Time-resolved optical spectroscopy of heterosupramolecular assemblies based on nanostructured TiO2 films modified by chemisorption of covalently linked ruthenium and viologen complex components

Described is the preparation of transparent nanostructured TiO2 (anatase) a nd Sb-doped SnO2 films supported on F-doped;conducting glass. Also describe d is the modification of these films by chemisorption of RV, bis(4,4 ' -bis (phosphonomethyl)-2,2 ' -bipyridine) (5-((1 ' -ethyl-4,4 ' -bipyridinediium -1-yl)butyl)-2,2 ' -bipyridine)ruthenium-(II) tetrakis(hexafluorophosphate) , to form the covalent heterosupramolecular assemblies TiO2-RV and SnO2-RV, respectively. Visible light excitation of the ruthenium complex component, R, results in electron injection into the TiO2 or SnO2:Sb nanocrystal comp onent (60%) and electron transfer to the viologen component (40%), V. In th e case of TiO2-RV, however, long-lived formation of the radical cation of t he V component, V.+, is observed. In the case of SnO2-RV, long-lived format ion of V.+ is not observed. These findings, based on a detailed study of th e time-resolved optical spectroscopy of TiO2-RV and SnO2:Sb-RV, are account ed for by proposing that long-lived V.+ is formed by TiO2 nanocrystal media ted electron transfer to the V component.