Chiral nanostructures derived from europium(iii) complexes for enhanced circularly polarised luminescence and antibacterial activity

Abstract

Nanomaterials that exhibit a multitude of properties are gaining vast attention in recent years. Minimising the material consumption and simplifying the manifold synthetic routes adopted for the preparation of diverse molecules and materials are the major advantages offered by such materials. Herein, we report the synthesis of a series of optically active heterobimetallic Eu(III) complexes with the general formula M⁺[Eu((+)–tfac)₄]⁻ (M = Cs, Rb, K, Na) using chiral 3-trifluoroacetylcamphorate as the ligand. The metal coordinated complex forms an interesting one-dimensional polymer crystal which further extends to arrays resulting in a coordination network structure. The synthesized complexes exhibited high circularly polarized luminescence. The optical activity was dependent on the size of the alkali metal cation and was found to increase with the increase in the size of the ion. The caesium derivative of the complex exhibited a remarkably high luminescence dissymmetry value and a high luminescence quantum yield. The complexes undergo self-assembly in suitably selected solvents forming chiral nanostructures. The aggregated structures of all the four derivatives showed high chiral luminescence both in the solution state and solid films. In addition to chiral luminescence, the complexes exhibited promising antibacterial activity towards multidrug resistant bacterial strains Staphylococcus aureus and Enterococcus faecalis, microbes that form the root cause of consequential co-morbidities and mortality to humankind. Moreover, the high luminescence quantum yield exhibited by the complexes shows promise towards bioimaging applications. The facile approach opens new avenues for finding potential applications for the lanthanide based nanosystems, both as efficient chiral luminescent materials and as effective antibacterial agents.