Effects of the Ligand Structures on the Photoelectric Activities, a Model Study Based on Titanium-Oxo Clusters Anchored with S-Heterocyclic Ligands.

Titanium oxo clusters (TOCs) have become one of the worldwide hot research topics because they are excellent molecular TiO materials having unique photoactive properties and can been used as models of dye-sensitized solar cells (DSSCs). S-Heterocyclic ligands such as thiophene (Th) and tetrathiafulvalene (TTF) derivatives have been widely used in electronic or photoelectronic devices and solar cells. However, a study of the synthesis and properties of TOCs anchored with Th and TTF derivatives is missing. Herein four such TOCs as single crystals were synthesized and structurally characterized: [Ti3O(OiPr)8(LTh)2] (1), [Ti4O2(OiPr)10(LTTF)2] (2), [Ti6O4(OiPr)10(LTh)2(O3PPh)2] (3), and [Ti6O4(OiPr)10(LTTF)2(O3PPh)2] (4). Charge transfer from the Th or TTF electron donor to the TOC core was evaluated by electronic spectra and theoretical calculations. This work first systematically investigated the photoelectrochemistry of TOCs with different conjugated S-heterocyclic ligands in molecular levels. The photocurrent densities of these cluster-modified TiO2 electrodes were examined using DSSCs, which were well responsive to irradiation. The photocurrents of TTF cluster-modified electrodes are higher than those of the Th cluster-modified electrodes because of the sulfur-rich conjugated system.