Fluorescent properties of 8-phenylBODIPY in ethanol - ethylene glycol mixed solutions.

Fluorescent characteristics of two BODIPY dyes in solutions were investigated under the viscosity variations. Investigated dyes differ in the nature of 8-substituent of ligand molecule. Viscosity variation was achieved by changing of solvent composition in the binary system ethanol - ethylene glycol and solvent temperature. 8-Phenyl substituted BODIPY is found to exhibit properties of molecular rotor, i.e. its fluorescent characteristics are highly dependent on the viscosity or rigidity of the microenvironment. Increased temperature leads to a linear decrease of fluorescence parameters unlike the solvent composition variation where fluorescence change is nonlinear. The highest specific change in the fluorescence was observed in pure ethanol. Change in the nonradiative decay rate constant values with the increasing of viscosity indicates that the analyzed phenyl substituted complex is a true molecular rotor. Investigated 8-phenylBODIPY could be recommended as promising viscosity sensor in different organic media.