J. Am. Chem. Soc. 2000, 122, 5411-5412

5411

The Molecular Abacus: STM Manipulation ofCyclodextrin Necklace
Hidemi Shigekawa,*,†,‡ Koji Miyake,† Jun Sumaoka,‡
Akira Harada,§ and Makoto Komiyama*,‡
Institute of Applied Physics and CREST
Japan Science and Technology Corporation (JST)
UniVersity of Tsukuba, Tsukuba, Ibaraki 305-8573, Japan
Department of Chemistry and Biotechnology
Research Center for AdVanced Science and Technology
The UniVersity Tokyo, Komaba, Tokyo 153-8904, Japan
Department of Chemistry, Graduate School of Science
Osaka UniVersity, Toyonaka, Osaka, 560-0043, Japan
ReceiVed January 3, 2000
Preparation of molecular devices has been one of the most
attractive goals for scientists.1-3 A number of nanostructured
supramolecular assemblies have been proposed heretofore. Amongthem, “molecular shuttles”, which travel back and forth onmolecular rails, are particularly promising.1-9 These molecular
shuttles can store molecular information in terms of shuttleposition. Applications to molecular machines have also beenproposed. However, the following problems remain to besolved: (1) how to initiate and terminate shuttle movement at apredetermined time, (2) how to control the direction of themovement, and (3) how to read the shuttle position.
Since Eigler’s pioneering research,10,11 the scanning tunnelingmicroscope (STM) 12 and atomic force microscope (AFM) havebeen recognized as two of the most powerful tools for theactuation of atoms and molecules.13-15 The possibility of developing a molecular counting-device was demonstrated by repositioning C60 molecules along the steps of a Cu metal surface.16 Thesefindings have spurred us toward STM manipulation of themolecular necklace of cyclodextrin (CyD) 17 (Figure 1) to develop
a “molecular abacus” which fulfills the above-mentioned criteria,* Corresponding authors. E-mail: hidemi@ims.tsukuba.ac.jp. http://dora.ims.tsukuba.ac.jp. E-mail: mkomi@chembio.t.u-tokyo.ac.jp.
† Institute of Applied Physics and CREST, Japan Science and Technology
Corporation (JST).
‡ The University of Tokyo.
§Osaka University.
(1) Lehn, J.-M. Supramolecular Chemistry; VCH: Weinheim, 1995.
(2) (a) Nepogodiev, S. A.; Stoddart, J. F. Chem. ReV. 1998, 98, 19591976. (b) Balzani, V.; Gómez-López, M.; Stoddart, J. F. Acc. Chem. Res.
1998, 31, 405-414. (c) Raymo, F. M.; Stoddart, J. F. Chem. ReV. 1999, 99,1643-1663.
(3) Sauvage, J.-P. Acc. Chem. Res. 1998, 31, 611-619.
(4) Anelli, P. L.; Spencer, N.; Stoddart, J. F. J. Am. Chem. Soc. 1991, 113,5131-5133.
(5) Ashton, P. R.; Philp, D.; Spencer, N.; Stoddart, J. F. J. Chem. Soc.,
Chem. Commun. 1992, 1124-1128.
(6) Benniston, A. C.; Harriman, A. Angew. Chem. 1993, 105, 1553-1555.
(7) Bissell, R. A.; Cordova, E.; Kaifer, A. E.; Stoddart, J. F. Nature 1994,369 133-136.
(8) Gibson, H. W. Large Ring Molecules; Semlyen, J. A., Ed.; Wiley:
Chichester, 1996; p 191.
(9) Murakami, H.; Kawabuchi, A.; Kotoo, K.; Kunitake, M.; Nakashima,
N. J. Am. Chem. Soc. 1997, 119, 7605-7606.
(10) Eigler, D. M.; Shewizer, E. K. Nature 1990, 344, 524-526.
(11) Eigler, D. M.; Lutz, C. P.; Rudge, W. E. Nature 1991, 352, 600603.
(12) (a) Binnig, G.; Rohre, H.; Gerber, Ch.; Weibel, E. Phys. ReV. Lett.
1982, 49, 57-61. (b) Binnig, G.; Rohre, H.; Gerber, Ch.; Weibel, E. Phys.
ReV. Lett. 1983, 50, 120-123. (c) Binnig, G.; Quate, C. F.; Gerber, Ch. Phys.
ReV. Lett. 1986, 56, 930-933.
(13) Jung, T. A.; Schlittler, R. R.; Gimzewski, J. K.; Tang, H.; Joachim,C. Science 1996, 271, 181-184.
(14) Wada, Y. Surf. Sci. 1997, 386, 265-278.
(15) Shen, T. C.; Wang, C.; Abeln, G. C.; Tucker, J. R.; Lyding, J. W.;
Avouris, Ph.; Walkup, R. E. Science 1995, 268, 1590-1592.
(16) Cuberes, M. T.; Schlittler, R. R.; Gimzewski, J. K. Appl. Phys. Lett.
1996, 69, 3016-3018.
(17) (a) Harada, A.; Li, J.; Kamachi, M. Nature 1992, 356, 325-327. (b)Harada, A.; Li, J.; Kamachi, M. Nature 1994, 370, 126-128.

