Synthesis and characterization of cyclometalated iridium(III) complexes containing benzoxazole derivatives and different ancillary ligands

The synthesis, structures, electrochemistry, and photophysics of a series of cyclometalated iridium(III) complexes based on benzoxazole derivatives and different β-diketonate ligands are reported. These complexes have a general formula C∧N2Ir(LL′) [where C∧N is a monoanionic cyclometalating ligand; 2-phenylbenzoxazolato (pbo), 2-(4-chlorophenyl)benzoxazolato (cpbo), 2-phenyl-5-chlorobenzoxazolato (pcbo), 2-(3,5-difluorophenyl)benzoxazole (fpbo), or 2-(2-naphthyl)benzoxazolato (nbo), and LL′ is an ancillary ligand; acetylacetonate (acac), dibenzoylmethanate (dbm), or 1,1,1,5,5,5-hexafluoroacetylacetonate (hfacac)]. The complexes (pcbo)2Ir(acac) (3), (dfpbo)2Ir(acac) (4), (cpbo)2Ir(dbm) (7), (dfpbo)2Ir(dbm) (8), and (dfpbo)2Ir(hfacac) (9) have been structurally characterized by X-ray crystallography. All of the complexes show reversible oxidation between 0.45 and 1.07 V, versus Fc/Fc+, and have short luminescence lifetime (τ = 0.1–1.3 μs) at room temperature. Except complex 9, the radiative decay rate (kr) and nonradiative decay rate (knr) of the (C∧N)2Ir(LL′) complexes have been determined by using the lifetime and quantum efficiency. The kr ranges between 2.0 × 103 and 3.0 × 105 s−1 and knr spans a narrower range of values (5.0 × 105 to 7.0 × 106 s−1).