π-Stacked dimerization of an antiaromatic homoHPHAC monocation

Abstract

An antiaromatic homoHPHAC monocation unexpectedly forms a slipped π-stacked structure in solution and the solid state, representing a rare example of an antiaromatic π-dimer. In acetone-d₆ at 298 K, the association constant is 5.5 × 10² M⁻¹ (ΔH = -22.0 kJ mol⁻¹, ΔS = -22.5 J K⁻¹ mol⁻¹), with dimerization accompanied by attenuation of antiaromatic destabilization.