Effect of the Anchoring Groups on the Photostability of Ruthenium(II) Polypyridyl Sensitizers

Ruthenium(II) polypyridyl derivatives are widely used as sensitizer molecules in water-splitting dye-sensitized photoelectrochemical cells (WS-DSPECs) to harvest solar energy and generate hydrogen and oxygen gas from water. The desorption of sensitizer molecules from the TiO2 surface during long-term illumination is a significant problem for the phoatostability of these cells. Another factor that limits the efficiency of the cells is the low injection yield from the dye excited state to the electrode at neutral pH. To address these two problems, the effects of different anchoring groups (carboxylate or phosphonate) at the 4,4’-positions of bipyridine were systematically studied. In this report, three ruthenium(II) polypyridyl sensitizers were synthesized and characterized. Results from stability measurements showed that the phosphonate anchoring groups can enhance the photostability of ruthenium(II) sensitizers over the pH range from 4.9 to 6.9 compared with carboxylate substitutions