How does an oxygen atom in the side chain affect the photophysical properties of alkoxy-substituted organopolysilane homopolymers and copolymers?

Alkoxy-substituted organopolysilane homopolymer (poly[SiMe(OR)]n) and random copolymers (poly[SiMe(OR)]m[SiMeR′]n were synthesized and the solvatochromism and thermochromism for their absorption and fluorescence spectra were examined. The band maxima shifted to longer wavelengths with an increase in the ratio of the alkoxy side chains; however, the influence of the solvent was very small. The thermochromic shifts are dependent on the number of alkoxy side chains. Molecular dynamics calculation showed that the conformation of the polysilanes was determined by the Coulomb interaction between the alkoxy side chains, and the conformations of the polyalkoxysilanes are similar to those of polyalkylsilanes (poly[SiRR′]n). Molecular orbital (MO) calculations manifested that the interaction between the orbitals of the oxygen atom in the side chain and those of the silicon atom in main chain (σ conjugation system) was larger in LUMO than in HOMO, and the decrease in LUMO energy shifted the absorption maxima to longer wavelength.