New Exciplex-forming Cohost Systems Harnessing Acceptors With Phenanthrene and Phenanthroline Core for Near-Infrared OLEDs.

Two new acceptors, C-BPhCN and N-BPhCN, with 2,3-dicyanopyrazinophenanthrene and pyrazino[2,3-f][1,10]phenanthroline-2,3-dicarbonitrile core and ortho-linked biphenyl peripherals were synthesized and characterized. The exciplex formation of C-BPhCN and N-BPhCN as acceptor (A) and SBFC-G1 as donor (D) was examined. Through optimization, the device using a D:A (2:1) blend in emitting layer (EML) exhibited maximum external quantum efficiency (EQE_max) of 8.26% and 5.25% with electroluminescence peak (EL λ_max) centered at 581 and 595 nm, respectively. A new D-A-D configured near-infrared (NIR) fluorescent emitter DMACBBT was introduced as a dopant in the exciplex-forming cohost system. By tuning the thickness of the electron transporting layer (ETL), the EQE_max of the device employing SBFC-G1:C-BPhCN (2:1): 9 wt % DMACBBT as the EML reached 1.03% with EL λ_max at 808 nm. The counterpart device utilizing SBFC-G1:N-BPhCN (2:1): 9 wt % DMACBBT as the EML exhibited an EQE_max of 1.01% and EL λ_max at 817 nm. The stability of the NIR OLED device was measured, yielding lifetimes (T₆₀) of 182 and 126 h for SBFC-G1:C-BPhCN and SBFC-G1:N-BPhCN cohost-based devices, respectively. This work highlights the high efficiency of NIR OLEDs that can be practically realized by using the exciplex cohost systems with a tailor-made NIR fluorescent emitter.