Staggered through-space interaction enables hybridized local and charge-transfer regulation for multi-resonance TADF emitter

Boron/nitrogen-based multi-resonance thermally activated delayed fluorescence (MR-TADF) materials offer narrowband emission with high efficiency, but their performance is often hindered by inefficient reverse intersystem crossing (RISC) and exciton quenching. Herein, we present BNCz-IPXZ, a new MR-TADF emitter featuring a staggered through-space interaction between a rigid MR acceptor (BNCz) and a planar indolo[3,2,1-kl]phenoxazine (IPXZ) donor. This staggered face-to-face arrangement induces a hybridized local and charge-transfer excited state character, significantly enhancing spin-flipping with a RISC rate of 8.21 × 10⁴ s⁻¹. The integration of a rigid MR core and planar donor also restricts structural relaxation and suppresses nonradiative decay, resulting in narrowband emission and a high photoluminescence quantum yield of up to 92 %. Organic light-emitting diodes incorporating BNCz-IPXZ exhibit narrowband green electroluminescence with a peak external quantum efficiency of 32.1 % and a full width at half maximum of 40 nm. These findings demonstrate a rational design approach for achieving efficient, narrowband MR-TADF emitters through staggered through-space HLCT engineering.