High-efficiency solution-processed light-emitting diode based on a phosphorescent Ag3Cu5 cluster complex

Abstract

A dpppy-protected (dpppy = 2,6-bis(diphenylphosphino)pyridine) d¹⁰–d¹⁰ heterooctanuclear cluster complex [Ag₃Cu₅(ebzcz)₆(dpppy)₃](ClO₄)₂ (Hebzcz = 1-(3,6-di-tert-butylcarbazol-9-yl)-4-ethynylbenzene) was prepared by self-assembly reaction and characterized by single crystal X-ray diffraction. The diphosphine-supported Ag₃Cu₅ cluster structure is highly stabilized through substantial Cu–Ag and Cu–Cu intermetallic interactions. Since the Ag₃Cu₅ cluster is sufficiently shielded by bulky ligands (three ebzcz and three dpppy), thermally non-radiative relaxation is strongly prohibited so as to give brilliant photoluminescence under ambient conditions. As revealed by TD-DFT studies, the luminescence arises from metal cluster-centred ³[d → p/s] and ³[π (ebzcz) → π* (dpppy)] ³LLCT (ligand-to-ligand charge transfer) transitions. Taking advantage of Ag₃Cu₅ cluster complex as a phosphorescent dopant, a high-efficiency solution-processed organic light-emitting diode is achieved with a peak current efficiency of 38.1 cd A⁻¹, a power efficiency of 29.9 lm W⁻¹ and an external quantum efficiency of 14.7%.