Efficient photoswitchable organometallic complexes with azobenzene and stilbene units: the case of Au(I)

Two families of hetero- and homoleptic mononuclear Au(I) complexes with alkynyl ligands containing an azo (XN) or stilbene (XC) group have been prepared and characterized by spectroscopic methods and single crystal XRD. Each family contains complexes with phosphine and carbene ancillary ligands and bis-alkynyl species. The Au(I) complexes obtained in the present study demonstrate transformation of the trans- to cis-form of the photoswitchable group under near-UV irradiation, which was investigated by spectroscopic and computational methods. In contrast to stilbene derivatives XC, the bathochromic shift of absorption for azobenzene Au(i) complexes XN demonstrates sensitivity to the nature of the ancillary ligand. It was found that the quantum yield of trans -> cis photoisomerization of organogold(i) derivatives is comparable to that for native photoswitches, and alkynyl-carbene complex 5C with a stilbene group demonstrates a substantially higher quantum yield and shows more impressive photochromic behaviour. The conservation of the photoisomerisation quantum yield for {metallocentre + photoswitch} molecular systems in comparison with native photoswitch molecules is rare, and the enhancement of this value is a unique case to date. It was found that a change in the configuration of the ligand environment due to photoswitching of the stilbene fragments in homoleptic bis-alkynyl Au(i) complex 6C leads to the activation of triplet emission and luminescent visualization of the "on-off" process.