Thermal stability of cis-dithiocyanato(2,2 '-bipyridyl4,4 ' dicarboxylate)ruthenium(II) photosensitizer in the free form and on nanocrystalline TiO2films

Thermal stability of ruthenium (II) complexes of the type [Ru(H(2)dcbpy)(2) (NCs)(2)] 1, (Bu4N)(2)[Ru(Hdcbpy)(2)(NCS)(2)] 2, (Bu4N)(4) [Ru(dcbpy)(2)(NC S)(2)] 3, and (Im)(4)[Ru(dcbpy)(2)(NCS)(2)] 4, where dcbpy=2, 2'-bipyridyl- 4,4'dicarboxylate, Bu4N+=tetrabutylammonium, and Im=dimethylethylimidazoliu m, has been studied using thermoanalytical techniques, IR, UV-VIS, and H-1 NMR spectroscopic methods. These complexes show remarkable stability in bot h nitrogen and air atmospheres at high temperatures, ranging from 180 degre es C for 2 to 250 degrees C for 1. The only process that is observed at low er temperatures is the dehydration which occurs between 40 and 110 degrees C. High temperature processes including deamination of the counterion as we ll as decarboxylation and decomposition of the complex occur between 200 an d 400 degrees C with different characteristics in air and in nitrogen. The decarboxylation reaction is an endothermic process in nitrogen atmosphere a nd overlaps with decomposition of the complexes. In air, on the other hand, it is an exothermic process distinctively separated from decomposition. Hi gher thermal stability is observed for 1 and 2 when anchored onto nanocryst aline TiO2 films. The activation energy of decarboxylation is estimated for 1 in the free form (ca, 103 kJ mol(-1)) and on TiO2 (ca. 126 kJ mol(-1)). (C) 2000 Elsevier Science B.V. All rights reserved.