POLAR INTERACTION-INDUCED NEW PHYSICAL PROPERTIES OF POLYSILANES

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Polar polysilanes with general formula of {R-Si-R'}_n, where R and/or R' represents alkyl, aryl or ethereal groups such as -(CH_2)_3-O-(CH_2CH_2O)_m-R, m=0-3, -(CH_2)_3-O-Ph, -(CH_2)_4-O-C_3H_7, (CH_2)_5-O-C_2H_5, and -(CH_2)_6-O-CH_3, were prepared by wutz-type coupling reaction of the corresponding dichlorosilanes. Most of the prepared polysilanes became soluble in polar solvents such as THF, CH_3CN and alcohols. Polysilanes with oligo-ethereal side groups were found to be water-soluble and show diverse polar interaction with polar solvents as well as ionic species. The first solvatochromism was observed for polysilanes of [CH_3-Si-(CH_2)_3-O-(CH_2CH_2O)_m-R (m=0-3) ; they show continuous red shift by decreasing the polarity of solvent. Unusual discontinuous type of solvatochromism was also found for poly(bis(4-propoxybutyl) silane and analogues when they make strong hydrogen bonding with hexafluoro-2-propanol. The polar side groups in the polysilanes were found to yield ionic complex with LiClO_4 in the solid state. Thermochromic behavior of theses complexes was highly dependent on the ratio of Li/Si ; red-shift was induced on cooling when the Li/Si was small while blue-shift was induced when the ratio was >4. Thermochromic behavior of the above polar polysilanes were compared with the hydrogen bond induced solvatochromism and found that there were no direct similarity between these polar-interaction induced chromotropisms. As the extension of the research, a new cooling rate dependent thermochromism was found for many polydialkylsilanes.