Multiresponsive Luminescent Cationic Cyclometalated Gold(III) Amphiphiles and Their Supramolecular Assembly.

A new class of amphiphilic tridentate cyclometalated gold(III) complexes has been designed and synthesized as luminescent supramolecular building blocks. Positively charged trimethylammonium (-CH2NMe3+) containing alkynyl ligands have been incorporated to introduce the electrostatic interactions. The X-ray crystal structures of two of the complexes have been determined, and the existence of π-π interactions between molecules has been observed. Steady-state and time-resolved absorption and emission studies have been carried out to investigate the nature of the excited states. The complexes are found to exhibit self-assembly properties with the assistance of π-π stacking and hydrophobic interactions and possibly weak Au···Au interaction, resulting in notable emergence of low-energy absorption bands and luminescence changes. The presence of a large hydrophobic moiety is found to be crucial for the formation of aggregates, especially in polar media where hydrophobic interactions play an important role. The nature of the counterion has been shown to have a significant effect on the extent of self-assembly in different media. Upon aggregation, nanofibers are formed in polar media, while nanorods are observed in nonpolar media in one of the representative complexes. Interestingly, a small modification on the alkynyl ligand resulted in the formation of nanoribbons instead. Intriguing luminescence mechanochromic properties have also been observed. This orthogonal and rational molecular design strategy has been shown to be effective in the construction of gold(III)-based smart and multiresponsive materials.

Luminescent Bis-Cyclometalated Gold(III) Complexes with Alkynyl Ligands of Hexaphenylbenzene and Hexabenzocoronene Derivatives and Their Supramolecular Assembly.

A series of luminescent bis-cyclometalated gold(III) complexes with different nuclearities and various alkynyl ligands derived from hexaphenylbenzene (HPB) and hexabenzocoronene (HBC) have been synthesized. The energies of the low-energy metal-perturbed intraligand (IL) π-π*(R-C^N^C) absorptions of the HPB-alkynyl gold(III) complexes have been fine-tuned by attaching various substituent groups to the bis-cyclometalating ligands. Similarly, the metal-perturbed 3 IL [π→π*(R-C^N^C)] emissions of the complexes show energy shifts according to the electronic nature of the bis-cyclometalating ligands. On the contrary, the absorption and emission spectra of the HBC-alkynyl gold(III) complex have been assigned as dominated by the IL transitions of the HBC-alkynyl unit, as supported by transient absorption studies. The supramolecular assembly morphologies of the gold(III) complexes have been studied by TEM and SEM, along with comparisons across different complexes based on the molecular structures, and their assembly processes monitored by concentration-dependent and variable-temperature 1 H NMR spectroscopy studies.

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) π-π* excited states of the bis-cyclometalating ligands with some mixing of 3 IL π-π* 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 π-π 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 1 H NMR spectroscopy.

Synthesis, characterization, self-assembly, gelation, morphology and computational studies of alkynylgold(III) complexes of 2,6-bis(benzimidazol-2'-yl)pyridine derivatives.

A novel class of alkynylgold(III) complexes of the dianionic ligands derived from 2,6-bis(benzimidazol-2'-yl)pyridine (H2bzimpy) derivatives has been synthesized and characterized. The structure of one of the complexes has also been determined by X-ray crystallography. Electronic absorption studies showed low-energy absorption bands at 378-466 nm, which are tentatively assigned as metal-perturbed π-π* intraligand transitions of the bzimpy(2-) ligands. A computational study has been performed to provide further insights into the nature of the electronic transitions for this class of complexes. One of the complexes has been found to show gelation properties, driven by π-π and hydrophobic-hydrophobic interactions. This complex exhibited concentration- and temperature-dependent (1)H NMR spectra. The morphology of the gel has been characterized by transmission electron microscopy (TEM) and scanning electron microscopy (SEM).