ИСТИНА

During the past two decades the room-temperature ionic liquids (IL) were extensively studied as prospective media for various applications. The investigations of trapping and transport of excess electrons generated by ionizing radiation in IL may contribute to better understanding of properties of these unusual media. The time resolved optical spectroscopy studies on irradiated IL revealed the short-lived absorption bands in the near-IR region attributed to solvated electrons [1]. However, the nature of these species is not fully clear. We have investigated a number of glassy IL by EPR, and here we report the first evidence for a physically trapped electron in a pyrrolidinium-type IL at low temperature. Excess electrons were generated by X-ray irradiation of degassed glassy IL at 77 K. A high pressure arc mercury lamp was used for photobleaching experiments. The EPR spectrum of the irradiated N-Butyl-N-methylpyrrolidinium Bis(trifluoromethanesulfonyl)imide (P14+NTf2-) is a superposition of broad multiplet and sharp singlet signal. The latter signal is clearly seen at low microwave power and shows remarkable saturation with increasing the power level. Such a saturation behavior is a typical characteristic of the signals of trapped electrons in low-temperature organic glasses. Furthermore, the relative intensity of the singlet signal decreases with increasing of the absorbed dose value. This effect (the “dose saturation”) is also a common feature of trapped electrons. 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 sharp singlet signal with ΔB = 0.47 mT. This signal decays slowly at 77 K, presumably due to electron tunneling. Even though the yield of trapped electrons revealed by EPR is low, this result appears to be of basic significance, in view of conflicting previous findings. This work was supported by the Russian Foundation for Basic Research (project no. 12-03-01009-a). References [1] James F. Wishart et al., J. Phys. Chem. B 107 (30), 7261 (2003).