Stabilizing Cationic Perylene Dimers through Pancake Bonding and Equal Charge Share

Abstract

A cationic perylene salt was synthesized by chemical oxidation through treatment of perylene with triethyloxonium hexachloroantimonate in dichloromethane and characterized by single crystal X-ray diffraction as [(C₂₀H₁₂)₂]^•+(SbCl₆)⁻. EPR spectrometry confirmed the formation of an organic radical with a g-factor of 2.0024. X-ray diffraction analysis revealed a 1D column stacking of perylene molecules with alternating interplanar distances of 3.255(2)–3.340(2) Å and 3.409(2)–3.466(3) Å, indicative of the dimer formation within infinite π-stacks. Within a dimer, a large π-surface overlap and a slight loss of planarity for perylene were also observed. As these structural characteristics are consistent with pancake bonding for a perylene dimer, further insights into bonding were sought with the help of density functional theory. The calculations revealed that the pancake interaction contributes significantly to the stabilization of the stacked perylene dimer, providing approximately 8.0–10.0 kcal/mol per pair. Further stabilization is achieved by an even distribution of the positive charge in the monocationic dimer. A direct comparison with the close analogue revealed the critical role of the solid-state packing effects in achieving a higher degree of overlap between the perylene monomers in the title product.