Excimer Formation in Vinyl Polymers. I. Temperature Dependence in Fluid Solution

The fluorescence spectra of solutions of poly (2-vinyl naphthalene) in both fluid and glassy solvents have been studied at room temperature and at liquid-nitrogen temperature. Excimer emission was observed at all temperatures in glassy solution, but this emission is quenched at lower temperature in fluid solution. This behavior is interpreted in terms of excimer-forming main chain conformations which are of higher energy than the most favored conformation and maintain thermal equilibrium in fluid solution only. The temperature dependence of monomer chromophore emission in fluid solution is accurately fit with a kinetic model of intrachain excimer formation in which the chain conformer lifetime is limited by collision with solvent molecules. In n-propyl benzene solution, the energy barrier to excimer formation above the lowest-energy chain conformation was found to be 3608 cal/mole.