Achieving an efficient blue organic light-emitting diode (OLED) device (CIEy &lt; 0.15) with high color purity remains a challenge. Herein, we demonstrated the role of donor substitution position in a thermally activated delayed fluorescence (TADF) emitter to achieve deep blue emission with improved color purity. A novel (4-(3,6-di-tert-butyl-9H-carbazol-9-yl)phenyl)(6-(3,6-di-tert-butyl-9H-carbazol-9-yl)pyridin-3-yl)methanone (3BPy-pDTC) was synthesized, where two tert-butyl carbazolyl (DTC) donors linearly connected on the para position of benzoyl pyridine (3BPy) acceptor core. The 3BPy-pDTC emitter shows a low singlet-triplet splitting (ΔEST) of 0.19 eV with significant overlap between hole and electron, which leads to a high photoluminescence quantum yield (PLQY) of 93%. 3BPy-pDTC exhibits narrow emission spectra with the full-width at half maximum (FWHM) of 58 nm. The OLED device using 3BPy-pDTC dopant provided a high external quantum efficiency (EQE) of 25% with deep blue emission at lmax of 458 nm. The device based on 3BPy-pDTC shows color purity in the deep blue region compared to its meta substituted counterpart (3BPy-mDTC) due to the locked geometry via intramolecular H-bonding and balanced excited-state charge transfer (CT) interactions. The current study paves the way for developing deep-blue TADF emitters with high efficiency and color purity.

Achieving deep blue and narrowband thermally activated delayed fluorescence emitter by adjusting charge transfer interactions

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ACS Fall 2022

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