Does Aromaticity Drive Metal Cation Binding to Nanographenes? Insights Into Regioselectivity and Cation- π $$ \pi $$...

Nanographenes, a subclass of polycyclic aromatic hydrocarbons (PAHs), have attracted significant interest due to their unique electronic properties and broad applications in materials science, optoelectronics, energy storage, and organic chemistry. Here we investigate the interactions of alkali and alkaline-earth metal cations (Li⁺, Na⁺, K⁺, Be²⁺, Mg²⁺, Ca²⁺) with five D ${}_{6h}$ -symmetric PAHs/nanographenes ranging from benzene to circumcircumcircumcoronene, aiming to elucidate the roles of aromaticity and topology in governing cation binding. We find that cation binding is strongest at the most aromatic peripheral six-membered rings. Energy decomposition analysis reveals that binding is dominated by orbital interactions rather than electrostatics, with Be²⁺ displaying anomalous, strongly covalent character and minimal ionic contribution. We introduce a novel ring-based reactivity descriptor combining the Fukui function and electronic delocalization, which accurately predicts binding energies. In addition, a local topological indicator shows a strong correlation with cation-PAH interactions and enables reliable predictions for graphene. Overall, our results demonstrate that aromaticity alone does not govern cation binding, but its interplay with local reactivity and topology is decisive, providing a unified framework that bridges chemical topology and computational chemistry.