Light-induced rearrangements of chemisorbed dyes on anatase(101)

Photoinduced mol. rearrangements are important in daily events essential for life such as visual perception and photo-protection of light harvesting complexes in plants. In this study we demonstrate that similar photorearrangements appear in an analogous technol. application where the device performance is controlled by chromophores in sensitized anatase TiO2, one of the main components for light-harvesting in dye-sensitized solar cells. STM reveals that illumination leads to distortions of org. dyes contg. conjugated backbones and of cis-bis(isothiocyanate)-bis-(2,2'-bipyridyl-4,4'-dicarboxylate)ruthenium(ii)-bis(tetrabutylammonium), known as N719. The dyes were adsorbed in a closed-packed mode on an anatase(101) single crystal surface and imaged in the dark and under white light illumination in an ultra-high vacuum. STM images of N719 clearly suggest rearrangements caused by rotation of the dye. Conversely, org. dyes rearrange by photoisomerization depending on the no. of double bonds, their position in the mol. structure, and the ligand modifications.