Luminescence Control in Polyesters via Chain-Motion–Regulated Through-Space Electronic Interaction

Stimuli-responsive luminescent polymers translate changes in molecular mobility or transformation into optical outputs, but most systems rely on synthetically elaborate architectures that hinder broad implementation. Here, a very simple polyester, synthesized via ring-opening alternating copolymerization (ROAC) of phthalic anhydride (PA) and heteroatom-containing ethyl glycidyl ether (EGE), displays a reversible thermofluorochromism from cyan to green across the temperature range of 113–333 K. Through systematic variation of polymer structure combined with temperature-dependent photoluminescence and dynamic mechanical analysis, we identify a chain-motion–regulated through-space electronic interaction (TSEI) mechanism in which the ether side chain contributes to TSEI formation and modulates the emission through its β-relaxation, enabling the observed spectral transformation. Additionally, the presence of TSEI between carbonyl and phthalate groups enables persistent cryogenic phosphorescence in PA-containing polyesters. These findings not only highlight the potential of thermally responsive luminescent polyesters but also establish a versatile platform for the rational design of phosphorescent and thermo-responsive nonconventional luminescent materials (NLMs).