Solvent Dependence of the Fluorescence Lifetimes of Xanthene Dyes

Abstract

Fluorescence lifetimes of Ave representative xanthene dye species-the rhodamine B zwitterion (RB=), the rhoda-mine B cation (RB+), the rhodamine 6G cation (R6G+), the rhodamine 101 zwitterion (R101) and the fluorescein dianion (F2-)-were measured in H2O, D2O and in a series of alcohol solvents ranging from methanol to octanol. The lifetimes of both RB= and RB+ increased markedly as the solvent was varied from water to octanol. In contrast, the lifetimes of R6G+ and R101± decreased slightly over the alcohol series and that of F2- increased only slightly in the same series. For all the dyes studied the fluorescence lifetimes observed in D2O were slightly longer than those in H2O. Possible causes for the variations observed are discussed.