Metal Complexes with Azolate-Functionalized Multidentate Ligands: Tactical Designs and Optoelectronic Applications

This review is aimed at updating the recent development on the metal complexes bearing azolate-containing chelates that have received a growing attention from both the industrial and academic sectors. Particular emphasis is given to the luminescent metal complexes, for which tridentate and multidentate bonding interactions give rise to both higher ligand field strength and better rigidity versus their bidentate counterparts-consequently, this is beneficial to the chemical stability and emission efficiency needed for applications such as organic light-emitting diodes and bio-imaging. Their basic designs involve chelates, such as monoanionic 6-azolyl 2,2'-bipyridine, dianionic 2,6-diazolylpyridine, and 2-azolyl-6-phenylpyridine, and the core metal ion spanning from main group elements, such as Ga-III and In-III, to the late transition metal ions such as Ru-II, Os-II, Ir-III, and Pt-II and even the lanthanides. Furthermore, the great versatility of these azolate chelates for assembling the robust and emissive metal complexes, provides bright prospect in future optoelectronic investigations.