Kinetico-mechanistic insights into the photodynamic process of AuI complexes with the CNC6H4NNC6H5 (iso-Ph) azobenzene ligand

Abstract

A family of neutral isocyanide monoazo Au^I complexes [AuCl(iso-Ph)], [Au(C₆F₅)(iso-Ph)] and [Au(CCpy)(iso-Ph)] (iso-Ph being CN–C₆H₄–NN–Ph) and a closely related cationic bisazo symmetrical derivative, [Au(iso-Ph)₂](OTf), have been prepared. All the compounds have been structurally characterized using the conventional techniques HRMS, NMR, UV-Vis and IR spectroscopy. Moreover, the structure of the [AuCl(iso-Ph)] compound has been determined by XRD. These compounds undergo more efficient trans-to-cis photoisomerisation upon irradiation at 365 nm than that of the free iso-Ph ligand. The reverse cis-to-trans thermal process has been investigated using different solvents, temperatures and pressures to determine the values of the activation parameters and thus, the corresponding isomerisation mechanism. A change in the operating mechanism (from charge-separated rotational to inversional) has been observed upon going from the monoazo to the bisazo compounds. This effect has been attributed to the difference in the electronic density at the Au^I centre in the transition state between the unsymmetrical and the symmetrical species.