Intramolecular Hydrogen Bonding Enables 5.9% External Quantum Efficiency in Radical-Based Near-Infrared Organic Light-Emitting Diodes with Emission beyond 850 nm

Organic open-shell emitters capable of near-infrared (NIR) emission are of growing interest for optoelectronic and bioimaging applications, yet achieving high efficiency remains a fundamental challenge due to severe nonradiative losses. Here, we report a rational design strategy that integrates intramolecular hydrogen bonding and rotational restriction to construct highly emissive NIR radicals. Incorporating a pyrimidine-modified tris(2,4,6-trichlorophenyl)methyl scaffold with donor units yields two radicals, Pm-DMNA and Pm-TPA, featuring planar donor-acceptor geometries and rigidified conformations. These structural features enhance charge-transfer interactions while effectively suppressing vibrational deactivation pathways. As a result, Pm-DMNA exhibits a photoluminescence quantum efficiency (PLQE) of 36% at 783 nm and enables organic light-emitting diodes (OLEDs) with a record-high external quantum efficiency (EQE) of 5.9% beyond 850 nm. This work illustrates a generalizable approach for engineering efficient open-shell emitters through precise conformational control.