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 solidstate packing patterns. The radical species [4Se-PAH]3[BArF4]2 and [4Se-PAH]2[SbF6]2 assemble into columnar stacks, whereas [4Se-PAH]4[Al(ORF)4]4 adopts a discrete tetrameric stacking arrangement, in which four π-scaffolds are fully separated by counterions [Al(ORF)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. Pressuredependent conductivity measurements show that both [4Se-PAH]4[Al(ORF)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.