A reversibly photoswitchable mononuclear palladium(ii) complex with ortho-diethylated azobenzene ligands

Abstract

A mononuclear palladium(II) complex (PdCl₂(2Et-Azo)₂), with sterically bulky ortho-diethylated azobenzenes (2Et-Azo) in the long-lived cis form, was designed to achieve reversible photoswitching originating from a reversible change in its molecular structure. An X-ray crystallographic study indicated that the metal center in the complex has a trans square-planar structure, with two 2Et-Azo ligands coordinated to a palladium ion in a monodentate manner. Alternating UV and visible light irradiation of PdCl₂(2Et-Azo)₂ gave rise to reversible changes in the molecular structure between the trans and cis forms, confirmed by UV-vis absorption and NMR spectroscopic measurements. Neither significant decomposition nor fast dissociation of PdCl₂(2Et-Azo)₂ was observed by UV and visible light irradiation. Furthermore, slow thermal back-isomerization occurred over the course of 2 days at ambient temperature, which may be closely related to the stability of the cis form of the ortho-alkylated azobenzene ligand.