INTRAMOLECULAR ENERGY-TRANSFER IN POLYESTERS AND MODEL COMPOUNDS CONTAINING ANTHRACENE AND NAPHTHALENE GROUPS SEPARATED BY METHYLENE AND OXYETHYLENE SPACERS

Steady state fluorescence has been used to study the efficiency of nonradiative singlet energy transfer for naphthalene --> naphthalene and naphthalene --> anthracene for polyesters and their bichromophoric model compounds. Polyesters containing only naphthalene groups were derived from 2,6-naphthalene dicarboxylic acid as the rigid unit, and two series of glycols, HO-(CH2)(m)-OH and HO-(CH2CH2O)(n)-OH, where m = 2-6 and n = 1-4, as flexible spacers. Bichromophoric model compounds were derived from 2-naphthoic acid and the same glycols. In order to study the transfer for naphthalene --> anthracene, a first attempt was made by studying bichromophoric model compounds D-(CH2)(m)-A, where D and A denote 2-naphthoate (donor) and 9-anthranoate (acceptor) groups, respectively. The fluorescence anisotropy measurements in a solid matrix of glassy poly(methyl methacrylate), for the compounds containing only naphthalene groups, and the simple excitation and emission spectra, for the compounds containing naphthalene and anthracene groups, clearly demonstrate the presence of non-radiative singlet-singlet energy transfer, the efficiency of which depends mainly on m (or n). A theoretical treatment using the rotational isomeric state model of the conformation of these molecules has also been performed. The combination of the experiments and the theoretical analysis establishes that the Forster radii are 1.2 and 1.4 nm for the naphthalene --> naphthalene transfer in the bichromophoric model compounds and polyesters, respectively, and 1.6 +/- 0.2 nm for the naphthalene --> anthracene transfer in the model compounds studied.