Far- and deep-ultraviolet spectroscopy applied for ionic liquids

Abstract

Recently, ionic liquids faced on electrodes have been intensively studied because they have been expected as novel electrolytes having high safety and functions. In this study, we constructed an attenuated total reflectance spectroscopic system which worked under electrochemical environments, and investigated electronic states of the ionic liquids near the electrode surface. In accordance with an applied voltage, electronic transition spectra in 150-450 nm range of an ionic liquid consisted of imidazolium cation and iodine anion varied. In particular, absorption due to a charge transfer from the anion to the cation drastically increased at positive potentials. The amount of spectral change and the contact area between the electrode and the ionic liquid were in a positive relationship, and thus, the spectral variations reflected the behavior of the interfacial ionic liquid on the electrode. Time dependence and hysteresis were also discussed. The newly developed system will be applied not only for the ionic liquids but also for various electrochemical materials such as organic semiconductors.