Highly Efficient Near-Infrared Electroluminescence up to 800 nm Using Platinum(II) Phosphors

Near-infrared organic light-emitting diodes (NIR OLEDs) enable many unique applications ranging from night-vision displays and photodynamic therapies. However, the development of efficient NIR OLEDs with a low efficiency roll-off is still challenging. Here, a series of new heteroleptic Pt(II) complexes (1–4) flanked by both pyridyl pyrimidinate and functional azolate chelates are synthesized. The reduced ππ* energy gap of the pyridyl pyrimidinate chelate, and strong intermolecular interaction and high crystallinity in vacuum-deposited thin films engender strong intermolecular charge transfer transition including metal–metal-to-ligand charge transfer; thereby, exhibiting efficient photoluminescence within 776–832 nm and short radiative lifetimes of 0.52–0.79 µs. Consequently, nondoped NIR-emitting OLEDs based on these Pt(II) complexes are fabricated, to which Pt(II) complexes 2 and 4 give record high maximum external quantum efficiency of 10.61% at 794 nm and 9.58% at 803 nm, respectively. Moreover, low efficiency roll-off is also observed, among which the device efficiencies of 2 and 4 are at least four times higher than that of the best NIR-emitting OLEDs recorded at current density of 100 mA cm⁻².