Mixed Emission of Acenaphtho[1,2-b] Quinoxaline Regioisomers

National Centre for Research and Development, Poland, Grant No. LIDER/21/0077/L-11/19/NCBR/2020; Polish Ministry of Education and Science to outstanding young scientists (2/DSP/2021); Polish National Science Centre, Grant No. 2022/45/B/ST5/03712; Polish National Science Centre, Grant No. 2022/45/B/ST4/00800.

The development of new materials exhibiting thermally activated delayed fluorescence (TADF) for organic light-emitting device (OLED) applications, along with studies on the nature of their interaction with the host matrix in the emissive layer of the device, has recently received significant attention. A deeper investigation into the influence of the matrix can expectedly improve the rational design of TADF emitters. Under these circumstances, we report two D–A–D regioisomers that comprise an acenaphthenequinone (ACQ) core. Although both structures differ solely in the substitution position of the carbazole (Cz), which is attached at position 9 in F1 and at position 10 in F3, this study explores the mixed emission behavior of regioisomeric TADF emitters. Electrochemical and photophysical analyses revealed distinct redox behavior, emission properties, and performance of the OLED device between the two isomers. While both emitters show promising potential for OLED applications, the differences in their structural arrangement significantly influence their charge-transfer characteristics and device efficiency, which is manifested by their distinct external quantum efficiency (EQE) performance. The highest EQE of 12.6% was denoted for F3 (3,10), while the dye with TBCz attached in position 3,9 (F1) disclosed considerably lower performance of 7.4%. These results shed light on the critical role of the position of substituents along with the matrix environment toward efficient design of TADF OLED emitters. These results will provide a better understanding of the influence of the host matrix and adopt the structure of the emitter in a way that allows the development of highly efficient OLED devices.

Published as part of The Journal of Physical Chemistry C special issue “TADF-Active Systems: Mechanism, Applications, and Future Directions”.