INTRAMOLECULAR EXCIMER FORMATION AND ENERGY-TRANSFER IN ALTERNATING CARBAZOLE COPOLYMERS

Alternating copolymers of N-vinylcarbazole (VCz) with diethyl fumarate (DEF), maleic anhydride (MAn), and citraconic anhydride (CAn) (a-CzEF , a-CzMAn, and a-CzCAn, respectively) were synthesized. The fluorescen ce spectra of a-CzEF and a-CzCAn changed as a function of the monomer feed ratios although all the copolymers had nearly 50 mol % of VCz con tent (f(Cz)), indicating the presence of excimer-forming sites in the polymer chain. The copolymer obtained at f(Cz) = 0.5 in the monomer fe ed was found to be the most desirable ''alternating'' copolymer with t he highest fluorescence quantum yield. Comparison of the spectral feat ures for a-CzMAn and a-CzCAn showed that hindered groups on comonomers effectively restricted the excimeric interaction in copolymers. A sma ll number of anthryl energy traps were covalently incorporated into a- CzEF and a random copolymer of VCz and methyl methacrylate with f(Cz) = 0.5 (r-CzMMA(50)) by terpolymerization with 9-anthrylmethyl methacry late. Energy transfer to anthracene was more favorable in a-CzEF than in r-CzMMA(50). This result strongly suggests that longer-range energy transfer assisted by efficient energy migration is occurring in the a lternating copolymer, which may be due in part to the large Forster ra dius for carbazole-carbazole for self-transfer (approximately 2.1 nm).