Electrochemical charging of a fullerene-functionalized self-assembled monolayer on Au(111)

Article abstract of DOI:10.1021/jo049939j

A fullerene derivative 10 with a terminal thiol group dissolves easily in common organic solvents and forms a densely packed self-assembled monolayer on gold surfaces. The functionalization of C₆₀ is based on the 1,3-dipolar cycloaddition of th

Full text of DOI:10.1021/jo049939j

Electr och em ica l Ch a r gin g of a F u ller en e-F u n ction a lized
Self-Assem bled Mon ola yer on Au (111)
Tao Gu, J ames K. Whitesell, and Marye Anne Fox*
Department of Chemistry, North Carolina State University, Raleigh, North Carolina 27695-8204
mafox@ncsu.edu
Received J anuary 8, 2004
A fullerene derivative 10 with a terminal thiol group dissolves easily in common organic solvents
and forms a densely packed self-assembled monolayer on gold surfaces. The functionalization of
C60 is based on the 1,3-dipolar cycloaddition of the azomethine ylide generated in situ from the
corresponding aldehyde and N-methylglycine. The monolayers were characterized by grazing angle
reflectance FTIR spectroscopy, scan tunneling microscopy, and cyclic voltammetry. The cyclic
voltammogram of a SAM of 10 showed two well-resolved reversible cathodic waves corresponding
to the first two one-electron reductions of the fullerene fragment.
In tr od u ction
solid surface. C60 moieties serve as excellent electron
acceptors in molecularly designed donor acceptor diad
and triad systems.2f-i There have been some reports of
SAMs of C60 and its derivatives, including preparation,
electrochemistry, and surface structural characteri-
zation.2j-r
It is well established that alkanethiols with a poly-
methylene chain (number of the methylenes g 10) form
densely packed monolayers on gold surfaces.3 In addition,
the presence of an amido group in a chain enhances the
stability of monolayers as a result of the intermolecular
hydrogen bonding.4 Accordingly, a fullerene connected
through a rigid diphenylacetylene amide linker to a
terminal thiol was designed. The long linker and the
incorporation of the lateral alkoxy chains give this
derivative 10 appreciable solubility. The physical proper-
ties of the C60-alkanethiol in bulk solution and as a two-
Scientific interest in nanotechnology1a-e and in the opti-
cal, magnetic, and electronic properties of nanoarrays1f,g
derives from a desire for a full understanding of how
complex organic aggregates and organic-inorganic com-
posite assemblies can be constructed from simple molec-
ular precursors. It is also important to establish how the
physical properties of the resulting material vary with
the size of the component array.1 Current theories fail
to provide a convincing predictive model of how the
aggregated properties of integrated chemical systems
differ from those in which the individual molecular
components are randomly dispersed.1h-p Advances in this
field thus require architecturally defined arrays in which
a clear correlation between structure and photochemical
reactivity can be explored.
Our research group has focused on preparing self-
assembled ω-functionalized alkanethiol monolayers on
freshly deposited metal surfaces.2a-e The unique three-
dimensional structure of C60 has prompted many re-
searchers to employ it in various material science appli-
cations, and we have chosen to examine its disposition
when bound through a rigid and a flexible linker to a
(2) Wolf, M. O.; Fox, M. A. J . Am. Chem. Soc. 1995, 117, 1845. (b)
Fox, M. A.; Wooten, M. D. Langmuir 1997, 13, 7099. (c) Li, W.; Lynch,
V.; Thompson, H.; Fox, M. A. J . Am. Chem. Soc. 1997, 119, 7211. (d)
Wolf, M. O.; Fox, M. A. Langmuir 1996, 12, 955. (e) Fox, M. A.;
Whitesell, J . K.; McKerrow, A. J . Langmuir 1998, 14, 816. (f) Martın,
N.; Sanchez, L.; Illescas B.; Perez, I. Chem. Rev. 1998, 98, 2527. (g)
Guldi, D. M.; Prato, M. Acc. Chem. Res. 2000, 33, 695. (h) Gust, D.;
Moore, T. A.; Moore, A. J . Acc. Chem. Res. 2001, 34, 40. (i) Guldi, D.
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Chem. Commun. 2000, 339. (m) Bard, A. J .; Faulkner, L. R. Electro-
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H.; Azumi, R.; Tanaka, M.; Nakamura, T.; Yunome, G.; Abe, M.;
Yamago, S.; Nakamura, E. Langmuir 1995, 11, 660. (q) Nakanishi,
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Mathias J . P.; Seto, C. T. Science 1991, 254, 1312. (c) Wang, D.;
Thomas, S. G.; Wang, K. L.; Xia, Y.; Whitesides, G. M. Appl. Phys.
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10.1021/jo049939j CCC: $27.50 © 2004 American Chemical Society
Published on Web 04/28/2004
J . Org. Chem. 2004, 69, 4075-4080
4075

Gu et al.
