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 tBO-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 (ηext,maxs) of 4.61%
and 5.03%. Additionally, as hosts for green multiresonance (MR) emitters,
they deliver narrow EL spectra and excellent ηext,maxs up to 34.36%. This molecular strategy could advance high-performance
short-wavelength emitters for optoelectronic devices.