A ruthenium tetrazole complex-based high efficiency near infrared light electrochemical cell

We report on the exploitation of a new tetrazole-substituted 1,10-phenanthroline and a 2,2'-bipyridine (bpy) ancillary ligand modified with an electron-donating group in cationic ruthenium complexes. This complex, placed in between two electrodes without any polymer, demonstrates high efficiency near-infrared (NIR) electroluminescence (EL). The comparison between bpy and its methyl-substituted ancillary ligand shows that the cationic Ru tetrazolate complex containing methyl groups exhibits a red shift in the EL wavelength from 620 to 800 nm compared to [Ru(bpy)₃]²⁺ and an almost twofold reduction in the turn-on voltage, i.e., from 5 to 3 V, with respect to 5-tetrazole-1,10-phenanthroline. An external quantum efficiency of 0.95% for the dimethyl derivative is demonstrated, which is a remarkable result for non-doped NIR light electrochemical cells based on ruthenium polypyridyl.