C O M M U N I C A T I O N S
(18) Smith, J.; Jindrˇich, J.; Cˇ astul´ık, J.; Kottas, G.; Schwab, P.; Trujillo, M.;
Rubio, S.; Brotin, T.; Michl, J., unpublished results.
(19) Kabalka, G. W.; Namboodiri, V.; Wang, L. Chem. Commun. 2001, 775.
(20) Miyaura, N.; Suzuki, A. Chem. ReV. 1995, 95, 2457.
(21) Brotin, T.; Posp´ısˇil, L.; Fiedler, J.; King, B. T.; Michl, J. J. Phys. Chem.
B 1998, 102, 10062.
It would be interesting to drive the rotator flipping of 2 on
Au(111) at microwave frequencies. According to molecular dynam-
ics runs31 for B conformers, an alternating electric field perpen-
dicular to the surface will induce unidirectional rotation in the MMP
and, to a smaller degree, MPM isomers and random flipping in the
MMM isomer. The directionality is due to the asymmetry of the
(22) Posp´ısˇil, L.; Varaksa, N.; Magnera, T. F.; Brotin, T.; Noll, B. C.; Michl,
J., unpublished.
rotational potential about the direction of the surface normal.43
A
(23) BLYP, def-SV(P) basis set, with ECP-60-MWB for Hg, using the RI
approximation: Eichkorn, K.; Weigend, F.; Treutler, O.; Ahlrichs, R.
Chem. Phys. Lett. 1995, 242, 652. TURBOMOLE program suite, http://
(24) Below -80 °C, a weak broad signal appears at somewhat lower δ values,
presumably due to a minor diastereomer. 1H and 13C spectra do not change
down to -110 °C.
(25) Almenningen, A.; Bastiansen, O.; Fernholt, L.; Cyvin, B. N.; Cyving, S.
J.; Samdal, S. J. Mol. Struct. 1985, 128, 59.
(26) Substrates were either purchased from Molecular Imaging, Inc., or prepared
by thermal evaporation of gold at 1 Å/s on mica that had been heated to
350 °C at 5 × 10-7 Torr for at least 2 h. The film was then heated to 450
°C for 30 min, allowed to cool under vacuum, and annealed with a
hydrogen flame immediately before use. STM imaging showed large
terraces of Au(111).
typical run for the MMP form (90 GHz, 3 × 109 V/m, 300 K) can
be viewed by clicking on Figure 1B in the web edition. At low
temperatures, 2 is calculated to behave as an approximately critically
damped single-molecule parametric oscillator. The choice of electric
field frequency and amplitude dictates the frequency of the net
unidirectional rotation of its rotator, from zero to synchronous with
1
the field, with intermediate subharmonic steps (1/2, /4). At room
temperature, stereoisomer interconversion will be rapid, and the
average behavior of each rotor molecule will be bidirectional.
In summary, we have fabricated and characterized surface-
mounted altitudinal rotors 1 and 2 on gold and have provided
evidence that at room temperature the flipping of the rotator in a
fraction of rotors 2 is subject to a small enough barrier to occur
spontaneously and to be controllable by the electric field of an STM
tip. In the MMP (and PPM) and, to a small degree, the MPM (and
PMP) stereoisomers, unidirectional rotation is predicted in alternat-
ing electric field.
(27) Rudolph Research AutoEL instrument.
(28) QCM100, Stanford Research Systems, simultaneously monitored the
frequency and resistance changes of the crystal as the rotors were deposited
from a ∼10-6 M solution onto a 5 MHz, 1” diameter, AT-cut quartz crystal
with a polished gold surface.
(29) A Physical Electronics model 5800 XPS spectrometer with a hemispherical
analyzer, a resistive multichannel detector, and a monochromatic Al KR
line (1486.6 eV) X-ray source was used. Survey scans from 10 to 1000
eV were acquired with a pass energy of 187.5 eV in steps of 0.8 eV.
Higher resolution spectra of Co, F, Hg, and S were obtained with a pass
energy of 23.5 eV in steps of 0.1 eV and confirmed the presence of the
elements expected for each sample. An attempt is underway to determine
the abundance of bound and unbound thioether sulfur atoms, the degree
of oxidation, and the likely role of Hg atoms in surface adhesion.
