Photochromism of 3-butyl-1-methyl-2-phenylazoimidazolium in room temperature ionic liquids |
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Authors: | Tooru Asaka Nobuyuki Akai Akio Kawai Kazuhiko Shibuya |
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Institution: | Department of Chemistry, Graduate School of Science and Engineering, Tokyo Institute of Technology, 2-12-1 H89, Ohokayama, Meguro-ku, Tokyo 152-8551, Japan |
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Abstract: | We studied the photochromism of a newly synthesized ionic liquid, 2PA-Bmim]Tf2N (2PA-Bmim]+: 3-butyl-1-methyl-2-phenylazoimidazolium, Tf2N?: bis(trifluoromethanesulfonyl)-amide) which is characterized by a phenylazo group substituted on the imidazolium ring. The melting point of 2PA-Bmim]Tf2N is 329 K. The absorption spectrum of 2PA-Bmim]+ dissolved in conventional organic solvents or in ionic liquids changes drastically upon UV-light irradiation, which is attributed to the photoisomerization of the phenylazo group from E- to Z-forms during irradiation and the backward thermal isomerization from Z- to E-forms in the dark. The E–Z photoisomerization quantum yield, Φiso, was determined by 355 nm laser photolysis. The Φiso value slightly depends on solvent viscosity, from 0.12 in 3-butyl-1-methylimidazolium PF6? (η = 241 cP) to 0.19 in toluene (η < 1 cP). On the other hand, no solvent dependence was observed for Arrhenius parameters of the backward Z–E thermal isomerization. We discuss the isomerization mechanism and the reason why the E–Z photoisomerization yield depends on solvent viscosity. |
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