Aromatic self-assembled monolayers with pentafluoro-λ⁶-sulfanyl (−SF₅) termination: Molecular organization and charge transport properties

A series of molecules with oligophenylene backbone, thiolate anchoring group, and pentafluoro-λ⁶-sulfanyl (−SF₅) tail group was synthesized and used as precursors to form self-assembled monolayers (SAMs) on Au(111) substrates. The resulting SAMs feature dense molecular packing, upright molecular orientation, and chemically homogeneous SAM-ambient interface, comprised entirely of the −SF₅ moieties. These SAMs exhibit exceptional wetting and electrostatic properties, showing advancing water contact angles up to 103° and work function values up to 5.96 eV—probably the highest values reported for any aromatic monolayers on gold. They also feature a comparably low value of the tunnelling decay coefficient (0.38 ± 0.07 Å⁻¹), typical of oligophenylene backbone, which is not affected by the introduction of the −SF₅ group. The latter also hardly affects the current densities at a specific bias compared to analogous monolayers with other electronegative tail groups. The superior electrostatic and good charge transport properties of the designed, SF₅-terminated SAMs make them potentially useful for interface engineering in organic electronics and photovoltaics.