Polarized Fluorescence and Absorption Spectra of Tetracene in p-Terphenyl

Abstract

Polarized absorption and fluorescence spectra of the 5000 Å ${}^1{B}_{\text{2u}}{\rightleftharpoons }^1{A}_{\text{1g}}$ transitions of tetracene (naphthacene) dissolved in p‐terphenyl have been measured at 4.2°K. The vibronic band‐widths are sufficiently sharp to permit resolution of a 3 cm⁻¹ site splitting and to enable assignments to be made of the 12 ground and excited state a_1g and several b_3g fundamentals between 300 and 1600 cm⁻¹. The phonon structures in absorption and fluorescence are characteristic of strong and weak electron—phonon coupling, respectively. A dependence of the structure in the tetracene fluorescence spectrum on the wavelength of the exciting light has been observed. It is shown that this wavelength dependence is the result of unusual crystal site relaxation processes which occur through electron—phonon coupling mechanisms.