EFFECT OF COIL COLLAPSE ON PHOTON-HARVESTING POLYMERS WITH CARBAZOLE CHROMOPHORES

Steady-state and time-dependent fluorescence measurements were made fo r copolymers with pendant carbazole chromophores as a function of poly mer 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 decre ase in donor quantum yield. It was found that classical excimer format ion is small. for the polymers studied, while self-quenching is preval ent and competes for donor energy. The result is that, as the efficien cy of energy transfer increases, the quantum yield and fluorescence li fetime of the donor decrease while the fluorescence intensity of the a cceptor increases. It is quite likely that if self-quenching were elim inated, the efficiency of electronic energy transfer would approach un ity for a small degree of coil collapse.