EPR evidence for a physically trapped excess electron in a glassy ionic liquid

The fate of excess electron produced in room temperature ionic liquids is an attractive and important topic, and its kinetics and optical absorption spectrum have been studied using pulse radiolysis and laser photolysis. However, there has been no clear evidence for existence of the solvated electron in EPR experiments. Here we report that an EPR spectrum of irradiated glassy pyrrolidinium-based ionic liquid at 77 K reveals a sharp singlet signal (line width of 0.47 mT), which can be attributed to a physically trapped (solvated) electron. The EPR signal shows easy microwave power saturation and is effectively bleached with red light (>600 nm). The present results have important implications for the characterization of trapped or solvated electrons in ionic liquids and better understanding of their structure and reactivity.