Direct Time-Resolved Infrared Measurement of Electron Injection in Dye-Sensitized Titanium Dioxide Films

Abstract

Time-resolved infrared (IR) spectroscopy in the 6 μm region was employed to study the excited-state properties of [Ru(4,4‘-(COOCH 2 CH 3 ) 2 -2,2‘-bipyridine)(2,2‘-bipyridine) 2 ] +2 and [Ru(4,4‘-(COOCH 2 CH 3 ) 2 -2,2‘-bipyridine)(4,4‘-(CH 3 ) 2 -2,2‘-bipyridine) 2 ] +2 in solution and anchored to nanostructured thin films of TiO 2 and ZrO 2 . Excited-state spectra reveal a shift in the ν(C O) of the ester groups for the free molecules in solution as well as attached to insulating ZrO 2 substrates. For these molecules attached to TiO 2 semiconductor films, a transient absorption appears that is attributed to electrons injected into TiO 2 . This absorption appears within the instrumental time resolution (ca. 30 ps) yielding an approximate 20 ps upper limit time constant for electron transfer from the sensitizer excited state to TiO 2 .