Fullerene/thiol-terminated molecules

Article abstract of DOI:10.1021/jo901701j

(Graph Presented) A series of fullerene-terminated oligo(phenylene ethynylene) (OPEs) have been synthesized for potential use in electronic or optoelectronic device monolayers. Electronic properties such as the energy levels and the distribution of HOMOs

Full text of DOI:10.1021/jo901701j

pubs.acs.org/joc
Fullerene/Thiol-Terminated Molecules
Yasuhiro Shirai,†,‡ Jason M. Guerrero,† Takashi Sasaki,† Tao He,† Huanjun Ding,§
Guillaume Vives,† Byung-Chan Yu,†, Long Cheng,† Austen K. Flatt,† Priscilla G. Taylor,†
Yongli Gao,§ and James M. Tour*,†
†Department of Chemistry, Smalley Institute for Nanoscale Science and Technology, Rice University,
MS-222, 6100 Main Street, Houston, Texas 77005, ‡ICYS-MANA, National Institute for Materials Science,
1-1 Namiki, Tsukuba, Ibaraki, 305-0044, Japan, §Department of Physics and Astronomy, University of
Rochester, Rochester, New York 14627, and Department of Chemistry, Mokwon University, Daejon,
302-729, Republic of Korea
tour@rice.edu
Received August 13, 2009
A series of fullerene-terminated oligo(phenylene ethynylene) (OPEs) have been synthesized for
potential use in electronic or optoelectronic device monolayers. Electronic properties such as the
energy levels and the distribution of HOMOs and LUMOs of fullerene-terminated OPEs have been
calculated using the ab initio method at the B3LYP/6-31G(d) level. The calculations have revealed the
concentration of frontier orbitals on the fullerene cage and a narrow distribution of HOMO-LUMO
energy gaps. Ultraviolet photoelectron spectroscopy and inverse photoemission spectroscopy studies
have been performed to further examine the electronic properties of the fullerene-terminated OPEs on
gold surfaces. The obtained broad photoelectron spectra suggest that there are strong intermolecular
interactions in the fullerene self-assembled monolayers, and the small bandgap (∼1.5 eV), determined
by the photoelectron spectroscopy, indicates the unique nature of the fullerene-terminated OPEs in
which the C60 moiety can be connected to the Au surface through the conjugated OPE backbone.
Introduction
electronics using oligo(phenylene ethynylene) OPE devices7-10
gained attention after the successful demonstration of switch-
ing effects using this class of compounds.11-13 To further
advance the development of OPE-based monlayers, we have
Design, synthesis, and application of conjugated molecules
have received great attention since the suggestion in 1974 of
the miniaturization of electronic circuits to a molecular scale.1
A variety of molecules have been synthesized,2-4 and the
characterization of these nanoscale electronic wires have shown
promising results such as in solar harvesting devices5 and other
optoelectronic systems.6 Our early approaches to molecular
(7) Tour, J. M.; Rawlett, A. M.; Kozaki, M.; Yao, Y. X.; Jagessar, R. C.;
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Campbell, I. Chem Eur. J. 2001, 7, 5118–5134.
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Tour, J. M. Appl. Phys. Lett. 2000, 77, 1224–1226.
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DOI: 10.1021/jo901701j
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Published on Web 09/16/2009
J. Org. Chem. 2009, 74, 7885–7897 7885
2009 American Chemical Society

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FIGURE 1. Fullerene-terminated molecules presented in this work.
investigated fullerene-OPE hybrid devices (Figure 1). Ful-
lerenes have gained considerable attention since their discovery
due to their unusual structure and optical and electrical proper-
ties, and there has been a tremendous amount of research aimed
at developing new fullerene-based materials with novel and
potentially useful applications.14,15 Fullerenes are also attractive
candidates for anchoring molecule wires on electrode surfaces
because of their high affinity for noble metals and large
contacting area. The efficacy of the fullerene-based anchoring
group have been demonstrated in single-molecule electronic
measurements.16 The unique combination of the well-known
thiol-based self-assembled monolayer (SAM) chemistry14 with
the advantageous properties of fullerene derivatives could lead
to advances in this field.15,16 To that end, we have demonstrated
the self-assembly of fullerene-OPE hybrid devices on Au
surfaces and delineated the specific mechanisms associated with
self-assembly of fullerene-OPE hybrids.17
Here we expand the synthesis of a series of fullerene-termi-
nated molecules by introducing a variety of functional groups
and describe their electronic properties with the aid of theore-
tical calculations and ultraviolet photoelectron spectroscopy
(UPS) and inverse photoemission spectroscopy (IPES) methods.
The variety of the fullerene-terminated molecules with thiol and
protected thiol alligator clips can be easily expanded using our
in situ ethynylation method.18 Moreover, the fine-tuning of
the electronic properties in the fullerene-terminated OPEs was
successfully demonstrated with a combination of molecular
design and theoretical calculations. A clear correlation was
(14) Love, J. C.; Estroff, L. A.; Kriebel, J. K.; Nuzzo, R. G.; Whitesides,
G. M. Chem. Rev. 2005, 105, 1103–1169.
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Phys. Lett. 2000, 77, 3595–3597. (b) Martin, C. A; Ding, D.; Sørensen, J. K.;
Bjørnholm, T.; van Ruitenbeek, J. M.; van der Zant, H. S. J. J. Am. Chem.
Soc. 2008, 130, 13198–13199.
(17) Shirai, Y.; Cheng, L.; Chen, B.; Tour, J. M. J. Am. Chem. Soc. 2006,
128, 13479–13489.
(18) Shirai, Y.; Zhao, Y. M.; Cheng, L.; Tour, J. M. Org. Lett. 2004, 6,
2129–2132.
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observed between the electron-donating or -accepting character-
istics of the functional groups and the HOMO/LUMO energy
levels. The attachment of C60 with alkynes is also interesting in
that one can expect periconjugation19,20 effects due to the close
proximity between the fullerene cage and the OPE π systems.
The UPS and IPES studies are evidence that the C60 moiety can
be connected to the Au surface through the conjugated OPE
backbone. The estimated HOMO-LUMO bandgap (∼1.5 eV)
by UPS and IPES was measurable and clearly smaller than the
bandgap of C60-SAMs in which the C60 moieties were attached
to Au surfaces with a saturated carbon backbone.21
SCHEME 1. Synthesis of the Fullerene-Terminated Compounds 1 and 7
Results and Discussion
Synthesis of Fullerene-Terminated OPEs 1 and 7. The
fullerene-OPE hybrids 1 and 7 can be synthesized in a single
step from the known compound 1322 using the in situ ethynyla-
tion method18 with moderate yields (Scheme 1). The ethyl-
TMS group (-CH2CH2TMS) was employed as the protecting
group for the sulfur atom because it can tolerate the in situ
ethynylation reaction using lithium hexamethyldisylazide
(LHMDS). Once the fullerene moiety is attached, the ethyl-
TMS protecting group can be easily removed using tetrabutyl-
ammonium fluoride (TBAF) in THF (1-Me-SH) or converted
to the acetyl group (1-Me-SAc) using AgBF4 and acetyl
chloride (AcCl).23 The in situ deprotection and self-assembly
of the ethyl-TMS protected derivatives have been shown pre-
viously;24 however, in our hands, it was difficult to obtain
consistent assembly results.25 We also found in our previous
work that the thiol esters (-SAc) were more convenient and
reliable.17 The functional group attached on the fullerene cage
can be modified in the ethynylation step by quenching the
fullerene anions with the appropriate alkyl iodide or a proton.
In the synthesis of 7, 1-iodoheptane was used to introduce a
bulky group at the fullerene site to reduce the cross-sectional
mismatch that was one of the causes for the head-to-tail
assemblies in fullerene SAMs.17 Unfortunately, this synthesis
approach proved to be difficult, with a low yield presumably
because of the lower reactivity of the 1-iodoheptane toward the
fullerene anions.
Synthesis of Fullerene-Terminated OPEs 2-6. A series of
fullerene-terminated compounds 2-6 were synthesized via Pd-
catalyzed coupling reactions and removal of the TMS groups
followed by the fullerene coupling reaction (Scheme 2). With
this synthesis scheme, simple modification of the functional
groups in the compound 14 can result in the rapid generation
of the wide variety of the fullerene-terminated molecules. We
have previously demonstrated the combinatorial synthesis of
OPE tetramers on a solid support.26 In this work, we were able
(19) Hamasaki, R.; Ito, M.; Lamrani, M.; Mitsuishi, M.; Miyashita, T.;
Yamamoto, Y. J. Mater. Chem. 2003, 13, 21–26.
(20) Zhao, Y. M.; Shirai, Y.; Slepkov, A. D.; Cheng, L.; Alemany, L. B.;
Sasaki, T.; Hegmann, F. A.; Tour, J. M. Chem.;Eur. J. 2005, 11, 3643–3658.
(21) Patnaik, A.; Setoyama, H.; Ueno, N. J. Chem. Phys. 2004, 120, 6214–
6221.
(22) Yu, C. J.; Chong, Y. C.; Kayyem, J. F.; Gozin, M. J. Org. Chem.
1999, 64, 2070–2079.
(23) Grundberg, H.; Andergran, M.; Nilsson, U. J. Tetrahedron Lett.
1999, 40, 1811–1814.
