Covalent Immobilization of Redox-Active Fe(κ2-dppe)(η5-C5Me5)-Based π-Conjugated Wires on Oxide-Free Hydrogen-Terminated Silicon Surfaces

Abstract

Several redox-active Fe(κ2-dppe)(η5-C5Me5) arylacetylide complexes (dppe = 1,2-bis(diphenylphosphino)ethane) featuring a pendant ethynyl (1b–d and 2) or ethenyl (3) group have been grafted on oxide-free hydrogen-terminated silicon (Si–H) surfaces through a covalent interfacial Si–C bond. They form densely packed redox-active monolayers. The charge-transfer process between the terminal redox center and the underlying silicon interface was subsequently studied by cyclic voltammetry. The latter turned out to be strongly dependent on the nature of the spacer linking the organometallic end groups to the silicon surface, the highest charge-transfer rates being obtained for monolayers anchored through conjugated and unsaturated spacers. Although the rates measured were among the highest values obtained for redox-active systems grafted to Si–H surfaces, this study nevertheless suggests that the electron tunnelling is not entirely controlling the interfacial charge-transfer process for the shorter linkers tested. In this respect, strategies to improve further the charge-transfer kinetics of the produced redox-active films are briefly discussed.