Efficient Electrogenerated Chemiluminescence from Bis-Cyclometalated Iridium(III) Complexes with Substituted 2-Phenylquinoline Ligands

Abstract

The ECL behavior of bis-cyclometalated (pq)2Ir(LX) complexes, in which pq is a 2-phenylquinoline anion and LX is a monoanionic bidentate ligand (e.g., acetylacetonate, picolinate, etc.), and the specific influences of the electrochemical stability and photoluminescence quantum yield (PL QY) of luminophores on ECL generation have been investigated. In this study, efficient ECLs, some of which even approached ΦECL = 0.88 (18× higher than that of Ru(bpy)32+), have been observed in the annihilation process. The simultaneous accumulation to excited singlet S1 and triplet T1 states and the spin−orbit coupling characteristics of transition metal complexes are expected to produce efficient annihilation ECL, which permits the high efficiency to exceed PL QY. A cyclic voltammetric study has revealed that the ECL intensity depends primarily on the electrochemical stability of the redox precursors of (pq)2Ir(LX)s. For example, (pq)2Ir(acac) (acac = acetylacetonate anion), which shows irreversible reduction, has produ...