Synthesis of Light and pH Sensitive Gel with Nanophotochromic Cross-links and Investigation of its Applicability in Chemical Sensors

Taheri, Shima | 2019

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 51766 (03)
  4. University: Sharif University of Technology
  5. Department: Chemistry
  6. Advisor(s): Pourjavadi, Ali
  7. Abstract:
  8. Photochromism is defined as a reversible transformation of a chemical species between two forms having different absorption spectra induced in one or both directions by photoirradiation. Among various organic photochromic compounds, including spiropyrans, azobenzenes, spirooxazines, dyarylethenes and fulgides, spiropyranes have been attracted more attention due to their more sensitivity towards photo, pH, heat, pressure and solvent polarity. UV irradiation of spiropyrans, breaks the C-O bond of pyran ring and makes cis-trans isomers. Therefore, closed structure of the molecule, named as spiro (SP), is converting into the flattered and conjugated merocyanine (MC). Mc is photochromism, polar and hydrophile, which its stability is strongly dependent on the solvent and it could be stable in highly polar or acidic solvents due to H-bonding, which demonstrates Vis adsorption in about 500-600 nm. In the closed structure of molecule (spiro structure), conjugation disturbes and a colorless, non-polar, hydrophobe, and stable structure is formed, which has adsorption peak in UV region. The reversible transformation of MC to SP structure takes place by heat or visible irradiation. In this study, photochromic compound of spiropyran was synthesized through five steps. Afterwards, acryloyl chloride was used to prepare acrylated spiropyran (SPMON), which can be polymerized with modified silica nanoparticles with 3-methacryloxypropyltrimethoxysilane. FTIR analyses and melting point of the synthesized compounds were used to confirm their structures. Exact chemical structures of spiropyran compound and its acrylated derivative were confirm with 13C, 1H NMR spectroscopy. Size distribution of the photochromic polymeric nanparticles, their surface charge and thermal properties were analyzed by DLS, Zete-potential and TGA analyses, respectively. Photochromic properties of these compounds were investigated by UV-Vis spectroscopy. Afterwards, this photochromic nanostructure was used to synthesis pH and photo responsive acrylated gels through radical polymerization. Increasing of mechanical strength of the synthesized photochromic gels was tested by stress-strain mechanical analyses. The observed higher mechanical strength is due to H-bonding between compound of the gel, through SP-MC transition by UV irradiation. FTIR analyses and SEM images were used to characterize chemical structure and surface morphology of the gels, respectively. Finally, application of these gels in chemical sensors were studied by three external stimuli of UV irradiation, pH and solvents with different polarity
  9. Keywords:
  10. Photochromism ; Spiropyran ; Crosslinking ; Gel Synthesis ; Chemosensor

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