Abstract: As an important subclass of xanthene dyes, fluorane dyes represent a significant group of heterocyclic compounds. Their molecular structure exhibits remarkable responsiveness to external stimuli, leading to distinct color changes. Owing to their excellent photophysical properties, fluorane dyes find substantial applications in biological imaging as bioactive structures, dyes, or fluorescent reagents. This science popularization experiment employs fluorane dye as the functional component to prepare microencapsulated fluorane dyes. The prepared dye microcapsules were formulated into inks to demonstrate thermochromic phenomena through oil and gouache painting techniques. To enhance accessibility for kindergarten and elementary school children, we further developed the dye ink into an instrumented form by designing an ink-filled thermochromic brush. The brush features compact size, lightweight construction, and portability, while all required materials are readily available, significantly reducing experimental preparation efforts. Through interactive demonstrations, this experiment allows participants to witness the marvels of scientific transformations, thereby fostering their interest in chemistry.

Key words: Fluorane, Dye, Thermochromic, Microcapsules, Demonstration experiment