Revisiting the superaromatic stabilization energy as a local aromaticity index for excited states

Journal article, 2023

The graph theory of aromaticity is a useful framework for analyzing the aromatic properties of polycyclic aromatic hydrocarbons. We present here the magnetically based superaromatic stabilization energy (m-SSE) as a local aromaticity index and validate it against its topologically based counterpart t-SSE. By comparing to DFT-computed aromaticity indices of triplet state excited polybenzenoid hydrocarbons, we find that semi-quantitative agreement can be reached by using the variable (Formula presented.) method to account for bond-length alternation. The m-SSE can further be separated into orbital and circuit contributions to gain insight into the basis of the aromatic properties of individual rings. Fully automated algorithms for calculating both m-SSE and t-SSE are now available in the COULSON package. We envision that these graph theoretical aromaticity indices will be of great use to the community to analyze the local aromaticity of excited states.