(24) Creager, S.; Yu, C. J.; Bamdad, C.; O’Connor, S.; MacLean, T.;
Lam, E.; Chong, Y.; Olsen, G. T.; Luo, J. Y.; Gozin, M.; Kayyem, J. F.
J. Am. Chem. Soc. 1999, 121, 1059–1064.
(25) Dirk, S. M.; Price, D. W.; Chanteau, S.; Kosynkin, D. V.; Tour, J. M.
Tetrahedron 2001, 57, 5109–5121.
(26) Hwang, J. J.; Tour, J. M. Tetrahedron 2002, 58, 10387–10405.
to synthesize -H (neutral), -Et (electron rich), -CF3 (elec-
tron deficient), -OPr (electron rich), and -NO2 (electron
deficient) derivatives of the fullerene-terminated systems 2-6.
The ethyl-TMS protecting groups for the sulfur atom were
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SCHEME 2. Synthesis of the Fullerene-Terminated Molecules 2-6
removed as before, except for the nitro derivative 3, that was
found to undergo side reactions to form insoluble materials
during the deprotection step.
synthesized (Schemes 4-6). The ethyl-TMS-protected sulfur
atom was introduced by the lithiation of 2-(trimethylsilyl)-
ethanethiol followed by a condensation reaction with 3-iodo-
benzyl bromide (22) affording the product 23. Each leg of the
tripod base (25) was obtained by a Pd-catalyzed reaction
with TMSA followed by the removal of the TMS group, and
then the legs (25) were coupled to the center part (26) to give
the ethoxyl-terminated tripod 27. The aryllithium generated
from the bromide 28 displaces the ethoxyl group of 27 to give
the product 29. Finally, the tripod 30 was obtained after
deprotection of the terminal alkyne. The fullerene tripod 10
was obtained after the in situ ethynylation of fullerenes
and the conversion of the sulfur protecting groups using
the same strategies with AgBF4. The fullerene tripod with
azobenzene functionality (11) was also synthesized from the
tripod 30 by introducing the azobenzene moiety 3127 before
the fullerene coupling and the protecting group exchange
reaction (Scheme 6).
Synthesis of Fullerene-Terminated Alkyl Thiol 8 and Disul-
fide 9. Fullerene-terminated compounds incorporating a long
alkyl chain were prepared as thiol ester 8 and disulfide 9
(Scheme 3). The 4-iodophenol was alkylated with 1,12-dibromo-
dodecane, and the monofunctionalized bromododecane 17 was
isolated using chromatography. The ethyl-TMS protected sulfur
atom was introduced by the lithiation of 2-(trimethylsilyl)-
ethanethiol followed by a condensation reaction with bromodo-
decane 17, giving the product 18. After the introduction of the
terminal alkyne via Pd-catalyzed reaction with trimethylsilylacety-
lene (TMSA) and the removal of the TMS group, the fullerene
moiety was coupled to give the fullerene-terminated alkyl thiol 21.
The sulfur atom protecting group was converted from ethyl-TMS
to the thiol ester with the same strategy as in previous reactions to
give the product 8. Basic deprotection of the thiol ester 8 and
oxidative coupling of the resulting thiol in air can easily generate
the disulfide 9.
Synthesis of the Fullerene-Triazene Hybrid 12. The ful-
lerene-triazene hybrid 12 can be easily synthesized from the
Synthesis of Fullerene-Tripods 10 and 11. Fullerene-termi-
nated compounds incorporating a tripod base were also
(27) Yu, B. C.; Shirai, Y.; Tour, J. M. Tetrahedron 2006, 62, 10303–10310.
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SCHEME 3. Synthesis of the Fullerene-Terminated Alkyl Thiol 8
and Disulfide 9
can generally provide higher charge transport efficiency.30
Molecules with deep-lying HOMO and LUMO levels can
possibly result in better candidates for n-type organic semi-
conductors. The spatial distribution or extent of these MOs
within the molecule is also important because the rectifying
behaviors of molecules can be predicted.31,32 Unfortunately,
although MO theory is of immense utility, popular compu-
tational methods such as the B3LYP/6-31G(d) protocol
cannot provide accurate (absolute) MO energy values.
Nevertheless, the method is quite reliable for predicting
molecular geometry and total energies.33 We calculated total
energies using B3LYP/6-31G(d) implemented in the Gaus-
sian03 program, and geometry optimizations were done
using the HF/3-21G* level of theory. The calculated frontier
MO energies (HOMO and LUMO eigenvalues in the total
energy calculation) for our fullerene-terminated OPEs 1-6
are tabulated along with the similar OPEs without C60 for
comparison (Figure 2 and Table 1). In order to minimize
calculation time, the propoxyl groups of 6 were replaced by
methoxyl substituents for the calculation. The frontier MOs
for the pristine C60 was also calculated to compare with our
devices. It is clear from Table 1 that the HOMO-LUMO
gaps (HLG)s of our fullerene-terminated compounds 1-5
(2.75-2.77 eV) are almost identical to that of pristine C60
(2.76 eV) even though our devices contain various func-
tional groups with different electron-donating (-Et for 4)
and -accepting (-NO2 and -CF3 for 3 and 5, respectively)
characters or length of OPEs (one benzene ring for 1 and two
rings for 2). This is unusual compared with common OPE-
based devices (2Ph, 3Ph, 6Ph, see Figure 2 for structures),
whose HLGs vary depending on the functional groups
attached to the OPE backbone. Only the molecule with
-OMe groups (6) gave a unique HLG (2.53 eV), which
was the smallest of all. On the other hand, reasonable
correlations between these electron-donating or -accepting
characters of functional groups and HOMO/LUMO energy
levels are clearly observed (Figure 2). Both HOMO and
LUMO levels are aligned in the order of increasing elec-
tron-donating characters, -NO2 < -CF3 < -H < -Et <
-OMe groups. The molecule with the nitro group (3) has the
lowest HOMO and LUMO levels, and the molecule with
methoxyl groups (6) gives the highest energy levels for both
HOMO and LUMO. The size of the OPE backbone has
almost no effect because compounds 1 and 2 share almost
identical HOMO and LUMO levels. The HOMO and
LUMO levels of pristine C60 are deeper than that of our
devices by ∼0.2 eV, and this calculation result suggests that
the electron-accepting power of fullerene is reduced when it is
functionalized. This is a physically observable phenomenon,
which we and other groups have previously reported in the
study of fullerene-OPE hybrid devices using cyclic voltamme-
try.16 The redox waves for fullerene derivatives always shift
toward more negative potentials relative to pristine
C60, possibly due to the decrease of π-delocalization on the
fullerene cage after the introduction of two sp3 carbon atoms.
triazene 35 with a terminal alkyne using the in situ ethynyl-
ation method (Scheme 6). This strategy can be useful to
assemble fullerene-terminated molecules on silicon sur-
faces.28
Theoretical Study on Fullerene-Terminated OPEs. The
molecular orbital (MO) level is an important concept in
explaining the fundamental behaviors of molecules, such as
reactivity and kinetics. Furthermore, MO theory has been
utilized as a powerful tool in the field of molecular electronics
to describe charge-transfer processes on molecules. Electron
transfer through molecules can be influenced by several
factors such as molecular length, conformation, and various
functional groups present within the molecule, and these
factors eventually determine the frontier MOs such as the
highest occupied MO (HOMO), lowest unoccupied MO
(LUMO), and HOMO-LUMO gap energies.29 Thus, it is
quite common to extract trends in molecular behavior based
on the MOs. For example, a smaller HOMO-LUMO gap
(30) Ishii, H.; Sugiyama, K.; Ito, E.; Seki, K. Adv. Mater. 1999, 11, 605–þ.
(31) Mizuseki, H.; Niimura, K.; Majumder, C.; Kawazoe, Y. Comput.
Mater. Sci. 2003, 27, 161–165.
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SCHEME 4. Synthesis of the Fullerene Tripod 10
The examination of the spatial distribution of these MOs
suggests that the frontier MOs in these fullerene-terminated
molecules are dominated by the fullerene-related MOs. This
can be demonstrated when these frontier MOs are plotted on
molecules (Figure 3). Except for compound 6, all frontier
MOs reside predominantly on the fullerene cage, giving a
narrow distribution of HLGs for fullerene-terminated OPEs.
Ultraviolet Photoelectron Spectroscopy and Inverse Photo-
emission Spectroscopy Rsults on Fullerene-Terminated OPE.
The electronic structure of the fullerene-terminated OPE
monolayer on the Au surface was examined. Figure 4 shows
the distribution of the occupied and empty electronic states
determined by the UPS and IPES, respectively. The simu-
lated density of states (DOS) of the model compound (inset
of Figure 4) was also plotted along with the experimental
spectra. The simulated DOS was shifted for the best fit with
the experimental spectra, and the vertical bars along with the
DOS spectrum show the positions of the calculated MOs.
The convolution of the MOs was performed using a Gaus-
sian function with fwhm of 0.5 eV. The MO calculation was
performed by applying B3LYP/LanL2DZ theory to the
compound 2-Me-S adsorbed at the 3-fold hollow site of
the Au cluster (inset of Figure 4). The small Au cluster
containing three gold atoms was used as the Au surface for
the calculation because we are interested in the qualitative
picture of MOs on surfaces. The strength of the small cluster
approach has been justified with theoretical studies of self-
assembled monolayers on metal surfaces.21,34-36 During the
structure optimization using the HF/LanL2DZ method, the
˚
Au-Au bond distances were fixed at 2.884 A and equivalent
S-Au distances were maintained. All other parameters were
allowed to relax during the structure optimization. The
optimized molecular structure is shown in the inset of
Figure 4.
