Solid-state photochromism of spironaphthoxazine loaded microcapsules with photo-patterning and thermo-regulating features.

One of the biggest challenges in the field of photoresponsive spirooxazines is their fast reverse isomerization. Polar phase change materials beside spirooxazines not only stabilize their colored-form, but also induce thermo-regulating properties to the whole system. Moreover, encapsulation is a key route to protect them and provide safe application of photochromic materials in solid-state matrices. A solution of spironaphthoxazine in oleic acid was encapsulated through solvent evaporation technique and the obtained microcapsules were incorporated in a transparent polymeric coating and also non-woven cotton fabrics. A systematic study on the reverse isomerization rate of spironaphthoxazine, photo-patterning and thermo-regulating features of the microcapsules was performed. Comprehensive analyses demonstrated successful encapsulation of oleic acid and spironaphthoxazine. Microcapsules showed reversible color changes upon UV-Vis irradiation below melting point of oleic acid and a 85% decrease in discoloration rate compared to those without oleic acid. They also exhibited excellent photoswitchability, making them suitable for anti-counterfeiting applications. Their thermo-regulating feature in cotton fabrics was studied by using of infrared camera and they represented energy saving potentiality. Optically monitoring of temperature around melting point of oleic acid is another feature of these microcapsules.