Spiro-fluorene locked multi-resonance delayed fluorescence helical framework: efficient circularly polarized electroluminescent materials

Abstract

Due to their excellent optical properties, circularly polarized multiple resonance thermally activated delayed fluorescence (CP-MR-TADF) compounds are highly suitable for applications as chiral emitters with high efficiency and high color purity. However, challenges due to limited molecular design strategies often hinder their application in circularly polarized organic light-emitting diodes (CP-OLEDs). In this work, based on an intramolecular-locking strategy, a carbon bridge was introduced to fuse the tert-butyl carbazole moiety within the MR skeleton, merging the intrinsically helical chirality into the MR framework. The designed molecule was modified by incorporating a locking group with significant spatial hindrance, named Spiro-3TCzBN. Consequently, the optimized CP-OLEDs with (P/M)-Spiro-3TCzBN emitters achieved remarkable maximum external quantum efficiencies of 34.6% and 34.9%, respectively, accompanied by clear circularly polarized electroluminescence signals with electroluminescence dissymmetry factors of −3.51 × 10⁻⁴ and +4.26 × 10⁻⁴. Furthermore, the electroluminescence spectra of Spiro-3TCzBN-based OLEDs show a notably stable profile as the doping level increases from 1 to 10 wt%. These results indicate that the conformational locking strategy is a compelling design approach for helicene, which is expected to be a potential chiral optical material for next-generation high-resolution CP-OLED displays.