Diazonium-Based Covalent Molecular Wiring of Single-Layer Graphene Leads to Enhanced Unidirectional Photocurrent Generation through the p-doping Effect

Development of robust and cost-effective smart materials requiresrational chemical nanoengineering to provide viable technological solutions for awide range of applications. Recently, a powerful approach based on theelectrografting of diazonium salts has attracted a great deal of attention due to itsnumerous technological advantages. Several studies on graphene-based materialsreveal that the covalent attachment of aryl groups via the above approach could leadto additional beneficial properties of this versatile material. Here, we developed thecovalently linked metalorganic wires on two transparent, cheap, and conductivematerials:fluorine-doped tin oxide (FTO) and FTO/single-layer graphene (FTO/SLG). The wires are terminated with nitrilotriacetic acid metal complexes, whichare universal molecular anchors to immobilize His6-tagged proteins, such asbiophotocatalysts and other types of redox-active proteins of great interest inbiotechnology, optoelectronics, and artificial photosynthesis. We show for thefirsttime that the covalent grafting of a diazonium salt precursor on two differentelectron-rich surfaces leads to the formation of the molecular wires that promote p-doping of SLG concomitantly with a significantlyenhanced unidirectional cathodic photocurrent up to 1 mu Acm-2. Density functional theory modeling reveals that the exceptionallyhigh photocurrent values are due to two distinct mechanisms of electron transfer originating from different orbitals/bands of thediazonium-derived wires depending on the nature of the chelating metal redox center. Importantly, the novel metalorganic interfacesreported here exhibit minimized back electron transfer, which is essential for the maximization of solar conversion efficiency.