Precise control of optical properties and global conformations by marked substituent effects in poly(alkyl(methoxyphenyl)silane) homo- and copolymers

A series of poly(alkyl(methoxyphenyl)silane) homopolymers and poly [(alkyl( methoxyphenyl)silane)-co-((S)-2-methylbutyl(methoxyphenyl)silane)I copolyme rs containing 20%. chiral monomer units were synthesized, and marked substi tuent effects on their absorption characteristics and the global and local conformations in THF solution were observed. In the homopolymers, upon incr ease of the alkyl side chain length, the global backbone conformations chan ged from a considerably shrunken random coil to a stiff extended structure, and the UV absorptivity and absorption wavelength maximum in the Si main c hain region were easily controlled by a combination of the alkyl substituen ts and position of the methoxy group on the phenyl ring. In the achiral-chi ral copolymers, preferential screw-sense helical conformations of the Si ba ckbone were induced by the cooperative effect of the chiral substituents. I n addition, we found that the sign of the circular dichroism (CD) peak in t he aryl absorption region of the copolymers depended on the methoxy group p osition in chiral monomer units.