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; however, 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 reversible thermofluorochromism from cyan to green across the temperature range of 113–333 K. Through systematic variation of the 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 β‐relaxation, enabling the observed spectral transformation. Additionally, the presence of a TSEI between the 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).