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

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. Mononuclear Au( i ) complexes with ligands containing azobenzene or stilbene demonstrate efficient trans → cis photoisomerization and luminescent response of the "on-off" process.