Multifaceted regulation of chiroptical properties and self-assembly behaviors of chiral fluorescent polymers

Abstract

The multifaceted regulation of the chiroptical properties and self-assembly behaviors of chiral fluorescent polymers is of great significance yet remains challenging to achieve. Herein, a series of novel salen-based chiral fluorescent polymers with aggregation-induced emission and varied substitution manners were facilely and efficiently synthesized. Multiple factors were systematically investigated on the chiroptical properties and self-assembly performance of these polymers, which include molecular structures, solvent environments, metal coordination, and liquid crystal (LC) assemblies. Sutle change in the solvent composition can lead to diverse assembly morphologies of all these chiral polymers, from single-handed helical fibers, helical toroids or loops, to spherical structures, consequently leading to an aggregation-reduced circular dichroism (CD) phenomenon. The polymers bearing salen units show highly selective and reversible coordination with Zn²⁺ and can also induce multiple responses in the absorption, luminescence, CD, and circularly polarized luminescence (CPL) of these chiral fluorescent polymers via a coordination- and dissociation-initiated self-assembly tuning. Furthermore, a small amount of the chiral fluorescent polymer in can induce achiral nematic 4-cyano-4′-n-pentylbiphenyl (5CB) to form ordered chiral nematic LC phase with significant improvement in their CD and CPL signal. The absolute absorption and luminescent dissymmetry factors of the resulting supramolecular assemblies can reach the order of 10⁻¹.