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 beta-diketonate ligands are reported. These complexes have a general formula C boolean AND N2Ir(LL') [ where C boolean AND 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)(2)Ir(acac) (3), (dfpbo)(2)Ir(acac) (4), (cpbo)(2)Ir(dbm) (7), (dfpbo)(2)Ir(dbm) (8), and (dfpbo)(2)Ir(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 (tau = 0.1-1.3 mu s) at room temperature. Except complex 9, the radiative decay rate (k(r)) and nonradiative decay rate (k(nr)) of the (C boolean AND N)(2)Ir(LL') complexes have been determined by using the lifetime and quantum efficiency. The kr ranges between 2.0 x 10(3) and 3.0 x 10(5) s(1) and knr spans a narrower range of values (5.0 x 10(5) to 7.0 x 10(6) s(1)). (C) 2008 Elsevier B.V. All rights reserved.