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

Abstract

A new photoswitchable anion receptor 1 based on a tetra-meta-substituted azobenzene skeleton has been readily synthesized in two steps. Titration studies (¹H 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 (τ_1/2 = 11 days) is not accelerated by anion binding.