| Author: | Kwan, Shuk Ying |
| Title: | Photocontrolled supramolecular assembly of stiff-stilbene bola amphiphiles in aqueous media |
| Advisors: | Leung, K. C. Franco (ABCT) |
| Degree: | M.Phil. |
| Year: | 2024 |
| Department: | Department of Applied Biology and Chemical Technology |
| Pages: | x, 214 pages : color illustrations |
| Language: | English |
| Abstract: | Molecular photoswitches are organic aromatic molecules which can be switched on/off by photoirradiation. Photoswitches are widely employed in different research areas such as chemical biology and smart materials due to their intrinsic photochemical properties. Amphiphiles, consisting of a hydrophobic tail and a hydrophilic head, are able to form various supramolecular structures e.g., vesicles, nanofibers, and nanotubes. Stimuli-responsive synthetic amphiphiles have been drawn attention of chemists for recent decades. Geometrical structural transformations of molecular switches would be a result of manipulation by external stimuli including pH, light, and heat. Light is regarded as a non-invasive stimulus that provides benefits in tunable wavelength and intensity. Photoresponsive molecular amphiphiles are able to assemble into supramolecular nanostructures and have a structural transformation upon photoirradiation at microscopic level. When comparing to the design of the first generation of molecular motor, a five-membered ring fused stiff-stilbene is featured with a relatively planar structure. Therefore, the design of stiff-stilbene amphiphiles have a higher tendency to assemble nanostructures with high packing parameters. In this thesis, a series of stiff-stilbene amphiphiles (SAs) were synthesized and their photoswitchability in both organic and aqueous media were studied. On the other hand, the assemblies of SAs were examined by transmission electron microscopy and their critical aggregation concentrations were confirmed by dynamic light scattering. The first chapter is the literature review of molecular photoswitches especially stiff-stilbene and photoswitchable amphiphiles. The second chapter is about the co-assembly of oppositely charged SAs at different length scale. It is previously reported that motor amphiphiles functionalized with anionic phosphite and cationic quaternary groups were not able to form a macroscopic string. To study the potential of co-assembly of SAs, stiff-stilbene amphiphiles functionalized with anionic phosphite and cationic quaternary groups were synthesized. It is found out that both anionic and cationic SAs could not afford a macroscopic string. However, co-assembled of anionic and cationic SAs was feasible to form a stable macroscopic string in an inorganic salt solution even deionized water. On the other hand, the macroscopic string of co-assembled SAs retained stable upon photoirradiation. This approach demonstrates a new method to a photocontrolled stable soft material. The third chapter is about multiple responsiveness of amino acid-based SAs. Currently, it remains challenging to control the supramolecular systems which respond to multiple stimuli. To achieve different functionalities, a series of SAs functionalized with different amino acid groups were synthesized. To study the morphological and helical transformation of SAs, different stimuli including pH, light, and solvent were applied. It is found out that the morphology of SAs is partially influenced by different stimuli when only a subtle change of helicity is observed. Indeed, the effect of the size of amino acids in co-assembly of SA achiral and chiral nanotubes is revealed. Moreover, those amino acid-based SAs are capable to form a stable macroscopic string in the presence of an inorganic salt solution. Indeed, they remain stable and show subtle changes upon photoirradiation. In short, it demonstrates self-assembly of amino acid-based SAs in water and their responsiveness to various external stimuli. The forth chapter is an experimental section about the operation condition of instruments related to this thesis. The fifth chapter is the conclusion of this thesis. |
| Rights: | All rights reserved |
| Access: | open access |
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