Multiple Spiro Donor Design Strategy for Horizontally Oriented TADF Emitters Enabling High-Performance Solution-Processed OLEDs

Abstract

Solution-processed organic light-emitting diodes (OLEDs) are attractive for cost-effective optoelectronic devices, but their performance is constrained by poor control over transition dipole moment orientation, which limit light out-coupling efficiency. Here, we present a rational molecular design strategy to address these challenges by developing a novel thermally activated delayed fluorescence (TADF) emitter, 3SFAc-TRZ, featuring a rigid triazine core, multiple spiro-acridine donor units, and peripheral fluorene substituents with solubilizing alkyl chains. This design affords a planar molecular framework with degenerate frontier orbitals, enabling strong charge-transfer character and an exceptionally small singlet-triplet energy gap. Therfore, efficient TADF with a high photoluminescence quantum yield of 76% and a rapid reverse intersystem crossing is achieved in film. Importantly, 3SFAc-TRZ exhibits remarkable horizontal dipole ratios of 80% and 76% in spin-coated neat and doped films. When employed in solution-processed OLEDs, the emitter achieves a high maximum external quantum efficiency of 30.03% with well suppressed efficiency roll-off. These results highlight the effectiveness of the molecular design strategy in enhancing horizontal dipole orientation, showing great promise for advancing high-performance solution processable OLEDs.