Molecular Rotor of Cs 2 ([18]crown-6) 3 in the Solid State Coupled with the Magnetism of [Ni(dmit) 2 ] Tomoyuki Akutagawa,* ,†,‡,¶ Kozo Shitagami, ‡ Sadafumi Nishihara, ‡ Sadamu Takeda, ⊥ Tatsuo Hasegawa, †, ‡ Takayoshi Nakamura,* ,†,‡,¶ Yuko Hosokoshi, | Katsuya Inoue, | Satoshi Ikeuchi, § Yuji Miyazaki, § and Kazuya Saito § Contribution from the Research Institute for Electronic Science, Hokkaido UniVersity, Sapporo 060-0812, Japan, Graduate School of EnVironmental Earth Science, Hokkaido UniVersity, Sapporo 060-0810, Japan, CREST, Japan Science and Technology Corporation (JST), Kawaguchi 332-0012, Japan, Graduate School of Science, Hokkaido UniVersity, Sapporo 060-0810, Japan, Institute for Molecular Science, Okazaki 444-8585, Japan, and Research Center for Molecular Thermodynamics, Graduate School of Science, Osaka UniVersity, Toyonaka, Osaka 560-0043, Japan Received October 26, 2004; E-mail: takuta@imd.es.hokudai.ac.jp (T.A.); tnaka@imd.es.hokudai.ac.jp (T.N.) Abstract: Nanoscale molecular rotors that can be driven in the solid state have been realized in Cs2([18]- crown-6)3[Ni(dmit)2]2 crystals. To provide interactions between the molecular motion of the rotor and the electronic system, [Ni(dmit)2] - ions, which bear one S ) 1 /2 spin on each molecule, were introduced into the crystal. Rotation of the [18]crown-6 molecules within a Cs2([18]crown-6)3 supramolecule above 220 K was confirmed using X-ray diffraction, NMR, and specific heat measurements. Strong correlations were observed between the magnetic behavior of the [Ni(dmit)2] - ions and molecular rotation. Furthermore, braking of the molecular rotation within the crystal was achieved by the application of hydrostatic pressure. Introduction Molecular motors serve as important nanoscale molecular machines for energy conversion and in the transport of substances in biological systems. 1,2 Biological molecular ma- chines, such as ATPase in cell membranes, actin/myosin in muscles, and kinesin motor on microtubes, yield significantly high energy conversion efficiencies of up to nearly 100%. 1,3-5 In these biological machines, the energy needed to operate the nanoscale motors is supplied chemically from a nonequilibrium energy gradient under thermal fluctuations within the limits of the second law of thermodynamics. 2 With energy conversion efficiencies comparable to those of highly efficient biological motors, artificial molecular motors can be utilized for nanoscale electronic devices such as quantum electronic pumps and quantum ratchets. 6,7 Adiabatic unidirec- tional molecular rotors can be applied to novel energy conver- sion systems that can extract kinetic energy via Maxwell’s demon within the second law of thermodynamics. 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