A Photoswitchable Heteroditopic Ion-Pair Receptor

Designing light-switchable hetero­ditopic receptors is challenging because it necessitates simultaneous (de)­activation of two separate binding sites. Herein, we present the first photo­switchable hetero­ditopic ion-pair receptor in which both cation and anion binding sites are simultaneously and reversibly switched OFF and ON by a single photo­switch. Our receptor is simple, low molecular weight, and readily synthesized from commercially available precursors. Single-crystal X-ray structures and NMR spectroscopic titrations support ion-pair binding to the receptor both in the solid state and in solution, with strong positive cooperativity between the cation and anion binding. The receptor can be completely switched OFF by UV light-triggered photo­isomerization of an acyl­hydrazone CN double bond and remains kinetically stable in the deactivated form due to an intra­molecular hydrogen bond. Its re-activation could be achieved by light irradiation or, more effectively, by fast acid-catalyzed back-isomerization. Our simple photo­switchable ion-pair receptor may serve as a blueprint for the design of new generations of switchable receptors, transporters, soft materials, and self-assembled systems, where incorporation of a functional hetero­ditopic ON/OFF photo­switch has been challenging up to now.