Self-assembled-monolayers (SAMs) of aromatic thiolates on metal surfaces are candidates for molecular “quantum dots” or “wires”. We probe the interfacial electronic structure using two-photon photoemission in SAMs of pentafluorothiophenolate (C 6 F 5 S - ) on Cu(111). Compared to gas-phase C 6 F 5 SH, the σ* LUMO in the assembled molecule is stabilized by 3.1 eV and the HOMO−LUMO gap is reduced by 5.7 eV. Ab initio calculations reveal that stabilization of molecular states is, to a great extent, a consequence of the strong electronic coupling between metal and molecular orbitals via the −S− bridge. This strong electronic coupling is absent when the molecule is not directly bonded to the surface, as in the case of C 6 F 6 weakly adsorbed on Cu(111).
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Vondrák et al. (1999) studied this question.