Efficient blue thermally activated delayed fluorescent emitters based on a boranaphtho[3,2,1-de]anthracene acceptor

Abstract

A series of blue thermally activated delayed fluorescence (TADF) emitters have been developed by the combination of boranaphtho[3,2,1-de]anthracene (BO) acceptor (A) and sprio-acridine-fluorene donors (D). Different phenyl substitutions are induced for the comprehension of structure–property relationship. Systematic characterization of thermal, photophysical, electrochemical and electroluminescent (EL) properties have been carried out in detail. The photophysical analysis suggests that these D–A type emitters possess decent TADF properties with high photoluminescence quantum yield of up to 99%. A high reverse inter-system crossing constant (k_RISC) of 1.52 × 10⁶ s⁻¹ is achieved by emitter MH without phenyl decoration. Benefitting from their high PLQYs as blue emitters, the doped organic light-emitting diodes (OLEDs) based on these compounds achieve attractive EL performances. The blue-emitting OLEDs with CIE (0.141. 0.215) based on MH exhibits a maximum external quantum efficiency (EQE_max) of 23.9%, current efficiency (CE_max) of 42.9 cd A⁻¹ and power efficiency (PE_max) of 42.1 lm W⁻¹. As the number of the phenyl group increases, the value of EQE_max shows a slight decrease to 20.3% of MP and 19.3% of PP accompanied with a drop of y of CIE coordinates to 0.197 and 0.188, respectively.