Thermal Effect and Quenching of Exciplex Fluorescence of Polystyrene Derivatives by Dimethyl Terephthalate in Solid Films

The effects of added dimethyl terephthalate to the fluorescence emission of poly(4-ethoxystyrene), poly(4-methoxystyrene), poly(4-methoxy α-methyl styrene) and poly(4-methoxyphenyl-styrene) were studied in solid films and in dichloromethane solution. A quenching of the excimer emission was accompanied with the appearance of a strong exciplex emission in solid films. In dichloromethane solution, only quenching of the excimer emission was noticed, but no exciplex emission was detected. Increase in the temperature of solutions or solid films of these polymers caused a decrease in the intensity of exciplex and an increase in the polymer emissions. This thermal effect was attributed to the thermal distraction of the formed exciplex chromophores that can enhance excimer emission. The thermostability of these polymers depends on electronic nature of substituent and their ability to stabilize radicals forming on chain scission. A kinetic model is proposed to account for these observations concerning the singlet excited state of polymers. The activation energies of intermolecular exciplex formation were calculated.