Development of new adaptive materials based on spiropyran molecular photoswitches

Spiropyrans are a family of photochromic compounds that can be reversibly switched between two states: a colourless, non-polar, uncharged spiro form (SP) and a highly coloured, polar, conjugated, zwitterionic merocyanine form (MC), i.e. SP → MC (UV light), MC → SP (green, white light). Furthermore, the MC form possesses a phenolate group that can reversibly bind metal ions and this ion binding is also photo-reversible, as when the MC-ion complex reverts to the passive SP form (upon green/white light exposure), it releases the bound ions. Using molecular-switches based on spiropyran-like molecules, new materials were produced whose properties such as metal-ion uptake/release and polarity can be controlled under external photonic stimulation. Spiropyran derivatives were immobilised on polystyrene and silica microbeads and evaluated for their reversible photoswitchable metal ion binding behaviour. When in the MC form, in the presence of metal ions such as Cu2+ and Zn2+, further spectral and colour changes occurred that were found to vary according which metal ion was bound. Subsequent irradiation with white light caused reformation of the SP form and release of the metal ion. This process was shown to be repeatable at least several times. The spiropyran functionalised silica microbeads were packed into a capillary column and the new stationary phase demonstrated to form the basis of a photodynamic system for retention, detection and release of metal ions pumped into the capillary. In parallel other spiropyran derivatives were incorporated into monolithic stationary phases. The spiropyran-functionalised polymer was switched between a protonated MC form and a neutral SP form upon white light irradiation. The monoliths were encased on a microfluidic chip and the system filled with an acid electrolyte. When a voltage was applied at the two ends of the encased monolith, electro-osmotic flow was generated and the flow rate shown to be variable upon white light exposure as a consequence of the formation of the SP form and the formation/disruption of the surface charge necessary for efficient electro-osmotic pumping. In this thesis the synthesis and the characterisation of these new materials is described and the switchable optical properties evaluated