Organic light-emitting diodes (OLEDs) are used in display technology.  Phosphorescent materials for such OLEDs have a higher theoretical efficiency than fluorescent materials, but finding phosphorescent materials for stable blue OLEDs is a challenge. An alternative is the use of so-called thermally activated delayed fluorescence (TADF) molecules, which also have high efficiencies.

Youichi Tsuchiya, Hajime Nakanotani, Chihaya Adachi, Kyushu University, Fukuoka, Japan, and colleagues have synthesized trifluoromethane-modified carbazole derivatives as stable blue TADF emitters. The team obtained the desired molecules by a S_NAr reaction of tetrafluorophthalonitrile with CF₃-modified carbazoles using sodium hydride in tetrahydrofuran (THF). The products were purified by sublimation.

The team found that the trifluoromethane groups induced a blue shift of about 40–55 nm in the compound’s emission compared with hydrogen-substituted analogues. This was attributed to the electron-withdrawing nature of the CF₃ groups. The modification also improved the photoluminescence yield and the stability. According to the researchers, these results show that CF₃-modified carbazoles are promising for the development of stable, efficient, deep-blue emitting TADF molecules.

• Trifluoromethane modification of thermally activated delayed fluorescence molecules for high-efficiency blue organic light-emitting diodes,
  Masayuki Yokoyama, Ko Inada, Youichi Tsuchiya, Hajime Nakanotani, Chihaya Adachi,
  Chem. Commun. 2018.
  https://doi.org/10.1039/c8cc03425g