Narrow-band circularly polarized red electroluminescence in trinuclear clusters

Abstract

Through the elaborate design of an ethynyl-naphthalimide ligand with a phenylethylamino group as chiral origin, we report the synthesis, characterization, photophysical and electroluminescence properties of a pair of chiral PtAu₂ trinuclear clusters with high-efficiency circularly polarized narrow-band red emission. As demonstrated by experimental and theoretical studies, the phosphorescence of the trinuclear cluster originates from the intraligand (³IL) triplet state of ethynyl-naphthalimide having a chiral benzylamino moiety. The R/S-PtAu₂ clusters exhibit significant circularly polarized luminescence (CPL) properties with an asymmetry factor of approximately ±1 × 10⁻³. Organic light-emitting diodes (OLEDs) based on chiral PtAu₂ clusters demonstrate circularly polarized electroluminescence (CPEL) performance with an asymmetry factor of approximately ±7 × 10⁻⁴ and an external quantum efficiency (EQE) of 13.7%. The devices exhibit narrow-band red emission and high color purity with CIE 1931 coordinates of (0.68, 0.32) and a full width at half maximum (FWHM) of 29 nm. Both circular dichroism (CD) and CPL studies demonstrate the excellent chiral absorption and emission characteristics of trinuclear cluster enantiomers in the ground state as well as in the excited state.