ИСТИНА

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 the first EPR evidence of physically trapped electron in a pyrrolidinium-type ionic liquid at low temperature [1]. Here we report the results of the study on paramagnetic intermediates produced by irradiation in a number of ionic liquids of different composition at low temperature. N-metyl-N-butylpyrrolidinium bis(trifluoromethanesulfonyl) imide (P14+NTf2-), 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. The samples of ILs were irradiated with X-rays (20 keV) at 77 K. The EPR spectra of the irradiated samples of ILs reveal superposition of a broad multiplet signal and a narrow singlet signal (ΔB ~ 0.5 mT), attributed to the trapped electron. Experiments with electron scavengers were carried out to investigate the properties of this species. The optical absorption spectra of irradiated ILs in the visible region reveal an absorption band with λmax ≈ 500 nm, presumably attributed to some kind of “hole” species. Photolysis of ILs with red light (λ >700 nm) results in decay of the narrow singlet signal in the EPR spectrum and decrease in the intensity of the absorption band in the visible region. A decay of singlet signal attributed to the trapped electron and decrease of the absorption band under photolysis may be explained by the photoinduced recombination of trapped electron and the “hole” species. 1. E.V. Saenko, K. Takahashi, V.I. Feldman, J. Phys. Chem. Lett. 4 (2013) 2896. This work was supported by the Russian Foundation for Basic Research (project no. 14-03-31978).