To further probe the different binding properties of E and Z isomers, we turned to 1 H NMR spectroscopy to obtain more detailed structural information about the binding interactions. Owing to the fast thermal relaxation of the active E form, it was not possible to study the binding by NMR at ambient temperature, because the ligand reverts to the inactive Z form too quickly on the timescale of the NMR experiment. Therefore, we studied the ligand binding at lower temperature (5 °C) in order to discriminate the different binding properties of the two isomers. In each case, ligand aliquots were added and the spectral changes of the G4