Robust and Reversible Thermofluorescence in Solvent-Free Thermoplastic Polyurethane Composites

Thermofluorescent materials, whose emission behavior can be modulated in response to temperature changes, offer a compelling platform for studying dynamic heat flow and developing smart materials for various advanced applications. To address the issues of fabrication complexity and poor robustness in existing systems, an efficient, solvent-free blending method is developed to prepare thermofluorescent polymer composites by incorporating indenoquinacridone (IQA) dye into thermoplastic polyurethane (TPU) matrix. The thermofluorescent mechanism arises from a temperature-sensitive transition between aggregated and dissociated states of IQA, regulated by competing hydrogen bonds from the TPU matrix. This reversible, noncovalent mechanism enables high-contrast optical signals while maintaining excellent durability and UV resistance—performance unmatched by other organic thermochromic or thermofluorescent dyes. The intrinsic robustness of IQA allows it to endure high-temperature processing methods such as extrusion, injection molding, and fused deposition modeling (FDM) 3D printing. FDM-printed cuboids exhibit clear optical responses to temperature change, demonstrating real-time visualization of heat conduction in complex objects. The integration of robust thermofluorescence with favorable mechanical and processing properties in these composites paves the way for scalable applications in thermal imaging, smart materials, and temperature-responsive devices.