DIRECT TIME-RESOLVED INFRARED MEASUREMENT OF ELECTRON INJECTION IN DYE-SENSITIZED TITANIUM-DIOXIDE FILMS

Time-resolved infrared (IR) spectroscopy in the 6 mu m region was empl oyed to study the excited-state properties of 2CH3)(2)-2,2'-bipyridine )(2,2'-bipyridine)(2)](+2) and pyridine)(4,4'-(C-H-3)(2)-2,2'-bipyridi ne)(2)](+2) in solution and anchored to nanostructured thin films of T iO2 and ZrO2. Excited-state spectra reveal a shift in the nu(C=O) of t he ester groups for the free molecules in solution as well as attached to insulating ZrO2 substrates. For these molecules attached to TiO2 s emiconductor films, a transient absorption appears that is attributed to electrons injected into TiO2. This absorption appears within the in strumental time resolution (ca. 30 ps) yielding an approximate 20 ps u pper limit time constant for electron transfer from the sensitizer exc ited state to TiO2.