Novel deep red to near-infrared phosphorescent iridium(III) complexes bearing pyrenyl: Syntheses, structures and modulation of the photophysical properties

The extension of π-conjugation and the introduction of substituents are efficient channel for achieving low-energy emitting phosphors. To investigate the influence of substituent effect on the deep-red or near-infrared iridium(III) complexes containing great π-conjugation cyclometalating ligands, we synthesized four pyrenyl-based heteroleptic Ir(III) complexes bearing electron-withdrawing or -donating groups. The four Ir(III) complexes comprise 5-R-2-(1-pyrenyl)pyridine (R = H, CF3, F, CH3) as the main ligands and 2,2,6,6-tetramethyl-heptane-3,5-dione as ancillary ligands. Their structures and coordination geometries are determined by single crystal X-ray diffraction. It is found that the emission profiles of four complexes are located on deep red to near-infrared region and -CF3 substitution leads to a bathochromic shift of 11 nm relative to the unsubstituted complex. From density functional theory calculation results as well as electrochemical analysis, their HOMO and LUMO energy levels fall in the order of substituents -CF3 < -F < -H < -CH3. Intriguingly, the electron density distributions of LUMOs of both -CF3 and -CH3 substituted complexes are more susceptible than their HOMOs, while the HOMO of the -F substituted complex is more susceptible. Our work showcases the vital significance of substituent effect on modulating the electronic structure of deep-red or near-infrared iridium complexes cyclometalated by great π-conjugation cyclometalating ligands.