Understanding the Structure of Reversible Coordination Polymers Based on Europium in Electrostatic Assemblies Using Time-Resolved Luminescence

In situ characterization of the structure of reversible coordination polymers remains a challenge because of their dynamic and concentration-responsive nature. It is especially difficult to determine these structures in their self assemblies where their degree of polymerization responds to the local concentration. In this paper, we report on the structure of reversible lanthanide coordination polymers in electrostatic assemblies using time-resolved luminescence (TRL) measurement. The reversible coordinating system is composed of the bifunctional ligand 1,11-bis(2,6-dicarboxypyridin-4-yloxy)-3,6,9-trioxaundecane (L2EO4) and europium ion Eu3+. Upon mixing with the positively charged diblock copolymer poly(2-vinylpyridine)-b-poly(ethylene oxide) (P2VP(41)-b-PEO205), electrostatic polyion micelles are formed and the negatively charged L2EO4-Eu coordination complex simultaneously transforms into coordination "polymers" in the micellar core. By virtue of the water-sensitive luminescence of Eu3, we are able to obtain the structural information of the L2EO4-Eu coordination polymers before and after the formation of polyion micelles. Upon analyzing the fluorescence decay curves of Eu3+ before and after micellization, the fraction of Eu3+ fully coordinated with L2EO4 is found to increase from 32 to 83%, which verifies the occurrence of chain extension of the L2EO4-Eu coordination polymers in the micellar core. Our work provides a qualitative picture for the structure change of reversible coordination polymers, which allows us to look into these "invisible" structures.National Natural Science Foundation of China [21422302, 21573011, 21473005]; Beijing National Laboratory for Molecular Sciences (BNLMS)SCI(E)EIPubMedARTICLEjbhuang@pku.edu.cn; yunyan@pku.edu.cn235830-58373