Radical self-assembled monolayers on Au(111) formed by the adsorption of closed-shell molecules

Using density-functional theory band-structure calculations, we show how the exothermic adsorption of conjugated closed-shell organic semiconductor molecules on an Au(111) surface can turn them into radicals. For this to happen, we suggest the use of a thiocarbonyl docking group instead of the commonly applied thiols. The radicalisation of the adsorbed molecules resulting from the formation of the Au-S bond leads to reduced electron-and hole-injection barriers. The calculations predict two energetically close solutions for the adsorbed monolayer, one being non-magnetic and metallic and another being magnetic with reduced density of states at the Fermi energy.