Sensitivity of the hidden TADF to the linking topology of di-tert-butyl-carbazolyl and benzonitrile moieties in the molecules of emitters or hosts intended for efficient blue OLEDs

• Published in: Journal of photochemistry and photobiology. A, Chemistry. Vol. 440; p. 114686
• Main Authors: Chen, Chia-Hsun, Lin, Kun-Rong, Lin, Chi-Feng, Starykov, Hryhorii, Bucinskas, Audrius, Gudeika, Dalius, Bezvikonnyi, Oleksandr, Simokaitiene, Jurate, Volyniuk, Dmytro, Grazulevicius, Juozas V., Lee, Jiun-Haw, Chiu, Tien-Lung
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.06.2023
• ISSN: 1010-6030; 1873-2666
• DOI: 10.1016/j.jphotochem.2023.114686

[Display omitted] •Blue organic light-emitting diodes with external quantum efficiency of 22.8%•Deep-blue host-free devices with external quantum efficiency of 5.17%•Hosts with similar hole and electron mobilities exceeding 2.4 × 10−5 cm2 V−1 s−1.•Organic semiconductors with electron affinity of 2.78 eV and ionization potential of 5.58 eV.•Hidden thermally activated delayed fluorescence of derivatives of benzonitrile-substituted di-tert-butyl-carbazole. With the aim of detecting hidden thermally activated delayed fluorescence (TADF), six organic compounds were synthesized and characterized as emitters and hosts of blue organic light-emitting diodes (OLEDs). The effect of the linking topology of di-tert-butyl-carbazolyl and benzonitrile moieties in donor–acceptor-donor type molecules on device efficiencies was investigated. Just by altering the linking position of di-tert-butyl-carbazolyl moieties at benzonitrile fragment of the emitters and hosts of the blue TADF OLEDs, their maximum external quantum efficiencies (EQEs) can be changed from 1.13 to 5.17 % as well as from 13.8 to the record-high 22.8%. After the comprehensive investigations of the properties including the charge mobility measurements by time-of-flight technique, steady-state and time-resolved photoluminescence and electroluminescence studies, good correlation between EQE of OLEDs and the properties of the isomers with the differently linked donor and acceptor moieties were observed.