Solid-state near-infrared (NIR) light-emitting devices have recently received considerable attention as NIR light sources that can penetrate deep into human tissue and are suitable forb ioimaging and labeling. In addition, solidstate NIR light-emitting electrochemical cells (LECs) have shown several promising advantages over NIR organicl ightemittingd evices (OLEDs). However,a mong the reported NIR LECs based on ionic transition-metal complexes (iTMCs), there is currently no iridium-based LEC that displays NIR electroluminescence (EL) peaksn ear to or above 800 nm. In this report we demonstrate as imple methodf or adjusting the energy gap between the highest-occupied molecular orbital (HOMO) and the lowest-unoccupied molecular orbital (LUMO)o fi ridium-based iTMCs to generate NIR emission.We describe as eries of novel ionic iridium complexes with very small energy gaps, namely NIR1-NIR6,i nw hich 2,3-diphenylbenzo[g]quinoxaline moieties mainly take charge of the HOMO energy levels and 2,2'-biquinoline, 2-(quinolin-2yl)quinazoline, and 2,2'-bibenzo[d]thiazole moieties mainly control the LUMO energy levels. All the complexes exhibited NIR phosphorescence, with emission maximau pt o8 50 nm, and have been applied as componentsi nL ECs, showing a maximume xternal quantum efficiency (EQE) of 0.05 %i nt he EL devices. By using ah ost-guest emissive system,w ith the iridiumc omplex RED as the host and the complex NIR3 or NIR6 as guest, the highest EQE of the LECs can be further enhanced to above 0.1 %.Supporting information and the ORCID identification number(s) for the author(s) of this articlecan be found under: https://doi.

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