Vibronic Spin–Orbit Interaction in the Phosphorescence Spectrum of Phenazine

Abstract

The polarization of the phosphorescence spectrum (PS) of phenazine in 3‐methylpentane and EPA as solvents was measured. If the strong 0, 0 band, which was negative polarized, is disregarded, the other bands are found about equally positive and negative polarized. This indicates the presence of a rather strong in‐plane component of the emitting oscillator. The Raman and infrared spectra and a sharp PS of phenazine in n‐heptane as a solvent were recorded. A vibrational analysis of these spectra was performed and the results compared with the polarization of the PS of phenazine in 3‐methylpentane and EPA. All negative‐polarized lines of the PS could be assigned to Raman frequencies and all positive‐polarized lines to infrared modes. The presence of the positive‐polarized lines (out‐of‐plane modes) of appreciable intensity indicated rather strong vibronic spin–orbit (SO) coupling (second‐order perturbations) in phenazine. The possible coupling schemes could be: $$S_{\mathrm{(\pi ,\pi *)}}\leftrightarrow {\displaystyle {lim}^{\mathrm{SO}}}{T}_{\mathrm{(n,\pi *)}}\mathrm{or}{T}_{\mathrm{(\sigma ,\pi *)}}\leftrightarrow {\displaystyle {lim}^{\mathrm{OP\; vibr}}}{T}_{\mathrm{(\pi ,\pi *)}}$$ or, $$S_{\mathrm{(\pi ,\pi *)}}\leftrightarrow {\displaystyle {lim}^{\mathrm{OP\; vibr}}}{S}_{\mathrm{(n,\pi *)}}\mathrm{or}{S}_{\mathrm{(\sigma ,\pi *)}}\leftrightarrow {\displaystyle {lim}^{\mathrm{SO}}}{T}_{\mathrm{(\pi ,\pi *)}}.$$ Both coupling schemes involve out‐of‐plane vibrations (OP vibr).