The electronic spectra of fluorene, dibenzofuan and carbazole

Abstract

The lowest energy π → π ∗ transition of fluorene vapor has its origin at 33773 cm −1 and has been assigned as a 1A → 1L b transition. Two π → π ∗ transitions have been observed for dibenzofuran vapor. The one with the origin at 31488 cm −1 has been assigned as a 1A → 1L b transition; while the one which originates at 33647 cm −1 was assigned 1A → 1L a . The strong π → π ∗ transition of carbazole which originated at 36346 cm −1, was assigned 1A → 1L a . The weaker π → π ∗ band system, originating at 30694 cm −1, was assigned 1A → 1L b . Tentative assignments were made for the 30694 cm −1 band system of carbazobe. Molecular orbital calculations were performed which predicted that (i) carbazole would have the lowest transition energy, dibenzofuran intermediate, and fluorene the highest, (ii) the lowest singlet-singlet transition would be polarized along the axis which contains the hetero-atom, and (iii) this lowest transition should be weaker than the second lowest transition. All of these predictions have been confirmed experimentally.