Energy transfer from rhodamine 6G to thionine in an anionic microemulsion

The transfer of electronic excitation energy from rhodamine 6G as an energy donor to thionine as an acceptor has been studied in anionic microemulsion by the method of fluorescence quenching and sensitization. The concentrations of both donor and acceptor used in this study are quite high, in the range of 10−3 M. Both radiative and nonradiative processes have been taken into account, with the major contribution coming from the nonradiative path. An energy transfer efficiency up to 50% has been observed, and the rate constant of the nonradiative energy transfer from rhodamine 6G to monomeric thionine is 5 × 1011 M−1 s−1. This indicates that the nonradiative energy transfer belongs to the long-range Forster-type of dipole–dipole interaction. The results also show why the efficiency of a photogalvanic cell based on the thionine–iron system in anionic microemulsion is enhanced by the incorporation of an auxiliary absorber.