Excimer formation in vinyl polymers. II. Rigid solutions of poly(2-vinylnaphthalene) and polystyrene

Excimer formation has been examined in solid films of poly(2-vinylnaphthalene) (P2VN) and polystyrene (PS) as a function of sample temperature from 373 to 4.2°K and film preparation temperature between 373 and 295°K. The concentration of suitable excimer forming sites in the solid state is fixed by the temperature at which the film is cast. A statistical model based on the rotational isomeric state approximation is used to formulate an expression for the fraction of excimer forming sites in the solid systems. This model makes use of the excimer site conformation energy, found to be 2500 cal for P2VN. Excimer sampling in solid solution is shown to be consistent with an activated exciton migration to preformed excimer sites. The mechanism for this process is attributed to a modulation of interchromophore separation resulting from longitudinal acoustical vibrations of the polymer chain. A semianalytical expression for the enhancement of the excitation migration is developed which has the same general form as the experimental results. The effective vibrational frequency is found to be 157 cm−1 for PS and 84 cm−1 for P2VN.