Exploring Triplet Aromaticity in Azaboracyclooctatetraenes Using New Descriptors Based on Electron Density Partitioning

ABSTRACT Understanding aromaticity in excited states remains a fundamental challenge in chemistry. Baird aromaticity describes the stabilization of a molecule's lowest triplet excited state due to cyclic conjugation, similar to how Huckel's rule applies to the ground state. In this work, we employ a new set of descriptors, derived from the Distributed Multipole Analysis (DMA) method, to systematically analyze the electronic delocalization and triplet aromaticity of cyclooctatetraene ( COT ) and its BN/CC isosteres in their lowest triplet states ( T 1 ). The descriptors are built from the components of the electric quadrupole tensor Q 2 , the first in the DMA expansion to include out‐of‐plane electron contributions. The Q 2 ‐based aromaticity descriptors allow for an accurate quantification of the delocalized electron density, thereby providing global and local measures of π‐delocalization. Comparison with magnetic ( NICS ), geometric ( HOMA ), and electronic ( MCI ) descriptors reveals a good agreement, confirming that the new descriptors efficiently capture changes in electronic delocalization in rings containing BN substitutions. The analysis also shows that the connectivity between the B and N atoms, rather than the number of heteroatoms, governs the degree of Baird aromaticity: adjacent BN pairs reduce π‐delocalization, whereas alternating or opposite arrangements enhance it. These results indicate that the Q 2 ‐based descriptors provide an alternative framework for exploring the multidimensional nature of triplet‐state aromaticity.