Rational Medium‐Range Charge Transfer Strategy Toward Highly Efficient Violet‐Blue Organic Light‐Emitting Diodes with Narrowed Emission

Abstract The spectral narrowing engineering of pure‐organic emitters attracts great research interests in realizing high color purity. Here, the adjusted medium‐range charge transfer (MCT) strategy of TIC‐BO with rigid planar structure by fusing two typical UV‐emitting multiple resonance (MR) fragments via the ingenious double‐halide cyclized coupling reaction is reported. The resulting TIC‐BO with MCT nature shows efficient violet‐blue emission in dilute toluene and evaporated host–guest films, and desirably narrowed spectra are achieved by the suppression of structural relaxation and the shortened charge transfer states. The single‐doped device with TIC‐BO as emitter shows narrowed violet‐blue electroluminescence peaked at 428 nm with full‐width at half‐maximum of 43 nm (0.28 eV), and the Commission Internationale de l’Éclairage coordinates of (0.160, 0.050). A maximum external quantum efficiency (EQE_max) of 20.50% is achieved, which is among the best results of the corresponding violet‐blue emitting region. Further introduction of a stronger electron‐donating carbazole group makes TIC‐BNO exhibit red‐shifted sky‐blue emission with MR‐dominant properties, and good device performance is received with EQE_max of 34.58%. The outstanding performances of TIC‐BO successfully demonstrate the significance and prospect of the proposed molecular design strategy.