Fluorescence polarization theory for asymmetric rotors: Rotational dynamics in the regular and statistical limits

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Abstract
Classical and quantum theories of ensemble averaged fluorescence polarization are presented for the asymmetric rotor in the regular, rigid rotor limit and in the limit of statistical vibration–rotation energy transfer in the isolated molecule. Planar asymmetric rotors are explored in detail, with special emphasis on p-difluorobenzene and pyrimidine. The classical polarizations are nearly identical to the quantum results, but are 1000 times faster to calculate. For nearly all molecular geometries, our results predict the transition from regular to statistical rotational motion will sharply reduce the fluorescence polarization, signaling the onset of intramolecular vibration–rotation energy transfer.