The work function of the clean Au substrate was 5.2 eV in
our work, and it was decreased to 4.4 eV after the SAM
formation. The decrease of the work function by ∼0.8 eV is
in accord with previous studies of self-assembled monolayers
on metal surfaces.21,30 The ionization potential (IP), electron
affinity (EA), and bandgap (Eg) energies were estimated to
be 5.2, 3.7, and 1.5 eV, respectively, from the onset of the
photoelectron spectra. The observed UPS spectrum was
broad comparing to that of the simulated DOS spectrum.
The broadening can be a result of the strong intermolecular
interactions in the SAM. Our previous study on fullerene
(34) Johansson, A.; Stafstrom, S. Chem. Phys. Lett. 2000, 322, 301–306.
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Chem. Soc. 2000, 122, 4700–4707.
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SCHEME 5. Synthesis of the Fullerene Tripod 11
SCHEME 6. Synthesis of the Fullerene-Terminated Device 12
molecules (70%) were found to be in the bound state,
attached on the gold surface by S-Au bonding. The struc-
ture of this bound species is expected to be similar to the
model shown in the inset of Figure 4.34,21 Thus, the observed
photoelectron spectra should be the sum of the signals from
the 70% bound and 30% unbound species in slightly differ-
ent electronic and/or chemical environments, resulting in the
rather broad spectrum. Although this situation makes de-
tailed analysis of the UPS and IPES spectra difficult, the
observed bandgap (1.5 eV) is measurable. The bandgap
energy of 3.2 eV was estimated using UPS and IPES for
C60 monolayers on Au surfaces37 and 2.7 eV for the C60-
SAMs on Au using XPS and UPS.21 In the later example, the
C60 moiety was connected to the Au surface through a
saturated carbon backbone. The observed smaller bandgap
for our system is presumably due to the unique nature of
fullerene-terminated OPEs, in which the C60 moiety can be
connected to the Au surface through the conjugated OPE
SAMs revealed the existence of mixed species such as head-
to-tail assemblies due to the strong fullerene-Au and/
or fullerene-fullerene interactions. For 2-Me-SAc, about
30% of the sulfur atoms in the SAM were found to be in
an unbound state using XPS analysis.17 The majority of
(37) Ohno, T. R.; Chen, Y.; Harvey, S. E.; Kroll, G. H.; Weaver, J. H.;
Haufler, R. E.; Smalley, R. E. Phys. Rev. B 1991, 44, 13747–13755.
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FIGURE 2. Calculated MO energy levels. The inset shows chemical
structures for 2Ph, 3Ph, and 6Ph. The structures of 1-6 are shown in
Figure 1.
TABLE 1. Molecular Orbital Energies Calculated Using B3LYP/6-31G(d)
Theorya
energies (eV)
compd
C60
HOMO
LUMO
HOMO-LUMO gap
-5.99
-5.76
-5.74
-5.84
-5.72
-5.80
-5.46
-5.64
-6.00
-5.20
-3.23
-3.00
-2.99
-3.07
-2.97
-3.03
-2.93
-1.72
-2.70
-1.59
2.76
2.76
2.76
2.77
2.75
2.76
2.53
3.92
3.30
3.61
1
2 (-H)
3 (-NO2)
4 (-Et)
5 (-CF3)
6 (-OMe)
2Ph
3Ph
6Ph
aFor the structures of 1-6, see Figure 1. The structures of 2Ph, 3Ph
and 6Ph are shown in Figure 2.
,
backbone. The previous study on the reduction of the
bandgap for C60 on metal surfaces has been explained in
terms of Fermi-level alignment resulting from the mixing
between the LUMO and filled metal states.37 A similar
mechanism can be applicable to our system with the ful-
lerene-terminated OPEs on Au surfaces.
Conclusions
In this paper, we have reported efficient synthesis routes for
the generation of a variety of fullerene-terminated compounds
(Figure 1). Theoretical studies using DFT calculations have
been performed to reveal the electronic nature of those ful-
lerene-terminated OPEs. The calculation indicated that the
frontier MOs of fullerene-terminated OPEs reside mainly on
the fullerene cage and give the narrow distribution of HLG
values regardless of the functional groups of the OPE moiety.
The fine-tuning of the electronic properties in the fullerene-
terminated OPEs was successfully demonstrated with the
combination of molecular design and theoretical calculations.
FIGURE 3. HOMO and LUMO molecular orbitals of representa-
tive fullerene-terminated OPEs.
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FIGURE 4. (a) UPS and (b) IPES spectra of 2-Me-SAc assembled on the Au surface. The inset shows the molecular conformation of 2-Me-S
on Au cluster that was used for the simulation of DOS. (c) UPS spectrum enlarged 5 times in vertical scale. (d) Simulated DOS of the model
system (inset) with the vertical bars representing MO energies obtained by DFT method.
A clear correlation was observed between the electron-donating
or -accepting characteristics of the functional groups and the
HOMO/LUMO energy levels. The electronic structure of ful-
lerene-terminated OPEs on Au surfaces was also studied using
UPS and IPES methods. The broad nature of the UPS and
IPES spectra can be an indication of strong intermolecular
interactions, a result which agrees with our previous findings on
the self-assembly of these fullerene-terminated molecules on
Au surfaces.17 The observed small bandgap (1.5 eV) shows
the unique nature of our fullerene-terminated OPEs, in which
the C60 moiety can be coupled to the Au surface through the
conjugated OPE backbone.
using a VG ESCA Lab system equipped with both UPS and
IPES.40-42 The spectrometer chamber of the UHV system had a
base pressure of 8 ꢀ 10-11 Torr. Occupied states spectra were
obtained by UPS using the unfiltered He I line (21.2 eV) of a
discharge lamp with the samples biased at -5.0 V to avoid the
influence of the detector work function and to observe the true low
energy secondary cutoff. The typical instrumental resolution for
UPS measurements ranges from ∼0.03 to 0.1 eV with photon
energy dispersion of less than 20 meV. Unoccupied states were
measured by IPES using a custom-made spectrometer composed of
a commercial Kimball Physics ELG-2 electron gun and a bandpass
photon detector. IPES was done in the isochromat mode using a
photon detector centered at a fixed energy of 9.8 eV. The combined
resolution (electron þ photon) of the IPES spectrometer was
determined to be ∼0.6 eV from the width of the Fermi edge
measured on a clean polycrystalline Au film. The UPS and IPES
energy scales were aligned by measuring the position of the Fermi
level on a freshly evaporated Au film. The position of the vacuum
level, Evac, was measured for each surface using the onset of the
secondary cutoff in the UPS spectra. The HOMO/LUMO level
was determined directly using the onset edge in the UPS/IPES
spectra instead of the peak value. All measurements were per-
formed at room temperature.
Synthesis Details for All New Compounds. General Procedure
for the Coupling of a Terminal Alkyne with an Aryl Halide Using a
Palladium-Catalyzed Cross-Coupling (Sonogashira) Protocol.
To an oven-dried round-bottom flask equipped with a magnetic
stir bar were added the aryl halide, the terminal alkyne, PdCl2-
(PPh3)2 (ca. 2 mol % per aryl halide), and CuI (ca. 4 mol % per
aryl halide). A solvent system of TEA and/or THF was added
depending on the substrates. Upon completion, the reaction was
quenched with a saturated solution of NH4Cl. The organic layer
was then diluted with hexanes, diethyl ether, or CH2Cl2 and
washed with water or saturated NH4Cl (1ꢀ). The combined
aqueous layers were extracted with hexanes, diethyl ether, or
CH2Cl2 (2ꢀ). The combined organic layers were dried over
MgSO4 and filtered, and the solvent was removed from the
filtrate in vacuo to afford the crude product, which was purified
Experimental Section
Materials. The synthesis of compounds 1-Me-xxx, 2-Me-
xxx, 8-10, and 13 have been detailed in the literature.17
Precursors 14a-e,26 15a,38 15e,38 16a,38 16e,38 31,27 and 3539
were prepared according to literature procedures. All reactions
were performed under an atmosphere of nitrogen unless stated
otherwise. Reagent-grade diethyl ether and tetrahydrofuran
(THF) were distilled from sodium benzophenone ketyl. Triethyl-
amine (TEA) and CH2Cl2 were distilled over CaH2. Fullerene
(99.5þ% pure) was purchased from MTR Ltd. and used as
received. LHMDS (1 M solution in THF) and TBAF (1 M solu-
tion in THF) were obtained from Aldrich and used as received.
Flash column chromatography was performed using 230-
400 mesh silica gel from EM Science. Thin-layer chromatography
was performed using glass plates precoated with silica gel 40 F254
purchased from EM Science. Melting points were uncorrected.
Ultrasonicated fullerene slurry in THF was prepared in general
ultrasonic cleaners.
Ultraviolet Photoelectron Spectroscopy (UPS) and Inverse
Photoemission Spectroscopy (IPES). Photoemission spectroscopy
of occupied and unoccupied states of the system was performed
(38) Ying, J. W.; Ren, T. J. Organomet. Chem. 2006, 691, 4021–4027.
