Highly Stable Red-Light-Emitting Electrochemical Cells

The synthesis and characterization of a series of new cyclometalated iridium(III) complexes [Ir(ppy)₂(N∧N)][PF₆] in which Hppy = 2-phenylpyridine and N∧N is (pyridin-2-yl)benzo[d]thiazole (L1), 2-(4-(tert-butyl)pyridin-2-yl)benzo[d]thiazole (L2), 2-(6-phenylpyridin-2-yl)benzo[d]thiazole (L3), 2-(4-(tert-butyl)-6-phenylpyridin-2-yl)benzo[d]thiazole (L4), 2,6-bis(benzo[d]thiazol-2-yl)pyridine (L5), 2-(pyridin-2-yl)benzo[d]oxazole (L6), or 2,2'-dibenzo[d]thiazole (L7) are reported. The single crystal structures of [Ir(ppy)₂(L1)][PF₆]·1.5CH₂Cl₂, [Ir(ppy)₂(L6)][PF₆]·CH₂Cl₂, and [Ir(ppy)₂(L7)][PF₆] have been determined. The new complexes are efficient red emitters and have been used in the active layers in light-emitting electrochemical cells (LECs). The effects of modifications of the 2-(pyridin-2-yl)benzo[d]thiazole ligand on the photoluminescence and LEC performance have been examined. Extremely stable red-emitting LECs are obtained, and when [Ir(ppy)₂(L1)][PF₆], [Ir(ppy)₂(L2)][PF₆], or [Ir(ppy)₂(L3)][PF₆] are used in the active layer, device lifetimes greater than 1000, 6000, and 4000 h, respectively, are observed.