CD Stretching Modes are Sensitive to the Microenvironment in Ionic Liquids

Area of Science:

• Electrochemistry
• Surface Science
• Materials Science

Background:

• Understanding the electrical double layer structure in ionic liquids (IL) is vital for electrochemical technologies.
• Amphiphilic ionic liquids offer unique properties for surface studies.
• Imidazolium-based ILs are widely used in various electrochemical applications.

Purpose of the Study:

• To investigate the potential-dependent structural rearrangements of an amphiphilic imidazolium-based ionic liquid on a Au(111) surface.
• To explore changes in the IL's microenvironment using a perdeuterated alkyl chain.
• To correlate electrochemical behavior with molecular-level structural changes.

Main Methods:

• Synthesis of an imidazolium-based amphiphilic ionic liquid with a perdeuterated alkyl chain.
• Electrochemical measurements to study ion organization on the electrode surface.
• In situ infrared (IR) spectroscopy to analyze molecular orientation and environment.
• Quantum chemical calculations to support spectral assignments.

Main Results:

• Two distinct states of ion organization on the electrode surface were identified via electrochemical measurements.
• In situ IR spectroscopy revealed potential-dependent reorientation of alkyl chains in imidazolium cations.
• A new, potential-dependent band in the methylene-d2 stretching modes of the perdeuterated IL was observed, influenced by the anion.
• This new band, assigned to alkyl chains in a polar environment, indicates potential-dependent segregation of polar and nonpolar regions.

Conclusions:

• The study demonstrates potential-driven structural changes in ionic liquid layers at electrode interfaces.
• The observed spectral changes provide a measure of the segregation between polar and nonpolar environments near the electrode.
• This work offers insights into the structure-property relationships of ionic liquids for electrochemical applications.