Electron Transfer Capability in Atomic Hydrogen Reactions for Imidazole Groups Bound to the Insulating Alkanethiolate Layer on Au(111)

The charge transfer capability associated with chemical reactions at metal-organic interfaces was studied via the atomic H addition reaction for an imidazole-terminated alkanethiolate self-assembled monolayer (Im-SAM) film on Au(111) at room temperature, using near-edge X-ray absorption fine structure spectroscopy, infrared reflection absorption spectroscopy, work function measurements, and density functional theory calculations. The imidazolium cation is a stable species in liquids; therefore, it is pertinent to determine whether the hydrogenation reactions of the imidazole groups produce imidazolium cations accompanied by electron transfer to the Au substrate, even in the absence of solvate and/or counterions on the insulating alkanethiolate layer. The experiments made it clear that the imidazolium moieties were formed during the irradiation of Im-SAM with atomic H. Theoretical model calculations also revealed that the total energies and molecular orbital levels satisfied the imidazolium cation formation associated with electron transfer. In a detailed analysis of the work function change depending on H irradiation, we confirmed that some of the imidazolium radicals became cations in Im-SAM.