Electronic structure of emeraldine and related molecules

Abstract

The CNDO/S3 molecular orbital model is applied to describe the electronic structure of aniline, (C6H5)NH2, emeraldine, (C6H5)N(C6H4)N(C6H4)NH(C6H4)NH2, its hydrogenated and dehydrogenated forms, and its singly and doubly protonated forms. The cation eigenvalue spectrum, i.e., density of valence states (DOVS), is found to be sensitive to molecular conformation which, in turn, can be inferred from comparison of the calculated DOVS with suitable measured photoemission spectra. For fixed molecular conformation, the major effect of hydrogenation of emeraldine is the occupation of its lowest empty molecular orbital with accompanying electronic and atomic relaxation. Dehydrogenation leads to the emptying of its highest filled molecular orbital. Protonation leads to rearrangements of the valence electron charge among the filled orbitals but not to deviations from a closed shell system. Protonation-induced atomic relaxation can create major changes in the character of the highest filled or lowest empty orbitals. Changes in molecular conformation (e.g., upon hydrogenation or protonation) can yield large alterations in both the DOVS and the character of the radical cation eigenstates. Comparison of calculated DOVS with photoemission spectra from thin films of polyemeraldine does not suffice to determine the molecular conformation, however, because of the low resolution of the measured spectra.