A multi-resonance TADF non-conjugated copolymer with near-unity photoluminescence quantum yield for efficient solution-processed OLEDs†

Multi-resonance thermally activated delayed fluorescence (MR-TADF) emitters have emerged as promising candidates for high-resolution OLEDs due to their near-unity exciton utilization efficiency and narrow-band emission. Highly efficient solution-processed OLEDs based on MR-TADF emitters are highly desired due to their combined advantages of cost-effective fabrication, compatibility with large-area flexible substrates, and potential to simultaneously achieve high color purity and superior device efficiency. Herein, we designed and synthesized a series of novel MR-TADF non-conjugated copolymers PBN_xDPOT_y by integrating MR-TADF moieties (DBNCz) and phosphine oxide moieties (DPOT) into non-conjugated polystyrene skeletons. This architecture synergistically combines narrow-band emission, through-space charge transfer (TSCT) with steric hindrance effects to achieve narrow emission (FWHM = 28–53 nm) with a record-high photoluminescence quantum yield (PLQY = 99.6%). Solution-processed OLEDs employing a PBN3DPOT97 emitter demonstrate exceptional performance with an FWHM of 39 nm, EQE of 12.7%, and CIE coordinates of (0.16, 0.40). Theoretical calculation results show that the narrow-band emission in the copolymers PBN_xDPOT_y can be attributed to the MR-TADF moieties (DBNCz). Furthermore, spatial HOMO–LUMO distributions facilitates enhanced TSCT, resulting in superior device performance. This work establishes a new molecular design strategy for developing highly efficient MR-TADF non-conjugated copolymers for solution-processed OLEDs.