Efficient radical-based near-infrared organic light-emitting diodes with an emission peak exceeding 800 nm

Abstract

Near-infrared (NIR) organic light-emitting diodes (OLEDs) have attracted increasing attention due to their potential applications in night vision displays, optical communications and information security devices. However, due to the low quantum efficiency of NIR emitters and inefficient utilization of triplet excitons, efficient NIR OLEDs have been a challenge. Herein, a new luminescent radical, N-(4′-(bis(2,4,6-trichlorophenyl)methyl)-3′,5′-dichloro-[1,1′-biphenyl]-4-yl)-N-(naphthalen-2-yl)naphthalen-2-amine (TTM-NPNA), was designed and synthesized. TTM-NPNA shows not only deep NIR emission but also high photoluminescence quantum efficiency (PLQE). Even in toluene and 5.0 wt% TTM-NPNA:CBP doped film, it still maintains PLQE of 24% and 16%, respectively, with emission peaks over 800 nm. In addition, TTM-NPNA exhibits excellent thermal and electrochemical stability and has a non-Aufbau electronic structure. An OLED based on TTM-NPNA shows a maximum external quantum efficiency (EQE) of 3.9% with a peak wavelength of 822 nm, which is among the highest EQE values for metal-free NIR-OLEDs with an emission peak exceeding 800 nm. This study demonstrates the great potential of radicals as NIR-OLED emitters.