Excited-State dynamics of conjugated polycarbosilane oligomers with branched dimethyl or diphenyl group

Abstract

Dimethyl or diphenyl branched conjugated polycarbosilane oligomers in solutions, including poly((1,4-bis(thiophenyl)buta-1,3-diyne)-alt-(dimethylsilane)), poly- ((1,4-bis(thiophenyl)buta-1,3-diyne)-alt-(diphenylsilane)),poly((1,4-bis(phenyl)buta- 1,3-diyne)-alt-(dimethylsilane)), and poly((1,4-bis(phenyl)buta-1,3-diyne)-alt-(diphenyl- silane)), were investigated by steady-state and picosecond time-resolved spectroscopies to elucidate the effect of silicon-atom introduction into the p-conjugated copolymer backbone and the substitution of the aromatic phenyl group on the silicon atom. The introduction of silicon atoms into p-conjugated copolymer backbones induces slow decay emission components with lifetimes of about 450 ps in addition to p-p* local excited- state relaxations in the time-resolved fluorescence decay profiles. The diphenyls, which are branched in the silicon atoms, bring about broad, structureless emission bands in the low-frequency region of the steady-state fluorescence spectra. However, such broad bands do not occur in the case of dimethyl branched conjugated polycarbosilane oli- gomers. The time-resolved and solvent-dependent studies of these bands imply that the excited-state dynamics of diphenyl branched conjugated polycarbosilane oligomers can be related to an intramolecular charge-transfer dynamics through an inductive and (d-p) p-conjugation effect between the p-conjugated backbone and the branched phenyl ring. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2901-2908, 1999