| Author: | Cheung, Leong Hung |
| Title: | Exploration of photoresponsive molecular amphiphiles |
| Advisors: | Leung, K. C. Franco (ABCT) |
| Degree: | Ph.D. |
| Year: | 2025 |
| Department: | Department of Applied Biology and Chemical Technology |
| Pages: | xxvi, 357 pages : color illustrations |
| Language: | English |
| Abstract: | Photo-responsive molecular amphiphiles are organic molecules featuring both amphiphilicity and photo-responsibility. These molecules are wonderful for constructing smart functional materials of which light can serve as a non-invasive stimulation for controlling their functional properties. However, there are three major limitations encountered in the contemporary photo-responsive molecular amphiphiles. One of those is that the majority of photo-responsive molecular amphiphiles are responsive with energetic ultraviolet light. The second is limiting examples of photo-responsive molecular amphiphiles allowing construction of supramolecular macroscopic structures from small molecules for demonstrating the future responsive materials. The third is rare examples of photo-responsive molecular amphiphiles responsive with multiple stimulus. It is desired to develop more analogs of photo-responsive molecular amphiphiles bearing multi-stimuli responsibility, controlled by visible-light or demonstration of macroscopic functional properties. With regard of the targeted objectives, this thesis includes five chapters to elucidate the findings of all novel photo-responsive molecular amphiphiles. The first chapter is an introduction of photo-responsive molecular amphiphiles. The conception of designing photo-responsive molecular amphiphiles is divided into two sections, photosynthesis and amphiphiles. With the description of the two elements of photo-responsive molecular amphiphiles, a brief overview of this thesis is provided for transition into four included works, SAHis, MBA, DA1, and co-assembly strategy of DA1 with 6SA. By applying shear-flow assembly method in a divalent calcium cations solution, all the molecules can assemble into macroscopic structures for distinct macroscopic functional behavior. The second chapter describes a novel stiff-stilbene amphiphile, SAHis bearing basic amphiphilicity, photo-responsiveness and three pH responsive functional groups (phenolic, imidazole and carboxylic groups). The microscopic supramolecular assembled helical nanoribbons of SAHis can be responsive with light, pH tuning and counterions screening for microscopic morphological changes. The macroscopic SAHis structures can serve as bio-functional materials, such as potential materials for photo-controlled drug release to inhibit liver cancer cell growth and cell-material interfaces. The third chapter illustrates a new second generation molecular motor amphiphile, MBAs of which the thermal helix inversion after photo-induced rotary motion can be controlled by the upper-half rotor core modification. With the bola-amphiphilic features, low aspect-ratio nanostructures of MBAs can assemble as bio-compatible macroscopic scaffold and demonstrate the other example for photo-controlled macroscopic bending motion. Comparing with the original molecular motor amphiphiles, the demonstration expands the molecular outline for constructing photo-controlled robotics materials. The fourth chapter includes a unique donor-acceptor Stenhouse adduct amphiphile, DA1. The unprecedented aqueous stability of DA1 inhibits the traditional spontaneous ring-closing isomerization in aqueous environment. The large aspect ratio of supramolecular nanostructures of DA1 are discovered with inhibited stimulation responsiveness for supramolecular morphological transformation. With the macroscopic structural formation assisted from large aspect ratio supramolecular structural assembly, the multiple length-scale DA1 assembly structure is responsible with visible-light irradiation to demonstrate multiple length-scale supramolecular transformation which is potential for visible-light controlled macroscopic disassembly induced entrapped cargo release. The fifth chapter is the extension of the DA1 mentioned in the fourth chapter. Regarding the limited visible-light wavelength precision, co-assembly strategy is employed to render aggregation inhibition for DA1 to recover the visible-light responsibility. A six-membered fused ring stiff-stilbene amphiphile, 6SA is synthesized for creating planar environment for co-assembly with DA1 in different ratios. The optimized ratio of 6SA and DA1 solutions are applied for fabricating co-assembled macroscopic structures. Red-light irradiation on the resulting macroscopic scaffold can observe DA1 blue-color decoration due to inhibiting aggregation effect of DA1. This demonstration provides alternative co-assembly strategies to construct high stimulation wavelength precision of DA1 for responsive materials. The sixth chapter is the conclusion of this thesis. With the tools to study and translation of photo-responsive molecular amphiphiles, such as cell related demonstration, electron microscopies, fluorescence spectroscopy, NMR spectroscopy, polarized optical microscopy, UV-vis absorption spectroscopy and X-ray diffraction methods, the scopes exploration of photo-responsive molecular amphiphiles, multiple length scale and macroscopic material characterization are accomplished for paving the way to design and construct future functional material by multiple-length scale supramolecular assembly of photo-responsive molecular amphiphiles. |
| Rights: | All rights reserved |
| Access: | open access |
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