1. Deep blue thermally activated delayed fluorescent emitters based on methyl-modified acridin-9(10H)-one acceptor.
- Author
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Li, Yixue, Mei, Yongqiang, Liu, Botao, Xu, Min, Sun, Haiyan, Wu, Qi, Wan, Huihui, Liu, Di, and Li, Jiuyan
- Subjects
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CARBAZOLE , *DELAYED fluorescence , *FRONTIER orbitals , *RADIATIONLESS transitions , *OSCILLATOR strengths , *QUANTUM efficiency , *ANTHRACENE derivatives - Abstract
Developing deep blue thermally activated delayed fluorescence (TADF) materials with high efficiencies and good color purities is still a formidable challenge. Here, two novel deep blue TADF emitters, namely MePhCz-AD and MePhCz-AD-Py, were synthesized by incorporating two 3,6-diphenyl-9 H -carbazole donors onto the methyl-modified acridin-9(10 H)-one (AD) acceptor, respectively. The high rigidity of AD acceptor effectively suppressed non-radiative transition and vibration relaxation of excited states, which is favorable for a good emitting quantum yield and narrow spectral width. The presence of methyl groups at 2,7-sites of AD ring slightly reduced the acceptor strength and contributed to the deep blue emission color. Incorporation of phenyls at 3,6-sites of carbazole ring delocalized the distribution of the highest occupied molecular orbital (HOMO), promoting the radiative decay process. As a result, these two emitters showed deep blue TADF with fast radiative decay rates k R > 107 s−1. In addition, with the introduction of pyridyl (Py) group at 10-site of AD ring instead of phenyl, both the spin-orbital coupling (SOC) constant between high-lying triplet states and the lowest singlet excited state (S 1) and thus the reverse intersystem crossing rate constant (k RISC) were dramatically promoted for MePhCz-AD-Py. The organic light-emitting diode with MePhCz-AD-Py as doped emitter exhibited a maximum external quantum efficiency (EQE max) of 15.4% with a relatively narrow FWHM of 60 nm and the deep-blue color coordinates of (0.15, 0.15). A deep blue TADF emitter MePhCz-AD-Py based on diphenylcarbazole as donors and acridin-9(10 H)-one as acceptor with methyl at 2,7-sites and pyridyl at 10-site exhibited both fast k RISC of 3.7 × 104 s−1 and k R of 4.1 × 107 s−1 due to a large SOC and an enlarged oscillator strength. The deep blue OLED with MePhCz-AD-Py as doped emitter realizes an EQE max of 15.4% with CIE coordinates of (0.15, 0.15). [Display omitted] • Deep blue TADF emitters are developed with methyl-modified acridin-9(10 H)-one as acceptor. • Pyridyl is introduced to 10-site of acceptor to increase the SOC and RISC rate constant k RISC. • High EQE of 15.4% and CIE (0.15, 0.15) were obtained for deep blue OLED. [ABSTRACT FROM AUTHOR]
- Published
- 2023
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