SCHEME 1. Syn th esis of F u ller en e-Alk a n eth iol 10a
a
Reagents and conditions: (i) 1-bromooctane, K2CO3, DMF, 80 °C, 24 h; (ii) I2, KIO3, H2SO4, CH3COOH, 80 °C, 12 h; (iii) n-BuLi (1
equiv), Et2O, 0 °C, 15 min, and then DMF, 0 °C to room temperature (rt), 2 h; (iv) (triisopropylsilyl)acetylene, PdCl2(PPh3)2, CuI, Et3N,
rt, 24 h; (v) 2,2-dimethylpropane-1,3-diol, p-TsOH, C6H6, heating, 24 h; (vi) TBAF, THF, 0 °C, 1 h; (vii) iodoaniline, PdCl2(PPh3)2, CuI,
Et3N, rt, 24 h; (viii) Br(CH2)11COOH, CDMT, THF, 0 °C; (ix) CF3CO2H, CH2Cl2, H2O, rt, 5 h; (x) C60, N-methylglycine, toluene, reflux, 16
h; (xi) hexamethyldisilathiane, TBAF, -10 to 0 °C, 30 min.
dimensional self-assembled monolayer (SAM) on gold
were therefore explored.
forded 7 in 91% yield. Deprotection of 7 with CF3COOH
in CH2Cl2/H2O afforded aldehyde 8 in 85% yield.
The functionalization of C60 is based on the 1,3-dipolar
cycloaddition of the azomethine ylide generated in situ
from the corresponding aldehyde and N-methylglycine.6
In a typical procedure, a solution of the aldehyde 8 (200
mg), C60 (234 mg), and N-methylglycine (145 mg) in
toluene (250 mL) was heated to reflux under Ar for 16 h.
After cooling, the resulting solution was evaporated to
dryness and column chromatography yielded fullerene-
alkyl bromide 9 (160 mg, 40%).
The thiol was introduced by a convenient (trimethyl-
silyl)thioxy-dehalogenation reaction.7 Tetrabutylammo-
nium trimethylsilanethiolate (Me3SiS-Bu4N+), generated
in situ by adding a solution of TBAF to hexamethyldisi-
lathiane in THF, reacted rapidly with 9 at ambient
temperature. Fullerene-alkanethiol 10, obtained in good
yield (78%), dissolved easily in common organic solvents
such as chloroform, methylene chloride, toluene, etc. But
the solubility decreased markedly after the compound
was dried, probably because of autoxidation of the
terminal thiol to the corresponding disulfide. Self-as-
sembled monolayers may be formed either by the direct
self-assembly of the thiol or of the corresponding disulfide
produced during the workup. The absorption spectrum
Resu lts a n d Discu ssion
Syn th esis. The synthesis of the fullerene derivative
studied here is depicted in Scheme 1. Reaction of hyd-
roquinone with 1-bromooctane in DMF at 80 °C in the
presence of K2CO3, followed by iodination of the resulting
1,4-dioctyloxybenzene, yielded 1. Compound 2 was ob-
tained in 63% yield by treatment of 1 with n-BuLi (1
equiv) in Et2O at 0 °C followed by quenching with DMF.
Compound 2 was then subjected to a Pd-catalyzed cross-
coupling reaction5 with (triisopropylsilyl)acetylene to give
alkynylated 3 in 89% yield. Reaction of 3 with 2,2-
dimethylpropane-1,3-diol in refluxing benzene in the
presence of a catalytic amount of p-toluenesulfonic acid
(p-TsOH) gave the protected aldehyde 4 in 96% yield.
Terminal alkyne 5 was obtained in 84% yield by depro-
tection of 4 with tetrabutylammonium fluoride (TBAF).
6 was obtained in 59% yield by Pd-catalyzed cross
coupling between 5 and iodoaniline. Condensation of
compound 6 with 12-bromododecanoic acid in the pres-
ence of 2-chloro-4,6-dimethoxy-1,3,5-triazine (CDMT) af-
(5) Takahashi, S.; Kuroyama, Y.; Sonogashira, K.; Nagihara, N.
Synthesis 1980, 00, 627. (b) Metal-catalyzed Cross-coupling Reactions;
Diederich, F., Stang, P. J ., Eds.; Wiley-VCH: Weinheim, Germany,
1998.
(6) Prato, M.; Maggini, M. Acc. Chem. Res. 1998, 31, 519.
(7) Hu, J .; Fox, M. A. J . Org. Chem. 1999, 64, 4959.
4076 J . Org. Chem., Vol. 69, No. 12, 2004

Electrochemical Charging of a Monolayer on Au(111)
F IGURE 1. GAR-FTIR of SAMs of fullerene-alkanethiol 10
on Au(111) (full line) and the FTIR of fullerene-alkanethiol
10 in KBr (dotted line).
