Enhancing the Antiaromaticity of s-Indacene through Naphthothiophene Fusion

Addressing the instability of antiaromatic compounds often involves protection with bulky groups and/or fusion of aromatic rings, thus decreasing paratropicity. We report four naphthothiophene-fused s -indacene isomers, one of which is more antiaromatic than parent s -indacene. This surprising result is examined computationally through nucleus-independent chemical shift XY calculations and experimentally via nuclear magnetic resonance spectroscopy, X-ray crystallography, ultraviolet–visible spectrophotometry, and cyclic voltammetry, with the latter two indicating that this molecule possesses the lowest highest occupied molecular orbital–lowest unoccupied molecular orbital energy gap observed for heterocycle-fused s -indacene.