Highly phosphorescent iridium complexes with chromophoric 2-(2-hydroxyphenyl)oxazole-based ancillary ligands: Interligand energy-harvesting phosphorescence

We disclose a controlled phosphorescence color tuning in a series of cyclometalated heteroleptic Ir(III) complexes (Ir(III) bis(2-(2,4- difluorophenyl)pyridinato-C,N^2′)(LX)) containing chromophoric 2-(2-hydroxyphenyl)oxazole-derivative ancillary ligands (LX). From a cyclometalated chloride-bridged Ir(III) dimer, three highly emissive cyclometalated heteroleptic Ir(III) complexes were obtained in good yields, each with a different conjugative plane in the chromophoric ancillary ligand (i.e., 2-(2-hydroxyphenyl)-4-methyloxazole, 2-(2-hydroxyphenyl)-6-methylbenzoxazole, and 2-(2-hydroxyphenyl)naphthoxazole). The three Ir(III) complexes showed highly efficient greenish blue (500 nm), green (525 nm), and yellow (552 nm) phosphorescence, respectively; a regular ca. 0.11 eV bathochromic shift was observed for each additional phenyl ring fused to the oxazole ring in the ancillary ligand. From the absorption, electrochemical measurements, static and transient photoluminescence (PL), and time-dependent density functional theory (TD-DFT) calculations, it can be concluded that the Ir(III) complexes have a single emission center with dual excitation paths. Finally, this characteristic energy-harvesting phosphorescence was further demonstrated in electrophosphorescence devices.