Intramolecular Excitation Energy Transfer in Bichromophoric Compounds in Stretched Polymer Films

Abstract

Intramolecular excitation energy transfer has been investigated with bichromophoric compounds in which naphthalene and anthracene as donor (D) and acceptor (A), respectively, are linked through a methylene chain, i.e., 9-anthryl-(CH2)n-1-naphthyl (AnN) with n = 1, 3, and 6 methylene units as spacer. The respective compounds were dispersed in stretched PVA films with the expectation that the methylene chain takes preferred conformations elongated in the direction of stretching polymer films so that the D−A distances are determined by the methylene chain length. From analyses of picosecond time-resolved fluorescence spectra and the fluorescence decay kinetics, it has been found that the energy transfer rates show a systematic change depending on the number of the methylene chain units: 47.6 × 1010 s-1 in A1N, 1.96 × 1010 s-1 in A3N, and 0.15 × 1010 s-1 in A6N at 10 K. These changes in the energy transfer rate are basically consistent with the theoretical estimation based on the Forster's mechanism, with so...