Deep-Blue Narrowband Hetero[6]helicenes Showing Circularly Polarized Thermally Activated Delayed Fluorescence Toward High-Performance OLEDs

Helicenes exhibit substantial potential as circularly polarized luminescence (CPL) active molecules. However, their application in circularly polarized organic light-emitting diodes (CP-OLEDs) is typically hindered by the challenge of integrating both high color purity and efficient triplet-harvesting capability, particularly in the blue spectral region. Herein, a series of hetero[6]helicene-based emitters that is strategically engineered through the helical extension of a deep-blue double-boron-based multiple resonance thermally activated delayed fluorescence (MR-TADF) motif, is introduced. Importantly, the helical extension does not cause apparent structural deformation or perturb frontier molecular orbitals; thus, preserving the deep-blue emission and MR-TADF characteristics of the parent molecule. This approach also leads to reduced reorganization energy, resulting in emitters with narrower linewidth and higher photoluminescence quantum yield. Further, the helical motif enhances the racemization barrier and leads to improved CPL performance with luminescence dissymmetry factor values up to 1.5 x 10-3. Exploiting these merits, devices incorporating the chiral dopants demonstrate deep-blue emission within the Broadcast Service Television 2020 color-gamut range, record external quantum efficiencies (EQEs) up to 29.3%, and have distinctive circularly polarized electroluminescence (CPEL) signals. Overall, the authors' findings underscore the helical extension as a promising strategy for designing narrowband chiroptical materials and advancing high-definition displays. A helical extension strategy is introduced to engineer deep-blue hetero[6]helicene-based emitters for circularly polarized OLEDs. Besides satisfactory chiroptical performance, this strategy endows the emitters with enhanced quantum yield and narrower emission bands compared to their precursor. The devices display record efficiencies, high color purity, and distinct circularly polarized electroluminescence, marking a significant advance in chiroptical materials for high-definition displays.image