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      Second Generation Light-Driven Molecular Motors. Unidirectional Rotation Controlled by a Single Stereogenic Center with Near-Perfect Photoequilibria and Acceleration of the Speed of Rotation by Structural Modification

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          Abstract

          Nine new molecular motors, consisting of a 2,3-dihydro-2-methylnaphtho[2,1-b]thiopyran or 2,3-dihydro-3-methylphenanthrene upper part and a (thio)xanthene, 10,10-dimethylanthracene, or dibenzocycloheptene lower part, connected by a central double bond, were synthesized. A single stereogenic center, bearing a methyl substituent, is present in each of the motors. MOPAC93-AM1 calculations, NMR studies, and X-ray analysis revealed that these compounds have stable isomers with pseudoaxial orientation of the methyl substituent and less-stable isomers with pseudoequatorial orientation of the methyl substituent. The photochemical and thermal isomerization processes of the motors were studied by NMR and CD spectroscopy. The new molecular motors all show two cis-trans isomerizations upon irradiation, each followed by a thermal helix inversion, resulting in a 360 degrees rotation around the central double bond of the upper part with respect to the lower part. The direction of rotation is controlled by a single stereogenic center created by the methyl substituent at the upper part. The speed of rotation, governed by the two thermal steps, was adjusted to a great extent by structural modifications, with half-lives for the thermal isomerization steps ranging from t(1/2)(theta) 233-0.67 h. The photochemical conversions of two new motors proceeded with near-perfect photoequilibria of 1:99.

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          Author and article information

          Journal
          Journal of the American Chemical Society
          J. Am. Chem. Soc.
          American Chemical Society (ACS)
          0002-7863
          1520-5126
          May 2002
          May 2002
          : 124
          : 18
          : 5037-5051
          Article
          10.1021/ja012499i
          11982368
          390e3004-e233-46c0-9c65-cac40f0793fd
          © 2002
          History

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