Manipulating molecular alignment: organoselenium radical cations with tailored Π-stacking architectures

Abstract

Radicals featuring π-conjugated systems have garnered extensive attention due to their intriguing structures and unique physicochemical properties. However, open-shell polycyclic aromatic hydrocarbons (PAHs) with columnar stacking architectures remain scarce. Herein, we present three novel selenium-containing open-shell PAHs with well-defined solid-state packing patterns. The radical species [4Se-PAH]₃[BAr^F₄]₂ and [4Se-PAH]₂[SbF₆]₂ assemble into columnar stacks, whereas [4Se-PAH]₄[Al(OR^F)₄]₄ adopts a discrete tetrameric stacking arrangement, in which four π-scaffolds are fully separated by counterions [Al(OR^F)₄]⁻. Single-crystal X-ray analysis reveals shortened Se–Se bonds (2.2863(12)–2.3074(12) Å) and near-planar geometries, suggesting partial π-bond character, which is further supported by theoretical calculations. Electron paramagnetic resonance spectroscopy unequivocally confirmed the radical nature of all three species. Pressure-dependent conductivity measurements show that both [4Se-PAH]₄[Al(OR^F)₄]₄ and [4Se-PAH]₂[SbF₆]₂ exhibit high electrical conductivity. These findings offer a rare example of π-stacked selenium radical systems with tunable packing structures and electronic properties.