CD Stretching Modes are Sensitive to the Microenvironment in Ionic Liquids

Abstract

Knowledge of the structure of the electrical double layer in ionic liquids is crucial for their applications in electrochemical technologies. We report the synthesis and applicability of an imidazolium-based amphiphilic ionic liquid with a perdeuterated alkyl chain for studies of electric potential-dependent rearrangements, and changes in the microenvironment in a monolayer on a Au(111) surface. Electrochemical measurements show two states of the organization of ions on the electrode surface. In situ IR spectroscopy shows that the alkyl chains in imidazolium cations change their orientation depending on the adsorption state. The methylene- d 2 stretching modes in the perdeuterated SAIL display a reversible, potential-dependent appearance of a new band. The presence of this mode also depends on the anion in the SAIL. Supported by quantum chemical calculations, this new mode is assigned to a second n as (CD 2 ) band in alkyl-chain fragments embedded in a polar environment of the anions/solvent present in the vicinity of the imidazolium cation and electrode. It is a measure of the potential-dependent segregation between polar and non-polar environments in the layers of a SAIL closest to the electrode.