Synthesis and Characterization of a [1,2,6]Diazaphosphonine Oxide: An Example of a Photoswitchable Phosphorus-Containing Cyclic Azobenzene

We report herein the synthesis and characterization of a phosphorus-containing cyclic azobenzene as a new photoswitchable scaffold. This backbone reveals high bidirectional photoswitching yields and high thermal stability for both isomers, with t_1/2 > 90 days at 60 °C. Both E- and Z-isomers have been characterized by UV–vis spectroscopy and X-ray crystallography.