Photoreversible ion-binding using spiropyran modified silica microbeads

In this paper, we report the covalent immobilisation of spiropyran on silica microbeads of 5 μm diameter and subsequent evaluation of the photoswitchable behaviour and light-modulated ion-binding properties of the spiropyran modified silica microbeads towards a range of different metal ions. The beads can be effectively switched using light emitting diodes between a white spiropyran form (by irradiation with a white 430–760 nm light emitting diode) and a pink merocyanine form (upon irradiation with a UV light 375 nm emitting diodes) that undergoes, under exposure to certain metal ions (such as Cu2+ and Zn2+, final concentration of 7.7 × 10–4 M in ethanol solution), a further reversible spectral and colour change due to the formation of merocyanine-metal ion complexes. Furthermore, the accumulated ions can subsequently released from the beads on demand using light emitting diodes to reform the inactive spiro form. Keywords: photoreversible ion binding