Structure-Property Relationships of Thiolated Polymer Ligands Governing the Luminescence and Sensing Performance of Copper Nanoclusters

Copper nanoclusters (CuNCs) are promising luminescent nanomaterials whose optical properties are strongly governed by the chemical environment provided by their stabilizing ligands. Here, we explore how subtle structural variations in polymer-bound thiol ligands affect the formation, photoluminescence, stability, and sensing response of CuNCs. A family of thermoresponsive poly(methoxy triethylene glycol methacrylate) (MEO ₃ MA)-based statistical copolymers containing protected thiol functionalities with different spacer structures was synthesized by reversible addition-fragmentation chain-transfer polymerization and used as polymeric ligands for the in situ generation of CuNCs. Keeping the thermoresponsive polymer backbone essentially unchanged allowed the effect of ligand architecture to be isolated. Remarkably different optical behaviors emerged depending on the structure of the sulfur-containing side chain. One ligand environment promoted highly emissive and comparatively stable CuNCs that underwent an unusual aging-induced evolution from red to intense green fluorescence, whereas the other polymer architectures produced less persistent emission. Ligand structure also determined the response toward external analytes, leading either to fluorescence quenching or enhancement in the presence of mercury(II) ions (Hg ²⁺ ) and to different responses toward chromate ions (CrO ₄ ²⁻ ). These findings reveal that seemingly minor changes in the molecular architecture surrounding the metal core can profoundly modify CuNC photophysics and recognition behavior, providing a simple strategy for engineering responsive polymer-nanocluster hybrids.