ELECTRON-PAIR (DE)COUPLING IN ANILINE RADICAL-CATION AND ITS IMPLICATIONS FOR ORGANIC MIXED-VALENCE SYSTEMS

The electron pair (de)coupling induced by a NH2.+ group to the bonds o f a phenyl ring is investigated by means of polyelectron population an alysis; the used density operators are built on the basis of both natu ral atomic orbitals (AOs) of ab initio-correlated molecular orbital (M O) wave functions, as well as the model orthogonal AOs of Parr-Pariser -Pople (PPP)+full configuration interaction (CI) ones. On the basis of two-electron, two-hole investigations, we calculate the electron pair localizations as well as the cooperation of opposite spins or charges to form bonds. The investigations of various electronic events referr ing to the simultaneous presence of a charge (+) and a radical center (.) lead to rules concerning the relative importance. of various reson ance structures. As shown, the observed quinoid (de)coupling of electr on pairs of the phenyl group is in the origin of the corresponding geo metrical deformations. Given these results, we investigate the key ele ctronic reasons responsible for the localized (bi- or tristable) or de localized behavior of monooxidized aromatic polyamines.