Multilayer Chiral 3D AIE-Active Polymers as Ultrasensitive Fe³⁺/Cr⁶⁺ Fluorescent Probes

Two multilayer chiral three-dimensional (3D) polymers exhibiting aggregation-induced emission (AIE) properties were successfully synthesized through Suzuki-Miyaura crosslinking reactions. Deliberately designed with different terminal functional groups (bromine vs. boronic ester), these polymers served as a model system to probe the profound influence of molecular structure on nanoscale aggregation and macroscopic function. Both polymers demonstrated significant AIE behavior, but the variant with less sterically hindered termini formed more uniform aggregates, leading to superior AIE performance. This property enabled their application as ultrasensitive fluorescent probes for the detection of Fe³⁺ and Cr⁶⁺ ions in tetrahydrofuran (THF), achieving detection limits at the nanomolar (nM) level. The materials exhibited outstanding selectivity against competing ions: binding of Fe³⁺ or Cr⁶⁺ inhibited electron transfer, resulting in fluorescence quenching. The distinct terminal groups were found to influence the sensing mechanism, with the boronic ester functionality introducing an additional redox-based pathway for enhanced Fe³⁺ sensitivity. This study establishes a comprehensive design paradigm for AIE-active materials, linking precise structural engineering to extended sensing functions. These multifunctional polymers show great potential for applications in environmental monitoring, biomedical diagnostics, and the development of advanced smart sensors.