Thioflavin T as a molecular rotor: fluorescent properties of thioflavin T in solvents with different viscosity.

TLDR: The photophysical model successfully explains the fluorescent properties of ThT in solvents with different viscosities and supports the idea that the reason for the characteristic increase in the ThT fluorescence intensity accompanying its incorporation into the amyloid fibrils is determined by the rigidity of the dye environment.

Abstract: The effect of solvent viscosity on thioflavin T (ThT) fluorescent properties is analyzed to understand the molecular mechanisms of the characteristic increase in ThT fluorescence intensity accompanying its incorporation into the amyloid-like fibrils. To this end, the dependencies of the ThT quantum yield and fluorescence lifetime on temperature and glycerol content in the water−glycerol mixtures are studied. It has been found that fluorescent properties of ThT are typical for the specific class of fluorophores known as molecular rotors. It has been established that the low ThT fluorescence intensity in the solvents with low viscosity is caused by the nonradiative deactivation of the excited state associated with the torsional motion of the ThT benzthiazole and aminobenzene rings relative to each other, which results in the transition of ThT molecule to nonfluorescent twisted internal charge transfer (TICT) state. The rate of this process is determined by the solvent viscosity, whereas the emission does oc...