Effect of coil collapse on photon-harvesting polymers with carbazole chromophores

Steady-state and time-dependent fluorescence measurements were made for copolymers with pendant carbazole chromophores as a function of polymer coil collapse induced by the addition of a nonsolvent. The results show that although the efficiency of electronic energy transport to a covalently bound trap increases with coil contraction, this increase is part of a complex chain of events, the most important being a decrease in donor quantum yield. It was found that classical excimer formation is small. for the polymers studied, while self-quenching is prevalent and competes for donor energy. The result is that, as the efficiency of energy transfer increases, the quantum yield and fluorescence lifetime of the donor decrease while the fluorescence intensity of the acceptor increases. It is quite likely that if self-quenching were eliminated, the efficiency of electronic energy transfer would approach unity for a small degree of coil collapse.