Donor Engineering in TADF Emitters with Hybrid Short-Range and Long-Range Charge-Transfer Excitations toward High-Performance Electroluminescence

Abstract

Thermally activated delayed fluorescence (TADF) materials that simultaneously exhibit short-range (SR) and long-range (LR) charge-transfer (CT) excited states represent a promising new class of emitters for organic light-emitting diodes (OLEDs). Such systems combine the advantages of conventional donor–acceptor (D–A) and multi-resonance (MR) emitters, including high photoluminescence quantum yield (PLQY), fast radiative decay (k_r) and reverse intersystem crossing rates (k_RISC), and narrowband emission profiles. However, their molecular design principles and structure–property relationships remain largely unexplored. In this work, two new TADF emitters featuring both SR-CT and LR-CT excited states were developed by attaching electron donors to an MR fragment via a boron–meta–donor linkage. Together with reference compounds, these emitters enable a systematic investigation of the influence of the donor structure and linkage mode on the key photophysical properties of such light-emitting materials. Compared with conventional boron–para–donor linked emitters, the boron–meta–donor linked designs display highly hybridized SR–LR–CT character, manifested in distinctive emission bandwidths, enhanced solvatochromism, and donor-strength-dependent excited-state kinetics. Leveraging these features, high-performance narrowband OLEDs were fabricated, achieving a maximum external quantum efficiency (EQE_max) of 35.1% and exhibiting remarkably low efficiency roll-off, with an EQE of 18.1% maintained at a luminance of 10,000 cd·m⁻².

Keywords

Organic light emitting diodes / Multi-resonance / Thermally activated delayed fluorescence / Color-purity / Reverse intersystem crossing / Charge-transfer excited states / Organoboron / Spin–orbit coupling / Fused-ring systems

RIGHTS & PERMISSIONS

2025 SIOC, CAS, Shanghai, & WILEY-VCH GmbH