Now, researchers at Arizona State University, US, have reported the synthesis of porphyrin- and ruthenium-based dyes containing a remarkably stable trialkoxysilane linker protected with triethanolamine. These stable "silatrane" molecules may be purified using silica gel column chromatography and do not hydrolyse in air. At moderate temperatures the dyes react with metal oxides to form a molecular layer. SEM images of nanoporous SnO2 surfaces with attached dyes show no evidence of the pore blockage that often occurs because of siloxane polymerization.

The study, published in the journal Nanotechnology compares the photoelectrochemical performance of porphyrin and ruthenium dyes bearing either a carboxylic acid or the new amidopropylsilatrane linkage attached to nanoporous semiconductive SnO2 films on conductive glass electrodes (such electrodes use energy from light to drive electrical current production in an electrochemical cell).

Transient spectroscopy was used to determine the rate of electron recombination events that are detrimental to cell performance, revealing that the longer surface linker on the silatrane was able to decrease the recombination rate. The result was an increase in yield of electrical current per absorbed photon of light with the silatrane linkage. Although ruthenium dyes with carboxylic acid linkages readily desorb from metal oxide surfaces in aqueous solutions buffered at neutral pH, the ruthenium-based silatrane dye was strongly bound to SnO2 and able to function with high efficiency in a photoelectrochemical cell under such conditions.

Silatranes have the potential to covalently bind molecules to many metal oxide species, opening the door to applications featuring stably functionalized films or particles. In particular, this method allows the use of water-soluble molecules attached to metal oxides in aqueous solutions over a wide pH range.