A Theoretical Information Approach to Ring and Total Aromaticity in Ground and Excited States

Applying the Shannon equation to the density matrix of a molecule, an information index is specified for the quantitative estimation of the ring and total aromaticity of molecules in ground · and excited states. The approach is applicable within each LCAO- method. The information index reproduces well the classification of molecules as aromatic, nonaromatic, and antiaromatic. It also correlates with results of other authors obtained by radically different approaches. A tendency is found for the aromaticity of aromatic molecules to decrease and of antiaromatic molecules to increase when the molecule is excited to the S1-state