Adsorption Studies of Counterions Carried by the Sensitizer cis-Dithiocyanato(2,2‘-bipyridyl-4,4‘-dicarboxylate) Ruthenium(II) on Nanocrystalline TiO2 Films

Adsorption studies of counterions carried by the ruthenium(II) complexes (Bu 4 N) 2 [Ru(Hdcbpy) 2 (NCS) 2 ] ( 1 ), (Bu 4 N) 4 [Ru(dcbpy) 2 (NCS) 2 ] ( 2 ), and [Ru(H 2 dcbpy) 2 (NCS) 2 ] ( 3 ) (dcbpy = 2,2‘-bipyridyl-4,4‘-dicarboxylate, Bu 4 N = tetrabutylammonium) on TiO 2 have been carried out by using thermoanalytical techniques, NMR, and ATR−FTIR spectroscopic methods. The thermogravimetric analysis (TGA) data of the adsorbed complexes 1 and 2 on TiO 2 show the presence of 1 and ≤1.3 cations coadsorbed per ruthenium center, respectively. These complexes in the adsorbed state on TiO 2 show remarkable stability in air atmospheres at high temperatures up to 180 °C. The only process that is observed at lower temperatures is the dehydration, which occurs between 40 and 110 °C. At high temperature the processes are deamination of the tetrabutylammonium counterion as well as decarboxylation and decomposition of the complex between 200 and 400 °C. The NMR data of the desorbed complexes 1 and 2 from the TiO 2 surface show the presence of 1 and ≤1.5 cations, which is in close agreement with the TGA data. Comparative analysis of the ATR−FTIR spectra of complexes 1 and 2 between the free and the adsorbed forms also indicates the presence of 1 and ≤1.5 cations per ruthenium center, respectively.