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 1 H-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