Abstract
Micro-capillaries, capable of light-regulated binding and qualitative detection of divalent metal ions in continuous flow, have been realised through functionalisation with spiropyran photochromic brush-type coatings. Upon irradiation with UV light, the coating switches from the passive non-binding spiropyran form to the active merocyanine form, which binds different divalent metal ions (Zn2+, Co2+, Cu2+, Ni2+, Cd2+), as they pass through the micro-capillary. Furthermore, the merocyanine visible absorbance spectrum changes upon metal ion binding, enabling the ion uptake to be detected optically. Irradiation with white light causes reversion of the merocyanine to the passive spiropyran form, with simultaneous release of the bound metal ion from the micro-capillary coating.
Highlights
The photochromic properties of spirobenzopyrans were first discovered by Fischer and Hirshberg in 1952 [1]
The functionalised micro-capillary model we have developed can act as a photonically controlled self-indicating system for controlled metal ion uptake and release, operating in a continuous flow regime
Photochromism of spiropyran derivatives is reliant on the interconversion between the closed spiropyran form and the open merocyanine form
Summary
The photochromic properties of spirobenzopyrans were first discovered by Fischer and Hirshberg in 1952 [1]. Upon irradiation with UV light, spiropyrans isomerise to the more polar, open merocyanine form. Metal ions can complex with the open merocyanine form, thereby influencing this isomerisation process. Irradiation with visible light results in a high concentration of the closed form, thereby releasing the metal ion. It is possible to trigger metal ion binding by irradiation with UV light and to reverse this process through white light irradiation of the coloured complex. This regenerates the inactive spiropyran form and results in the release of metal ions [17]
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