Reaction of Ru(II) diazafluorenone compound with nanocrystalline TiO2 thin film.

The Ru(II) compounds Ru(bpy)(2)(mcbH) and Ru(bpy)(2)(dafo), bpy is 2,2'-bipyridine where mcbH is 3-(CO(2)H)-2,2'-bipyridine and dafo is 4,5-diazafluoren-9-one, were synthesized, characterized, and anchored to nanocrystalline mesoporous TiO(2) thin films for excited state and interfacial electron transfer studies. X-ray crystallographic studies of Ru(bpy)(2)(mcbH)(Cl) revealed a long Ru-N distance to the unsubstituted pyridine ligand of mcbH. Reaction of Ru(bpy)(2)(dafo) with TiO(2) thin films resulted in interfacial chemistry. The IR, (1)H NMR, UV-vis, and photoluminescence spectral data indicated a room-temperature ring-opening reaction of the dafo ligand of Ru(bpy)(2)(dafo) that ultimately yielded a carboxylate group in the 3-position of bipyridine anchored to TiO(2). Comparative reactions of Ru(bpy)(2)(mcbH) with TiO(2) were performed and support this conclusion. In regenerative photoelectrochemical solar cells with 0.5 M LiI/0.05 M I(2) in acetonitrile, photocurrent action spectra were observed for both sensitized materials. The incident photon-to-current efficiency (IPCE) was significantly lower for Ru(bpy)(2)(dafo)/TiO(2), behavior attributed to a lower excited-state injection yield.