Fluorescence lifetimes and quantum yields of ten rhodamine derivatives: Structural effect on emission mechanism in different solvents

Abstract

To get consistent data for ten rhodamine dyes, the fluorescence lifetime, fluorescence quantum yield and spectral properties were measured under the same conditions in four typical solvents by using time-correlated single photon counting and steady state fluorometer. The comparable data make it possible to discuss the mechanism that controls the fluorescence properties of the rhodamine dyes. The data showed that the molecular structure and solvent have remarkable effects. The second alkyl and the rigidity of the alkyls on N atoms are the determining factors for fluorescence lifetime and quantum yields, whereas the substitution on phenyls has little influence. The increase of the solvent polarity decreases both the fluorescence lifetime and fluorescence quantum yield. These results support that the intra-molecular photoinduced electron transfer (PET) may occur from the xanthene moiety to the linked phenyl. The rate constant of radiation process, however, shows no dependence on both the chemical structure and solvents but a constant value (0.21×109s−1). The rate constant of nonradiation process, on the other hand, is varied with both the structure and the solvent used.