Tetra-(meta-butylcarbamoyl)azobenzene: A Rationally Designed Photoswitch with Binding Affinity for Oxoanions in a Long-Lived Z-State

A new photoswitchable anion receptor 1 based on a tetra-meta-substituted azobenzene skeleton has been readily synthesized in two steps. Titration studies (H-1 NMR) and theoretical predictions (DFT/M06-2X/6-31G(d)/DMSO-SM8) revealed that nonplanar Z-1 is a better host for anions than E-1, which results from the greater ability of four amide NH protons in the Z-state to cooperatively bind oxoanions, in particular tetrahedral H2PO4- and H2AsO4-. Furthermore, the thermal decay of Z-1 (tau(1/2) = 11 days) is not accelerated by anion binding.