Molecular Orientation-Directed Isomerization in Indolocarbazole-Embedded Multiple Resonance Emitter Enables...

Multiple resonance thermally activated delayed fluorescence (MR-TADF) emitters are considered ideal candidates for high-definition displays; however, simultaneously accessing high-efficiency, narrowband, pure-green emission remains a significant challenge. Here, we propose an orientation-directed isomerization strategy on the indolocarbazole (ICz) building block to construct a previously unexplored syn-oriented para-N-π-N dual-boron-containing architecture. This design delicately balances the strong intramolecular charge transfer (ICT) arising from para-N-π-N topology and short-range charge transfer (SRCT) within a rigid ICz framework, achieving the desired narrowband emission. The proof-of-concept emitter DBN-cpICz shows pure-green photoluminescence in toluene (λ_PL = 520 nm, full-width at half-maximum (FWHM) = 20 nm, and Commission Internationale de l'Éclairage (CIE) coordinates = (0.17, 0.74)). An organic light-emitting diode using DBN-cpICz delivers pure-green electroluminescence at 522 nm, with an FWHM of 24 nm and CIE coordinates of (0.20, 0.73), exceeding the NTSC green requirement and approaching the BT.2020 standard, together with a maximum external quantum efficiency of 36.4%. The intrinsic relationship between the N-π-N electronic topology of ICz and its well-defined excited-state characteristics enables robust green spectral anchoring, thereby providing a solid molecular engineering principle for the development of efficient, narrowband, pure-green MR-TADF emitters.