A new photo-switchable “on-off” host–guest system

A new photo-switchable “on-off” host–guest system comprising cucurbit[7]uril (CB[7]) and a photoresponsive cinnamamide derivative (trans-(3-phenyl-acryloylamino)-acetic acid, E-1) is studied. The cinnamamide derivative and CB[7] forms a stable 1 : 1 host–guest complex (CB[7]·E-1) with a high binding constant (K = 2.1 × 104 M−1). Irradiation of UV light (300 nm) to an aqueous solution of CB[7]·E-1 induces the E- to Z-conformational change of the cinnamamide derivative, which then leads to the dissociation of the complex as evidenced by UV-visible and 1H-NMR spectroscopy. The reverse process, photo-induced host–guest complex formation between CB[7] and Z-1 is achieved by irradiation of UV light at 254 nm. The photo-switchable “on-off” host–guest system shows high reversibility and switching efficiency, which makes it potentially useful in designing photoresponsive gating systems.