A rare case for binding a diquat salt by two cyclo[6]aramides

The non-aggregational cyclo[6]aramide has demonstrated 2:1 host–guest complexation towards diquat with very strong binding ability (K ₁ = 5.41 × 10⁴ M^− 1, K ₂ = 4.33 × 10⁶ M^− 1). The donor–acceptor binding process of the macrocycle and the quaternary salt was investigated by ¹H NMR, ESI mass spectrometry and UV–vis spectroscopy. The binding mode is supported by both experiments and theoretical simulations. This work provides the first example of using recently developed H-bonded aromatic oligoamide macrocycles for binding diquat in solution.