Figure 1. (a) Structure of the “molecular necklace”, and three modes(b, c, and d) of the shuttle manipulation by STM.

Figure 2. A typical STM image of the molecular necklace (a) and its
schematic structure (b).

1-3. Here, we demonstrate that the selected R-CyD molecule(s)in this polyrotaxane is reversibly shuttled using a STM. All
manipulation is carried out under ambient conditions, since theR-CyD molecules are noncovalently bound to poly(ethyleneglycol) (PEG).
The specimens for STM were prepared by dripping aqueous
solution of the 1µM molecular necklace dissolved in 0.1 N NaOH
onto freshly cleaved MoS2, followed by evaporating the liquid
under ambient conditions. The concentration of the material wassufficiently diluted for the molecular necklace to be observed
independently, and the molecular necklaces were formed following the procedure in ref 17.
Figure 2a shows a typical STM image of the molecular necklace
on a MoS2 substrate (sample bias voltage +200 mV, tunnelingcurrent 900 pA, and a Pt/Ir tip). Regularly aligned R-CyDs areclearly observed. As schematically shown in Figure 2b, the main
chain of PEG runs along the surface of the substrate, and theR-CyDs lie with their longitudinal axis parallel to the surface.
The rotaxane structure of the molecular necklace has been clearly

10.1021/ja000037j CCC: $19.00 © 2000 American Chemical Society
Published on Web 05/20/2000

5412 J. Am. Chem. Soc., Vol. 122, No. 22, 2000

Communications to the Editor

Figure 4. STM images of the pair-shuttling (Figure 1c).

Figure 3. STM images of the simple-shuttling (Figure 1b).

visualized on an atomic scale. It is noteworthy that stable imaging
was accomplished at room temperature in air.18
First, one of the R-CyDs in the molecular necklace wasmechanically pushed by the STM tip along the main chain ofPEG, as has been performed previously to manipulate atoms/
molecules on the surface of the substrate.10,11,13-16,19 An exampleof the shuttling is shown in Figure 3. The images were acquired
before and after each manipulation, respectively. As designed,
the target R-CyD (designated by the yellow arrow in Figure 3a)
moved by the tip-sweep from right to left (compare images aand b in Figure 3). Since the PEG chain is railed diagonal in thiscase, the target R-CyD stably moved by 2.4 nm in the direction
along the chain. This is the first observation of ring-component
manipulation along the chain of an interlocked molecule. All theother R-CyDs retained their initial positions. Upon moving thetip in the reverse direction, the R-CyD retraced its path andreturned to its original position (image c). Thus, the shuttling of
one R-CyD could be stably repeated. There is no requirement
for a specific surface structure on the substrate for guiding theshuttle in a prescribed manner.
It was also possible to move a pair of R-CyDs simultaneously(Figure 4). The two R-CyDs, being adjacent to each other in themolecular necklace, were reversibly manipulated while keeping
their mutual conformation intact. Furthermore, the main axis of
the molecular necklace could be bent with the tip by pushing it
laterally in the perpendicular direction (Figure 5). A hook-shape(18) This is partially because the structure of R-CyD fairly matches withthe lattice of MoS2: Miyake, K.; Aiso, Y.; Komiyama, M.; Harada, A.;
Kamachi, M.; Shigekawa, H. Jpn. J. Appl. Phys. 1994, 33, 3720-3722.
(19) For the manipulation, the interaction between the STM tip and thetarget molecule(s) was adjusted first by changing the sample bias voltage andthe tunneling current. In the cases of this paper, they were changed from thestable measurement condition (+200 mV, 900 pA) to the manipulation mode(-200 mV, 700 pA). Then, the tip was swept in the designed direction using
the constant height mode, and pushed the R-CyD molecule(s).

Figure 5. STM images of the bending (Figure 1d).

is shown to be formed by this synchronized repositioning ofseveral R-CyDs. Even this drastic transformation was stablyreproduceable.
In previous actuations of atoms and molecules using a STM
or an AFM, strictly controlled conditions (ultrahigh vacuum, lowtemperature (e.g., liquid He), or specifically structured substrates)
were required. However, the present manipulation of R-CyDs isstable in air at room temperature, mainly due to the characteristic
structure of the polyrotaxane. The system can be further advanced
by combining the three modes of transformation and also byattaching functional groups (e.g., photoresponsive or redox-activegroups) to CyDs; this is currently being attempted. The presentfinding will be a milestone in the development of moleculardevices, which are the ultimate devices in terms of large-scale
integration.
Acknowledgment. This work was supported by the Grants-in-Aidfor Scientific Research from the Ministry of Education, Science, andCulture, Japan.

JA000037J