(39) Flatt, A. K.; Chen, B.; Taylor, P. G.; Chen, M. X.; Tour, J. M. Chem.
Mater. 2006, 18, 4513–4518.
(40) He, T.; Ding, H. J.; Peor, N.; Lu, M.; Corley, D. A.; Chen, B.; Ofir,
Y.; Gao, Y. L.; Yitzchaik, S.; Tour, J. M. J. Am. Chem. Soc. 2008, 130, 1699–
1710.
(41) Yan, L.; Watkins, N. J.; Zorba, S.; Gao, Y. L.; Tang, C. W. Appl.
Phys. Lett. 2001, 79, 4148–4150.
(42) Ding, H. J.; Zorba, S.; Gao, Y. L.; Ma, L. P.; Yang, Y. J. Appl. Phys.
2006, 100, 113706.
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Shirai et al.
JOCArticle
by column chromatography (silica gel). Eluents and other slight
modifications are described below for each compound.
with C60 (0.22 g, 0.31 mmol), THF (120 mL), LHMDS
(1.0 mL, 1.0 mmol), and MeI (5 mL, 80 mmol). Crude products
were dissolved in CS2, directly loaded onto flash column, and
eluted with 100% CS2 in hexanes. The product was further
purified using another flash column with graduated elution of
5-75% CS2 in hexanes and then CS2/CH2Cl2/hexanes (4:1:5) to
afford the product (0.079 g, 23%) as a brown solid: FTIR (KBr)
2950, 2922, 2208, 1713, 1606, 1588, 1541, 1514, 1344, 1248 cm-1
General Procedure for the Addition of C60 to Terminal Alkynes
Using LHMDS, in Situ Ethynylation Method. To an oven-dried
round-bottom flask equipped with a magnetic stir bar was
added the terminal alkyne and C60 (2 equiv per terminal alkyne
H). After addition of THF, the mixture was bath-sonicated for
at least 3 h. To the greenish-brown suspension formed after the
sonication was added LHMDS dropwise at room temperature
over 0.5 to 1.5 h. As the reaction progressed, the mixture turned
into a deep greenish-black solution. During and after the
addition of the LHMDS, small aliquots from the reaction were
extracted and quenched with trifluoroacetic acid (TFA) or
methyl iodide (MeI), dried, and redissolved in CS2 for TLC
analysis (developed in a mixture of CS2, CH2Cl2, and hexanes).
Completion of the reaction was confirmed by the disappearance
of the starting materials. The reaction usually completed within
1.5 h from the beginning of LHMDS addition. Upon comple-
tion, the reaction was quenched with TFA or MeI to give a
brownish slurry. When MeI was used, the reaction was stirred at
room temperature for at least 6 h. Excess TFA or MeI and
solvent were then removed in vacuo to afford a crude product
that was purified by flash column chromatography (silica gel).
Eluents and other slight modifications are described below for
each compound.
Compound 1-H-TMS. Compound 13 (0.080 g, 0.34 mmol)
was subjected to the general in situ ethynylation procedure with
C60 (0.12 g, 0.17 mmol), THF (100 mL), LHMDS (0.5 mL,
0.5 mmol), and TFA (0.23 mL). Crude products were dissolved
in CS2, directly loaded onto a flash column, and eluted with
7-20% CS2 in hexanes. The product was further purified using
another flash column with graduated elution of 50-100% CS2
in hexanes to afford the product (0.086 g, 54%) as a brown solid:
FTIR (KBr) 2945, 1488, 1246, 1092, 838 cm-1; 1H NMR (CS2/
CDCl3, 1:1, 500 MHz) δ 7.66 (d, J=8.4 Hz, 2H), 7.31 (d, J=8.4
Hz, 2H), 7.11 (s, 1H), 3.04-3.01 (m, 2H), 1.02-0.98 (m, 2H),
0.10 (s, 9H); 13C NMR (CS2/CDCl3, 1:1, 125 MHz) δ 151.5,
151.3, 147.6, 147.3, 146.6, 146.4, 146.3, 146.19, 146.17, 145.8,
145.63, 145.61, 145.5, 145.4, 145.3, 144.7, 144.5, 143.2, 142.6,
142.5, 142.1, 142.01, 141.97, 141.9, 141.7, 141.6, 140.4, 140.3,
136.1, 135.1 (30 signals from sp2-C in the C60 core), 139.7, 132.3,
127.6, 118.9, 92.4, 83.6, 61.9 (CH in the C60 core), 55.1
(quaternary sp3-C in the C60 core), 28.8, 16.6, -1.7; MALDI-
TOF MS m/z (sulfur as the matrix) calcd for C73H18SSi 955.1,
found 955.0 (Mþ).
Compound 2-H-TMS. Compound 16a (0.094 g, 0.28 mmol)
was subjected to the general in situ ethynylation procedure with
C60 (0.13 g, 0.18 mmol), THF (100 mL), LHMDS (0.65 mL,
0.65 mmol), and TFA (0.1 mL, 1.3 mmol). Crude products were
dissolved in CS2, directly loaded onto a flash column, and eluted
with 100% CS2 in hexanes. The product was further purified using
another flash column with graduated elution of 5-50% CS2 in
hexanes then CS2/CH2Cl2/hexanes (3:1:6) to afford the product
(0.061 g, 21%) as a brown solid: FTIR (KBr) 2945, 1507, 1246,
1086 cm-1; 1H NMR (CS2/CDCl3, 1:2, 500 MHz) δ 7.78 (d, J=
8.2 Hz, 2H), 7.61 (d, J=8.1 Hz, 2H), 7.44 (d, J=8.2 Hz, 2H), 7.24
(d, J=8.2 Hz, 2H), 7.16 (s, 1H), 3.03-3.00 (m, 2H), 1.02-0.92
(m, 2H), 0.12 (s, 9H); 13C NMR (CS2/CDCl3, 1:2, 125 MHz) δ
151.5, 151.2, 147.7, 147.4, 146.7, 146.53, 146.50, 146.34, 146.33,
145.9, 145.8, 145.7, 145.62, 145.55, 145.47, 144.8, 144.6, 143.3,
142.73, 142.70, 142.23, 142.17, 142.1, 142.0, 141.8, 141.7, 140.52,
140.49, 139.2 (Ar), 136.2, 135.3 (30 signals from sp2-C in the C60
core), 132.2, 132.0, 131.7, 127.7, 124.3, 122.2, 119.7, 94.2, 92.2,
89.6, 83.7, 62.0 (CH in the C60 core), 55.3 (quaternary sp3-C in the
1
(drop cast); H NMR (CS2/CDCl3, 1:5, 500 MHz) δ 8.47 (d,
J=1.5 Hz, 1H), 7.95 (dd, J=1.5, 8.3 Hz, 1H), 7.78 (d, J=8.3 Hz,
1H), 7.51 (d, J=8.6 Hz, 2H), 7.26 (d, J=8.6 Hz, 2H), 3.52
C
(s, 3H), 3.03-2.99 (m, 2H), 0.99-0.96 (m, 2H), 0.08 (s, 9H); 13
NMR (CS2:CDCl3, 1:5, 125 MHz) δ 156.6, 152.6, 149.4 (Ar),
148.0, 147.8, 146.6, 146.5, 146.4, 146.3, 145.9, 145.7, 145.6,
145.5, 145.4, 145.01, 144.98, 144.8, 144.6, 143.2, 142.71,
142.66, 142.21, 142.16, 142.1, 142.0, 141.7, 141.6, 140.7 (Ar),
140.4, 140.2, 135.7, 134.7 (30 signals from sp2-C in the C60 core),
134.5, 134.2, 132.4, 128.2, 127.3, 123.1, 119.1, 118.5, 99.8, 92.6,
85.2, 82.8, 61.7 (CCH3 in the C60 core), 59.7 (quaternary sp3-C in
the C60 core), 33.0, 28.6, 16.6, -1.7; MALDI-TOF MS m/z
(sulfur as the matrix) calcd for C82H23NO2SSi 1114.2, found
1114.2 (Mþ).
Compound 3-H-TMS. Compound 16b (0.091 g, 0.24 mmol)
was subjected to the general in situ ethynylation procedure with
C60 (0.12 g, 0.16 mmol), THF (100 mL), LHMDS (1.8 mL,
1.8 mmol), and TFA (0.9 mL, 11.7 mmol). Crude products were
dissolved in CS2, directly loaded onto flash column, and eluted
with 100% CS2 in hexanes then CS2/CH2Cl2/hexanes (6:1:3) to
afford the product (0.055 g, 31%) as a brown solid: FTIR (KBr)
2945, 2204, 1540, 1521, 1498, 1342, 1246, 1087 cm-1; 1H NMR
(CS2:CDCl3, 1:1, 500 MHz) δ 8.49 (d, J=1.7 Hz, 1H), 7.96 (dd,
J=8.0, 1.7 Hz, 1H), 7.77 (d, J=8.0 Hz, 1H), 7.49 (d, J=6.6 Hz,
2H), 7.22 (d, J=6.6 Hz 2H), 7.12 (s, 1H), 3.01-2.97 (m, 2H),
0.99-0.95 (m, 2H), 0.09 (s, 9H); 13C NMR (CS2:CDCl3, 1:1, 125
MHz) δ 151.0, 150.3, 149.3 (Ar), 147.6, 147.3, 146.5, 146.44,
146.38, 146.24, 146.23, 145.8, 145.7, 145.51, 145.46, 145.42,
145.35, 144.7, 144.4, 143.2, 142.64, 142.60, 142.1, 142.05,
141.99, 141.74, 141.69, 141.64, 140.8 (Ar), 140.43, 140.41,
135.9, 135.5 (Ar), 135.3 (30 signals from sp2-C in the C60 core),
134.4, 132.3, 128.3, 127.2, 122.8, 119.2, 118.5, 100.0, 96.2, 85.3,
81.2, 61.5 (CH in the C60 core), 55.0 (quaternary sp3-C in the C60
core), 28.6, 16.6, -1.8; MALDI-TOF MS m/z (sulfur as the
matrix) calcd for C81H21NO2SSi 1100.2, found 1101.2 (Mþ).
