Semiempirical calculations on the redox potentials and electronic absorption spectrum of tetraazaannulenes

In this work we have carried out empirical Huckel and semiempirical INDO/S MO calculations on a few tetraazaannulene compounds and obtained an estimat e for the redox potentials of 17,21-dichloro-5,7, 12,14-tetramethyl-dibenzo [b,i][1,4,8,11]-tetraaza[14]annulene. Our calculated value of 0.79 V for th e oxidation potential is very close to the experimental value of 0.73 V. Fo r the still unknown reduction potential, we have obtained a value close to -2.2 V. We are also interested in the UV-visible spectra of some of these c ompounds. We have obtained the absorption electronic spectra of the free li gands using the INDO/S technique as parametrized by Zerner and coworkers. A s expected, the calculated spectra is associated with pi --> pi* excitation s: the strong absorptions at 344, 274, 250, and 224 nm of the observed spec trum are all very well described. (C) 2001 Elsevier Science B.V. All rights reserved.