Temperature-Dependent Rotational Dynamics of a Polar Probe in Non-Polar Aprotic Solvents: Interplay of Solvent Viscosity and Size Effect.

Rotational dynamics of 3-(benzo[d]thiazol-2-yl)-7-(diethylamino)-2 H-chromen-2-one (3BT7D2H-one) probe in non-polar aprotic 1,4 dioxane, toluene and cyclohexane solvents of different and comparable viscosity are studied with varying temperature using steady-state and fluorescence depolarization technique. The experimental reorientation time is compared with the hydrodynamic Stoke's-Einstein-Debye(SED). The experimentally measured rotational reorientation times are higher in 1,4 dioxane attributed to its solvent viscosity. In cyclohexane, the solute rotational dynamics behavior shows a transition from sub-slip to SED slip boundary conditions with varying temperatures. Solvent viscosity, size, and subtle changes in the molecular shape of solute play an important role in the rotational dynamics of polar probes in non-polar aprotic solvents.