Naphthalimide–arylamine derivatives with aggregation induced delayed fluorescence for realizing efficient green to red electroluminescence

Abstract

Aggregation-induced emission (AIE) can enhance luminescent intensity in the solid-state by suppressing concentration quenching and exciton annihilation, while thermally activated delayed fluorescence (TADF) can offer highly efficient luminescence by harvesting singlet and triplet excitons. High performance organic light-emitting diode (OLED) materials with simultaneous TADF and AIE features are in high demand. Herein, we proposed a rational molecular design that exhibits both features, i.e., aggregation-induced emission-delayed fluorescence (AIDF), and green to red fluorescence with high photoluminescence quantum yield (up to 87.4% in doped films). Two D–A type emitters NAI–BiFA and NAI–PhBiFA are developed based on a central naphthalimide acceptor core and arylamine donor units. In comparison with NAI–BiFA, NAI–PhBiFA inserts the phenyl linker between the D and A units, forming a spatially twisted structure and resulting in a blue shift emission. While a non-doped OLED employing NAI–PhBiFA as an orange emitter exhibited an external quantum efficiency (EQE) of only 1.39%, a doped OLED based on NAI–PhBiFA demonstrated a remarkable improvement including a maximum EQE of 7.59%, a maximum current efficiency (CE) of 27.95 cd A⁻¹ and a maximum power efficiency (PE) of 20.97 lm W⁻¹. In addition, a host-free device employing NAI–BiFA as an emitter achieved CIE (0.65, 0.34), which is very close to the National Television Standards Committee's (NTSC) standard red (0.67, 0.33). The high efficiencies and low roll-offs in both the doped or non-doped devices demonstrate that our molecular design strategy is highly promising for a variety of OLED applications.