F IGURE 2. Cyclic voltammograms of C60 (dotted line) and
60-derivative 10 (full line) in acetonitrile/toluene (1:4 v/v) on
a glassy carbon electrode with 0.1 M n-Bu4NPF6 as supporting
C
electrolyte at 100 mV/s scan rate at room temperature.
TABLE 1. Mod e Assign m en ts a n d F r equ en cies (cm -1
)
for a Tr a n sm ission F TIR Sp ectr u m of Com p ou n d 10 in
KBr a n d GAR-F TIR Sp ectr u m of SAM of Com p ou n d 10
metric stretching 2920 cm-1 and alkyl C-H symmetric
stretching 2850 cm-1 are moderately stronger than
aromatic stretching in the bulk spectrum, whereas they
have similar intensities in the GAR-FTIR of the SAM.
That is, the aromatic stretching bands became rela-
tively stronger compared to the alkyl stretching bands
in the SAM and compared to the bulk. Selection rules9
for reflectance infrared spectroscopy of anisotropic films
on a conducting surface allow only those transition
moments that have a component perpendicular to the
plane of the substrate surface to exhibit appreciable
absorbance. However, because the aromatic absorptions
result from overtones and are therefore complex in origin,
it is not possible to use the infrared data conclusively to
establish the orientation of the rigid diphenylacetylenes
relative to the gold surface.
assgntsa
10 in KBr SAM of 10
arom CH str
3056
aliph CH2 asym str
aliph CH2 sym str
CdO str
2922
2851
1664
1593
1516
1495
1463
1410
1201
1030
2934
2852
1690
1593
1521
1500
1460
1419
1209
1055
arom C-C ring str
arom C-C ring str
N-H deformation
CH3 asym deformation or CH2 scissor
CH2-CdO deformation
CH2 wag and twist or C-O-C asym str
CH2 out of plane bend or C-O-C sym str
a
The following abbreviations are used: arom for aromatic; aliph
for aliphatic; str for stretch; sym for symmetric; asym for asym-
metric.
Electr och em ica l P r op er ties of th e 10-F u n ction -
a lized Gold SAM. Fullerene-alkanethiol 10 in solution
(CH3CN/toluene) exhibited voltammetric behavior (Fig-
ure 2) very similar to that of C60 itself.2j Three reversible
reduction peaks were observed when the potential was
scanned to -1.9 V (E1/2 ) -1.116, -1.526, and -2.105 V
vs Fc/Fc+). These electron-transfer processes are presum-
ably fullerene centered but shifted -110, -110, and -180
mV, respectively, from those observed for C60. Such shifts
are diagnostic of chemical modification of the fullerene
and are a consequence of the disruption of the extended
fullerene π network affected by chemical modification.6
Fullerene-alkanethiol SAM was prepared by soaking
a polished gold electrode for 24 h in a 1 mM toluene
solution of 10. The electrode was then thoroughly rinsed
with toluene and absolute ethanol and water and dried
under Ar before being immersed in acetonitrile-toluene
with 0.1 M n-Bu4NPF6. The cyclic voltammogram of a
SAM of 10 showed two well-resolved reversible cathodic
waves with E01 ) -0.65 V and E02 ) -1.04 V vs Ag/AgCl
corresponding to the first two one-electron reductions of
the fullerene fragment (Figure 3).
of 10 in CH2Cl2 exhibited the characteristic peaks ex-
pected for a C60-pyrrolidine at 432 and 706 nm6 and for
aromatic rings at 306 and 334 nm.
Gr a zin g An gle Reflecta n ce In fr a r ed Sp ectr u m of
SAMs of 10. Infrared spectroscopy is a powerful tool for
the investigation of SAMs of thiols on gold. At the
simplest level, reflectance spectroscopy can confirm the
presence of molecules adsorbed on a surface. A compari-
son of the reflectance spectrum of the SAM with a
transmission spectrum of the compound as KBr pellet
confirms the identity of the molecules in the SAM, i.e.,
that the deposition process did not induce unexpected
cross-reaction.
The peaks of the GAR-FTIR spectrum of the SAMs of
the fullerene-thiol compound correspond well with the
peaks in transmission FTIR of the bulk fullerene-thiol
in KBr (Figure 1 and Table 1). For example, the 1521
and 1593 cm-1 peaks assigned as aromatic C-C ring
stretches, 1660-1700 cm-1 carbonyl peak, and the 1030
cm-1 ether peak group appear in both spectra. A band
from the thiol S-H stretch is not present in the bulk
spectrum, but these bands are characteristically weak
so their absence is understandable.8 Alkyl C-H asym-
Within the range of scan rates investigated, peak
currents increased linearly with the scan rate while the
(8) Reese, S.; Fox, M. A. J . Phys. Chem. B 1998, 102, 9820. (b)
Silverstein, R. M.; Bassler, G. C.; Morril, T. C. Spectrometric Identifica-
tion of Organic Compounds; Wiley: New York, 1991; Chapter 3.