Compound 4-TMS. Compound 16c (0.100 g, 0.275 mmol) was
subjected to the general in situ ethynylation procedure with C60
(0.297 g, 0.413 mmol), THF (125 mL), LHMDS (0.600 mL,
0.600 mmol), and MeI (6 mL). Crude products were dissolved in
CS2, directly loaded onto flash column, and eluted with 1-40%
CS2 in hexanes. The product was further purified using another
flash column with graduated elution from hexanes to CS2/
CH2Cl2/hexanes (1:3:6) to afford the product (0.093 g, 31%)
as a brown solid: FTIR (KBr) 2960, 1496, 1429, 1248 cm-1; 1H
NMR (CS2/CDCl3, 1:5, 400 MHz) δ 7.65 (s, 1H), 7.59 (m, 2H),
7.46 (d, J=8.1 Hz, 2H), 7.28 (s, 1H), 3.53 (s, 3H), 2.99 (m, 4H),
1.39 (t, J=7.5 Hz, 3H), 0.97 (m, 2H), 0.07 (s, 9H); 13C NMR
(CS2:CDCl3, 1:5, 100 MHz) δ 157.1, 153.4, 148.0, 147.8, 146.6,
146.5, 146.4, 146.3, 146.0, 145.61, 145.56, 145.5, 145.4, 145.3,
145.1, 144.8, 144.7, 143.2, 143.1, 142.6, 142.2, 142.1, 142.0,
141.7, 141.6, 140.3, 140.2, 138.7, 134.6, 134.4, 132.2, 131.9,
311.8, 131.76, 131.6, 129.4, 128.0, 123.2, 122.4, 120.0, 94.9,
89.5, 88.1, 85.4, 61.8, 59.9, 33.0, 29.0, 27.8, 16.7, 14.7, -1.7;
MALDI-TOF MS m/z (sulfur as the matrix) calcd for C84H28SSi
1096, found 1096 (Mþ).
Compound 4-SAc. To a round-bottom flask equipped with a
magnetic stirrer were added compound 4-TMS (32 mg, 0. 029
mmol), excess AcCl (1 mL), CH2Cl2 (20 mL), and AgBF4 (17 mg,
0.08 mmol). The reaction mixture was stirred for 1 h at room
temperature and then quenched with saturated NaHCO3 and
C
60 core), 29.0, 16.8, -1.6; MALDI-TOF MS m/z (sulfur as the
matrix) calcd for C81H22SSi 1055.2, found 1056.4 (Mþ).
Compound 3-Me-TMS. Compound 16b (0.15 g, 0.40 mmol)
was subjected to the general in situ ethynylation procedure
7894 J. Org. Chem. Vol. 74, No. 20, 2009

Shirai et al.
JOCArticle
diluted with CH2Cl2 and water. The aqueous layer was extracted
with CH2Cl2 (ꢀ1). The combined organic layers were dried over
MgSO4, filtered, and concentrated under vacuum. Crude material
was loaded onto flash column using pure CS2 and eluted with
hexane, CS2/CH2Cl2/hexane (1:1:3), and then CS2/CH2Cl2/hexane
(5:2:3) to give the product 4-SAc as a brown powder (12.0 mg,
(240 mg, 0.333 mmol), THF (120 mL), LHMDS (0.6 mL,
0.6 mmol), and MeI (1 mL). Crude products were dissolved in
CS2, directly loaded onto a flash column, and eluted with
1-40% CS2 in hexanes. The product was further purified using
another flash column with gradual elution from hexanes to CS2/
CH2Cl2/hexanes (5:1:4) to afford the product (80 mg, 30%) as a
brown solid: FTIR (KBr) 2925, 2854, 1742, 1443, 144, 1377,
1259, 1213, 1097, 859 cm-1; 1H NMR (CDCl3, 500 MHz) δ 7.47
(d, 2H, J=8.19 Hz), 7.26 (d, 2H, J=8.19 Hz), 7.20 (s, 1H), 7.10
(s, 1H), 4.10 (t, 2H, J=6.40 Hz), 4.07 (t, 2H, J=6.40 Hz), 3.56
(s, 3H), 3.00 (m, 2H), 1.94 (m, 4H), 1.16 (t, 3H, J=7.40 Hz), 1.13
(t, 3H, J = 7.40 Hz), 0.96 (m, 2H), 0.07 (s, 9H); 13C NMR
(CDCl3), 126 MHz) δ 157.3, 154.7, 153.59, 153.56, 148.0, 147.8,
146.56, 146.48, 146.34, 146.30, 146.03, 145.58, 145.55, 145.49,
145.38, 145.36, 145.2, 144.8, 144.7, 143.2, 142.67, 142.63, 142.22,
142.16, 142.13, 141.7, 141.5, 140.3, 140.2, 138.6, 134.6, 134.5,
131.9, 127.8, 120.2, 117.4, 116.3, 114.8, 113.0, 95.1, 93.5, 86.3,
82.0, 71.4, 70.9, 61.8, 60.2, 33.3, 29.0, 23.0, 22.9, 16.7, 10.9, 10.8,
-1.7; MALDI-TOF MS m/z (sulfur as the matrix) calcd for
C88H36SSi 1185, found 1185 (Mþ).
40%): FTIR (KBr) 2963, 2923, 1709, 1495 cm-1 1H NMR
;
(CS2/CDCl3, 1:1, 400 MHz) δ 7.64 (m, 1H), 7.57 (m, 4H), 7.41
(d, J=8 Hz, 2H), 3.53 (s, 3H), 2.96 (q, J=8 Hz, 2H), 2.45 (s, 3H),
1.39 (t, J=8 Hz, 3H); 13C NMR (CS2/CDCl3, 1:1, 100 MHz) δ
157.0, 153.2, 147.9, 147.7, 146.52, 146.51, 146.4, 146.3, 146.2, 146.0,
145.6, 145.5, 145.4, 145.3, 145.2, 145.0, 144.8, 144.7, 143.2, 142.7,
142.6, 142.2, 142.13, 142.12, 142.0, 141.7, 141.5, 140.3, 140.2, 134.5,
134.4, 134.2, 132.3, 132.0, 131.6, 129.4, 128.4, 124.4, 122.8, 122.7,
94.2, 89.7, 89.6, 85.3, 61.7, 59.8, 33.0, 30.2, 29.9, 27.9, 14.8;
MALDI-TOF MS m/z (sulfur as the matrix) calcd for C81H18OS
1038, found 1038 (Mþ).
Compound 5-TMS. Compound 16d (0.130 g, 0.322 mmol) was
subjected to the general in situ ethynylation procedure with C60
(0.255 g, 0.354 mmol), THF (120 mL), LHMDS (3.217 mL,
3.217 mmol), and MeI (6 mL). Crude products were dissolved in
CS2, directly loaded onto flash column, and eluted with CS2.
The product was further purified using another flash column
with graduated elution from hexanes/CS2 (1:1) to afford the
product (0.163 g, 45%) as a brown solid: FTIR (KBr) 2959,
2919, 2855, 2226, 1499, 1420, 1322, 1254, 1171, 1134, 1046, 908,
843, 727 cm-1; 1H NMR (CDCl3, 500 MHz) δ 8.08 (d, 1H, J=
1.15 Hz), 7.91 (dd, 1H, J=1.56 Hz, J=7.93 Hz), 7.75 (d, 1H, J=
7.97 Hz), 7.49 (td, 1H, J=2.18 Hz, J=8.20 Hz), 7.28 (td, 1H, J=
2.00 Hz, J=8.31 Hz), 3.53 (s, 3H), 3.01 (m, 2H), 0.96 (m, 2H),
0.07 (s, 9H); 13C NMR (CDCl3), 125 MHz) δ 156.89, 152.95,
148.01, 147.8, 146.64, 146.54, 146.41, 146.37, 146.02, 145.70,
145.63, 145.54, 145.43, 145.15, 145.10, 144.85, 144.71, 143.28,
143.12, 142.74, 142.69, 142.26, 142.21, 142.19, 142.04, 141.73,
141.60, 140.40, 140.27, (30 signals from sp2-C in the C60 core),
139.83, 134.75 134.72, 134.35, 133.82, 132.08, 129.68, 129.64,
127.60, 124.34. 122.37, 119.01, 97.30, 91.57, 85.51, 83.72, 61.77
(CCH3 in the C60 core), 59.81 (quaternary sp3-C in the C60 core),
33.09, 28.78, 16.64, -1.70; MALDI-TOF MS m/z (CHCA as the
matrix) calcd for C83H23F3SSi 1136, found 1137 (Mþ).
