Circularly polarised photoluminescence and electroluminescence of chiral copper(i) dimers based on R/S-2,2′-bis(diphenylphosphino)-1,1′-binaphthalene ligands

Abstract

Due to the ability to emit circularly polarised luminescence (CPL) for application in many areas, chiral luminescent materials have undergone rapid development in recent years. Herein, three chiral copper(I) chloro-bridged dimers R/S-(BINAP)₂Cu(μ-X₂) (X = Cl, Br and I) based on R/S-2,2′-bis(diphenylphosphino)-1,1′-binaphthalene (R/S-BINAP) ligands were synthesized conveniently at room temperature with high yields above 95%. Though emissions of the compounds in solution are weak, the dimers in the powder form and doped films displayed strong luminescence. Furthermore, the small singlet–triplet energy level gap and the calculated theoretical frontier molecular orbital distribution overlap suggested that these dimers have thermally activated delayed fluorescence characteristics. In addition, R/S-(BINAP)₂Cu(μ-X₂) doped films showed mirror symmetric circular dichroism and CPL spectra with a high dissymmetry factor (g) above 1 × 10⁻². However, the corresponding circularly polarised organic light-emitting diodes (CP-OLEDs) fabricated by the evaporation method based on R/S-(BINAP)₂Cu(μ-I₂) exhibited a high maximum external quantum efficiency of 21.7%. Notably, the CP-OLEDs also displayed mirror imaged circularly polarised electroluminescence spectra with |g_EL| factors of around 3.0 × 10⁻³.