Polarization of the Luminescence of Phenanthrene

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Abstract
The polarization of the luminescence emitted when a randomly oriented array of phenanthrene molecules is excited with polarized light is discussed. Considerable attention is devoted to various correction methods in an effort to establish a correct zero‐polarization base line. The polarization of the fluorescence excitation spectrum, the fluorescence spectrum and the phosphorescence spectrum of phenanthrene have been determined. The polarization of the fluorescence spectrum validates Platt's assignment of the first four singlet electronic states of phenanthrene as 1Lb, 1La, 1Bb, and 1Cb in order of increasing energy. The possible occurrence of one or two other electronic states in the same energy interval, as suggested by Zimmermann and Joop, is discussed. The phosphorescence emission is primarily polarized out of plane. The results further suggest that either two perturbing singlet states are mixed into the lowest triplet state, or that two perturbing triplet states are mixed into the singlet ground state by spin‐orbital coupling; the Platt assignment of 3La for the lowest triplet state is supported. It has been found that polarization measurements are of considerable help in vibrational analysis, and may in certain cases uniquely determine vibrational types. A vibrational analysis of the fluorescence spectrum, phosphorescence spectrum and 1Lb absorption band is presented.