Compound 5-SAc. To a round-bottom flask equipped with a
magnetic stirrer were added compound 5 (0.050 mg, 0.045
mmol), excess AcCl (1 mL), CH2Cl2 (20 mL), and AgBF4
(0.026 mg, 0.134 mmol). The reaction mixture was stirred for
1 h at room temperature and then quenched with saturated
NaHCO3 and diluted with CH2Cl2 and water. The aqueous
layer was extracted with CH2Cl2 (ꢀ1). The combined organic
layers were dried over MgSO4, filtered, and concentrated under
vacuum. Crude material was loaded onto flash column using
pure CS2 and eluted with hexane and then CS2/CH2Cl2/hexane
(5:2:3) to give the product as a brown powder (33.5 mg, 70%):
FTIR (KBr) 2919, 2843, 2216, 1706, 1506, 1418, 1318, 1170,
1129, 1049, 828 cm-1; 1H NMR (CS2/CDCl3, 1:1, 500 MHz) δ
8.11 (d, 1H, J=0.91 Hz), 7.94 (dd, 1H, J=1.39 Hz, J=7.77 Hz),
7.78 (d, 1H, J=7.93 Hz), 7.63 (td, 2H, J=1.88 Hz, J=8.40 Hz)
7.46 (td, 2H, J=1.64 Hz, J=8.24 Hz), 3.54 (s, 3H), 2.47 (s, 3H);
13C NMR (CS2/CDCl3, 1:1, 125 MHz) δ; 156.87, 152.91, 148.01,
147.85, 146.65, 146.54, 146.41, 146.37, 146.02, 145.71, 145.63,
145.54, 145.43, 145.14, 145.10, 144.85, 144.71, 143.28, 143.26,
142.74, 142.70, 142.26, 142.21, 142.19, 142.03, 141.73, 141.60,
140.41, 140.27, 139.67, 134.78 (30 signals from sp2-C in the C60
core), 134.73, 134.34, 134.02, 132.35, 129.66, 129.20, 126.94,
123.62, 122.86, 119.74, 96.15, 91.81, 85.19, 83.62, 61.77 (CCH3
in the C60 core), 59.80 (quaternary sp3-C in the C60 core), 33.09,
29.75; MALDI-TOF MS m/z (CHCA as the matrix) calcd for
C80H13F3OS 1078, found 1079 (Mþ).
Compound 6-SAc. To a round-bottom flask equipped with a
magnetic stirrer were added compound 6-TMS (50 mg, 0.042
mmol), excess AcCl (1 mL), CH2Cl2 (20 mL), and AgBF4
(25 mg, 0.128 mmol). The reaction mixture was stirred for 1 h
at room temperature and then quenched with saturated NaH-
CO3 and diluted with CH2Cl2 and water. The aqueous layer was
extracted with CH2Cl2 (ꢀ1). The combined organic layers were
dried over MgSO4, filtered, and concentrated under vacuum.
Crude material was loaded onto flash column using pure CS2
and eluted with hexane, CS2/CH2Cl2/hexane (1:1:3), and then
CS2/CH2Cl2/hexane (5:2:3) to give the product as a brown
powder (11 mg, 24%): FTIR (KBr) 2923, 1716, 1626, 1383,
1
1181 cm-1; H NMR (CDCl3, 500 MHz) δ 7.59 (d, 2H, J =
8.19 Hz), 7.42 (d, 2H, J=8.19 Hz), 7.22 (s, 1H), 7.12 (s, 1H), 4.12
(t, 2H, J=6.40 Hz), 4.08 (t, 2H, J=6.40 Hz), 3.57 (s, 3H), 2.45 (s,
3H), 1.98 (m, 2H), 1.91 (m, 2H), 1.19 (t, 3H, J=7.40 Hz), 1.14
(t, 3H, J=7.40 Hz); 13C NMR (CDCl3, 125 MHz) δ 157.25,
154.65, 153.53, 153.50, 147.90, 147.74, 146.50, 146.43, 146.28,
146.24, 145.97, 145.52, 145.49, 145.43, 145.32, 145.30, 145.13,
144.76, 144.67, 143.17, 142.61, 142.57, 142.16, 142.10, 142.07,
141.63, 141.48, 140.24, 140.14, 138.51, 134.57, 134.41, 131.86,
127.73, 120.12, 117.35, 116.25, 114.73, 112.91, 95.04, 93.48,
86.19, 81.97, 71.29, 70.86, 61.76, 60.17, 33.26, 22.97, 22.82,
10.87, 10.70; MALDI-TOF MS m/z (sulfur as the matrix) calcd
for C85H26OS 1126, found 1127 (M þ Hþ).
Compound 7. Compound 13 (0.086 g, 0.37 mmol) was subjected
to the general in situ ethynylation procedure with C60 (0.22 g, 0.31
mmol), THF (120 mL), LHMDS (0.6 mL, 0.6 mmol), and C7H15I
(10 mL, 60 mmol). Crude products were dissolved in CS2, directly
loaded onto flash column, and eluted with 100% CS2 in hexanes.
The product was further purified using another flash column with
graduated elution of 5-50% CS2 in hexanes to afford the product
(0.022 g, 7%) as a brown solid: FTIR (KBr) 2947, 2920, 2849, 1711,
1489, 1461, 1429, 1247, 1088 cm-1; 1H NMR (CDCl3, 500 MHz) δ
7.68 (d, J=8.4 Hz, 2H), 7.36 (d, J=8.4 Hz, 2H), 3.78-3.74 (m, 2H),
3.07-3.04 (m, 2H), 2.62 (m, 2H), 1.81 (m, 2H), 1.59-1.55 (m, 2H),
1.42-1.38 (m, 4H), 1.02-1.01 (m, 2H), 1.00 (t, J=4.1 Hz, 3H), 0.10
(s, 9H); 13C NMR (CDCl3, 125 MHz) δ 156.1, 154.1, 147.9, 147.8,
146.6, 146.5, 146.33, 146.31, 146.0, 145.8, 145.57, 145.55, 145.5,
145.4, 145.3, 144.8, 144.7, 143.3, 142.69, 142.66, 142.237 (ꢀ 2),
142.13, 142.11, 141.7, 141.5, 140.3, 139.9, 134.9, 134.5 (30 signals
from sp2-C in the C60 core), 139.2, 132.4, 127.9, 119.4, 89.2, 84.3,
66.1 (CCH3 in the C60 core), 59.8 (quaternary sp3-C in the C60 core),
44.6, 32.0, 30.7, 30.4, 29.6, 28.9, 22.7, 16.7, 14.2, -1.66; MALDI-
TOF MS m/z (sulfur as the matrix) calcd for C80H32SSi 1053.3
(unable to obtain mass due to instability of molecular ion).
Compound 6-TMS. Compound 16e (100 mg, 0.222 mmol) was
subjected to the general in situ ethynylation procedure with C60
Compound 11. To a round-bottom flask equipped with a
magnetic stirrer were added 34 (36 mg, 0.018 mmol), CH2Cl2
J. Org. Chem. Vol. 74, No. 20, 2009 7895

Shirai et al.
JOCArticle
(10 mL), and AgBF4 (10-20 mg, 0.05-0.1 mmol). The reaction
mixture was stirred for 0.5 h at room temperature and then
quenched with saturated NaHCO3 and diluted with CH2Cl2 and
water. The aqueous layer was extracted with CH2Cl2 (ꢀ2).
The combined organic layers were dried over MgSO4, filtered,
and concentrated under vacuum. Crude material was loaded
onto flash column using pure CS2 and eluted with hexane,
CS2/CH2Cl2/hexane (2:4:4), CS2/CH2Cl2/hexane (2:5:3), CS2/
CH2Cl2/hexane (2:6:2), and then CS2/CH2Cl2/hexane (1:7:2) to
give the product 11 as brown solid (21.7 mg, 66%): FTIR (KBr)
2920, 1688, 1594, 1130, 1098 cm-1; 1H NMR (CDCl3, 500 MHz)
δ 8.05 (d, J=8.5 Hz, 2H), 7.99 (d, J=8.4 Hz, 2H), 7.95 (d,
J=8.6 Hz, 2H), 7.73 (d, J=8.5 Hz, 2H), 7.62-7.53 (m, 16H),
7.49 (m, 3H), 7.44-7.42 (m, 3H), 7.31-7.28 (m, 6H), 4.12 (s,
6H), 3.56 (s, 3H), 2.37 (s, 9H); 13C NMR (CDCl3, 125 MHz) δ
194.9 (Ac), 157.0, 153.2, 152.2 (Ar), 151.9 (Ar), 148.0, 147.8,
146.6, 146.5, 146.4, 146.3, 146.0, 145.64, 145.58, 145.5, 145.4,
145.2, 145.1, 144.8, 144.7, 143.2, 142.70, 142.66, 142.23, 142.173
(ꢀ 2), 142.1, 141.7, 141.6, 140.3, 140.2, 138.0 (Ar), 136.3 (Ar),
136.2 (Ar), 134.7, 134.4 (30 signals from sp2-C in the C60 core),
134.1, 133.5, 133.0, 132.6, 132.0, 131.14, 131.09, 130.6, 129.0,
128.7, 126.2, 125.5, 124.9, 124.5, 123.4, 123.24, 123.16, 96.1,
92.1, 91.0, 90.5, 89.4, 85.0, 61.8 (CCH3 in the C60 core), 59.9
(quaternary sp3-C in the C60 core), 33.1, 30.4, 29.7; MALDI-
TOF MS m/z (sulfur as the matrix) calcd for C134H54N2O3-
S3Si 1864.2 (unable to obtain mass due to instability of mole-
cular ion).
