High pressure studies of the effect of viscosity on fluorescence efficiency in crystal violet and auramine O

Abstract

The dependence of the fluorescence efficiency of the dyes crystal violet and auramine O on solvent viscosity at room temperature has been investigated using pressure to alter the viscosity. Pressures to 11 kbar on four polar solvents were utilized to obtain a 5 order of magnitude viscosity range. We confirm the η^2/3 dependence of fluorescence intensity on viscosity shown for crystal violet by Förster and Hoffman [T.H. Förster and G. Hoffman, Z. Physik. Chem. NF, 75, 63(1971)] and observe the same dependence for auramine O over a smaller range of viscosities with a large deviation at low viscosity. The effect of increasing solvent viscosity on the peak shift and half‐width change is briefly discussed in terms of a configuration coordinate model.