Europium‐Based Metal–Organic Framework with N─H···π Interaction and Intramolecular Energy Transfer Mechanisms for Self‐Electrochemiluminescence

Abstract

AbstractThis work proposes a europium‐based metal–organic framework ([Eu2(HNCP)4Cl4(H2O)2]n, named ZL‐1), featuring dinuclear Eu2(COO)2 clusters as connecting nodes, linked by benzimidazolyl tridentate ligand 2‐(4‐carboxyphenyl)‐imidazo[4,5‐f]‐1,10‐phenanthroline (HNCP) for efficient self‐electrochemiluminescence (self‐ECL). The cathodic ECL emission shows two peaks with a maximum intensity of 7500 a.u.at 0 ∼ −1.8 V in pH 9.0 phosphated buffered solution (PBS) without extra coreactant. The cleavage of N─H bond in benzimidazolyl group can occur under alkaline conditions to generate neutral radical ZL‐1•. After applying voltage, the ZL‐1 can be reduced twice to form ZL‐1Re1•− and ZL‐1Re2•−. Then, ZL‐1Re1•− and ZL‐1Re2•− react with ZL‐1•, accompanied by transferring energy from HNCP to central Eu3+ to produce excited ZL‐1Re1* and ZL‐1Re2* for ECL1 and ECL2 emissions. The local excitation in the HNCP unit is demonstrated with cyclic voltammetry (CV) and stepping pulse ECL. The stimulated and luminous species are confirmed by density functional theory calculations and ECL spectra. This design approach of self‐ECL materials, which coordinated functional ligands with lanthanide metal ions as 3D‐structured MOF, broadened the applications of ECL systems to loose conditions and facilitated mechanistic exploration of ECL processes.