(9) Ulman, A. An Introduction to Ultrathin Organic Films; Academic
Press: Boston, MA, 1991.
J . Org. Chem, Vol. 69, No. 12, 2004 4077

Gu et al.
F IGURE 5. High-resolution STM image (25 × 25 nm) of
SAMs generated from fullerene derivative 10 on Au(111). The
tunneling conditions were 700 mV bias and 70 pA tunneling
current.
F IGURE 3. Cyclic voltammograms of a SAM of fullerene-
alkanethiol 10 on a gold electrode in acetonitrile/toluene (1:4
v/v) with 0.1 M n-Bu4NPF6 as supporting electrolyte at room
temperature, with scan rates between 100 (smallest current)
and 800 (largest current) mV/s.
F IGURE 4. Anodic peak current at -0.65 V as a function of
sweep rate.
F IGURE 6. STM image of a 60 × 60 nm area of a decanethi-
olate monolayer containing inserted fullerene derivative mol-
ecules 10 on Au(111). The tunneling conditions were 1.0 V bias
and 10 pA tunneling current.
peak potentials and peak-to-peak separations (∆Ep) (17
and 29 mV for the first and the second reductions,
respectively) were independent of scan rates (Figure 4).
These characteristics together with the Gaussian shape
of the CV waves are typical for surface-confined electro-
active species.2k-m
Sca n n in g Tu n n elin g Micr oscop y. Figure 5 shows
an STM image of a SAM derived from the C60 derivative
on Au (111). This image demonstrates a high coverage
of surface-confined moieties but no evidence of ordering
or any discernible overlayer structure.
The fullerene moieties can be readily distinguished
with a nearest-neighbor distance of 13 Å in the most
densely packed regions. This corresponds well with the
electrochemistry measurements. This distance is higher
than the measured van der Waals diameter of underiva-
tized C60 adsorbates found in previous STM measure-
ments,10 which is understandable because of the existence
of the lateral chains of the C60 derivative.
We also studied SAMs formed by the insertion of the
fullerene-thiol or/and -disulfide into self-assembled
decanthiol monolayers. Figure 6 shows an STM image
of a decanethiolate SAM after immersion in a C60
derivative solution for 1 h. The white protrusions in this
image are assigned as fullerenes, while the black holes
are etch pits that form during the self-assembly process
and correspond to a depth of one gold monolayer.11 These
protrusions are absent in pure decanethiolate SAMs.12a
Integration of the area under the curve of SAM 10 on
Au observed for the first reduction led to a surface
coverage of Γ of (0.833-1.149) × 10-10 mol cm-2 (140-
200 Å2 molecule-1, calculated from 100 and 200 mV/s scan
rate, respectively). The occupied area/molecule is some-
what larger than that of the hexagonal (78 Å2 molecule-1
)
or the simple square (98-100 Å2 molecule-1) packing in
similar C60 LB films.2n-q This is likely related to the steric
blockage by the alkoxy chains on the aromatic ring.
In solution, when C60 itself is reduced, it may surround
itself with charge-compensating cations. When the SAM
of fullerene-thiol derivative undergoes sequential reduc-
tion processes, only those portions of the monolayer that
can incorporate charge-compensating ions will be elec-
trochemically active. Mirkin et al.2r reported that the
coverage-dependent electrochemical responses of fuller-
ene- thiol are attributed to the relative amounts of free
volume available in the different types of films. In our
case, however, there is sufficient free volume in the full
monolayer to incorporate charge-compensation ions to
satisfy the requirements of the dianion formed upon
electrochemical reduction of the film because the lateral
soft alkoxy chains incorporated into the C60-thiol com-
pound do not pack into a solid-phase matrix.
(10) Kelly, K. F.; Sarkar, D.; Prato, S.; Resh, J . S.; Hale, G. D.; Halas,
N. J . J . Vac. Sci. Technol., B 1996, 14, 593. (b) Altman, E. I.; Colton,
R. J . Surf. Sci. 1992, 279, 49.
(11) Poirier, G. E.; Tarlov, M. J . Langmuir 1994, 10, 2853. (b)
Scho¨dnenberger, C.; Sondag-Huethorst, J . A. M.; J orritsma, J .; Fok-
kink, L. G. J . Langmuir 1994, 10, 612.
The SAMs of 10 were stable under repetitive cycling
in the reduction region up to -1.1 V vs Ag/AgCl.
4078 J . Org. Chem., Vol. 69, No. 12, 2004

Electrochemical Charging of a Monolayer on Au(111)
30.2, 29.52, 29.47, 29.3, 26.2, 26.0, 23.2, 22.7, 21.8, 18.7, 18.5,
14.1, 11.34, 11.26.
