Enhanced Pi Conjugation and Donor/Acceptor Interactions in D-A-D Type Emitter for Highly Efficient Near-Infrared Organic Light-Emitting Diodes with an Emission Peak at 840 nm

Restricted by the energy gap rule, near-infrared (NIR) luminescent materials face great challenges. Here, we report a newly designed and synthesized organic molecule, 5,5′-([1,2,5]thiadiazolo[3,4-c]pyridine-4,7-diyl)bis(N,N-diphenylthiophen-2-amine) (DTPS-PT), which has strong donor and acceptor interactions for NIR emission applications. The results demonstrate that the higher planarity of the DTPS-PT molecular structure enhances the pi-conjugation and hybridization between the charge transfer state (CT) and localized pi states (LE). As a result, DTPS-PT exhibits NIR emissions from an LE involved in hybridized local and charge transfer (HLCT) states, showing a 79% high fluorescence quantum yield in the low polar solvent tetrachloromethane. For both doped and nondoped devices, the NIR OLEDs based on DTPS-PT achieved "real" NIR emission with the λonset above 700 nm. The best performing OLED device within the doped devices gave a maximum emission peak around 840 nm with a maximum radiance of 2202 mW Sr–1 m–2.