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

Dimethyl or diphenyl branched conjugated polycarbosilane oligomers in solut ions, including poly [[1,4-bis(thiophenyl)buta-1,3-diyne]-alt-(dimethylsila ne)1, poly[[1,4-bis(thiophenyl)buta-1,3-diyne]-alt-(diphenylsilane)I,poly [ [1,4-bis(phenyl)buta-1,3-diyne ne]-alt-(dimethylsilane)1:, and poly[[1,4-bi s(phenyl)buta-1,3-diyne]-alt silane)],were investigated by steady-state and :picosecond time-resolved spectroscopies to elucidate the effect of silicon -atom introduction into the pi-conjugated copolymer backbone and the substi tution of the aromatic phenyl group on the silicon atom. The introduction o f silicon atoms into pi-conjugated copolymer backbones induces slow decay e mission components with lifetimes of about 450 ps in addition to pi-pi* loc al excited-state relaxations in the time-resolved fluorescence decay profil es. The diphenyls, which are branched in the silicon atoms, bring about bro ad, structureless emission bands in the low-frequency region of the steady- state fluorescence spectra. However, such broad bands do not occur in the c ase of dimethyl branched conjugated polycarbosilane oligomers. The time-res olved and solvent-dependent studies of these bands imply that the excited-s tate dynamics of diphenyl branched conjugated polycarbosilane oligomers can be related to an intramolecular charge-transfer dynamics through an induct ive and (d-p) pi-conjugation effect between the pi-conjugated backbone and the branched phenyl ring. (C) 1999 John Wiley & Sons, Inc.