The Photodegradation of Dyes Studied by EPR Spectroscopy
| Main Authors: | , , , , |
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| Format: | Article |
| Language: | English Slovak |
| ISBN: | ISBN 80-227-1942-0 |
| Online Access: | http://www.viks.sk/chk/wpp2_2003.doc |
| Abstract: | SUMMARIES. The production of reactive radical species upon irradiation ( > 300 nm) of six triarylmethane dyes, i.e. Basic Fuchsin, Crystal Violet, Malachite Green, Acid Green 16, Victoria Blue, Acid Blue 93, as well as Methylene Blue and Eosin Y in different solvents (water, ethanol, dimethylsulfoxide). and on paper substrate was investigated by means of EPR spectroscopy. The EPR experiments using spin trapping agents evidenced the free radicals formation in both deoxygenated and aerated systems during pho-toexcitation. The photooxidation processes in presence of oxygen resulted in the electron transfer generating super-oxide anion radical (Type I process), simultaneously with energy transfer producing singlet oxygen (Type II process). CONCLUSION. The results of EPR investigations of six triarylmethane dyes (Basic Fuchsin, Malachite Green, Crystal Violet, Acid Green 16, Victoria Blue R. Acid Blue 93), as well as Methylene Blue and Eosin Y may be summarized as follows: ˙ The EPR spectra of investigated dyes (original powder samples measured at 290 K) are characterized by anisotropic paramagnetic signals at geff = 2.0044. which were attributed to the peroxidic intermediates produced by the autoxi-dation processes. The highest autoxidation deterioration was observed for dyes, which evidenced the most efficient production of singlet oxygen. ˙ The excitation of oxygenated aqueous solutions of Malachite Green, Crystal Violet, Acid Green 16 a Methylene Blue in the presence of DMPO spin trap resulted in the formation of EPR signal corresponding to DM POOH adduct. The hy-droxyl radicals were produced from the primary generated super-oxide anion radicals transformed by a sequence of reactions. ˙ Irradiation of triarylmethane dyes in argon-saturated DMSO solutions in the presence of DMPO and ND initiated the generation of various radical products evidenced as the corresponding spin adducts. Under oxygen, the effective electron transfer from the photoexcited dye molecules to oxygen was confirmed. The application of selective agent for singlet oxygen detection (TMP) brought evidence on the efficient formation of 1O2 in the irradiated DMSO solutions of Methylene Blue and Eosin Y, and additionally in most of triarylmethane dyes. ˙ The photochemical excitation of ethanolic solutions of dyes led to the formation of reactive radical species in both argon- or oxygen-saturated systems. The radical species identified upon irradiation of dye solutions in the presence of spin trap agents under various conditions reflected the significant influence of dye structure on their photostability; for triarylmethane dyes the dominant effect plays the character and number of substitutions on aryl-methane core. The results of EPR spin trapping experiments could be correlated with light induced photofading of arylmethane dyes on paper surfaces. |
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| ISBN: | ISBN 80-227-1942-0 |
