Thermal-Induced Chromism and Fluorescence Emission of Rhodamine B-Containing Polymers with Different Polarities: Tracking Temperature and Development of Thermochromic Labels

Thermochromicpolymers, as a highly applicable intelligentcategoryof innovative materials, are capable of changing their color withtemperature variations. Different characteristics of the matrix andspecially its polarity can be influential factors in the responsivityof thermochromic polymers. In this study, polystyrene, poly(methylmethacrylate), and poly(dimethylaminoethyl methacrylate) with differentpolarities were synthesized via reverse atom transfer radical polymerization.Thermochromic polymers were prepared by physical incorporation ofthe N-(rhodamine-B)lactam-ethylenediamine leuco dyeand HCl color developer into the three polymers. The effect of polarityof the polymers on their thermochromism and fluorescence propertieswas investigated. The thermochromic polymers changed their color fromcolorless to a colored state with increasing temperature due to theintermolecular proton transfer in the system. UV-vis and fluorescencespectroscopies were used to evaluate the thermochromism and fluorescenceproperties of the polymer systems, respectively, at different temperatures.The intensity of absorption and emission of the thermochromic polymersincreases with increasing temperature, where increasing polarity ofthe polymer matrix has an opposite effect on the intensity of absorptionand emission. The change in color with temperature variation was detectablewith the naked eye for the three polymer samples. In addition, investigationof the fatigue resistance and also response and recovery times ofthe samples showed temperature-sensing ability of the samples. Theseresults showed that all samples have high responsivity and colorationfor at least 10 heating-cooling cycles. Biocompatible thermochromiccellulosic papers were also fabricated, which showed irreversiblecoloration at different temperatures due to the removing solvent.Chromic labels with the ability of irreversible thermal-induced chromismwas used as preservation taggants, which indicate that the food materialswere kept at the right or wrong temperature. Therefore, they havea high potential for applications in various fields, such as temperaturesensors, condition preservation taggant or labels for food or cosmetic,and anticounterfeiting inks.