X-ray Photoelectron Spectroscopy of Cyano-Containing Ionic Liquids: C 1s Fitting Model and Impact of Anion Charge Delocalization on Binding Energies

We investigate four cyano-containing ionic liquids, 1-octyl-3-methylimidazolium thiocyanate, 1‑octyl-3-methylimidazolium dicyanamide, 1-octyl-3-methylimidazolium tricyanomethanide, and 1-octyl-3-methylimidazolium tetracyanoborate, using X-ray photoelectron spectroscopy. A four-component C 1s spectrum fitting model is developed in particular for these four ionic liquids, by modifying the existing model with additional anionic carbon contributions. The impact of the anion charge delocalization on the electronic environment of the cyano-nitrogen is discussed. It concludes that by increasing the number of the cyano group, a 0.5 eV binding energy shift can be observed for the three charge delocalized anions. For the non-delocalized anion, a much higher binding energy can be measured. There is a linear correlation of N 1s binding energy and the point charges located on cyano nitrogen atoms.