Binding of viologen derivatives to cucurbit[8]uril

► Binding of MV2+ to CB[8] host is stronger that in EV2+, PV2+ or BV2+ complexes. ► Encapsulated β hydrogens of viologen guest exhibit shielding in 1H NMR spectra. ► CO and CN stretching vibrations reveal frequency shift in opposite direction. ► Difference electron density and NBO analysis explain direction of frequency shifts.