Molecular Orbital Predictions of Organic Spectra

Abstract

The energies of the first two to five electronic transitions of 16 conjugated molecules are predicted as simple one‐electron LCAO molecular orbital transitions (with overlap included). Assignments of the observed levels to the predicted levels are made. Qualitative agreement is good when S=0.25 and β=23,000 cm⁻¹ for ring systems. It is shown that configuration interaction must be introduced to modify these energy predictions and to account for the intensities in some molecules (``round‐field'') such as benzene, triphenylene, coronene, and porphine. This interaction is less important in other molecules (``long‐field'') such as pyrene, biphenyl, and tetrahydroporphine. Empirical groupings of intensities and luminescence lifetimes are shown for the different singlet‐singlet and singlet‐triplet band types of round‐field hydrocarbons and for related molecules containing conjugated hetero‐atoms. The alteration of these groupings in long‐field molecules, and under jj‐coupling, is described.