Cyano-Modified Multi-Resonance Thermally Activated Delayed Fluorescent Emitters towards Pure-Green OLEDs with a CIE y Value of 0.74

Abstract

The development of pure-green organic emitters with ideal emission peak and ultra-narrow full-widths at half-maximum (FWHMs) remains a formidable challenge. Herein, we report two new green emitters, CNBN and MCNBN, which achieve extremely narrow FWHMs by synergistic rigid π-extension and cyano-substitution for sky-blue multi-resonance thermally activated delayed fluorescence (MR-TADF) core. The introduction of cyano groups induces red-shifts of emission to green region and dramatically minimize the FWHMs. In toluene solution, CNBN and MCNBN exhibit narrowband emission peaking at 501 nm and 510 nm with ultra-narrow FWHMs of 14 nm/0.066 eV and 15 nm/0.071 eV, respectively. Given the near-unity photoluminescence quantum yields and almost 100% horizontal dipole orientation, the electroluminescent (EL) devices based on CNBN and MCNBN deliver external quantum efficiencies (EQEs) exceeding 30% with FWHMs of 16 nm/0.072 eV and 17 nm/0.080 eV, respectively. Notably, the MCNBN-based device achieves pure-green emission peaking at 517 nm with Commission Internationale de l’Éclairage coordinates of (0.17, 0.74), closely aligning with the BT.2020 green standard.