Prediction of the ground state for indenofluorene-type systems with Clar's π-sextet model

This study introduces the Ground State Stability (GSS) rule that allows predicting the nature of the ground state of indenofluorene (IF)-type systems from the simple counting of the Clar's π-sextets in the closed- and open-shell configurations. The IF-type system exhibits a triplet ground state when acquiring double or more the number of Clar's π-sextets in the open-shell form relative to the closed-shell form; otherwise, it assumes an open-shell singlet ground state. Performed state-of-the-art DFT calculations and analysis of aromaticity for the systems of interest validate the effectiveness of the proposed rule. We demonstrate that aromaticity plays the most crucial role in determining the ground electronic state for such polycyclic hydrocarbons. The simplicity of the GSS rule makes it a robust strategy for identifying promising systems in the development of indenofluorene-type materials.