Potential Dependence of Electronic Transition Spectra of Interfacial Ionic Liquids Studied by Newly Developed Electrochemical Attenuated Total Reflectance Spectroscopy

Abstract

Recently, ionic liquids at the electrode/ionic liquid interface have been intensively studied because they are promising as novel alternatives to traditional electrolyte solutions that are both safe and functional. In this study, we constructed an attenuated total-reflectance spectroscopic system that operates under electrochemical conditions in order to investigate the electronic states of ionic liquids near the electrode surface. Upon application of voltage to an ionic liquid consisting of imidazolium cations and iodide anions, electronic transition spectra in the 150−450 nm range varied. In particular, absorbance due to charge transfer from the anion to the cation drastically increased at positive potentials. The extent of spectral change and contact area between the electrode and the ionic liquid were positively correlated, and thus spectral variations reflected the behavior of the interfacial ionic liquid on the electrode. In addition to potential dependence, time dependence and hysteresis were also investigated. The newly developed system can be applied not only for ionic liquids but foreseeably also for various electrochemical materials such as organic semiconductors.

Insight into the effect of contact ion pairs on C-H bond activation for the synthesis of Ru(III)-NHC complexes: A combined experimental and computational study

“…41 In addition, on increasing the concentration of the solution, a broad background absorption at 360 nm followed by a gradual rise in the curve from 326 nm was observed, which can be assigned as the CT band in ion pairs. 37,38,42 Similar to the previous reports, with increase in concentration, the intensity of CT band was also increased whereas the →* bands at shorter wavelength were diminished (See SI, Figure S9). 41 Both, NMR and UV-Vis investigations confirm the ion-pair interactions and existence of contact ion-pairs in [PyIm iPr •HX] in solutions.…”

“…Interactions between azolium cations and anions such as halides and other bulkier anions have been studied by several groups, and previous reports suggest that halides develop stronger and more stable interactions with imidazolium proton compared to bulkier anions (BF4,PF6, BPh4, etc.). [42][43][44] To investigate the structure of the [PyIm R ][X] (R=Me, i Pr) based ion pairs, a stepwise optimization process was followed. Initially, we optimized the pyridine imidazolium ligand Furthermore, halides or other counteranions were added to the optimized azolium cations, and the geometries were re-optimized to observe changes in the bond parameters and dihedral angles.…”

Changes in the Electronic Transitions of Polyethylene Glycol upon the Formation of a Coordinate Bond with Li+, Studied by ATR Far-Ultraviolet Spectroscopy

“…On the other hand, in concentrated ionic materials such as ionic liquids, electronic transitions in an anion or a cation can be observed in the FUV and deep-UV regions. − RTILs with imidazolium cations show two peaks because of the highest occupied molecular orbital (HOMO) – 1 (π)–lowest occupied molecular orbital (LUMO) (π*) and HOMO (π)–LUMO (π*) transitions, and these differences originate from the localization in the imidazolium ring by double bonding. Moreover, RTILs with a halide yield a CT transition, and the peak intensity of this transition changes slowly with a change in potential (from +200 to −200 V).…”

ATR-far-ultraviolet spectroscopy: a challenge to new σ chemistry

“…Recently, we constructed a new electrochemical-ATR-UV-visible spectroscopic system, which can measure the spectra under voltage applications. 28 In this system, working electrode films (∼10 nm thickness) such as metal (Pt) and organic film were deposited on an ATR prism. Subsequently, other liquid or solid materials was placed on the working electrode.…”