A New Type of Iridium () Phenylpyrazole Complexes: Synthesis, Photophysical Characterization

New heteroleptic iridium() complexes (ppz)₂Ir(LX), which consist of two cyclometalated ligands ppz(1-phenylpyrazole) together with an ancillary ligand LX (LX= 2-(2’-hydroxylphenyl)benzothiazole (BTZ), 2-(3’-methyl-2’-hydroxylphenyl) benzothiazole (3-MeBTZ), 2-(4’-methyl-2’-hydroxylphenyl) benzothiazole (4-MeBTZ) and 2-(4’-Trifluoromethyl-2’-hydroxylphenyl)benzothiazole (4-tfmBTZ)), were synthesized and characterized. The molecular structures and photophysical properties were characterized and analyzed comparatively. The results show that the four complexes have basically similar UV-Vis absorption spectra, fluorescence excitation and emission spectra. Their maximum emission peaks are located at 583-615 nm, and accompanied by a lower intensity emission band around 400 nm. The weak emissions around 400 nm are ascribed to the radiation transition of single state excition from ancillary ligand BTZ perturbed by metallic ion, and light emission around long-wavelength to the radiation transition of ³MLCT of Ir(BTZ) fragment. While the triplet state ³MLCT of Ir(ppz)₂ fragment might be quenched at room temperature. For all complexes, the excitations with maximum efficiency are located at 250-310 nm, which indicates that main contributor to light emitting is ligand-centered absorption(¹ π—π ^*) of ppz and BTZ rather than ³MLCT transitions, and thus provides a striking evidence that there is intersystem crossing from ¹π—π^* state to ³MLCT state in these complexes. Compared with Ir(ppz)₃, these complexes not only have stronger phosphorescence at room temperature but also their emission color can be tuned by modifying ancillary ligand.