ИСТИНА

Introduction The investigation of trapping and transport of excess electrons generated by light or ionizing radiation in ionic liquids (IL) is important for better understanding of the structure, dynamics and electronic properties of these unusual media and, in particular, of their radiation chemistry and photochemistry. Previously we have presented first EPR evidence of physically trapped electron in a pyrrolidinium-type ionic liquid at low temperature [1]. Here we report comparative EPR studies of the low-temperature radiolysis of ILs with different cations. Experimental N-metyl-N-propylpyrrolidinium bis(trifluoromethanesulfonyl) imide (P13+NTf2-) and N-metyl-N-propylpiperidinium bis(trifluoromethanesulfonyl) imide (PP13+NTf2-) (Kanto Chemical Co., Inc) were used without additional purification. ILs were placed into SK-4B glass ampoules (optically transparent at λ > 370 nm), which gave no background EPR signal after irradiation. Then the samples were degassed at the temperature of 363 K and irradiated with X-rays (30 keV) at 77 K. EPR spectra were measured at 77 K using an X-band (9.4GHz) spectrometer with 100 kHz high-frequency modulation manufactured by SPIN (St. Petersburg, Russia). A high pressure arc mercury lamp (250 W) equipped with a series of filters was used for photobleaching experiments. Results and Discussion The EPR spectra of the irradiated ILs show a superposition of a broad multiplet signal and a sharp singlet signal. The former signal may be attributed to the alkyl-type radicals from the cation. The latter signal is clearly seen at low microwave power and shows remarkable saturation with the increasing of microwave power level. Such a saturation behavior is a typical characteristic of the signals of trapped electrons in low-temperature organic glasses. Photolysis with near IR light (λ > 700 nm) results in significant decay of the singlet signal without any other changes in the spectrum pattern. Difference spectrum shows that the bleached species is characterized by a narrow singlet signal, which is attributed to a physically trapped electron. The slow kinetics of trapped electron decay at 77 K is in agreement with the assumption of electron decay by tunneling mechanism. Summary Our investigations demonstrate the EPR evidence of physically trapped electron in pyrrolidinium- and piperidinium-type glassy ionic liquids at low temperature. This work was supported by the Russian Foundation for Basic Research (project no. 14-03-31978). References [1] E.V. Saenko, et al., J. Phys. Chem. Lett. 4, 2896 (2013).