Highly sensitive photoresponsive polyamide 6 nanofibrous membrane containing embedded spiropyran

Photoresponsive materials with high photoresponse sensitivity and photofatigue resistance are indispensable for applications, such as textiles and sensors fields. Herein, we synthesized photoresponsive polyamide 6 (PA6) with spiropyran (SP) as molecular component, by incorporating spiropyran-containing diisocyanate activator into anionic ring-opening polymerization of ε -caprolactam. To improve photosensitivity and reduce response time, the corresponding nanofibrous membranes were obtained by electrospinning. The reversibility of the isomerization of SP resulted in colored nanofibrous membrane patterns, which can be written, erased, and rewritten, using UV light and visible light. It revealed that photosensitivity of nanofibrous membranes were further improved, when appropriate polyethylene glycol was covalently embedded into PA6 segments to increase the chain flexibility. Photoresponse reversibility and photofatigue resistance displayed that UV–vis absorbance intensity of SP-embedded PA6 nanofibrous membrane decreased just 13% after 10 cycles of UV light irradiation, while its absorbance intensity in UV–vis spectra after visible light irradiation has negligible decrease. For better understanding the structure, electronic characteristics and UV–vis absorbance peak of SP-embedded PA6, theoretical calculations were also carried out. Finally, UV absorption of transparent and flexible poly(dimethyl siloxane) (PDMS)/photoresponsive nanofibers composite film was assessed. The composite film was photochromic, and possessed excellent property for blocking ultraviolet radiation. Graphical abstract This work explores a strategy for synthesizing photoresponsive SP-embedded polyamide 6 by incorporating spiropyran-containing activator into anionic ring-opening polymerization of ε-caprolactam. SP-embedded PA6 nanofibrous membrane with excellent photosensitivity and photofatigue resistance was electrospun. The isomerization reversibility of spiropyran-merocyanine (SP-MC) resulted in colored patterns which can be written, erased, and rewritten using UV light and visible light. Transparent photochromic composite film for UV absorption and protection was also developed.