Time-Resolved Observation of Chiral-Index-Selective Wrapping on Single-Walled Carbon Nanotube with Non-Aromatic Polysilane

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• 作者：Woojung Chung ; Kazuyuki Nobusawa ; Hironari Kamikubo ; Mikio Kataoka ; Michiya Fujiki ; Masanobu Naito
• 刊名：The Journal of the American Chemical Society
• 出版年：2013
• 出版时间：February 13, 2013
• 年：2013
• 卷：135
• 期：6
• 页码：2374-2383
• 全文大小：619K
• 年卷期：v.135,no.6(February 13, 2013)
• ISSN：1520-5126

文摘

In the present paper, we ascertain two novel findings on chiral-index-selective binding/separating of single-walled carbon nanotubes (SWNTs) with a nonaromatic polymer, poly(dialkylsilane) (PSi). PSi is a typical 蟽-conjugated polymer, composed of alkyl side chains attached to the silicon (Si)-catenated main chain. First, PSi鈥檚 with linear alkyl side chains showed significant diameter-selective wrapping for SWNTs with ca. 0.9 nm in diameter, resulting in the selective separation of (7,6) and (9,4) SWNTs. Its driving force was demonstrated to be cooperative CH鈭捪€ interactions among the alkyl side chains of PSi鈥檚 and the curved graphene of SWNTs. Second, the dynamic wrapping behavior of PSi鈥檚 onto SWNTs was elucidated with time-resolved UV spectroscopy. Highly anisotropic UV absorption of PSi along the Si main chain was utilized as a 鈥渃hromophoric indicator鈥?to monitor the global/local conformations, which enabled us to track kinetic structural changes of PSi鈥檚 on SWNTs. Consequently, we concluded that upon wrapping, flexible/helical PSi with an average dihedral angle (蠁) of 145掳 and Kuhn鈥檚 segment length (位^鈥?) of 2.6 nm interconverted to the more stiffer/planar conformation with 170掳 and 位^鈥? of 7.4 nm. Furthermore, through kinetic analyses of the time-course UV spectra, we discovered the fact that PSi鈥檚 involve three distinct structural changes during wrapping. That is, (i) the very fast adsorption of several segments within dead time of mixing (<30 ms), following (ii) the gradual adsorption of loosely wrapped segments with the half-maximum values (蟿₁) of 31.4 ms, and (iii) the slow rearrangement of the entire chains with 蟿₂ of 123.1 ms, coupling with elongation of the segment lengths. The present results may be useful for rational design of polymers toward chiral-index-selective binding/separating of desired (n,m) SWNTs.