was filtered through a plug of silica gel using CH2Cl2/hexanes
mixture to give the product 16b as a reddish-brown solid (0.30 g,
99%): FTIR (KBr) 3288, 2951, 2209, 1588, 1498 cm-1; 1H NMR
(400 MHz, CDCl3) δ 8.19(s, 1H), 7.66 (s, 2H), 7.50 (d, J=6.7 Hz,
2H), 7.26 (d, J=6.7 Hz, 2H), 3.30 (s, 1H), 3.03-2.99 (m, 2H),
0.99-0.94 (m, 2H), 0.08 (s, 9H); 13C NMR (100 MHz, CDCl3) δ
149.4, 140.7, 136.0, 134.6, 132.6, 128.5, 127.6, 122.8, 119.2, 118.8,
99.5, 85.1, 81.5, 81.2, 28.8, 16.8, -1.5; EI-HRMS m/z calcd for
C21H21NO2SSi 379.1062, found 380.11362 ([M þ H]þ).
Compound 16c. See the general procedure for the Pd/Cu coup-
ling reaction. The materials used were 14c (0.353 g, 1.506 mmol), 13
(0.498 g, 1.506 mmol), PdCl2(PPh3)2 (0.025 g, 0.036 mmol), CuI
(0.010 g, 0.053 mmol), TEA (10 mL), and THF (20 mL) at room
temperature overnight. The residue was purified by flash column
chromatography with 1-5% CH2Cl2 in hexanes to give product
15c (0.471 g, 72%) as a yellow oil. The solid was then transferred to
a round-bottom flask equipped with a magnetic stirrer dissolved in
THF/MeOH (1:1) (30 mL) and K2CO3 (0.312 g, 2.26 mmol). The
reaction mixture was stirred for 1 h at room temperature and then
quenched with water and diluted with hexanes. The aqueous layer
was extracted with CH2Cl2 (ꢀ1). The combined organic layers
were dried over MgSO4, filtered, and concentrated under vacuum.
The crude material was filtered through a plug of silica gel using
CH2Cl2/hexanes (20%) mixture to give the product 16c as yellow/
orange oil (0.372 g, 99%): FTIR (KBr) 3294, 2952, 1590, 1496, 1248
cm-1; 1H NMR (400 MHz, CDCl3) δ 7.37 (m, 3H), 7.32 (d, J=
1 Hz, 1H), 7.24 (dd, J1=8 Hz, J2=1.5 Hz, 1H), 7.19 (d, J=8.5 Hz,
2H), 3.09 (s, 1H), 2.95 (m, 2H), 2.8 (q, J=7.5 Hz, 2H), 1.23 (t, J=
7.5 Hz, 3H), 0.88 (m, 2H), 0.00 (s, 9H); 13C NMR (100 MHz,
CDCl3) δ 146.2, 138.8, 132.1, 132.0, 131.8, 129.5, 128.0, 123.3,
122.0, 120.1, 94.8, 88.1, 83.8, 78.6, 29.1, 27.7, 16.8, 14.7, -1.6; EI-
HRMS m/z calcd for C23H26SSi 362.1524, found 362.1525.
Compound 12. Compound 35 (0.13 g, 0.65 mmol) was sub-
jected to the general in situ ethynylation procedure with C60
(0.22 g, 0.30 mmol), THF (100 mL), LHMDS (1.0 mL, 1.0
mmol), and MeI (6.0 mL, 96 mmol). Crude products were
dissolved in CS2, directly loaded onto a flash column, and
purified with gradual elution of 1-50% CS2 in hexanes to
afford the product 12 (0.15 g, 52%) as a brown solid: FTIR
(KBr) 2968, 2922, 2864, 1712, 1421, 1391, 1325, 1229, 1072
Compound 16d. See the general procedure for the Pd/Cu coup-
ling reaction. The materials used were 14d (0.269 g, 1.145 mmol),
13 (0.422 g, 1.145 mmol), PdCl2(PPh3)2 (0.025 g, 0.036 mmol),
CuI (0.010 g, 0.053 mmol), TEA (10 mL), and THF (20 mL) at
room temperature overnight. The residue was purified by flash
column chromatography with 1-5% CH2Cl2 in hexanes to give
product 15d (0.442 g, 81%) as a yellow oily solid. The solid was then
transferred to a round-bottom flask equipped with a magnetic
stirrer dissolved in THF/MeOH (1:1) (30 mL) and K2CO3 (0.237
g, 1.718 mmol). The reaction mixture was stirred for 1 h at room
temperature and then quenched with water and diluted with
hexanes. The aqueous layer was extracted with CH2Cl2 (ꢀ1). The
combined organic layers were dried over MgSO4, filtered, and
concentrated under vacuum. The crude material was filtered
through a plug of silica gel using CH2Cl2/hexanes (10%) mixture
to give the product 16d as a yellow shiny solid (0.360 g, 99%): FTIR
(KBr) 3240, 2946, 2913, 2886, 2217, 1589, 1502, 1420, 1318, 1251,
1170, 1140, 1083, 1053, 824 cm-1; 1H NMR (500 MHz, CDCl3) δ
7.80 (s, 1H), 7.61 (d, 2H, J=1.17 Hz), 7.45 (td, 2H, J=1.94 Hz, J=
8.66 Hz), 7.26 (td, 2H, J=1.98 Hz, J=8.57 Hz), 3.25 (s, 1H), 3.00
(m, 2H), 0.96 (m, 2H), 0.07 (s, 9H); 13C NMR (125 MHz, CDCl3) δ
139.7, 134.7, 133.6, 132.0, 131.8, 131.5, 129.74, 129.69, 129.63,
129.58, 127.6, 121.9, 119.0, 97.0, 85.3, 82.0, 80.3, 28.8, 16.7, -1.7;
EI-HRMS m/z calcd for C22H21F3SSi 402.1084, found 402.1085.
Compound 16e. See the general procedure for the Pd/Cu
coupling reaction. The materials used were 14e (0.200 g, 0.853
mmol), 13 (0.328 g, 0.853 mmol), PdCl2(PPh3)2 (0.030 g, 0.043
mmol), CuI (0.015 g, 0.079 mmol), TEA (10 mL), and THF
(20 mL) at room temperature overnight. The residue was puri-
fied by flash column chromatography with 10% ethyl acetate
in hexanes to give product 15e (0.318 g, 76%) as a orange oil.
The solid was then transferred to a round-bottom flask
equipped with a magnetic stirrer dissolved in THF/MeOH
(1:1) (30 mL) and K2CO3 (0.177 g, 1.280 mmol). The reaction
mixture was stirred for 1 h at room temperature and then
quenched with water and diluted with hexanes. The aqueous
1
cm-1; H NMR (CS2:CDCl3 (1:5), 500 MHz) δ 7.69 (d, J =
8.1 Hz, 2H), 7.47 (d, J=8.1 Hz, 2H), 3.81 (q, J=7.2 Hz, 4H), 3.53
(s, 3H), 1.32 (m, 6H); 13C NMR (CS2:CDCl3 (1:5), 125 MHz) δ
157.2, 153.7, 151.4 (Ar), 147.9, 147.7, 146.5, 146.4, 146.3, 146.2,
146.0, 145.52, 145.47, 145.4, 145.32, 145.29, 145.1, 144.74,
144.69, 143.2, 142.59, 142.57, 142.2, 142.14, 142.10, 142.09,
141.6, 141.5, 140.22, 140.16, 134.45, 134.42 (30 signals from
sp2-C in the C60 core), 132.7, 120.6, 118.7, 87.7, 86.1, 61.7 (CCH3
in the C60 core), 59.8 (quaternary sp3-C in the C60 core), 33.0;
MALDI-TOF MS m/z (sulfur as the matrix) calcd for C73H17H3
935.9, found 936.6 (Mþ).
Compound 15b. See the general procedure for the Pd/Cu
coupling reaction. The materials used were 14b (1.03 g, 2.98
mmol), 13 (0.615 g, 2.62 mmol), PdCl2(PPh3)2 (0.033 g, 0.047
mmol), CuI (0.014 g, 0.074 mmol), TEA (10 mL), and THF
(20 mL) at room temperature overnight. The residue was puri-
fied by flash column chromatography with 10-20% CH2Cl2 in
hexanes to give product 15b (0.99 g, 84%) as a yellow solid:
FTIR (KBr) 2954, 2211, 2163, 1588, 1542, 1499, 1346, 1249,
1
1089 cm-1; H NMR (500 MHz, CDCl3) δ 8.16 (s, 1H), 7.63
(s, 2H), 7.49 (d, J = 8.5 Hz, 2H), 7.26 (d, J = 8.5 Hz, 2H),
3.03-2.98 (m, 2H), 0.99-0.94 (m, 2H), 0.28 (s, 9H), 0.07 (s, 9H);
13C NMR (125 MHz, CDCl3) δ 149.4, 140.6, 135.8, 134.5, 132.5,
128.3, 127.6, 123.9, 118.9, 118.7, 102.2, 99.6, 99.3, 85.3, 28.8,
16.8, -0.1, -1.5; EI-HRMS m/z calcd for C24H29NO2SSi2
451.14, found 452.15 ([M þ H]þ).
