Efficient Folded\nMolecules with Intramolecular Through-Space Charge Transfer for\nNear-Ultraviolet Organic Light-Emitting Diodes

Organic light-emitting diodes (OLEDs)\ncapable of radiating\nnarrow-spectrum\nnear-ultraviolet (NUV) light have a wide range of potential applications\nbeyond traditional display purposes. Nevertheless, it remains difficult\nto achieve both a strong NUV emission and narrow emission spectrum\nsimultaneously. Herein, we report two folded NUV emitters (tCz-BO-BCz\nand tCz-BO-PCz) featuring through-space charge transfer (TSCT), which\nconsist of <i>tert</i>-butyl carbazole (tCz) as a bridging\ngroup, 5,9-dioxa-13b-boranaphtho[3,2,1-de]anthracene (BO) as an acceptor,\nand 9-phenyl-carbazole (BCz) and 9-(pyridin-2-yl)-9<i>H</i>-carbazole (PCz) as donors. They are fully characterized by crystallography,\nthermal measurement, cyclic voltammetry, steady-state and transient\nspectroscopy, and theoretical calculation. They show efficient NUV\nemissions with narrow full widths at half-maximum (fwhm) of 52 and\n44 nm and good photoluminescence quantum yields of 79 and 64% in doped\nfilms, respectively. Using tCz-BO-BCz and tCz-BO-PCz as emitters,\nefficient OLEDs are fabricated, providing narrow NUV light with electroluminescence\npeaks at 404 and 398 nm, fwhm values of 38 and 32 nm, and impressive\nexternal quantum efficiencies of 4.38 and 3.82%, respectively. The\nfolded TSCT configuration could be a promising design for developing\nefficient NUV emitters with narrow emission spectra for the application\nin OLEDs.