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Resonant transfer is an important mode of energy migration and occurs if the excited states of a donor molecule lie above or at the level ofthosein the acceptor.There are several treatments [1-3] of the theory for ensembles of interacting dipoles, but theoretical calculation of transport coefficients for particular cases is difficult because the final formulas contain constants of the compounds that are often not known. Also, there may be competing processes. Theoretical transfer coefficients are usually less than the observed ones, which is ascribed to ordered dipole arrays and to participation of migration via the solvent or via donor molecules [4-6].This paper continues our studies [7-12] of concentration quenching and serves to extend the concept of absence of specific quenching from resonant transfer between identical molecules to resonant transfer between other molecules. We have also derived the transfer coefficient as a function of the mean distance between donor and acceptor, and we describe experiments on migration via donor molecules.We used compounds very stable to light and having extensive overlap between donor emission and acceptor absorption. The donors were 3-methoxybenzanthrone (3-MB) and rhodamine 6G, while the aeceptors were rhodamine 6G, rhodamine C, and rose bengal. The solvents were ethanol, glycerol, and melaminep-toluenesulfamide-formaldehyde resin (MPTSF).

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