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

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( p -carboxyphenyl)anthracene (DPA) and 1,4-diazabicyclo[2.2.2]octane ( D-H 2 ) ligands can be oxidized, generating the cation radicals DPA +• and D-H 2 +•, respectively. The latter can be deprotonated to form the neutral radical ( D-H • ) 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 D-H 2 in aqueous solution. Moreover, with the process of second oxidation of D-H 2, 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.