Anal. Calcd for C39H68O4Si‚0.5H2O: C, 73.41; H, 10.89.
Found: C, 73.17; H, 11.08.
The atomic lattice of the underlying decanethiolate
monolayer is clearly observed, demonstrating that the
lattice of the SAM is preserved after the insertion
process.12 The fullerene molecules were found to be bound
near the step edges. Presumably, these molecules are
physisorbed at grain boundaries in the decanethiol
lattice. Thus, the C60 derivative molecules prefer to insert
into a preformed decanethiol monolayer as small clusters
rather than individually.
The incorporation of lateral chains in 10 improved
solubility necessary to form uniform SAMs. Also, the
ideal first and second one-electron reduction for the gold
electrode with a full monolayer of fullerene derivative
was obtained because of the sufficient free volume
present at the modified surface. At the same time, the
surface coverage decreased because of steric hindrance
by the lateral alkoxy chains on the aromatic ring.
Com p ou n d 5. To a stirring solution of 4 (12 g, 18 mmol) in
300 mL of THF at 0 °C was slowly added 20 mL of TBAF (1.0
M solution in THF). After 1 h, several drops of water were
added and diluted with CH2Cl2. The organic phase was washed
with H2O (3×), dried over MgSO4, and concentrated. The crude
compound was purified by column chromatography (SiO2, 1:1
hexane/CH2Cl2) to give 5 (7.7 g, 84%) as a yellow liquid.
1H NMR (300 MHz, CDCl3): δ 7.18 (s, H), 6.96 (s, H), 5.71
(s, H), 4.04 (t, J ) 6.5 Hz, 2H), 3.92 (t, J ) 6.5 Hz, 2H), 3.72
(d, J ) 11 Hz, 2H), 3.65 (d, J ) 11 Hz, 2H), 3.26 (s, H), 1.78
(m, 4H), 1.45-1.31 (m, 23H), 0.89 (m, 6H), 0.80 (s, 3H).
13C NMR (75 MHz, CDCl3): δ 154.7, 149.6, 128.7, 117.6,
112.5, 111.4, 96.7, 81.0, 80.2, 77.8, 69.5, 69.3, 31.8, 30.2, 29.5,
29.2, 26.0, 25.9, 23.1, 22.6, 21.8, 18.1, 17.6, 14.1, 13.3, 12.2.
Anal. Calcd for C30H48O4‚1.5H2O: C, 72.1; H, 10.28. Found:
C, 72.29; H, 11.0.
Com p ou n d 6. To a solution of 5 (7.7 g, 15 mmol) and
iodoaniline (3.3 g, 15 mmol) in 250 mL of dry triethylamine
under argon atmosphere were quickly added catalyst PdCl2-
(PPh3)2 and CuI. The reaction mixture was stirred at room
temperature for 24 h and filtered. The concentrated solution
was purified by chromatography (SiO2, 1:1 hexane/CH2Cl2) to
afford 6 (5.4 g, 59%) as yellow crystals. Mp: 67-69 °C.
1H NMR (300 MHz, CD2Cl2): δ 7.34 (d, J ) 8 Hz, 2H), 7.17
(s, H), 6.97(s, H), 6.63 (t, J ) 8 Hz, 2H), 5.72 (s, H), 4.05 (t, J
) 6.5 Hz, 2H), 3.95 (t, J ) 6.5 Hz, 2H), 3.80 (s, 2H), 3.76 (d, J
) 11 Hz, 2H), 3.66 (t, J ) 11 Hz, 2H), 1.81 (m, 4H), 1.55-1.28
(m, 20H), 1.30 (s, 3H), 0.89 (m, 6H), 0.80 (s, 3H).
13C NMR (75 MHz, CD2Cl2): δ 153.9, 149.8, 146.5, 132.9,
127.5, 116.7, 114.6, 112.94, 111.6, 96.9, 94.3, 83.9, 77.8, 69.6,
69.3, 31.8, 31.5, 30.2, 29.42, 29.37, 29.27, 26.04, 26.01, 23.2,
22.6, 21.8, 14.1.
Anal. Calcd for C36H53NO4‚0.5H2O: C, 75.48; H, 9.5; N, 2.44.
Found: C, 75.59; H, 9.56; N, 2.49.
Com p ou n d 7. To a solution of 2-chloro-4,6-dimethoxy-1,3,5-
triazine (CDMT) (0.96 g, 5.5 mmol) and 12-bromododecanoic
acid (1.5 g, 5.5 mmol) in 150 mL of THF at 0 °C was added
dropwise 4-methylmorpholine (NMM) (0.55 g, 5.5 mmol). After
0.5 h, the white precipitate appeared. 6 (2.7 g, 4.5 mmol) was
added and stirring continued at room temperature for 3 h. The
concentrated solution was purified by chromatography (SiO2,
1:1 to 0:1 hexane/CH2Cl2) to afford 7 (3.59 g, 91%) as a yellow
gel.
