Molecularly engineered electroplex emission for an efficient near-infrared light-emitting electrochemical cell (NIR-LEC)

Electroplex emission is rarely seen in ruthenium polypyridyl complexes, and there have been no reports from light-emitting electrochemical cells (LECs) to date. Here, for the first time, near-infrared (NIR) emission via the electroplex mechanism in a LEC based on a new blend of ruthenium polypyridyl complexes is described. The key factor in the design of the new complexes is the 0.4 V decrease in the oxidation half-potential of Ru( ii )/Ru( iii ) in [Ru(DPCO)(bpy) 2 ]ClO 4 (DPCO = diphenylcarbazone, bpy = 2,2 bipyridine), which is about one-third of the value for benchmark [Ru(bpy) 3 ](ClO 4 ) 2 , as well as the long lifetime of excited states of 350-450 ns. The LEC based on the new blend with a narrow band gap ( 1.0 eV) of a Ru(DPCO) complex and Ru(bpy) 3 2+ can produce an electroluminescence spectrum centred at about 700 nm, which extends to the NIR region with a high external quantum efficiency (EQE) of 0.93% at a very low turn-on voltage of 2.6 V. In particular, the very simple LEC structure was constructed from indium tin oxide (anode)/Ru(DPCO):Ru(bpy) 3 2+ /Ga:In (cathode), avoiding any polymer or transporting materials, as well as replacing Al or Au by a molten alloy cathode. This system has promising applications in the production of LECs via microcontact or inkjet printing. Electroplex emission is rarely seen in ruthenium polypyridyl complexes, and there have been no reports from light-emitting electrochemical cells (LECs) to date. Here, near-infrared (NIR) emission via the electroplex mechanism in a LEC was reported.