Dual Intrareticular Oxidation of Mixed-Ligand Metal–Organic Frameworks for Stepwise Electrochemiluminescence

Abstract

This work presents a mixed-ligand metal-organic framework (m-MOF) integrated with two ligands, one as a luminophore and the other as a coreactant, on one metal node for self-enhanced electrochemiluminescence (ECL). Both 9,10-di(<i>p</i>-carboxyphenyl)anthracene (DPA) and 1,4-diazabicyclo[2.2.2]octane (<b>D-H</b>_<b>2</b>) ligands can be oxidized, generating the cation radicals DPA^+• and <b>D-H</b>_<b>2</b>^+•, respectively. The latter can be deprotonated to form the neutral radical (<b>D-H</b>^•) and then react with DPA^+• to produce excited DPA* for ECL emission without exogenous coreactants. As a result of the incorporation into the MOF framework and the intrareticular charge transfer between the two ligands, the ECL intensity of the m-MOF was increased 26.5-fold compared with that of the mixture of DPA and <b>D-H</b>_<b>2</b> in aqueous solution. Moreover, with the process of second oxidation of <b>D-H</b>_<b>2</b>, stepwise ECL emission was observed as a result of local excitation in the DPA unit, which was identified through density functional theory calculations. Overall, the implementation of the mixed-ligand approach, which combines the luminophore and coreactant as linkers in reticular materials, enriches the fundamentals and applications of ECL systems.