Reaction of RuII Diazafluorenone Compound with Nanocrystalline TiO2 Thin Film

The Ru(II) compounds [Ru(bpy)(2)(mcbH)](2+) and [Ru(bpy)(2)(dafo)](2+), bpy is 2,2'-bipyridine where mcbH is 3-(CO2H)-2,2'-bipyridine and dafo is 4,5-diazafluoren-9-one, were synthesized, characterized, and anchored to nanocrystalline mesoporous TiO2 thin films for excited state and interfacial electron transfer studies. X-ray crystallographic studies of [Ru(bpy)(2)(mcbH)](PF6)(Cl) revealed a long Ru-N distance to the unsubstituted pyridine ligand of mcbH. Reaction of [Ru(bpy)(2)(dafo)](2+) with TiO2 thin films resulted in interfacial chemistry. The IR, H-1 NMR, UV-vis, and photoluminescence spectral data indicated a room-temperature ring-opening reaction of the dafo ligand of [Ru(bpy)2(dafo)](2+) that ultimately yielded a carboxylate group in the 3-position of bipyridine anchored to TiO2. Comparative reactions of [Ru(bpy)(2)(mcbH)](2+) with TiO2 were performed and support this conclusion. In regenerative photoelectrochemical solar cells with 0.5 M Lil/0.05 MI2 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)/TiO2, behavior attributed to a lower excited-state injection yield.