Synthesis of rhodamine B amine derivatives with improved light resistance and its application in thermochromic materials

Rhodamine B (RhB) is a widely utilized xanthene dye known for its strong fluorescence, high quantum yield, bright color, and versatility in various applications. However, RhB type dyes face significant limitations due to their susceptibility to photodegradation. Herein, four RhB amine derivatives (RhB-1, RhB-2, RhB-3, and RhB-4) were synthesized to improve the light resistance through functionalization of the 4′ position of the carboxyphenyl ring with acrylamide, butylamine, octylamine, and cyclohexanamine, respectively. The mechanism of improving light resistance was analyzed. The results show that the derivatives demonstrated significantly enhanced light resistance compared to RhB, with the ability to form supramolecular structures including dimers and aggregates that protect against UV degradation. Light resistance for RhB-1 was significantly improved with increasing concentration as the photodegradation efficacy drops from 84.8 % (1.5 × 10⁻⁵ mol/L) to 10 % (2.0 × 10⁻⁴ mol/L), due to the dominant changes from monomers to J-dimers to H-aggregates. When incorporated into three-component thermochromic systems, the derivatives not only improved the light resistance with double duration of UV irradiation but also expanded the range of color change temperatures. This work advances the development of RhB derivatives with superior optical properties and durability, enhancing its applicability in environments requiring prolonged exposure to light.