Dimerization and trimerization of rhodamine 6G in aqueous solution. Effect on the fluorescence quantum yield

Abstract

The trimerization equilibrium constant of rhodamine 6 G in aqueous solution as determined by absorption spectroscopy is higher than that of the dimer previously reported. Similarities observed between the absorption spectra of both aggregates are explained by exciton theory considering a sandwich structure for the aggregates. The lack of emission from the aggregates implies an important decrease in the fluorescence quantum yield of the dye, and the rate constant of the quenching produced by the dimer and trimer are calculated separately. The dominant mechanism for the quenching seems to be long-range energy transfer from the monomer to the aggregates, being affected by molecular diffusion as well as excitation energy migration between monomers.