Versatile Spiral Donor-Based Thermally Activated Delayed Fluorescence Materials for Highly Efficient TADF-OLED and TSF-OLED Applications

Herein, a design strategy is explored for thermally activated delayed fluorescence (TADF) materials by employing the meta-linkage of the spiral-donors 10H-spiro[acridine-9,9'-thioxanthene] (DspiroS) and 10',10'-dimethyl-10H,10'H-spiro[acridine-9,9'-anthracene] (DspiroAc) to the robust acceptor 2,4,6-triphenyl-1,3,5-triazine (TRZ). Two distinct TADF materials, m-DspiroS-TRZ and m-DspiroAc-TRZ, exhibiting unique photophysical properties and performance characteristics were synthesized. Interestingly, even subtle modifications in the molecular architecture can significantly impact the organization of materials in their aggregated state, thereby governing photophysical properties and inducing corresponding alterations in photoelectric characteristics. Notably, m-DspiroS-TRZ exhibits superior photophysical properties and exciton dynamics data, achieving a high photoluminescence quantum yield (PLQY) value of up to 95.9% and a rapid reverse intersystem crossing (RISC) rate (𝒌_{𝑹𝑰𝑺𝑪}) of 1.0 × 10⁶ s⁻¹. This positions m-DspiroS-TRZ as a potentially excellent terminal emissive and sensitizing host material, inspiring further exploration of its applications in electroluminescence. Consequently, TADF organic light-emitting device (TADF-OLED) and TADF-sensitized fluorescence (TSF-OLED) based on m-DspiroS-TRZ have achieved maximum external quantum efficiencies (EQEs) of 31.8% and 34.5%, respectively, demonstrating the significant versatile potential of m-DspiroS-TRZ.