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

Comprehensive Summary 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 .