Metal–phenanthroline fused Ti17 clusters, a single molecular source for sensitized photoconductive films

Abstract

Much attention has been paid to titanium oxo clusters (TOCs) because of their use as model compounds of bulk nanoscale titanium oxides. On the other hand, doping of TiO₂ with some metal complexes of 1,10-phenanthroline (phen) or bipyridine (bpy) results in low band-gap materials with high photovoltaic conversion efficiency. In this work, two metal–phenanthroline substituted titanium-oxo-clusters, [Ti₁₇O₂₈(OⁱPr)₁₆(Co^IIphen)₂] (C1) and [Ti₁₇O₂₈(OⁱPr)₁₈(Cd^IIphen)₂] (C2), were successfully prepared by one-step in situ solvothermal synthesis. The structures of the compounds are best described as an oxo-isopropanoxo Ti₁₇ parent fused with two M–phen moieties. They are the first examples of M–phen modified oxo-alkoxy titanium clusters. The band structure of the cluster is modified by the coordination of the metal complex and the absorption of the material is improved. The cluster can not only be used as a model for theoretical study, but can also be used as a precursor to prepare sensitized TiO films. Films (F1) with unique microstructures of hollow spheres, bowls, and doughnuts were obtained by a simple non-template coating method from the solution of Co–phen–TiO cluster C1. The size of the spheres is about 1–2 μm and the thickness of the shell is about 50 nm. Upon repetitive irradiation of the F1 film on the ITO electrode in a three electrode system, a clear photocurrent response was observed. The Co–phen moiety plays an important role in electron transition.