Bond overlap population analysis on through-space electron transfer in [3n]cyclophanes (n = 2 – 5)

Abstract Through-space electron transfer between the benzene rings of [3 n ]cyclophanes, n  = 2 – 5, was investigated using density functional theory calculations, CAM-B3LYP/6-311++G**. An external point charge, q , was placed on the axis perpendicular to a benzene ring of the cyclophane molecule. The dependence of the highest occupied molecular orbital (HOMO)–lowest unoccupied molecular orbital (LUMO) gap and bond overlap population (BOP) of cyclophanes on the values of q and n are discussed. The HOMO–LUMO gap generally decreases as q decreases and n increases. It is found from the BOP analysis that electron transfer occurs mainly through LUMO + 2 for n  = 2, LUMO for n  = 3 and n  = 4, and LUMO + 4 for n  = 5. The result that the values of the BOP for n  = 2 and 5 increase as q decreases means that the through-space electron transfer is enhanced by the negative charge on the neighboring molecule in the solid.