EPR study of photochemical transformations of triarylmethane dyes

摘要

The production of reactive radical species upon irradiation (gamma>300 nm) of six triarylmethane dyes,i.e.C.I.Basic Red 9 (42500;Basic Fuchsin),C.I.Basic Violet 3 (42555;Crystal Violet),C.I.Basic Green 4 (42000;Malachite Green Oxalate),C.I.Acid Green 16 (44025;Acid Green V),C.I.Basic Blue 11 (44040;Victoria Blue R),C.I.Acid Blue 93 (42780;Aniline Blue),as well as a phenothiazine dye C.I.Basic Blue 9 (52015;Methylene Blue) and a xanthene dye C.I.Acid Red 87 (45380;Eosin Y) in different solvents (water,ethanol,dimethylsulphoxide),and subsequently on paper substrate was investigated by means of EPR spectroscopy.The EPR experiments using spin trapping agents (5,5-dimethyl-1-pyrroline-N-oxide,DMPO and 2,3,5,6-tetramethyl nitrosobenzene,ND) showed evidence of the free radical formation in both deoxygenated and aerated systems during photoexcitation.The photooxidation processes in presence of oxygen resulted in the electron transfer generating super-oxide anion radicals (Type I process),simultaneously with energy transfer producing singlet oxygen (Type II process) confirmed by 2,2,6,6-tetramethyl-4-piperidinol (TMP).