Electronic Spectrum and Structure of Azulene

Abstract

A previously given theoretical method is applied to the azulene molecule. π‐electron energies, transtion moments, dipole moments, charge distributions, and bond orders are calculated for the ground state and for the lower singlet and triplet excited states. The same detailed procedure which had previously given good results for the polyacenes is used here. Configuration interaction is included for all singly excited configurations. Two parallel calculations, one starting with conventional Hückel MOs and the other with perimeter MOs, are carried through. Hückel MOs lead to numerical results in good agreement with available experimental spectral data. In this connection some previous assignments are confirmed and some new ones are proposed. For the π‐electron dipole moment for the ground state, one calculates 1.88 D with Hückel MOs and 3.36 D with perimeter MOs; the experimental value is 1 D. One may conclude that the present procedure gives results in substantial agreement with experiment provided that good MOs, e.g., Hückel MOs, are employed. For computation of excited state energies it is essential to include interaction among nearly degenerate configurations. More extensive configuration interaction, however, appears to improve the transition energies and especially the transition moments and dipole moments.