Preparation and characterization of photo-, thermo-, and solvatochromic materials containing benzospiropyran
Byrne, Robert (2007) Preparation and characterization of photo-, thermo-, and solvatochromic materials containing benzospiropyran. PhD thesis, Dublin City University.
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The photo-, thermo- and solvatochromic behavior of spiropyran derivatives in various media were investigated by spectroscopic methods in this thesis. It was found that the molecular environment controlled the BSP-MC equilibrium, solvatochromic shift and specific interactions with itself (aggregation) and with guest ions (metal ions).
A benzospiropyran derivative was immobilized via a diamino linker to a polymer support for chemical sensing applications. This is the first demonstration of the cycling of covalently immobilised spiropyran on a solid support to merocyanine for repeat detection of metal ions. These results demonstrate a polymer-modified surface that can adapt its hctionality through reversible molecular rearrangements triggered by external stimuli (photons).
The photo- thermo and solvatochromic behavior of spiropyran was studied in a selection of ionic liquids. Our results clearly show that the kinetics and thermodynamics of the process are sensitive to the nature of the ionic liquids cation. It was found that the polarity of ILs ranged from polar aprotic to polar protic solvents. It was also observed that the imidazolium and phosphonium cations formed complexes with the MC isomer; this is due to strong interactions with these cations. Relatively diffuse cations like irnidazolium can form a through space orbital interaction rather than just electrostatic interactions, thus inhibiting the MC conversion back to the aplanar isomer. One of the important practical outcomes of this work is that the phosphonium based system selectively exhibits photochromism only (i.e. no thermal relaxation), thus producing a potentially permanent effect or certainly a sufficiently long term effect for many applications. The control of this solute-solvent interaction by photons was coupled with an increase in viscosity and decreases in ionic conductivity. The demonstration of this reversible photo-viscosity effect has quite important practical outcomes as the rheological properties of the IL can be altered by photons. This "photo-rheological" material has the possibility to transduce photonic energy into mechanical energy.
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