Disulfide-Linked Symmetrical Polydiacetylene as Visualized Temperature Sensor for Heatstroke Monitor

Body temperature is a key physiological indicator, requiring continuous, full-range monitoring from normothermia to hyperthermia for effective heatstroke management. To address the limitations of mercury thermometers and existing sensors in visualized real-time screening, three monomers S-1, S-2, and S-3 featuring flexible aliphatic chains and ester terminals, anhydride terminals, and aromatic rings with amide hydrogen bonds and π-π stacking are designed and polymerized into Poly(S-1), Poly(S-2), and Poly(S-3), respectively. Among these polydiacetylenes (PDAs) with symmetric functionalization, Poly(S-1) exhibits a multi-step, naked-eye-visible thermochromic transition within 35°C-43°C, attributed to its flexible aliphatic chains and ester linkages that enable side-chain motion and main-chain conformational changes at low temperatures. In contrast, the rigid structural motifs present in Poly(S-2) and Poly(S-3) introduce stronger intermolecular forces and higher energy barriers, necessitating elevated temperatures to induce comparable thermochromic transitions. Notably, Poly(S-1) is successfully fabricated into a functional patch; its irreversible thermochromic nature within the physiological range meets the requirements of disposable medical devices, helping to prevent cross-infection and facilitating temperature recording. This study enables precise tuning of the thermochromic temperature of PDA materials, expands their applications in biomedical monitoring and smart responsive materials, and offers design insights and theoretical foundations for developing next-generation visual body temperature sensors.