1H NMR (400 MHz, CDCl3): δ 7.51 (d, J ) 9 Hz, 2H), 7.48
(d, J ) 9 Hz, 2H), 7.19 (s, H), 7.15 (s, H), 6.98 (s, H), 5.72 (s,
H), 4.06 (t, J ) 6.5 Hz, 2H), 3.95 (t, J ) 6.5 Hz, 2H), 3.76 (d,
J ) 11 Hz, 2H), 3.66 (d, J ) 11 Hz, 2H), 3.41 (t, J ) 6.5 Hz,
2H), 2.36 (t, J ) 7 Hz, 2H), 1.83 (m, 4H), 1.75 (m, 4H), 1.55-
1.29 (m, 34H), 1.33 (s, 3H), 0.89 (t, J ) 6.5 Hz, 3H), 0.87 (t, J
) 6.5 Hz, 3H), 0.80 (s, 3H).
Con clu sion s
A fullerene-thiol 10 dissolved easily in common or-
ganic solvents because of the presence of a lateral soft
alkoxy chain. Electrochemical measurements showed
that the surface-confined self-assembled monolayer of 10
exhibits ideal behavior (for the first and second one-
electron reductions) because the softly packed alkoxy
chains permit easy penetration of counterions into the
preformed monolayer. STM demonstrates a high coverage
of surface-confined fullerene-alkanethiol 10.
Exp er im en ta l Section
Grazing angle reflectance FTIR spectra were acquired using
p-polarized light at an incidence angle of 80°, equipped with
a liquid-nitrogen-cooled MCT/A detector. Typically, 512 scans
at a resolution of a 4 cm-1 were collected.
Cyclic voltammetry was performed using a conventional
three-electrode configuration, with a 3-mm-diameter glassy
carbon electrode or 1.6-mm-diameter modified Au electrode as
the working electrode and a platinum counter electrode and
Ag/AgCl as a pseudoreference. A glassy carbon electrode was
polished with alumina before being used. The gold electrode
was polished on the nylon disk with 1 µm diamond polish
slurry first and then with a microcloth disk with alumina
polish. STM measurements were performed with mechanically
cut Pt-Ir tips. Compounds 1-3 were prepared according to
previously reported procedures.13
Com p ou n d 4. A solution of aldehyde 3 (18 g, 33 mmol),
2,2-dimethylpropane-1,3-diol (6.9 g, 66 mmol), and p-TsOH
(200 mg) in benzene (300 mL) was heated to reflux for 24 h
using a Dean-Stark trap. After cooling, the solution was
washed with water, dried over MgSO4, and evaporated to
dryness to afford 4 (21 g, 96%) as a yellow liquid.
13C NMR (100 MHz, CDCl3): δ 171.4, 154.1, 149.8, 137.8,
132.3, 128.1, 119.5, 119.1, 116.8, 114.0, 111.5, 96.8, 93.2, 85.7,
77.8, 69.6, 69.3, 37.8, 34.1, 32.8, 31.8, 30.3, 29.4, 29.34, 29.31,
29.27, 29.25, 29.19, 28.7, 28.1, 26.02, 26.01, 25.5, 23.2, 22.65,
22.63, 21.8, 14.1.
Anal. Calcd for C48H74BrNO5: C, 69.88; H, 9.04; N, 1.69.
Found: C, 69.37; H, 8.82; N, 1.65. UV-vis (CH2Cl2): 306, 337,
400 (shoulder) nm.
1H NMR (300 MHz, CDCl3): δ 7.12 (s, H), 6.91 (s, H), 5.70
(s, H), 3.99 (t, J ) 6.5 Hz, 2H), 3.93 (t, J ) 6.5 Hz, 2H), 3.75
(d, J ) 11 Hz, 2H), 3.64 (d, J ) 11 Hz, 2H), 1.77 (m, 4H), 1.47
(m, 4H), 1.31 (m, 20H), 1.14 (s, 21H), 1.10 (s, 3H), 0.90 (t, J )
6.5 Hz, 3H), 0.89 (t, J ) 6.5 Hz, 3H), 0.79 (s, 3H).
13C NMR (75 MHz, CDCl3): δ 154.9, 149.5, 128.5, 117.6,
113.9, 110.9, 103.3, 96.9, 94.6, 77.8, 69.4, 69.1, 31.85, 31.78,
Com p ou n d 8. A mixture of 7 (2.5 g, 3.0 mmol) and CF3-
CO2H (40 mL) in 2:1 CH2Cl2/H2O (120 mL) was stirred at room
temperature for 5 h. The organic layer was then washed with
water (3×), dried over MgSO4, and evaporated to dryness.
