Tuning of HOMO-LUMO localization for achieving thermally activated delayed fluorescence

• Published in: Journal of luminescence 2022-01, Vol.241, p.118473, Article 118473
• Main Authors: Skaisgiris, Rokas, Serevičius, Tomas, Dodonova, Jelena, Banevičius, Dovydas, Kazlauskas, Karolis, Tumkevičius, Sigitas, Juršėnas, Saulius
• Format: Article
• Language: English
• Subjects: Carbazole; Diphenylamine; OLED; Pyrimidine; rISC; TADF
• ISSN: 0022-2313; 1872-7883
• DOI: 10.1016/j.jlumin.2021.118473

High emission yield and rapid reverse intersystem crossing are essential for efficient thermally activated delayed fluorescence (TADF) compounds. In this paper, we show that efficient TADF can be achieved by enhancing the localization of HOMO and LUMO in carbazole-pyrimidine compounds with rather flat molecular structure. Simple carbazole-pyrimidine Cbz-PYR was selected as a reference compound due to the pronounced room-temperature phosphorescence activity. The subsequent modifications of carbazole and pyrimidine units with diphenylamine and phenyl fragments resulted in weakened HOMO-LUMO communication, leading to the minimized singlet-triplet energy gap of only 111 meV. Due to the rather flat molecular geometry, TADF compounds showed remarkable radiative decay rate reaching 4.6 × 107 s−1 for the most efficient TADF-active carbazole-pyrimidine compound dCbz-pPYR, followed by high emission yield of 0.75. Efficient green electroluminescence with peak EQE of 18.3%. was shown for OLED device with dCbz-pPYR emitter. [Display omitted] •A series of RTP – TADF emitters were synthesized.•HOMO and LUMO localization enabled TADF.•Green electroluminescence with 18.3% EQE was shown.