1-(3'-amino)propylsilatrane derivatives as covalent surface linkers to nanoparticulate metal oxide films for use in photoelectrochemical cells

A triethanolamine-protected silane, 1-(3'-amino)propylsilatrane, was incorporated into the structure of porphyrin- and ruthenium-based dyes and used to link them to transparent semiconductor nanoparticulate metal oxide films. Silatrane reacts with the metal oxide to form strong, covalent silyl ether bonds. In this study, silatrane-functionalized dyes and analogous carboxylate-functionalized dyes were used as visible light sensitizers for porous nanoparticulate SnO2 photoanodes. The performance of the dyes was compared in photoelectrochemical cells incorporating either non-regenerative or regenerative redox components. The non-regenerative cell used NADH (β-nicotinamide adenine dinucleotide) as a sacrificial electron donor and Hg2SO4/Hg as a sacrificial cathode, whereas the regenerative cell used the iodide/triiodide redox couple. Experiments showed that the silyl ether bonding gave the electrodes increased stability toward sensitizer desorption compared to carboxylate surface linkages. Porphyrin-silatrane dyes also demonstrated similar or better performance than their carboxylate analogs in photoelectrochemical cells. The improvement correlates with the results from transient absorbance spectroscopy, which show that the longer linker on the silatrane porphyrins slows charge recombination between oxidized porphyrin and the electrode surface. The improved photoelectrochemical cell efficiency and stability of the silatrane-based dyes compared to carboxylates demonstrate that silatranes are promising agents for bonding organic molecules to metal oxide surfaces.