Photoluminescence of biphenyl-containing polymers

Poly(4-vinylbiphenyl) and copolymers of methyl methacrylate and 4-vinylbiphenyl show both monomeric (λ_max = 325 nm) and excimer (λ_max = 380 nm) fluorescence. The quantum yield of excimer emission increases and the monomeric emission decreases with increase in the fraction of vinylbiphenyl units in the copolymer. The decrease of the monomeric emission is closely related to a decrease in singlet lifetime. These results are interpreted in terms of a kinetic controlled excimer formation. Comparison of the emission in the homo and copolymers with that of the dimeric model compound shows that excimer formation in the polymer strongly depends upon the possibility of energy migration along sequences of vinylbiphenyl units. This conclusion is considered as of particular relevance due to the change in geometry of the biphenyl unit upon excitation.