INTRA-MOLECULAR EXCIMER FORMATION IN MACROMOLECULES .3. ENERGY MIGRATION AND EXCIMER FORMATION IN COPOLYMERS OF VINYLNAPHTHALENE AND METHYL ACRYLATE

Energy migration and intramolecular excimer formation have been examined in copolymers of 1-vinylnaphthalene and methyl acrylate. The degree of depolarization of fluorescence, p-1 from glassy solutions of the copolymers in 2-methyltetrahydrofuran at 77 K was used to characterize the extent of intramolecular energy migration which is described by the mean sequence length of naphthalene chromophores, ln. The proportionality of the ratio of excimer to monomer intensities of emission to the function ln·fnn implies that the excimer site concentration is proportional to the fraction of naphthalene pairs, fnn, in the copolymer. The same function has been shown previously to describe intramolecular excimer formation in 1-vinylnaphthalene/methyl methacrylate and other copolymers [20, 21]. Comparison of the data pertinent to the methyl acrylate copolymers with those of the methyl methacrylate series shows that (a) there is no evidence for long range intramolecular excimer formation in copolymers of vinylaromatic chromophores even in the relatively flexible methyl acrylate series; (b) intramolecular excimer formation, occurs more readily in the less sterically constrained methyl acrylate series consequent upon the fact that rotation into the excimer conformation will be less restricted and that (c) energy migration is more extensive in the methyl acrylate copolymers. It has been demonstrated that comparison of excimer formation efficiency in different copolymer systems is more meaningful when a common value of the function descriptive of the formation is used as opposed to a common chromophore concentration. Reactivity ratios of 1-vinylnaphthalene and methyl acrylate were determined as 1.18 and 0.39 respectively. © 1979.