(30) Imaged at room temperature with Nanoscope 3a, Digital Instruments, Inc.,
under hexadecane unless noted otherwise.
Acknowledgment. This paper is dedicated to Prof. Rudolf
Zahradn´ık on the occasion of his 75th anniversary. The work was
supported by the U.S. Army Research Office (DAAD19-01-1-0521).
D.H. thanks the Alexander von Humboldt Foundation for a Feodor
Lynen fellowship. The authors are grateful to Profs. C. P. Kubiak
and M. Lieberman for stimulating discussions.
(31) The TINK molecular dynamics program,2 based largely on the MOIL 6.2
code: Elber, R.; Roitberg, A.; Simmerling, C.; Goldstein, R.; Li, H.;
Verkhiver, G.; Keasar, C.; Zhang, J.; Ulitsky, A. Comput. Phys. Commun.
1994, 91, 159, uses the UFF energy function: Rappe, A. K.; Casewit, C.
J.; Colwell, K. S.; Goddard, W. A., III; Skiff, W. M. J. Am. Chem. Soc.
1992, 114, 10024. Interaction with the metal surface has been modeled
by bonds to selected Au atoms, all of which are fixed, and adding image
charges as in: Okuno, Y.; Yokoyama, T.; Yokoyama, S.; Kamikado, T.;
Mashiko, S. J. Am. Chem. Soc. 2002, 124, 7218. Electronic friction due
to the motion of the image charges within the metal (Tomassone, M. S.;
Widom, A. Phys. ReV. B 1997, 56, 4938) has been treated by Langevin
dynamics (van Gunsteren, W. F.; Berendsen, H. J. C. Mol. Phys. 1982,
45, 637), with an integrator based on: Paterlini, M. G.; Ferguson, D. M.
Chem. Phys. 1998, 236, 243.
Supporting Information Available: Details of synthesis and STM
images of 2 and 10 on Au(111) (PDF). This material is available free
References
(1) Tailored crystals are now being designed: Godinez, C. E.; Zepeda, G.;
Garcia-Garibay, M. A. J. Am. Chem. Soc. 2002, 124, 4701.
(2) Vacek, J.; Michl, J. New J. Chem. 1997, 21, 1259.
(3) Gimzewski, J. K.; Joachim, C.; Schlitter, R. R.; Langlais, V.; Tang, H.;
Johannsen, I. Science 1998, 281, 531.
(4) Hersam, M. C.; Guisinger, N. P.; Lyding, J. W. Nanotechnology 2000,
11, 70.
(5) Yasuda, R.; Noji, H.; Kinosita, K., Jr.; Yoshida, M. Cell 1998, 93, 1117.
Yasuda, R.; Noji, H.; Kinosita, K., Jr.; Itoh, H. Nature 2001, 410, 898.
(6) Vacek, J.; Michl, J. Proc. Natl. Acad. Sci. U.S.A. 2001, 98, 5481.
(7) Clarke, L. I.; Horinek, D.; Kottas, G. S.; Varaska, N.; Magnera, T. F.;
Hinderer, T. P.; Horansky, R. D.; Michl, J.; Price, J. C. Nanotechnology
2002, 13, 533.
(8) Jian, H.; Tour, J. M. J. Org. Chem. 2003, 68, 5091.
(9) Horinek, D.; Michl, J. J. Am. Chem. Soc. 2003, 125, 11900.
(10) Kelly, T. R.; Tellitu, I.; Sestelo, J. P. Angew. Chem., Int. Ed. Engl. 1997,
36, 1866. Kelly, T. R.; Silva, R. A.; De Silva, H.; Jasmin, S.; Zhao, Y. J.
Am. Chem. Soc. 2000, 122, 6935.
(11) Koumura, N.; Zijlstra, R. W. J.; van Delden, R. A.; Harada, N.; Feringa,
B. L. Nature 1999, 401, 152. Koumura, N. L.; Geertsema, E. M.; van
Gelder, M. B.; Meetsma, A.; Feringa, B. L. J. Am. Chem. Soc. 2002,
124, 5037. Leigh, D. A.; Wong, J. K. Y.; Dehez, F.; Zerbetto, F. Nature
2003, 424, 174.
