A molybdenum dithiolene complex as a potential photosensitiser for photoelectrochemical cells

Molybdenum dithiolene complexes with the general formula [MoTp*(NO)(L)], where Tp* = tris(3,5-dimethylpyrazolyl)hydroborate and L = toluene-3,4-dithiolate (L1), 1,2-benzenedithiolate (L2), or 3,6-dichloro-1,2-benzenedithiolate (L3), were found to exhibit the chemical and physical properties required for a photosensitiser in a photoelectrochemical cell. These complexes were characterised using micro-elemental, spectroscopic (IR and UV–vis) and electrochemical analyses. Cyclic voltammetry (CV) was used to determine the oxidation/reduction potentials and to calculate the energy band gap. All of the complexes had an energy band gap in the range 1.45–1.48 eV, which extends far into the visible light region. A TiO2 thin film to be used as a photoanode for photoelectrochemical cells was prepared using the paste technique on a Fluorine-doped Tin Oxide (FTO) plate and characterised using scanning electron microscope (SEM) and X-ray diffractometer (XRD). The [MoTp*(NO)(L)]-doped TiO2 photoanodes were analysed photochemically in a 1.0 M NaOH electrolyte solution using SCE reference and platinum counterelectrodes. The [MoTp*(NO)(L3)]-doped TiO2 photoanode exhibited an increased photoinduced current compared with the undoped TiO2 photoanode. The Cl atoms on the dithiolene group offered a better interaction between the photosensitiser molecule and the TiO2 photocatalyst by providing a means for halogen atom-induced chemical bonding. Based on the band edge calculations and the subsequent photocurrent results, these complexes may be potential photosensitisers for use in the preparation of photoelectrodes for photoelectrochemical cells.