Metal-free click polymerization of thiols and chalcone-derived internal olefins in air to prepare functional clusteroluminescent polythioethers for dual-response fluorescent probe

Thiol-ene click polymerization has become an effective synthetic tool for constructing diverse sulfur-containing polymers with advanced functions. However, the polymerization of internal alkene and thiol has been rarely used to prepare functional polymers because of large steric hindrance and relatively weak reactivity. In this work, a base-catalyzed click polymerization of thiols and internal olefins was successfully established in air. Notably, the polymerization went smoothly in halogen-containing solvent even without any catalyst via a radical step-growth polymerization. The polymerization enjoys excellent monomer applicability, which affords 16 well-defined polythioethers in high yields (up to 99 %) with high molecular weights (M_w up to 19,600), good thermal stability (T_d,5 % up to 326 °C), broadly regulated glass transition temperatures (-24∼95 °C), and unconventional fluorescence. Via a simple solvent regulation strategy, the vanillin-derived polythioether could be used as a turn-off fluorescence probe for Fe³⁺ ions in DMF/H₂O and a turn-on probe for Ag⁺ ions in THF, with low detection limits of 9.15 × 10^–7 mol/L and 4.60 × 10^–7 mol/L, respectively. Additionally, the detection of Ag⁺ presented a transformation from a clear solution to an emulsion, expanding the application prospects through observing colorimetric and fluorescent dual signals. Thus, this work not only holds significance in establishing an efficient polymerization, but also provides a strategy to prepare sensitive fluorescent probes for multiple metal ions.