PRACTICAL PPP MOLECULAR-ORBITAL CALCULATIONS OF ABSORPTION MAXIMA OF QUINONES

In order to calculate the excitation energies of linear para acenoquin ones (LPAs) more accurately by Pariser-Parr-Pople molecular orbital (P PP MO) method, the spectrochemical softness parameter k of a novel two centre electron repulsion integral new-gamma are evaluated based on s pectroactive portion (SP) in a molecular framework. SP is defined as t he longest acene portion, including a quinonoid ring of LPAs. The calc ulated results using the new-gamma are greatly improved compared with those using the conventional Nishimoto-Mataga gamma function. (C) 1998 Elsevier Science Ltd. All rights reserved.