Electronic States of Fluorene, Carbazole and Dibenzofuran

Abstract

The polarized reflection spectra of the fluorene, carbazole, and dibenzofuran crystals have been measured from 30000 to 53000 cm−1 and the absolute intensity of the absorption parallel to the a, b, and c axes of these crystals has been obtained by the Kramers-Kronig transformation; these data allowed an interpretation to be made for the solution spectra. Furthermore, the influence of the intermolecular interaction on each level has been examined. This analysis shows that the lowest excited state of the fluorene molecule is the B2 state, while those of the carbazole and dibenzofuran are the A1 states. In fluorene, the sum of the oscillator strengths of the transition to two lower excited states (α and α* states) is 0.39 in the molecule and 0.61 in the crystal. Such hyperchromism is also observed in the α, p, and β states of carbazole and the β state of dibenzofuran. On the other hand, the α* state of dibenzofuran is hypochromic and the oscillator strengths in the molecule (0.87) decrease to 0.36 in the crystal. However, the factor group splitting and the crystal field shift are small and a one to one correspondence can easily be obtained between the solution and crystalline spectra.