Ordered Helices in Chiral $\sigma$-conjugated Polysilanes

Molecular modeling of studies of poly[(S)-2-methylalkyl($n$-alkyl$'$)]silanes identify a tacticity insensitive steric packing constraint that underlies the existence of highly ordered helices in these polymers. Thus this family of polymers is dominated by extended repeating sequences of the D+/g-g- (main chain deviant, side chain gauche/gauche) conformational isomer. Solid-state films of poly[(S)-2-methylbutyl(nonyl)]silane have been studied by optical spectroscopy. Sharp photoabsorption and photoluminescence peaks are observed at both ambient and reduced temperatures. The observed photoabsorption and photoluminescence spectra are interpreted using H{\" u}ckel molecular orbital theory.