Photodegradation products of imidazolium ionic liquids by using 266nm laser irradiation are reported. It is found that photodegradation productsconsist of several highly colored and colorless products. The main photodegraded products are the imidazolium salt with butyl chain dissociated. Photodegradation depends on anion. Photostability was found to increase in the order : bis(trifluoromethanesulfonyl)imide (Tf2N)- > BF4- >Pf6-. C-2 substitution to methyl group of ionic liquids have a great effect to suppress the photo-degradation. Reaction mechanism is related to the C-2 proton acidity and hydrogen bonding between cation and anion. These results indicate that for photochemical reaction in imidazolium ionic liquids by using UV light source should be noted and the deactivation caused by the photolysis of ionic liquids should be considered.
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