Chiral co-assembly of a polyoxometalate complex with an achiral pyrene derivative enables redox-modulated circularly polarized luminescence

Abstract

We report the fabrication of helical structures with responsive circularly polarized lumunescence (CPL) via the chiral co-assembly of a cholesterol-modified Lindqvist type polyoxometalate (POM) and an achiral pyrenyl derivative. The chiral surfactant encapsulated POM (CSEP) complex was synthesized by combining (TBA)₂[Mo₆O₁₉] with cholesterol-containing organic surfactants through ion exchange. It was found that the CSEP complex self-assembled into left-handed helical structures in mixed organic solvents, which could serve as a chiral template that enables achiral pyrenyl fluorophores (Py) to exhibit chiroptical properties. When doping Py at a ratio of 5 wt% into the system, the chiral co-assembly with CSEP in the mixed organic solvent results in the formation of helical nanofibers, which emit blue CPL signals. Furthermore, the chiral helical structures can be dynamically transformed to spherical aggregates upon UV illumination, accompanied by photochromism. The disappearance of CPL signals corresponded to the disruption of the chiral morphology in the co-assembled nanostructures. More importantly, the morphology transformation is reversible. The nanospheres transform into helical nanofibers under the oxidation of H₂O₂, which could trigger the regeneration of CPL signals. This work contributes to the understanding and development of chiral supramolecular systems featuring stimulus-responsive CPL switches.