Temperature and ViscosityDependence of the NonradiativeDecay Rates of Auramine-O and Thioflavin-T in Glass-FormingSolvents.

Both auramine-O (AuO) and thioflavin-T (ThT) behave asfluorescentmolecular rotors, meaning that their (non)radiative properties aremarkedly affected by the intramolecular rotation of the molecule.In this article, steady-state and time-resolved fluorescence of AuOand ThT were measured in three alcohols, 1-propanol, 1-butanol, and1-pentanol, over a wide range of temperatures (86–260 K). Thesesolvents are glass-forming liquids, and their viscosity and dielectricrelaxation time increase by more than 10 orders of magnitude as thetemperature is lowered from room temperature to ?100 K. Accordingly,the fluorescence nonradiative rates constants of AuO and ThT in thesesolvents decrease by about 3 orders of magnitude at the latter temperaturerange. We found very good correspondence between the temperature dependenceof the nonradiative rate constant, knr, of both molecules and the dielectric relaxation rate of the solvents.The knrvalues of AuO are twice thoseof ThT along the whole temperature range. The temperature dependenceof knris consistent with the nonradiativemodel suggested by Glasbeek and co-workers.(1) [ABSTRACT FROM AUTHOR]