Thermal stability and photostability of water solutions of sulfophthalocyanines of Ru(II), Cu(II), Ni(II), Fe(III) and Co(II)

The thermal and photochemical stabilities were investigated for tetrasulfophthalocyanines of Cu, Co, Ni, Fe and Ru (MPcS) and for two monosulfophthalocyanines of Ru, either without (RuPcS1) or with the coordination of two units of DMSO in apical positions ([RuPcS1(DMSO)2]DMSO). The thermal degradation of all of the studied complexes never showed the formation of spectroscopically detectable intermediates. CuPcS was the most stable complex, while all of the Ru-sulfophthalocyanines were particularly prone to thermal degradation. Photodegradation showed a better selectivity, and as with thermal degradation, the order of reactivity goes from the most stable CuPcS, to the least stable Ru-sulfophthalocyanines (RuPcS, RuPcS1 and [RuPcS(DMSO)2]DMSO). In particular, when the RuPcS complex was irradiated, a stable intermediate was detected that had an absorption band at 532 nm and a mass spectrum attributable to the tetrasulfophthalocyanine from oxidative ring cleavage by the action of the singlet oxygen formed via 1*RuPcS photosensitization. The most probable molecular formula demonstrates a new complex, with a cleaved ring containing an –Ndouble bond; length as m-dashO group and two –OH groups that are all bonded at the two extremities of the open-chain molecule.