No abstract

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).

A new class of amphiphilic tridentate cyclometalated gold(III) complexes has been designed and synthesized as luminescent supramolecular building blocks. Positively charged trimethylammonium (−CH 2 NMe 3 + ) 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 selfassembly 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.