(s, 18H), 0.61 (s, 6H), 0.56 (s, 6H). 13C NMR (C6D6):
d = 150.97, 150.91, 150.53, 149.00, 143.99, 143.14, 143.11,
137.79, 134.37, 134.30, 132.56, 132.49, 132.39, 132.28,
130.42, 130.30, 128.95, 128.36, 128.21, 128.00, 127.64,
122.69, 122.65, 121.24, 121.01, 35.31, 32.00, ꢀ3.40. 29Si
NMR (C6D6): d = ꢀ21.04, ꢀ21.44. HRMS(FAB): Calc.
for C78H92ON4Si2Zn: 1204.6152. Found: 1204.6177.
Cambridge CB2 1EZ, UK (fax (int. code): +44 1223 336
033 or e-mail: deposit@ccdc.cam.ac.uk or www:
www:http://www.ccdc.cam.ac.uk). Supplementary data
associated with this article can be found, in the online ver-
sion, at doi:10.1016/j.jorganchem.2006.05.062.
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Acknowledgments
This work was supported by Grants-in-Aid for Scientific
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Dyad
FL
Dyad
FL
Ref
Ref
[31] U
=U
and s
=s
are described as following equations:
FL
FL
kDr yad
Dyad
FL
kDr yadþkDyadþkDyad
U
nr
EN;ET
¼
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kRr ef
kRr ef þk
Ref
FL
U
Ref
nr
Dyad
FL
Ref
FL
Ref
nr
s
kRr ef þ k
¼
Dyad
Dyad
nr
kDr yad þ k
þ kEN;ET
s
(f) A. Fukazawa, H. Tsuji, K. Tamao, J. Am. Chem. Soc. 128 (2006)
6800.
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Dyad
FL
Ref
FL
script indicates the dyads or the reference porphyrin. The U
=U
Dyad
FL
Ref
FL
values are essentially the same as the s
=s
values if the
Dyad
kDr yad and k
values are the same as that of the reference porphyrin.
nr
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`
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