LAUSR

Several platinum(ii) complexes with ligands containing azo groups have been prepared and structurally characterised, and their photoswitching between trans and cis azo group isomers has been studied. The azo groups in the cationic complexes [PtMe(bipy)(4-NC5H4-N[double bond, length as m-dash]N-4-C6H4X)][PF6], X = H, OH or NMe2, and in the dicationic complex [Pt(bipy)(4-H2NC6H4-N[double bond, length as m-dash]N-C6H5)2][OTf]2 undergo trans to cis photoswitching on irradiation at 365 nm. The complex [PtMe(bipy)(4-NC5H4-N[double bond, length as m-dash]N-4-C6H4NMe)2][PF6] also exhibits a reversible halochromic effect on protonation to give the dicationic complex [PtMe(bipy)(4-NC5H4-NH[double bond, length as m-dash]N-4-C6H4NMe2]2+. The nature of the frontier orbitals in the platinum(ii) complexes depends on the charge on the complex and on the degree of metal-ligand π-bonding.