Picosecond spectroscopic measurement of a solvent dependent change of rotational diffusion rotor shape

摘要

The rotational diffusion behavior of cresyl violet is observed to be solvent dependent, producing an induced orientational anisotropy function with single exponential decays in both ethylene glycol at 26thinsp;deg;C and 1hyphen;dodecanol at 37thinsp;deg;C, but a twohyphen;component decay in 1hyphen;dodecanol at 26thinsp;deg;C. It is clear from this data that cresyl violet is experiencing significant changes in its local solvation environment. Without knowledge of the orientation of the transition moment within the molecule, however, the interpretation of these results is ambiguous. A simple calculation is presented which allows for the estimation of the intramolecular orientation of the transition moment, thereby removing ambiguity from the interpretation. The observed behavior is shown to be consistent with cresyl violet reorienting as an oblate rotor in ethylene glycol and 1hyphen;dodecanol at 37thinsp;deg;C, and as a prolate rotor in 1hyphen;dodecanol at 26thinsp;deg;C.