Pyrido[2,3-b]pyrazine-based donor–acceptor emitters for high-efficiency TADF OLEDs

Organic emitters exhibiting thermally activated delayed fluorescence (TADF) have emerged as promising alternatives to phosphorescent metal complexes in organic light-emitting diodes (OLEDs). Purely organic TADF materials offer low cost and high efficiency, yet achieving specific emission colors and optimal device performance remains an active challenge. In this work, new pyrido[2,3-b]pyrazine derivatives linked via phenyl bridges to carbazole or phenothiazine groups were investigated. Their photophysical properties, including absorption, emission, photoluminescence quantum yields, excited-state lifetimes, and singlet–triplet energy gaps (ΔEST), were characterized. The compounds exhibited efficient TADF with ΔEST values as low as 0.16 eV and emission ranging from green to orange, with quantum yields up to 82 %. OLEDs employing these emitters achieved an external quantum efficiency (EQE) of 0.94 % in neat films, which increased to 21.3 % in optimized host–guest systems, demonstrating excellent performance near the theoretical limit for TADF-based devices. Acknowledgment: Funded by the European Union. Views and opinions expressed are however those of the author(s) only and do not necessarily reflect those of the European Union or the European Innovation Council and SMEs Executive Agency (EISMEA). Neither the European Union nor the granting authority can be held responsible for them. (SCOLED, Grant Agreement No. 101098813)