Exciton-phonon interaction in crystalline phenanthrene

Abstract

The polarized optical absorption spectrum of the first exciton band (the first progression member of ¹A₁ exciton band) of crystalline phenanthrene has been measured in the temperature range 81 to 293 °K. The exciton‐phonon interaction is discussed using Toyozawa's theory. The lower energy tail of the first exciton absorption band is confirmed to be expressed by Urbach's rule with the modified steepness parameter σ′_a = 2.39 and σ′_b = 2.35. The half‐width of the first exciton band is also confirmed to change linearly with temperature. The value of the steepness parameter and the temperature dependence of the half‐width provide experimental evidences that the exciton‐phonon interaction in crystalline phenanthrene is weak. The degree of the interaction is compared with that in anthracene. The assignment of the shoulder absorption band located at the first exciton absorption tail is discussed.