Column chromatography (SiO2, CH2Cl2) gave 8 (1.9 g, 85%)
as a yellow solid. Mp: 66-67.5 °C.
(12) Bumm, L. A.; Arnold, J . J .; Cygan, M. T.; Dunbar, T. D.; Burgin,
T. P.; J ones, L., II; Allara, D. L.; Tour, J . M.; Weiss, P. S. Science 1996,
271, 1705. (b) Cygan, M. T.; Dunbar, T. D.; Arnold, J . J .; Bumm, L. A.;
Shedlock, N. F.; Burgin, T. P.; J ones, L., II; Allara, D. L.; Tour, J . M.;
Weiss, P. S. J . Am. Chem. Soc. 1998, 120, 2721. (c) Kelly, K. F.; Shom,
T.-S.; Lee, T. R.; Halas, N. J . J . Phys. Chem. B 1999, 103, 8639.
(13) Gu, T.; Nierengarten, J .-F. Tetrahedron Lett. 2001, 42, 3175.
1H NMR (300 MHz, CDCl3): δ 10.44 (s, H), 7.56 (d, J ) 9
Hz, 2H), 7.51 (d, J ) 9 Hz, 2H), 7.31 (s, H), 7.22 (s, H), 7.10 (s,
H), 4.06 (t, J ) 6.5 Hz, 2H), 4.04 (t, J ) 6.5 Hz, 2H), 3.14 (t,
J . Org. Chem, Vol. 69, No. 12, 2004 4079

Gu et al.
J ) 6.5 Hz, 2H), 2.37 (t, J ) 7 Hz, 2H), 1.88-1.73 (m, 8H),
1.53-1.29 (m, 34H), 0.89 (t, J ) 6.5 Hz, 3H), 0.87 (t, J ) 6.5
Hz, 3H).
N-H), 7.02 (s, 1H, Ar-H), 5.54 (s, 1H, -CH<), 4.97 (d, J ) 9
Hz, 1H, -CH2-N), 4.31 (d, J ) 9 Hz, 1H, -CH2-N), 4.16-
3.98 (m, 3H, -OCH2), 3.70 (m, 1H, -OCH2), 2.82 (s, 3H, -N-
CH3), 2.67 (t, J ) 7 Hz, 2H, SHCH2), 2.35 (t, J ) 7.5 Hz, 2H,
COCH2), 1.89-1.27 (m, 48H), 0.87 (m, 6H).
13C NMR (75 MHz, CDCl3): δ 171.4, 156.6, 155.0, 154.1,
153.8, 151.5, 147.3, 146.7, 146.6, 146.24, 146.20, 146.1, 145.9,
145.7, 145.5, 145.4, 145.3, 145.2, 145.1, 144.6, 144.5, 144.4,
144.3, 143.0, 142.6, 142.5, 142.3, 142.2, 142.0, 141.7, 141.6,
140.2, 140.1, 139.7, 139.4, 137.9, 136.4, 136.3, 136.1, 134.6,
132.3, 127.1, 119.3, 119.0, 116.0, 114.7, 113.2, 93.5, 85.6, 75.6,
70.0, 69.8, 69.2, 68.7, 68.0, 40.1, 39.2, 37.9, 31.9, 31.8, 29.7,
29.5, 29.4, 29.31, 29.28, 29.24, 29.16, 28.4, 26.1, 25.6, 25.5,
22.73, 22.66, 14.2, 14.1.
13C NMR (75 MHz, CDCl3): δ 189.2, 171.5, 155.6, 153.5,
138.5, 132.6, 124.6, 120.7, 119.2, 118.3, 117.2, 109.8, 97.2, 85.1,
69.3, 69.2, 37.8, 34.0, 32.8, 31.7, 29.34, 29.29, 29.25, 29.14,
29.10, 28.7, 28.1, 26.0, 25.5, 22.6, 14.1.
Anal. Calcd for C43H64BrNO4‚0.5H2O: C, 69.05; H, 8.75; N,
1.87. Found: C, 69.02; H, 8.9; N, 1.87.
F u ller en e-Alk yl Br om id e 9. A mixture of 8 (200 mg,
0.271 mmol), C60 (234 mg, 0.325 mmol), and N-methylglycine
(145 mg, 1.624 mmol) in toluene (250 mL) was heated to reflux
under Ar for 16 h. After cooling, the resulting solution was
filtered and concentrated. The crude compound was purified
by column chromatographies (SiO2, 1:1 hexane/CH2Cl2) and
preparative TLC (SiO2, 1:1 hexane/CH2Cl2) to give 9 (160 mg,
40%) as a brown-black solid. Mp: 154-155 °C.
FTIR (KBr, cm-1): 2922, 2851, 1664, 1593, 1516, 1495, 1463,
1410, 1242, 1201. UV-vis (CH2Cl2): 306, 334, 432, 706 nm.
