DEPENDENCE OF THE INTRAMOLECULAR ELECTRONIC-ENERGY TRANSFER IN BICHROMOPHORIC MOLECULES ON THE INTERCHROMOPHORE BRIDGE

Results are presented on the intramolecular electronic energy transfer (intra-EET) in bichromophoric molecules of the type benzene-alpha-dik etone, in which the interchromophore bridge contains methyl substituen ts beta to the alpha-dicarbonyl acceptor chromophore. These results sh ow that singlet-singlet intra-EET is independent of substitution and c an be explained by a model assuming Dexter-type short-range exchange i nteraction. For singlet-triplet and triplet-triplet transfer, there ar e indications that the phosphorescence yield of the acceptor is larger than that for non-substituted bichromophoric molecules. This can be e xplained by through-bond interaction promoting EET via a long-range su perexchange mechanism, by variations in the non-radiative decay of the triplet state of the acceptor or by chemical reaction.