Aromaticity and antiaromaticity are pivotal concepts in chemistry, with significant implications for molecular properties and reactivity. In particular, thanks to their increased conductivity and small HOMO-LUMO energy gaps, antiaromatic molecules are promising for use in organic electronics. The inherent instability of such molecules is often addressed by carbocyclic fusion, which also reduces the antiaromaticity of the core structure. Herein, we have employed a computational approach to explore the effects of heterocyclic fusion on the s-indacene core, focusing on three main aspects: the impact of the heteroatom, the heterocycle, and extended conjugation. We found that the heteroatoms themselves can substantially modulate antiaromaticity, and that the site of substitution plays a large role in the extent of stabilization afforded. Heterocycle fusion further modulates antiaromaticity, though to a lesser extent than the heteroatom effect. This effect diminishes upon benzannelation, highlighting the complexity of aromatic and antiaromatic interplay. Our findings offer a nuanced understanding of the factors affecting antiaromaticity in s-indacene-based polycyclic systems, providing a conceptual framework for predicting and tuning these properties for applications in organic electronics. This work underscores the importance of both substitution position and heterocyclic fusion in designing stable antiaromatic compounds.
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