Phosphorylation amplified asymmetry of spiro[acridine-9,9′-xanthene] hosts for efficient blue and white thermal activated delay fluorescent diodes

Abstract

Single-emissive-layer thermally activated delayed fluorescence (TADF) white organic light-emitting diodes (WOLED) hold promise in next-generation low-cost energy-conservation lighting; however, they require high-performance host matrixes for efficient exciton formation and allocation. Herein, an asymmetric spiro core named spiro[acridine-9,9′-xanthene] (SXA) is used to construct phosphine oxide (PO) hosts through introducing one or two diphenylphosphine oxide groups at the 2 and 7 positions of the acridine ring, respectively, named 2PSXASPO and 27PSXADPO. In comparison to 2PSXASPO with substitution asymmetry, the molecular asymmetry of 27PSXADPO leads to stronger steric and inductive effects for comprehensively optimizing energy transfer, suppressing quenching and improving carrier flux balance. As a consequence, besides ∼100% photoluminescence quantum yield, 27PSXADPO endowed single-emissive-layer dually doped TADF WOLEDs with top-rank efficiencies of up to 64.0 cd A⁻¹ for current efficiency, 69.3 lm W⁻¹ for power efficiency and 22.9% for external quantum efficiency, respectively, which were 10 fold those of 2PSXASPO-hosted analogues. This work demonstrates the great potential of spirocyclic hosts for developing high-performance TADF lighting.