Homoleptic vs. Heteroleptic Orange Light-Emitting Iridium Complexes Chelated with Benzothiazole Derivatives

The homoleptic and heteroleptic iridium(III) complexes exhibiting orange phosphorescence were investigated to compare their emission colors, luminance efficiency, and stability. The homoleptic iridium complexes, Ir(pbt-R)(3), were prepared from the reaction of the iridium(III) precursor and phenylbenzothiazole derivatives. The heteroleptic ones containing the anions of 4-methyl-2,3-diphenylquinoline (4-Me-dpq) and 2-phenylbenzothiazole (pbt) as ligands, Ir(pbt-OMe)(2)(4-Me-2,3-dpq) and Ir(4-Me-2,3-dpq)(2)(pbt-OMe), were synthesized via the chloro-bridged iridium dimer. We investigated photoabsorption and photoluminescence (PL) properties of the iridium complexes and studied their bandgaps with cyclic voltammetry (CV). Orange phosphorescence with the PL maxima of 530-620nm was observed with these complexes, and the bandgaps between their highest occupied molecular orbitals (HOMOs) and the lowest unoccupied molecular orbitals (LUMOs) were correlated with CV data. The electro-luminescence (EL) study of these complexes was not possible due to lack of sublimability. The light-emitting mechanisms regarding the phosphorescence colors were discussed.