A deep blue thermally activated delayed fluorescence emitter: balance between charge transfer and color purity

An efficient blue organic light-emitting diode (OLED) device with high color purity is a challenging issue with technological relevance. Herein, we demonstrated the role of the donor substitution position in a thermally activated delayed fluorescence (TADF) emitter to achieve deep blue emission with improved color purity without reducing the device performance. 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 at the para position of the benzoyl pyridine (3BPy) acceptor core. The 3BPy-pDTC emitter shows a low Delta E-ST value of 0.19 eV with a subsequent overlap between holes and electrons which leads to a high photoluminescence quantum yield (PLQY) of 93%. Besides, this emitter exhibits narrow emission spectra with a full-width at half maximum (FWHM) of 58 nm. The OLED device using the 3BPy-pDTC dopant provided a high external quantum efficiency (EQE) of 25% with deep blue emission at lambda(max) of 458 nm. 3BPy-pDTC shows color purity in deep blue emission as compared to its meta substituted counterpart (3BPy-mDTC) due to the locked geometry via intramolecular H-bonding and weak excited state charge transfer (CT) interactions. The current study paves the way for developing deep-blue TADF emitters with high efficiency and color purity.

Automated summary

This study demonstrates the role of donor substitution position in achieving deep blue emission with improved color purity in an efficient blue organic light-emitting diode (OLED) device. A novel emitter is synthesized with low Delta E-ST value, high photoluminescence quantum yield, and narrow emission spectra. The OLED device using this emitter shows high external quantum efficiency and deep blue emission. This study paves the way for developing deep-blue TADF emitters with high efficiency and color purity.