Spectroscopic Evidence for Through-Space Arene–Sulfur–Arene Bonding Interaction in m-Terphenyl Thioether Radical Cations

Electronic absorption spectra and quantum chemical calculations of the radical cations of m-terphenyl tert-butyl thioethers, where the S–t-Bu bond is forced to be perpendicular to the central phenyl ring, show the occurrence of through-space [π···S···π]+ bonding interactions which lead to a stabilization of the thioether radical cations. In the corresponding methyl derivatives there is a competition between delocalization of the hole that is centered on a p-AO of the S atom into the π-system of the central phenyl ring or through space into the flanking phenyl groups, which leads to a mixture of planar and perpendicular conformations in the radical cation. Adding a second m-terphenyl tert-butyl thioether moiety does not lead to further delocalization; the spin and charge remain in one of the two halves of the radical cation. These findings have interesting implications with regard to the role of methionines as hopping stations in electron transfer through proteins.