Electron Density Shift in Imidazolium Derivatives upon Complexation with Cucurbit[6]uril

In this study, we have investigated the supramolecular interaction between series of 1‐alkyl‐3‐methylimidazolium guests with variable alkyl substituent lengths and cucurbit[6]uril (CB6) in the solution and the solid state. Correct interpretation of 1H NMR spectra was a key issue for determining the binding modes of the complexes in solution. Unusual chemical shifts of some protons in the 1H NMR spectra were explained by the polarization of the imidazolium aromatic ring upon the complexation with the host. The formation of 1:1 complex between 1‐ethyl‐3‐methylimidazolium and CB6 is in disagreement with previously reported findings describing an inclusion of two guest molecules in the CB6 cavity. Search for cavities: The complexation between 1‐alkyl‐3‐methylimidazolium guests and cucurbit[6]uril are accompanied by an electron density shift in the imidazolium ring. The modes of binding between the guests and host cavity are dependent on the length of alkyl chain (see figure).