Defying antiaromaticity - the curious case of pentalenopentalenes

Antiaromatic molecules offer attractive electronic properties but are intrinsically unstable. Annelation with arenes can stabilize antiaromatic cores, yet often suppresses the very properties of interest. Here, we investigate the (anti)aromatic character of two families of pentalenopentalene-based polycyclic hydrocarbons, bisbenzannelated and biscycloheptatriene-annelated, in both the S₀ and T₁ states. Despite exhibiting markedly different symmetry, open-shell character, and magnetic response, all systems follow a single unifying principle: a persistent preference for preserving local aromatic subunits. In T₁, the same behavior emerges through localization of spin density, maintaining local aromaticity and inducing a local reversal of aromatic character. Resonance structure analysis combined with the Randić conjugated circuit model provides a general framework for rationalization and a direct connection between behavior and topology. These findings underscore that neither Hückel nor Baird rules can be naïvely applied to polycyclic (anti)aromatic systems and offer design principles for persistent antiaromatic molecules.