Modular Imine Chelates with Variable Anionic Donors Promote Red Phosphorescence in Cyclometalated Iridium Complexes

The lack of red and deep-red emitting molecular phosphorswithhigh photoluminescence quantum yields remains a significant fundamentalchallenge and has implications in optoelectronic technologies forcolor displays and other consumer products. In this work, we introducea series of seven new red or deep-red emitting heteroleptic bis-cyclometalatediridium(III) complexes, supported by five different ancillary ligands(L<^>X) from the salicylaldimine and 2-picolinamide families. Previouswork had shown that electron-rich anionic chelating "L<^>X"ligands can be effective in supporting efficient red phosphorescence,and the complementary approach described here, in addition to beingsynthetically simpler, offers two key advantages over the previousdesigns. First, the "L" and "X" functionalitiescan be independently tuned, providing excellent control over the electronicenergy levels and excited-state dynamics. Second, these classes ofL<^>X ligands can have beneficial impacts on the excited-state dynamicsbut do not significantly perturb the emission color profile. Cyclicvoltammetry experiments show that the substituents on the L<^>X ligandimpact the HOMO energy but have a minimal effect on the LUMO energy.Photoluminescence measurements reveal that all the compounds luminescein the red or deep-red region as a function of the cyclometalatingligand and exhibit exceptionally high photoluminescence quantum yields(& phi;(PL)), comparable or superior to the best-performingred-emitting iridium complexes. Red and deep-redphosphorescent cyclometalated iridium complexessupported by ancillary ligands from the salicylaldime and 2-picolinamidefamilies are described. The nonradiative rate constant is sensitiveto the N-substituent on the ancillary ligand, allowingphotoluminescence quantum yield to be optimized, with values as highas 0.80 in solution and 0.93 in dilute polymer film for the red regionand similarly high in the deep red region.