Novel gold(i) diphosphine-based dimers with aurophilicity triggered multistimuli light-emitting properties

We report a design strategy for the preparation of stimuli-responsive materials with multicolour emission that is based on a single type of luminophore molecule comprising gold(i) and a flexible diphosphine ligand. Multistimuli-responsive luminescent dinuclear [Au₂(dpephos)₂](X)₂ (dpephos = bis(2-diphenylphosphino)-phenyl ether; X = NO₃, 1; CF₃SO₃, 2; BF₄, 3; PF₆, 4; SbF₆, 5) complexes were obtained by rapid mechanochemical syntheses. The single crystal X-ray diffraction analysis of complexes 1-5 revealed that the [Au₂(dpephos)₂]²⁺ cations do not exhibit short intramolecular aurophilic interactions. Supported by the structural flexibility of the dpephos ligand, these intramolecular Au⋯Au contacts are highly sensitive to external stimuli, such as light, temperature, mechanical grinding and exposure to solvent vapours. The ensuing materials, which comprise only gold(i)-diphosphine luminophores, can emit green, yellow and red colours, and the colour of the emitted light can be switched by light, heat or pressure. A change from green to yellow in the emission was observed upon heating to room temperature under the 365 nm excitation, whereas a change from yellow to red was achieved by mechanical grinding. Moreover, the green emission can be switched to red by changing the excitation wavelength to 312 nm. All these reversible luminescence colour changes are readily perceivable by the naked eye, and they are attributed to small structural modifications induced by external stimuli that also modulate the intramolecular Au⋯Au interaction. The red emission from these gold(i) diphosphine-based dimers can be attributed to the presence of intramolecular aurophilic interaction.