exhibits the spontaneous formation of one-dimensional arrays,
which are expected to play a dominant role in future nanoelec-
tronics. A new type of interfacial redox reaction accompany
electron-transfer can be performed without decomposition of the
nanoparticles by the redox-active dendron functionality, such as
DA2–SH. Our findings provide a general approach to tuning the
surface properties of metal nanoparticles by using redox-active
dendrons possessing various abilities. Further work is currently in
progress in this and related areas.
This work was supported in part by the Grant-in-Aid for
Scientific Research on Priority Areas (No. 17036067 ‘‘Chemistry of
Coordination Space’’) from the Ministry of Education, Science,
Sports and Culture, Japan.
Notes and references
1 (a) G. Schmid, Clusters and Colloids, VCH, Weinheim, 1994; (b)
D. L. Feldheim and C. A. Foss, Jr., Metal Nanoparticles, Marcel
Dekker, Inc., New York, 2002; (c) G. Schmid, Nanoparticles, Wiley-
VCH, Weinheim, 2004; (d) C. N. R. Rao, A. Muller and
A. K. Cheetham, The Chemistry of Nanomaterials, Wiley-VCH,
Weinheim, 2004, vol. 1.
2 M. Tamura and H. Fujihara, J. Am. Chem. Soc., 2003, 125, 15742.
3 (a) R. M. Crooks, B. I. Lemon, III and Y. M. Zhao, in Dendrimers III,
ed. F. Vogtle, Springer, Berlin, 2001, pp. 81–135; (b) K. Esumi, in
Colloid Chemistry II, ed. M. Antonietti, Springer, Berlin, 2003,
pp. 31–52.
Fig. 4 The FT-IR spectra of (a) the phenothiazine sulfoxide of DA2–Au
and (b) DA2–Au.
4 V. Chechik and R. M. Crooks, Langmuir, 1999, 15, 6364.
5 R. Wang, J. Yang, Z. Zheng, M. D. Carducci, J. Jiao and S. Seraphin,
Angew. Chem., Int. Ed., 2001, 40, 549.
6 (a) M.-K. Kim, Y.-M. Jeon, W. S. Jeon, H.-J. Kim, S. G. Hong,
C. G. Park and K. Kim, Chem. Commun., 2001, 667; (b) S. Nakao,
K. Torigoe, K. Kon-No and T. Yonezawa, J. Phys. Chem. B, 2002, 106,
12097.
7 (a) A. C. Templeton, W. P. Wuelfing and R. W. Murray, Acc. Chem.
Res., 2000, 33, 27; (b) M. Brust, M. Walker, D. Bethell, D. J. Schiffrin
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I. Vezmar and R. L. Whetten, J. Phys. Chem. B, 1997, 101, 3706.
9 (a) The particle size and distribution of DA2–Au were determined from
another domain in the same TEM grid (Electronic Supplementary
Information, Figure S1{); (b) The TEM image at lower magnification of
DA2–Au is shown in Figure S2 of Electronic Supplementary
Information{.
10 A similar result was recently reported for gold nanoparticles modified
with Fre´chet-type poly(phenyl ether)dendrons having an arylthiol group
at the focal point (ref. 6b).
11 The cyclic voltammogram (CV) of the gold nanoparticles in CH2Cl2 +
0.1 M Bu4NPF6 at a glassy carbon electrode showed the reversible redox
wave at the following potential (E1/2 vs. Ag/0.1 M AgNO3): +0.52 V for
D1–Au and DA1–Au, +0.46 V for D2–Au and DA2–Au.
12 (a) H. J. Shine, in Organic Free Radicals, ed. W. A. Pryor, Am. Chem.
Soc., Washington, 1978, ch. 22; (b) E. Bosch and J. K. Kochi, J. Chem.
Soc., Perkin Trans. 1, 1995, 1057.
13 Similar decomposition (desorption) was observed in the self-assembled
monolayers (SAMs) with a phenothiazine–thiol (M–SH as shown in
Fig. 1) on a gold electrode by treatment with NOBF4, i.e., the CV of the
M–SH–SAMs on a gold electrode showed the reversible redox peak at
+0.48 V, however the redox peak disappeared after treatment with
NOBF4.
14 (a) The reaction of octanethiol-stabilized gold nanoparticles with
NOBF4 in CH2Cl2–CH3CN resulted in the decomposition of the
nanoparticles; (b) The one-electron oxidant mediated decomposition of
the gold core has not been reported. We propose that the NO+ oxidant
may attack the gold surface of the particles. Mechanistic studies on its
decomposition are in progress.
Fig. 5 TEM micrograph of the phenothiazine sulfoxide of DA2–Au.
sulfoxide of DA2–Au which was characterized by FT-IR spectro-
scopy and TEM measurement. The FT-IR spectrum of the
phenothiazine sulfoxide of DA2–Au exhibited the SLO stretching
vibration at 1025 cm21 (Fig. 4). The TEM micrograph revealed
the formation of dispersed particles with a diameter of 1.5 ¡
0.3 nm (Fig. 5), but the stripe structure was not observed in the
phenothiazine sulfoxide of DA2–Au. These findings indicate that
DA2–Au did not undergo decomposition of the gold nanoparticles
upon treatment with NOBF4. The interfacial one-electron
oxidation accompanying the electron-transfer pathway of the
redox-active site at the periphery of the gold nanoparticles has
been accomplished without decomponsition of the nanoparticles
by using our new type of redox-active dendron. These results may
open a new route for the control of surface reactions on metal
nanoparticles.
In summary, the particle size and shape, and the reactivity of the
redox-active dendron-modified gold nanoparticles are greatly
affected by the dendron generation and the difference in the alkyl
chain length of the thiol at the focal point. Particularly, DA2–Au
304 | Chem. Commun., 2006, 302–304
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