Preparation of Bis-Polydiacetylene with Reversible Thermochromism and High Sensitivity toward Pb²⁺ Detection

The fabrication of stimulus-responsive polydiacetylene (PDA) materials with thermochromic reversibility is highly valuable for displays, optoelectronic devices, and sensors. Herein, a type of bis-diacetylene monomer (bis-DA) covalently linked by 1,4-phenylene diisocyanate was synthesized. Owing to the strong hydrogen-bonding interactions, a reversible color transition can be realized for the polymerized bis-diacetylene (bis-PDA) film in the temperature range from 30 to 150 °C. The excellent linear relationship between the colorimetric response values and temperature (from 90 to 150 °C) with an R2 value of 0.992 demonstrated that the as-prepared bis-PDA sensor can be used for the quantitative analysis of temperature. Meanwhile, the bis-PDA film displayed a reversible thermochromic property upon exposure to 980 nm near-infrared light at a relatively high power density. In addition, hybrid PDA vesicles that consist of DA and bis-DA monomers with a molar ratio of 1:1 can be utilized as sensitive, specific, and visual sensors for the detection of Pb2+ ions, with a satisfactory limit of detection of 0.15 μM. This work not only offers a fundamental understanding of the mechanism of the thermochromic property of PDA but also may broaden the applications of PDA-based sensors.