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

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Abstract
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 26 °C and 1-dodecanol at 37 °C, but a two-component decay in 1-dodecanol at 26 °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 1-dodecanol at 37 °C, and as a prolate rotor in 1-dodecanol at 26 °C.