Achieving Efficient Narrow-Spectrum Violet Organic Light-Emitting Diodes Based on Through-Space Charge Transfer Molecules

Violet organic light-emitting diodes (OLEDs) hold promise for advanced applications, yet achieving simultaneously high efficiency and color purity remains challenging. This study presents a rational design of violet emitters by establishing a through-space charge transfer (TSCT) framework that enhances high-level reverse intersystem crossing (hRISC) for the effective utilization of triplet excitons. Two TSCT emitters, BO-MX-ICz and t BO-MX-ICz, are tailored with a weak donor and acceptor bridged by 9,9-dimethylxanthene in a face-to-face stacking arrangement. These emitters show narrow violet photoluminescence (PL) with a high efficiency. Their OLEDs exhibit high-color-purity violet electroluminescence (EL) with peaks at 406 and 408 nm, a full width at half-maximum (fwhm) of 25 nm, and maximum external quantum efficiencies (η ext,max s) of 4.61% and 5.03%. Additionally, as hosts for green multiresonance (MR) emitters, they deliver narrow EL spectra and excellent η ext,max s up to 34.36%. This molecular strategy could advance high-performance short-wavelength emitters for optoelectronic devices.