Rational Medium-range Charge Transfer Strategy Towards Highly Efficient Violet-blue Organic Light-emitting Diodes with Narrowed Emission.

The spectral narrowing engineering of pure-organic emitters attracts great research interests in realizing high color purity. Here, we report the adjusted medium-range charge transfer (MCT) strategy of TIC-BO with rigid planar structure by fusing two typical ultraviolet-emitting multiple resonance (MR) fragments via the ingenious double-halide cyclized coupling (DHCC) reaction. 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 (EL) peaked at 428 nm with FWHM of 43 nm (0.28 eV), and the Commission Internationale de l'Éclairage (CIE) 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 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 demonstrates the significance and prospect of the proposed molecular design strategy. This article is protected by copyright. All rights reserved.