Excimer formation in vinyl polymers. III. Fluid and rigid solutions of poly(4-vinylbiphenyl)

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Abstract
Excimer formation has been examined in fluid and rigid solutions of poly(4-vinylbiphenyl) (PVBP) over the temperature range 373–77°K. The concentration of suitable excimer-forming sites is fixed by the temperature at which the film is cast. A statistical model for the excimer-forming site fraction was previously developed for poly(2-vinylnaphthalene) (P2VN) and is now shown to satisfactorily fit the PVBP data, using the excimer site conformation energy of 800 cal. Furthermore, as was previously demonstrated for P2VN and polystyrene (PS), excimer sampling in the rigid solution is shown to arise from an activated exciton migration to preformed excimer sites. The proposed mechanism for this process involves a modulation of interchromophore separation resulting from longitudinal acoustical vibrations of the polymer chain. An effective vibrational frequency for this process has been determined to be 150±30 cm−1 for PVBP. Finally, excimer sampling mechanisms for fluid and rigid solutions are compared in terms of qualitative potential energy concepts.