ELECTRONIC SPECTRA OF FLUORENE DIBENZOFUAN AND CARBAZOLE

The lowest energy π → π* transition of fluorene vapor has its origin at 33773 cm-1 and has been assigned as a 1A → 1Lb 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 → 1Lb transition; while the one which originates at 33647 cm-1 was assigned 1A → 1La. The strong π → π* transition of carbazole which originated at 36346 cm-1, was assigned 1A → 1La. The weaker π → π* band system, originating at 30694 cm-1, was assigned 1A → 1Lb. 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. © 1968.