Light-responsive chromogenic polymer as a dual probe for faster switching and selective detection of Fe3+ ion

Photochromic molecules like spiropyran are known to impart a diverse range of responsive characteristics to polymeric materials to transform them into functional polymeric materials for use in a variety of applications. Therefore, a biodegradable poly(L-lactide) conjugated to a spiropyran derivative was prepared through ring-opening polymerization. The light-responsive polymer was characterized using ¹H-NMR spectroscopy. Both aggregation-disaggregation of the polymer nanoparticles were studied using transmission electron microscopy and dynamic light scattering techniques. The polymer nanoparticles were prepared to have a 250–850 nm size, which was demonstrated to reversibly switch in an on-and-off manner as a result of spiropyran-merocyanine interconversion. The spiropyran-polymer system was demonstrated to detect ferric ions in an aqueous environment through a visual color change. The emergence of the shoulder peak at 410 nm confirms the formation of the PLLA MC-Fe³⁺ complex. The PLLA-SP displayed a limit of detection value of 0.26 µM for ferric ions. The PLLA-SP-Fe3 + complex also displays a light-controlled ON-OFF response. Considering the spectral change in the UV-visible region, trivalent Fe³⁺ might stabilize the merocyanine form of the polymer chain.