Compound 16b. To a round-bottom flask equipped with a
magnetic stirrer were added 15b (0.36 g, 0.8 mmol), THF/MeOH
(1:1) (30 mL), and K2CO3 (0.16 g, 1.2 mmol). The reaction mixture
was stirred for 1 h at room temperature and then quenched with
water and diluted with hexanes. The aqueous layer was extracted
with CH2Cl2 (ꢀ2). The combined organic layers were dried over
MgSO4, filtered, and concentrated under vacuum. Crude material
7896 J. Org. Chem. Vol. 74, No. 20, 2009

Shirai et al.
JOCArticle
layer was extracted with CH2Cl2 (ꢀ1). The combined organic
layers were dried over MgSO4, filtered, and concentrated under
vacuum. The crude material was purified by flash column
chromatography with 5% ethyl acetate in hexanes to give the
product 16e as a yellow/brown oily solid (0.261 g, 82%): FTIR
(KBr) 3281, 2960, 2873, 2104, 1592, 1509, 1409, 1384, 1247,
136.5, 136.4, 134.4, 133.7, 133.2, 132.8, 132.2, 131.34, 131.27, 130.4,
129.2, 128.7, 126.3, 125.18, 125.16, 124.8, 123.4, 123.3, 123.1, 92.2,
90.9, 90.7, 89.4, 83.5, 79.9, 35.9, 27.1, 17.2, -1.5; MALDI-TOF MS
m/z (sulfur as the matrix) calcd for C82H82N2S3Si4 1304.1, found
1304.0 (Mþ).
Compound 34. Compound 33 (0.17 g, 0.13 mmol) was subjected
to the general in situ ethynylation procedure with C60 (0.11 g,
0.16 mmol), THF (290 mL), LHMDS (0.6 mL, 0.6 mmol), and
MeI (2.5 mL, 40 mmol). Crude products were dissolved in CS2,
directly loaded onto the flash column, and purified with graduated
elution of 1-40% CS2 in hexanes then CS2/CH2Cl2/hexanes
(2:3:5) and CS2/CH2Cl2/hexanes (1:4:5) to afford the product
(0.057 g, 22%) as a brown solid: FTIR (KBr) 1703, 1595, 1360,
1248, 1221, 1097 cm-1; 1H NMR (CDCl3, 500 MHz) δ 8.05 (d, J=
8.4 Hz, 2H), 7.99 (d, J=8.5 Hz, 2H), 7.95 (d, J=8.4 Hz, 2H), 7.73
(d, J=8.5 Hz, 2H), 7.62-7.54 (m, 16H), 7.50 (m, 3H), 7.44-7.42
(m, 3H), 7.32-7.29 (m, 6H), 3.72 (s, 6H), 3.56 (s, 3H), 2.48-2.45
(m, 6H), 0.89-0.85 (m, 6H), 0.003 (s, 27H); 13C NMR (CDCl3,
125 MHz) δ 157.0, 153.2, 152.2 (Ar), 151.9 (Ar), 148.0, 147.8,
146.6, 146.5, 146.4, 146.3, 146.0, 145.64, 145.59, 145.5, 145.4, 145.2,
145.1, 144.8, 144.7, 143.2, 142.69, 142.66, 142.23, 142.18, 142.175
(ꢀ 2), 141.7, 141.6, 140.3, 140.2, 139.0 (Ar), 136.3 (Ar), 136.2 (Ar),
134.7, 134.4 (30 signals from sp2-C in the C60 core), 134.2, 133.5,
133.0, 132.6, 132.0, 131.14, 131.07, 130.2, 129.0, 128.5, 126.2, 125.5,
124.9, 124.5, 123.24, 123.16, 123.1, 96.1, 92.1, 91.0, 90.7, 89.2, 85.0,
61.8 (CCH3 in the C60 core), 59.9 (quaternary sp3-C in the C60
core), 35.6, 33.1, 26.9, 17.0, -1.8; MALDI-TOF MS m/z (sulfur as
the matrix) calcd for C143H84N2S3Si4 2038.8 (unable to obtain
mass due to instability of molecular ion).
1221, 1016, 861 cm-1 1H NMR (400 MHz, CDCl3) δ 7.42
;
(d, 2H, J=8.28 Hz), 7.24 (d, 2H, J=8.35 Hz), 6.98 (s, 1H), 6.97
(s, 1H), 3.97 (m, 4H), 3.34 (s, 1H), 3.01-2.96 (m, 2H), 1.90-1.80
(m, 4H), 1.11-1.04 (m, 6H), 0.97-0.92 (m, 2H), 0.05 (s, 9H); 13
C
NMR (100 MHz, CDCl3) δ 154.4, 153.6, 138.7, 132.1, 128.0,
120.3, 118.1, 117.0, 115.0, 113.7, 95.0, 86.2, 82.2, 80.2, 71.33,
71.30, 29.1, 22.9, 22.8, 16.8, 10.8, 10.7, -1.5; EI-HRMS m/z
calcd for C27H34O2SSi 450.2049, found 450.2049.
Compound 32. See the general procedure for the Pd/Cu coupling
reaction. The materials used were 3016 (0.456 g, 0.415 mmol), 31
(0.15 g, 0.37 mmol), PdCl2(PPh3)2 (0.009 g, 0.012 mmol), CuI
(0.003 g, 0.016 mmol), TEA (2 mL), and THF (10 mL) at room
temperature overnight. The residue was purified by flash column
chromatography with 5-33% CH2Cl2 in hexanes to give product
32 (0.28 g, 55%) as a clear red solid: FTIR (KBr) 3064, 2951, 2907,
2155, 1597, 1248, 1101 cm-1; 1H NMR (500 MHz, CDCl3) δ 7.93
(d, J=8.7 Hz, 2H), 7.89 (d, J=8.7 Hz, 2H), 7.70 (d, J=8.7 Hz, 2H),
7.63-7.53 (m, 18H), 7.51 (m, 3H), 7.45-7.42 (m, 3H), 7.32-7.29
(m, 6H), 3.73 (s, 6H), 2.50-2.45 (m, 6H), 0.90-0.86 (m, 6H), 0.29
(s, 9H), 0.01 (s, 27H); 13C NMR (125 MHz, CDCl3) δ 152.13,
152.12, 139.2, 136.5, 136.4, 134.3, 133.7, 133.1, 132.8, 132.2, 131.34,
131.29, 130.4, 129.3, 128.8, 126.273 ( ꢀ 2), 125.2, 124.8, 123.4,
123.3, 123.1, 104.8, 97.6, 92.1, 90.9, 90.8, 89.4, 35.9, 27.2, 17.2, 0.12,
-1.5; MALDI-TOF MS m/z (sulfur as the matrix) calcd for
C85H90N2S3Si5 1376.3 (unable to obtain mass due to instability
of molecular ion).
Acknowledgment. The Welch Foundation, DARPA/
AFOSR, the NSF NIRT (ECCS-0708765), and the NSF
Penn State MRSEC and Center for Nanoscale Science
funded this work. We thank Drs. I. Chester of FAR Re-
search, Inc., and R. Awartani of Petra Research, Inc., for
providing TMSA. This work was supported in part by World
Premier International Research Center (WPI) Initiative on
Materials Nanoarchitectonics, MEXT, Japan. Y.S. thanks
Iketani Science and Technology Foundation for funding.
Compound 33. To a round-bottom flask equipped with a
magnetic stirrer were added 32 (0.17 g, 0.12 mmol), THF/MeOH
(1:1) (20 mL), and K2CO3 (0.10 g, 0.72 mmol). The reaction
mixture was stirred for 1 h at room temperature and then quenched
with water and diluted with hexanes. The aqueous layer was
extracted with CH2Cl2 (ꢀ2). Combined organic layers were dried
over MgSO4, filtered, and concentrated under vacuum. The residue
was purified by flash column chromatography with 10-30%
CH2Cl2 in hexanes to give product 33 (0.12 g, 76%) as a clear red
solid: FTIR (KBr) 3289, 3064, 2923, 2852, 1597, 1247, 1101 cm-1
;
1H NMR (400 MHz, CDCl3) δ 7.95 (d, J=8.5 Hz, 2H), 7.91 (d, J=
8.5 Hz, 2H), 7.71 (d, J=8.5 Hz, 2H), 7.66 (d, J=8.5 Hz, 2H),
7.64-7.55 (m, 16H), 7.52 (m, 3H), 7.46-7.43 (m, 3H), 7.34-7.30
(m, 6H), 3.74 (s, 6H), 3.25 (s, 1H), 2.48 (m, 6H), 0.91-0.86 (m, 6H),
0.02 (s, 27H); 13C NMR (100 MHz, CDCl3) δ 152.4, 152.0, 139.2,
Supporting Information Available: Detailed NMR spectra
for all new compounds and total energy and atomic coordinates
of C60 and the molecules listed in Table 1 and Figure 4 inset. This
material is available free of charge via the Internet at http://
pubs.acs.org.
J. Org. Chem. Vol. 74, No. 20, 2009 7897