Polarization of the fluorescence of picene and dibenz[ a,h]anthracene

Abstract

The polarizations of the fluorescence and the fluorescence excitation spectra of picene and dibenz[ a,h]anthracene have been measured in a rigid glass at 77°K. For picene the polarization data support Platt's assignment of the first three singlet excited states as 1 L b , 1 L a , and 1 B b with transition moments polarized along the short, long, and long molecular axis, respectively. The polarization data for dibenz[ a,h]anthracene suggest the low energy excited states are not directly related to the low energy excited states in linear polyacenes. This result supports Hummel and Ruedenberg's conclusions that the excited states in dibenz[ a,h]anthracene are mixed and are not limited to polarizations along the long or short molecular axis. Vibrational analyses based on polarization data are given for the fluorescence and the absorption in the first excited singlet state for both compounds.