Molecular design strategy for orange-red thermally activated delayed fluorescence emitters via intramolecular energy transfer and their application in solution processable organic light-emitting diodes

Realizing effective orange-red/red emission is still far behind blue and green emission in thermally activated delayed fluorescence (TADF) materials. In this context, a novel strategy for achieving efficient orange-red/red TADF emitters is proposed via intramolecular energy transfer by encapsulating the red-emitting core with a blue emitting chromophore. Two novel compounds called TS-1 and TS-2 were prepared and characterized, in which two blue TADF emitting units are used as the end groups and a red TADF emitter as the molecular core (TA). Both compounds show clear TADF character with red emission at 655 nm in a neat film, suggesting an effective intramolecular energy transfer from the blue chromophores to the red one. Both TS-1 and TS-2 present higher photoluminescence quantum yields (70-90%) than the TA core (42%) due to the encapsulation and energy transfer. Solution-processable organic light-emitting diodes (OLEDs) exhibit a maximum external quantum efficiency of similar to 13% for compound TS-1, much higher than that of TA-based OLEDs (2.3%). This research is the first example for red TADF emitter via intramolecular energy transfer, which clearly provides an effective method for designing highly efficient red TADF molecules.

Automated summary

Efficient orange-red/red TADF emitters were achieved by encapsulating the red-emitting core with a blue emitting chromophore, demonstrating effective intramolecular energy transfer. The novel compounds showed higher photoluminescence quantum yields and improved external quantum efficiency in OLEDs compared to traditional TA-based OLEDs. This research provides an effective method for designing highly efficient red TADF molecules through intramolecular energy transfer.