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    CD Stretching Modes are Sensitive to the Microenvironment in Ionic Liquids

    Year: 2021

    Journal: Chem.-Eur. J., Volume 27, DEC 20, page 17808–17817

    Authors: Sieling, Thorben; Petersen, Thorben; Alpers, Torben; Christoffers, Jens; Kluener, Thorsten; Brand, Izabella

    Organizations: DFG [BR-3961-5]; DFG through the Major Research Instrumentation Program [INST 184/157.1 FUGG]; Projekt DEAL

    Keywords: ionic liquid; IR spectroscopy; LB monolayer; nanosegregation; perdeuterated hydrocarbon chain

    Knowledge of the structure of the electrical double layer in ionic liquids (IL) 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 IL display a reversible, potential-dependent appearance of a new band. The presence of this mode also depends on the anion in the IL. Supported by quantum chemical calculations, this new mode is assigned to a second nu(as)(CD2) 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 nonpolar environments in the layers of an IL closest to the electrode.
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