Through-space charge-transfer (TSCT) emitters have been extensively explored for thermally activated delayed fluorescence (TADF), but arranging various donors and acceptors into rigid cofacial conformations for various efficient TSCT TADF emitters has remained challenging. Here, we report a "fixing acceptor" design to reach various efficient TSCT TADF emitters. By chemically fixing the acceptor (benzophenone) with a rigid spiro-structure and cofacially aligning various donors with the fixed acceptor, a series of efficient TSCT TADF emitters have been developed. Single-crystal structures and theoretical calculations have verified closely packed cofacial donor/acceptor conformations and favorable TSCT in the emitters. In doped films, the emitters afford sky blue to yellow TADF emission, with high photoluminescence efficiencies up to 0.92 and reverse intersystem crossing rates up to 1.0 × 10 6 s −1 . Organic light-emitting diodes using the emitters afford sky blue to yellow electroluminescence with high external quantum efficiencies up to 20.9%. The work opens a new avenue toward a wide variety of efficient TSCT TADF emitters.

Exciplexes formed between donors and acceptors have been widely explored but isolating them from each other and tuning the interaction between the donor and acceptor have remained challenges. Here, we report donor/acceptor (D/A) pairs created by electrostatic interaction between a carbazole‐based anionic donor and a 1,3,5‐triazine‐based cationic acceptor and the exciplex formed within the pair. In a diluted film, the D/A pair affords an isolated exciplex which shows thermally activated delayed fluorescence (TADF). By changing the anchoring position of the imidazolium cation in the cationic acceptor, interactions between the donor and acceptor can be changed. Compared to the conventional exciplex formed in a neat film, the isolated exciplex exhibits a substantially higher luminescence efficiency. The D/A pairs show intriguing mechanochromic luminescence and mechanical grinding‐induced/reinforced TADF in the solid state and promising performances as emitters in organic light‐emitting diodes.

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Solid-state light-emitting electrochemical cells (LECs) using sustainable and eco-friendly materials and affording high brightness, efficiency, and stability are highly desired. Here, intrinsically ionic, thermally activated delayed fluorescence (TADF) materials 1-3 for efficient, bright, and stable LECs are reported. 1-3 feature carbazole-type donors and cationic triazine-type acceptors, which are located ortho to each other on the phenyl linkers. Through-space chargetransfer (CT) dominates the CT transitions in 1-3. In doped and neat films, 1-3 show blue and green TADF emission, respectively, with reverse intersystem crossing rates at around 7.0 × 10 5 s −1 . 1-3 possess excellent electrochemical stability (except for the oxidation of 1) and film-forming abilities. LECs using neat films of 1-3 as the single active layers afford green electroluminescence with peak brightness/peak external quantum efficiency (EQE) of up to 572 cd m −2 /6.8% under 4.0 V and peak brightness/peak EQE/halflifetime of up to 860 cd m −2 /5.4%/48 h under 50 A m −2 . A longer half-lifetime of 218 h has further been achieved at 162 cd m −2 under 10 A m −2 . The work reveals the bright prospect for the development of efficient, bright, and stable LECs with intrinsically-ionic TADF materials.

Cationic iridium complexes with carbazole-type counter-anions show enhanced performances compared to those with PF₆⁻ counter-anions in OLEDs.