(12) Tinkertoy is a trademark of Playskool, Inc., Pawtucket, RI 02862, and
designates a toy construction set of wooden sticks insertable into
connectors.
(13) Kaszynski, P.; Michl, J. J. Am. Chem. Soc. 1988, 110, 5225.
(14) Michl, J.; Kaszynski, P.; Friedli, A. C.; Murthy, G. S.; Yang, H.-C.;
Robinson, R. E.; McMurdie, N. D.; Kim, T. In Strain and Its Implications
in Organic Chemistry; de Meijere, A., Blechert, S., Eds.; NATO ASI
Series, Vol. 273; Kluwer Academic Publishers: Dordrecht, The Nether-
lands, 1989; p 463.
(32) Varaksa, N.; Posp´ısˇil, L.; Magnera, T. F.; Michl, J. Proc. Natl. Acad. Sci.
U.S.A. 2002, 99, 5012.
(33) Harrick, N. Internal Reflection Spectroscopy; John Wiley & Sons: New
York, 1967. Mulcahy, M.; Berets, S.; Milosevic, M.; Michl, J. J. Phys.
Chem. B 2004, 108, 1519.
(34) Glass microscope slides with 20 nm of Ti and 200 nm of Au, deposited
by thermal evaporation.
(35) Pearce, H. A.; Sheppard, N. Surf. Sci. 1976, 59, 205.
(36) tan2 R ) [Iiso(a)/IAu(a)]/[sin2 φIiso(b)/IAu(b)].
(37) Vibrations of a symmetry (ν/cm-1: 1014, 1229, 1259), and b symmetry
(ν/cm-1, φexp/deg, φcalcd/deg: 1273, 49, 24; 1150, 48, 43; 1091, 44, 71;
1072, 66, 60; 1047, 51, 82).
(38) Michl, J.; Thulstrup, E. W. Spectroscopy with Polarized Light. Solute
Alignment by Photoselection, in Liquid Crystals, Polymers, and Mem-
branes; VCH Publishers: Deerfield Beach, FL, 1995.
(39) Akiyama, R.; Matsumoto, T.; Kawai, T. Phys. ReV. B 2000, 62, 2034.
(40) Sakai, A. In AdVances in Materials Reasearch: AdVances in Scanning
Probe Microscopy; Sakurai, T., Watanabe, Y., Eds.; Springer-Verlag: New
York, 2000; p 143. Hasegawa, Y.; Jia, J. F.; Sakurai, T.; Li, Z. Q.; Ohno,
K.; Kawazoe, Y. In AdVances in Materials Reasearch: AdVances in
Scanning Probe Microscopy; Sakurai, T., Watanabe, Y., Eds.; Springer-
Verlag: New York, 2000; p 167.
(41) Differential BHI at 5 kHz 0.2 Å vertical modulation of the tip position
with lock-in detection and interleaved scanning with alternating polarity.
(42) At room temperature, thioether sulfur atoms are likely to move from one
to another Au atom with fair frequency. Even the much more strongly
attached thiols diffuse readily on the Au surface: Barrena, E.; Ocal, C.;
Salmeron, M. J. Chem. Phys. 1999, 111, 9797.
(43) For calculated induction of unidirectional rotation of a segment of a chiral
molecule by a linearly polarized laser pulse, see: Hoki, K.; Yamaki, M.;
Koseki, S.; Fujimura, Y. J. Chem. Phys. 2003, 118, 497; 2003, 119, 12393.
In our case, chirality is present but is not required.
(15) Kaszynski, P.; Friedli, A. C.; Michl, J. J. Am. Chem. Soc. 1992, 114,
601.
(16) Rausch, M. D.; Genetti, R. A. J. Org. Chem. 1970, 35, 3888.
(17) Harrison, R. M.; Brotin, T.; Noll, B. C.; Michl, J. Organometallics 1997,
16, 3401.
JA039482F
9
4542 J. AM. CHEM. SOC. VOL. 126, NO. 14, 2004