Understanding the structure–property relationships in polycyclic conjugated hydrocarbons (PCHs) is crucial for controlling their electronic properties and developing new optical function materials. Aromaticity is a fundamentally important and intriguing property of numerous organic chemical structures and has stimulated a myriad of experimental and theoretical investigations. Exploiting aromaticity rules for the rational design of optoelectronic materials with the desired photophysical characteristics is a challenging yet fascinating task.

In general, compounds exhibit one-state aromaticity in either the ground or excited state according to the Hückel’s and Baird’s rules. Thus, species with two-state aromaticity in the lowest singlet and triplet states (termed as adaptive aromaticity) are rare. Understanding the underlying mechanism for achieving adaptive aromaticity is important to enrich this rare family. Here we carry out density functional theory (DFT) calculations to probe the origin of adaptive aromaticity in metallapyridiniums.

Dinitrogen activation under mild conditions is important but extremely challenging due to the inert nature of the N-N triple bond evidenced by high bond dissociation energy (945 kJ/mol) and large HOMO-LUMO gap (10.8 eV). In comparison with largely developed transition metal systems, the reported main group species on dinitrogen activation are rare. Here, we carry out density functional theory calculations on methyleneboranes to understand the reaction mechanisms of their dinitrogen activation.