Exploring the Impact of Topological Variations on the Stability of the Ground Singlet and Lowest-Lying Triplet States of Catacondensed Hexabenzenoids

Polycyclic aromatic hydrocarbons (PAH) like tetracenes, pentacenes, hexacenes, and some higher acenes play a central role in organic electronics due to their unique electronic properties. The impact of topological variations on the relative stability of PAH isomers in different electronic states is poorly understood, with limited insights into how Clar p-sextets and topological features like bay, cove, fjord, and K-regions influence stability in their ground singlet (S0) and lowest-lying triplet (T1) states. In this work, we perform density functional theory calculations of the S0 and T1 states of the 37 catacondensed hexabenzenoids. We use a multivariate linear regression model with relative energy as the dependent variable and a series of topological parameters as the independent variables to quantify the effect of topology in the relative stability of the catacondensed hexabenzenoids. Our analysis shows that, in S0, stability is enhanced by an increase in the number of Clar p-sextets and K-regions and decreased by the presence of coves and fjords. In T1, the main stabilizing factors are the number of Clar p-sextets and the number of rings involved in the antiaromatic region, whereas topological regions like K-edges, bays, coves, or fjords are destabilizing.