Helical Shape Memory of Screw-Sense Switchable Polysilanes in Cast Films Akihiro Ohira, † Masashi Kunitake,* ,‡,§ Michiya Fujiki,* ,†,§ Masanobu Naito, † and Anubhav Saxena †,§ Graduate School of Materials Science, Nara Institute of Science and Technology, 8916-5, Takayama, Ikoma, Nara 630-0101, Japan, Department of Applied Chemistry and Biochemistry, Kumamoto University, 2-39-1 Kurokami, Kumamoto 860-8555, Japan, and CREST-JST, 4-1-8 Hon-cho, Kawaguchi, Saitama 332-0012, Japan Received March 16, 2004. Revised Manuscript Received June 18, 2004 The optically active poly[{(R)-3,7-dimethyloctyl-(S)-3-methylpentylsilane}-co-{decylisobutyl- silane}](PS-1) underwent a thermodriven helix-helix transition at 13 °C in isooctane. The casting of polymer solution from the pre- and post-transition temperatures led to P (right- handed) or M (left-handed) helical films, which gave positive and negative Cotton circular dichroism (CD) signals, respectively. This result suggests that the helical sense of PS-1 below and above transition temperature in the homogeneous solution was memorized in the cast films. Furthermore, the CD spectra of P- and M-helical films were mirror images to each other at 319 nm, indicating the 7 3 helical pitch of the polymers with opposite helical sense. Introduction Recently, a precise control over the optical activity of chiral polymers and supramolecules has received much attention because of its widespread applications in mat- erial science. 1 Among these, synthetic helical polymers exhibit many unique phenomena, for example, photo- isomerization and chiroptical amplification, 2 formation of thermotropic cholesteric liquid crystals, 3 molecular chirality recognition, 4 and helix-helix (P-M) transi- tion. 4-13 Especially, the P-M transition phenomenon, which involves reversible switching between the P (plus, right-handed) and M (minus, left-handed) screw-sense segments along the helical backbone, has attracted much interest in chiroptical materials. 4-13 The molecule- based chiroptical properties, such as memorizing and switching of helicity using the P-M transition phenom- enon in helical polymers, may have potential applica- tions in data storage, optical devices, chromatographic chiral separation, and liquid crystals for display. 14 The P-M transition phenomenon in solution was vir- tually unknown three decades ago, except in synthetic DNA 5 by changing in salt concentration (B-Z transi- tion), and in synthetic polypeptide 6 by varying the tem- perature. 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Mater. 2004, 16, 3919-3923 10.1021/cm0495616 CCC: $27.50 © 2004 American Chemical Society Published on Web 09/08/2004