Metallosupramolecular Multiblock Copolymers of Lanthanide Complexes by Seeded Living Polymerization

Abstract

Supramolecular block copolymers, derived via seeded living polymerization, are increasingly recognized for their rich structural and functional diversity, marking them as cuttingedge materials. The use of metal complexes in supramolecular block copolymerization not only offers a broad range of block copolymers through the structural similarity in the coordination geometry of the central metal ion but also controls spectroscopic properties, such as emission wavelength, emission strength, and fluorescence lifetime. However, the exploration of metallosupramolecular multiblock copolymerization based on metal complexes remains quite limited. In this work, we present a pioneering synthesis of metallosupramolecular multiblock copolymers utilizing Eu 3+ and Tb 3+ complexes as building blocks. This is achieved through the strategic manipulation of nonequilibrium self-assemblies via a living supramolecular polymerization approach. Our comprehensive exploration of both thermodynamically and kinetically regulated metallosupramolecular polymerizations, centered around Eu 3+ and Tb 3+ complexes with bisterpyridine-modified ligands containing R-alanine units and a long alkyl group, has highlighted intriguing behaviors. The monomeric [R-L 1 Eu(NO 3 ) 3 ] complex generates a spherical structure as the kinetic product. In contrast, the monomeric [R-L 1 Eu 2 (NO 3 ) 6 ] complex generates fiber aggregates as a thermodynamic product through intermolecular interactions such as π−π stacking, hydrophobic interaction, and H-bonds. Utilizing the Eu 3+ complex, we successfully conducted seed-induced living polymerization of the monomeric building unit under kinetically regulated conditions. This yielded a metallosupramolecular polymer of precisely controlled length with minimal polydispersity. Moreover, by copolymerizing the kinetically confined Tb 3+ complex state ("A" species) with a seed derived from the Eu 3+ complex ("B" species), we were able to fabricate metallosupramolecular tri-and pentablock copolymers with A−B−A, and B−A−B−A−B types, respectively, through a seed-end chain-growth mechanism.