Click-Derived Triazolylidenes as Chelating Ligands: Achievement of a Neutral and Luminescent Iridium(III)-Triazolide Complex

Versatility in the synthesis of triazole derivatives was exploited to obtain convenient mesoionic carbenes working as chelating or cyclo-metalating ligands for the preparation of cationic or neutral iridium(III) complexes. We present the synthesis and characterization of three new cationic cyclometalating iridium(III) complexes (1-3-BF4) and a neutral one (4), equipped with functionalized triazolylidene ligands. All the complexes are obtained in good yields, present irreversible or quasi-reversible oxidation and reduction processes, and display good photophysical stability. The complexes emit from (MLCT)-M-3 or (LC)-L-3 states, depending on the nature of the ancillary ligand. Compounds 1-3-BF4 display very low photoluminescence quantum yields (PLQY approximate to 1% in acetonitrile solution). Density functional theory calculations show that the luminescence of these three complexes is quenched by the presence of low-lying (MC)-M-3 states, leading to a reversible detachment of the neutral ancillary ligands coordination sphere. On the contrary, this nonradiative deactivation pathway is not present in the case of the neutral complex 4, which in fact shows PLQYs above 10% and is the best emitter of the series. Moreover, complex 4 represents the first reported example of a photochemically and thermally stable neutral triazolide iridium(III) complex.