ELECTRONIC-STRUCTURES OF CARBAZOLE AND ITS DERIVATIVES - A SEMIEMPIRICAL STUDY ON THE SUBSTITUTION EFFECTS OF CARBAZOLE

The electronic structures of carbazole, N-phenylcarbazole (NPC), cyano phenylcarbazole (CPC) and N-ethylcarbazole (NEC) have been calculated using the quantum chemical semi-empirical MINDO/3 method. In this pape r, electronic ground states and first singlet excited states of the sy stems mentioned were investigated. It is observed that the excitation energy of carbazole based on the calculated difference in heats of for mation agrees quite well with experimental data obtained from superson ic expansion studies. Calculated energy levels of molecular orbitals a nd their graphical forms are used qualitatively in elucidating the S-0 -->S-1 excitation electronic origin red shifts observed in carbazole d erivatives with respect to the electronic origin of the parent carbazo le. It is noted that the red shifts are not just a result of the desta bilization of the HOMO of carbazole but are also determined by the nat ure of the substituting moieties. It is also observed that the LUMO of CPC is not derived from the parent carbazole which partially explains the difference in electronic behaviour as compared with the other der ivatives. (C) 1997 Elsevier Science B.V.