PHOTOPHYSICS OF 10-SUBSTITUTED POLY(2-(9-ANTHRYL)ETHYL METHACRYLATES)

The emission spectra of a series of 10-substituted poly(2-(9-anthryl) ethyl methacrylates) have been studied in solution, frozen glass, and thin films. Excimer fluorescence contributes at least 50% of the observed emission in all homopolymers. Bulky substituents decrease interaction between adjacent and nonadjacent chromophores, thereby reducing self-quenching and increasing the quantum yield of fluorescence. At least two distinct types of excimers could be observed: those formed from interactions of adjacent chromophores and interactions of nonadjacent chromophores at folds or loops in the polymer chain. The contribution of these excimers was found to be dependent on the solvent and the molecular weight of the polymer. Delayed fluorescence spectra indicate that triplet energy migration occurs through the polymer chain until a low- energy trap, e.g., a preformed excimer site, is encountered. The number of traps decreases as the steric bulk of the substituent increases. The lack of monomer fluorescence in the thin films of the homopolymer is indicative of singlet energy migration in the polymers. Strong excimer emission observed from frozen 2-methyltetrahydrofuran glass results from singlet energy migration to an excimer-forming site. A kinetic model for fluorescence quenching by nitromethane is proposed. © 1990, American Chemical Society. All rights reserved.