Fine-tuned asymmetric blue multiple resonance thermally activated delayed fluorescence emitters with high efficiency and narrow emission band

Abstract

Asymmetric blue multiple resonance-type thermally activated delayed fluorescence (TADF) materials composed of diphenylamine combined with carbazole and acridine units were synthesized and evaluated to fine-tune the electronic and photophysical properties. The large and rigid π-conjugated carbazole moiety was introduced to induce red-shifted emission and a small full-width at half maximum (FWHM), whereas a bulky acridine moiety with strong electron donating properties was used to red-shift the emission and suppress intermolecular interactions. The two TADF materials showed a high photoluminescence quantum yield of over 90% and small FWHM. Diphenylamine and carbazole-substituted 7-(tert-butyl)-5-phenyl-5H-5,8b-diaza-15b-borabenzo[a]naphtho[1,2,3-hi]aceanthrylene (B-dpa-Cz) demonstrated an emission peak wavelength of 475 nm, a small FWHM of 27 nm, and a high external quantum efficiency of 20.1%. In contrast, diphenylamine and acridine-derived 6-(tert-butyl)-8-phenyl-8H-spiro[4b,8-diaza-12b-boradibenzo[a,j]perylene-16,9′-fluorene] (B-dpa-SpiroAc) exhibited a peak wavelength of 481 nm, a small FWHM of 33 nm, and a high external quantum efficiency of 25.1%. These results proved that the asymmetrically designed B-dpa-Cz and B-dpa-SpiroAc work well as multi resonance-type TADF emitters.