P r ep a r a tion of SAM. The gold surface to which the
monolayer was attached was prepared on a Si wafer by
evaporation of Cr (ca. 80 Å), followed by Au (ca. 2000 Å). The
metal evaporation of gold was conducted at the Biomedical
Microsensor Laboratory at North Carolina State University.
The freshly prepared gold surfaces were washed sequentially
with 7:3 H2SO4/40% aqueous H2O2, copious amounts of Milli-
pore-filtered water, and absolute ethanol, before being dried
under a stream of Ar. Monolayers of fullerene derivatives were
prepared by allowing a freshly cleaned gold wafer to soak for
24 h at room temperature in the dark in 5 mL of dilute solution
of fullerene derivative in toluene that had been degassed by
bubbling with Ar for 15 min. The SAMs were rinsed sequen-
tially with toluene, absolute ethanol, water, and then again
with ethanol, before being dried under Ar just before the
experiment.
1H NMR (300 MHz, CDCl3): δ 7.58 (s, 1H, Ar-H), 7.50 (d, J
) 8 Hz, 2H, Ar-H), 7.45 (d, J ) 8 Hz, 2H, Ar-H), 7.19 (s, 1H,
Ar-H), 7.02 (s, 1H, Ar-H), 5.54 (s, 1H, -CH<), 4.97 (d, J ) 9
Hz, 1H, -CH2-N), 4.31 (d, J ) 9 Hz, 1H, -CH2-N), 4.17-
3.98 (m, 3H, -OCH2), 3.70 (m, 1H, -OCH2), 3.40 (t, J ) 7 Hz,
2H, BrCH2), 2.82 (s, 3H, -N-CH3), 2.35 (t, J ) 7.5 Hz, 2H,
COCH2), 1.89-1.28 (m, 48H), 0.87 (m, 6H).
13C NMR (75 MHz, CDCl3): δ 171.3, 156.5, 154.9, 154.0,
153.7, 151.4, 147.2, 146.7, 146.6, 146.15, 146.13, 146.08,
146.02, 146.01, 145.99, 145.96, 145.85, 145.6, 145.5, 145.4,
145.2, 145.1, 145.0, 144.50, 144.45, 144.37, 144.3, 142.94,
142.91, 142.6, 142.54, 142.45, 142.19, 142.16, 142.10, 142.07,
142.05, 142.02, 142.00, 141.9, 141.6, 141.5, 140.1, 140.0, 139.6,
139.3, 137.9, 136.4, 136.2, 136.0, 134.5, 132.2, 127.0, 119.2,
118.9, 116.0, 114.7, 113.1, 93.5, 85.6, 76.4, 75.5, 69.9, 69.7, 69.2,
68.6, 40.1, 37.8, 34.0, 32.7, 31.83, 31.77, 29.40, 29.38, 29.31,
29.27, 29.24, 29.20, 29.16, 28.7, 28.1, 26.01, 25.97, 25.5, 22.7,
22.6, 14.2, 14.1.
Ack n ow led gm en t. This work was supported by the
United States Department of Energy. The authors
gratefully acknowledge Matthew Lewis and Dr. Chris-
topher B. Gorman for assistance with the STM experi-
ments. Mass spectra were obtained at the Mass Spec-
trometry Laboratory for Biotechnology. Partial funding
for the facility was obtained from the North Carolina
Biotechnology Center and the National Science Founda-
tion.
HRMS: calcd for C105H69BrN2O3, 1485.4570; found, 1485.
4427. FTIR (KBr, cm-1): 2920, 2850, 1633, 1592, 1515, 1493,
1463, 1429, 1411, 1383, 1331, 1306, 1271, 1177, 1029. UV-
vis (CH2Cl2): 306, 331, 430, 704 nm.
F u ller en e-Alk a n eth iol 10. A stirred solution of 9 (40 mg,
0.027 mmol) in 10 mL of freshly distilled THF was cooled to
-10 °C, and hexamethyldisilathiane (6.8 µL, 0.032 mmol) and
TBAF (29 µL, 0.029 mmol) were added. The resulting reaction
mixture was allowed to warm to room temperature while being
stirred for 30 min. The mixture was then diluted with CH2Cl2
and washed with aqueous NH4Cl (saturated). The organic
phase was dried over MgSO4 and concentrated to afford 10
(30 mg, 78%) as a brown-black solid.
Su p p or t in g In for m a t ion Ava ila b le: 1H NMR and 13C
NMR spectra for all the new compounds. This material is
available free of charge via the Internet at http://pubs.acs.org.
1H NMR (300 MHz, CDCl3): δ 7.58 (s, 1H, Ar-H), 7.50 (d, J
) 8 Hz, 2H, Ar-H), 7.45 (d, J ) 8 Hz, 2H, Ar-H), 7.29 (s, 1H,
J O049939J
4080 J . Org. Chem., Vol. 69, No. 12, 2004