<p>The exceptional versatility of chromogenic phases in polymers, such as conjugated polydiacetylene (PDA), plays a crucial role in durable sensing applications. This study explores the synthesis and application of PDA-based functionalized dyes as visual color indicators. The dyes were synthesized by modifying the head groups of 10,12-tricosadiynoic acid (T) with alcoholic ethers using Steglich esterification reaction. The functionalization of the dye derivative was confirmed through various analytical techniques. The composite films were then prepared by mixing the modified monomer dye with polyvinyl alcohol (PVA) and exposed to UV radiation for topochemical polymerization, forming PDA. The functionalized materials/PVA composite films exhibited an irreversible color transition above −8&#xa0;°C in thermochromic studies. The results indicate that these conjugated PDA-based thermochromic composite films, with their irreversible color change at low temperatures, can function as effective indicators and sensors for real-time monitoring and, delivering reliable information for security applications such as anti-counterfeiting.</p> Graphical Abstract <p>● This study presents conjugated low-temperature thermochromic dyes synthesized via Steglich esterification and embedded in a polymer matrix to form biocompatible thermochromic composite films. </p> <p>● The dyes exhibit irreversible thermochromic behavior above -8 °C, enabling their use as visual and real-time temperature-monitoring sensors.</p> <p>●These films offer reliable information for security applications, including anti-counterfeiting in low-temperature environments.</p> <p></p>