Adsorption studies of counterions carried by the sensitizer cis-dithiocyanato(2,2 '-bipyridyl-4,4 '-dicarboxylate) ruthenium(II) on nanocrystaline TiO2 films

Adsorption studies of counterions carried by the ruthenium(II) complexes (B u4N)(2)[Ru(Hdcbpy)(2)(NCS)(2)] (1), (Bu4N)(4)[Ru(dcbpy)(2)(NCS)(2)] (2), an d [Ru(H(2)dcbpy)(2)(NCS)(2)] (3) (dcbpy = 2,2'-bipyridyl-4,4'-dicarboxylate , Bu4N = tetrabutylammonium) on TiO2 have been carried out by using thermoa nalytical techniques, NMR, and ATR-FTIR spectroscopic methods. The thermogr avimetric analysis (TGA) data of the adsorbed complexes 1 and 2 on TiO2 sho w the presence of 1 and less than or equal to1.3 cations coadsorbed per rut henium center, respectively. These complexes in the adsorbed state on TiO2 show remarkable stability in air atmospheres at high temperatures up to 180 degreesC. The only process that is observed at lower temperatures is the d ehydration, which occurs between 40 and 110 degreesC. At high temperature t he processes are deamination of the tetrabutylammonium counterion as well a s decarboxylation and decomposition of the complex between 200 and 400 degr eesC. The NMR data of the desorbed complexes 1 and 2 from the TiO2 surface show the presence of 1 and less than or equal to1.5 cations, which is in cl ose agreement with the TGA data. Comparative analysis of the ATR-FTIR spect ra of complexes 1 and 2 between the free and the adsorbed forms also indica tes the presence of 1 and less than or equal to1.5 cations per ruthenium ce nter, respectively.