Luminescent Dinuclear Bis-Cyclometalated Gold(III) Alkynyls and Their Solvent-Dependent Morphologies through Supramolecular Self-Assembly

A series of luminescent bis-cyclometalated gold(III) complexes containing bridging alkynyl ligands of different natures has been synthesised and characterised. The photophysical properties of the complexes have been investigated through electronic absorption spectroscopy and emission studies. The vibronic emission bands are found to originate from the triplet intraligand (IL) pi-pi* excited states of the bis-cyclometalating ligands with some mixing of (IL)-I-3 pi-pi* character of the alkynyl ligands. The electrochemical study of a nonsymmetric dinuclear complex shows two successive reduction processes originating from the reductions of the two different cyclometalating ligands. The complexes are found to undergo supramolecular self-assembly processes driven by pi-pi stacking and hydrophobic/hydrophilic interactions to give honeycomb nanostructures, as revealed from the SEM images. Solvent-dependent morphological transformations have also been observed, which have been studied by SEM and H-1 NMR spectroscopy.