Aggregation-Induced Electrochemiluminescence from a Cyclometalated Iridium(III) Complex

Aggregation-induced emission has been extensively found in organic compounds and metal complexes. In contrast, aggregation-induced electrochemiluminescence (AI-ECL) is rarely observed. Here, we employ two tridentate ligands [2,2':6',2''-terpyridine (tpy) and 1,3-bis(1H-benzimidazol-2-yl)benzene (bbbiH(3))] to construct a cyclometalated iridium-(III) complex, [Ir(tpy)(bbbi)] (1), showing strong AI-ECL. Its crystal structure indicates that neighboring [Ir(tpy)(bbbi)] molecules are connected through both pi-pi-stacking interactions and hydrogen bonds. These supramolecular interactions can facilitate the self-assembly of complex 1 into nanoparticles in an aqueous solution. The efficient restriction of molecular vibration in these nanoparticles leads to strong AI-ECL emission of complex 1. In a dimethyl sulfoxide-water (H2O) mixture with a gradual increase in the H2O fraction from 20% to 98%, complex 1 showed a similar to 39-fold increase in the electrochemiluminescence (ECL) intensity, which was similar to 4.04 times as high as that of [Ru(bpy)(3)](2+) under the same experimental conditions. Moreover, the binding of bovine serum albumin to the nanoparticles of complex 1 can improve the ECL emission of this complex, facilitating the understanding of the mechanism of AI-ECL for future applications.