Photochromic sensing of La³⁺ and Lu³⁺ ions using poly(caprolactone) fibers doped with spiropyran dyes

Here, we report three spiropyran derivatives, which were then incorporated into poly(caprolactone) electrospun fibers as a platform for sensing heavy metals. The materials obtained showed distinct colorimetric responses to different ions, especially Lanthanum and Lutetium. We also demonstrated that it is possible to selectively identify and differentiate La³⁺ and Lu³⁺ ions by emission and detection by the unaided eye. Further analyses were conducted in solution to study spiropyran interaction with these ions, indicating the formation of complexes at a 2:1 ligand:metal ratio. In addition, emission lifetime showed an increased lifetime of the emissive species with the addition of La³⁺ or Lu³⁺ ions, also indicating the formation of coordination complexes. These results showed a promising prospect for a portable sensor for field use that may function as colorimetric sensors of toxic heavy metals. Overall, this study demonstrates the potential of spiropyran derivatives as versatile and tunable materials for surface modifications with various applications.