Efficient Folded Molecules with Intramolecular Through-Space Charge Transfer for Near-Ultraviolet Organic Light-Emitting Diodes

Organic light-emitting diodes (OLEDs)
capable of radiating
narrow-spectrum
near-ultraviolet (NUV) light have a wide range of potential applications
beyond traditional display purposes. Nevertheless, it remains difficult
to achieve both a strong NUV emission and narrow emission spectrum
simultaneously. Herein, we report two folded NUV emitters (tCz-BO-BCz
and tCz-BO-PCz) featuring through-space charge transfer (TSCT), which
consist of tert-butyl carbazole (tCz) as a bridging
group, 5,9-dioxa-13b-boranaphtho[3,2,1-de]anthracene (BO) as an acceptor,
and 9-phenyl-carbazole (BCz) and 9-(pyridin-2-yl)-9H-carbazole (PCz) as donors. They are fully characterized by crystallography,
thermal measurement, cyclic voltammetry, steady-state and transient
spectroscopy, and theoretical calculation. They show efficient NUV
emissions with narrow full widths at half-maximum (fwhm) of 52 and
44 nm and good photoluminescence quantum yields of 79 and 64% in doped
films, respectively. Using tCz-BO-BCz and tCz-BO-PCz as emitters,
efficient OLEDs are fabricated, providing narrow NUV light with electroluminescence
peaks at 404 and 398 nm, fwhm values of 38 and 32 nm, and impressive
external quantum efficiencies of 4.38 and 3.82%, respectively. The
folded TSCT configuration could be a promising design for developing
efficient NUV emitters with narrow emission spectra for the application
in OLEDs.