Luminescent Iridium(III) Cyclometalated Complexes with 1,2,3-Triazole “Click” Ligands

A series of cyclometalated iridium­(III)
complexes with either 4-(2-pyridyl)-1,2,3-triazole or 1-(2-picolyl)-1,2,3-triazole
ancillary ligands to give complexes with either 5- or 6-membered chelate
rings were synthesized and characterized by a combination of X-ray
crystallography, electron spin ionization–high-resolution mass
spectroscopy (ESI-HRMS), and nuclear magnetic resonance (NMR) spectroscopy.
The electronic properties of the complexes were probed using absorption
and emission spectroscopy, as well as cyclic voltammetry. The relative
stability of the complexes formed from each ligand class was measured,
and their excited-state properties were compared. The emissive properties
are, with the exception of complexes that contain a nitroaromatic
substituent, insensitive to functionalization of the ancillary pyridyl-1,2,3-triazole
ligand but tuning of the emission maxima was possible by modification
of the cyclometalating ligands. It is possible to prepare a wide range
of optimally substituted pyridyl-1,2,3-triazoles using copper Cu­(I)-catalyzed
azide alkyne cycloaddition, which is a commonly used “click”
reaction, and this family of ligands represent an useful alternative
to bipyridine ligands for the preparation of luminescent iridium­(III)
complexes.