Constitutional isomers of carbazole–benzoyl-pyrimidine-based thermally activated delayed fluorescence emitters for efficient OLEDs. Issue 44 (2nd November 2021)

• Record Type: Journal Article
• Authors: Pandidurai, Jayabalan; Jayakumar, Jayachandran; Chen, Yi-Kuan; Hsieh, Chia-Min; Cheng, Chien-Hong
• Is Part Of: Journal of materials chemistry. Volume 9:Issue 44(2021)
• Page Start: 15900
• Page End: 15909
• Publication Date: 2021-11-02
• Subjects: Materials -- Periodicals; Chemistry, Analytic -- Periodicals; Optical materials -- Research -- Periodicals; Electronics -- Materials -- Research -- Periodicals; 543.0284
• DOI: 10.1039/d1tc03998a
• Languages: English
• ISSNs: 2050-7526

Abstract

Abstract : Two pairs of constitutional isomeric TADF dopants (35CzBPym and 25CzBPym; 35tCzBPym and 25tCzBPym) containing benzoyl pyrimidine (BPym) as an acceptor and carbazoles (Czs) as donors were designed for high-efficiency OLEDs. Abstract : Thermally activated delayed fluorescence (TADF) emitters are highly useful to achieve 100% internal quantum efficiency (IQE) and high external quantum efficiency (EQE) by reverse intersystem crossing. Herein, four sky-blue to blueish-green TADF dopants, 35CzBPym, 35tCzBPym, 25CzBPym, and 25tCzBPym, containing benzoyl pyrimidine (BPym) as the acceptor and carbazoles (Czs) as the donors were designed, synthesized, and investigated. The as-prepared 35CzBPym and 25CzBPym isomers showed star and Y-shaped configurations as confirmed by a single-crystal X-ray diffractometer. Interestingly, Y-shaped emitters exhibit high photoluminescence quantum yields (PLQYs) (76–88%) together with small Δ E ST (45–90 meV) values, leading to very efficient TADF. The strong intramolecular interactions between the nearby pyrimidine and carbazole planes and hydrogen bonds are crucial for enhancing molecular rigidity resulting in the high PLQY. Thus, an electroluminescent device based on 25tCzBPym shows bluish-green emission (500 nm) with a maximum EQE of 23.3% and a low-efficiency roll-off at high luminance of 1000 cd m −2 (28%). Moreover, the present molecular design exhibits combined effects of intramolecular charge transfer, donor–acceptor interactions, and hydrogen bonding within the molecular structures, supported by the DFT calculations and single-crystal analyses.