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.