Photo-response behavior of electrospun nanofibers based on spiropyran-cyclodextrin modified polymer

Tunable and durable photochromic materials are a rapidly expanding area of interest, with applications ranging from biomedical devices to industrial-fields. Here we examine electrospun poly (methacrylic acid) PMAA nanofibers covalently modified with the highly photochromic molecule, spiropyran (SP) or a derivate SP which is firstly coupled to a cyclodextrin molecule (beta CDSP). The photochromic properties of the starting materials and of the nanofibers were investigated. beta CDSP, PMAA(SP) and PMAA-beta CDSP polymers exhibited a reverse photochromism. The kinetic results revealed a faster isomerization process for the beta CDSP molecule, than that for the PMAA-beta CDSP and for the PMAA(SP), the slowest one. The fastest isomerization is attributed to the presence of a large number of hydroxyl groups of the beta CD which stabilizes the merocyanine form via hydrogen bonding, and the slowest isomerization is related to the PMAA chain structure that stabilizes the spiropyran form. Thus, combining the PMAA and beta CD properties the photo-isomerization can be modulated. The photo-reversibility of this material was verified by UV-visible measurements cycling visible and UV light. Infrared spectroscopy and water contact angle were used for the nanofiber surface characterization, demonstrating the presence of the spiropyran on the mats surface and also showing a minimal effect on nanofiber size and shape when compared to PMAA fiber.