Functional Cholesteric Compounds Were Designed And Synthesized, Molecular Assembly, And Responses To Environmental Capacity,

Nature does wonders by crafting complex molecular and supramolecular architectures, which are vital for sustaining life. It is increasingly important for the development of stimuli-responsive supramolecular functional materials by the means of self-assembling. Therefore, creating a stimulus-induced organogel is even more challenging because of the especial need to design a smart molecular that can be changed by external stimulus. Supramolecular organogel can organize into regular nano-architectures through specific non-covalent interactions including hydrogen bonds, hydrophobic interactions,Ï€-Ï€interactions and Van der Waals forces. In this thesis, four series of naphthalic unit contained cholestoral gelators were designed and synthesized. The external stimulus (ultrasonic irradiation) morphology, mechanism of the gel formation and the packing fashion in the gel state were studied in details. The whole paper contains four parts as following:1. Ultrasound switch and thermal self-repair of morphology and surface wettability in a cholesterol-based self-assembly system.1) Designed and synthesized a novel family of asymmetric cholesterol-based fluorescent compounds 1a-1c with ALS (aromatic group A, linker L, steroidal group S); 1c has the ability for gelating a wide variety of organic solvents, such as 1-butanol, Acetone, p-xylene.2) Both the self-assembly and surface wettability of the compound 1c with two H-bond sites can be controlled by ultrasound stimuli and restored by a thermal process.3) The ultrasound irradiation provides heat and pressure, and thus results in the spontaneous formation of the intermolecular H bonds and aggregation-induced helical motif.2. Tunable structural gel formation by both sonication and thermal processing in a cholesterol-based self-assembly system.1) Three asymmetric cholesterol-based fluorescent organogelators 2a, 2b and 2c with ALS (aromatic group A- linker L- steroidal group S) structural character were prepared, which have similar structure but different alkyl chain spacers between the naphthalimide and amide.2) The locations of hydrogen bonds (by different alkyl chain lengths) show a strong effect on the solubility and gelling properties of these compounds.3) Both the self-assembly and surface wettability of those compounds can be controlled by ultrasound stimuli and renovated by a thermodynamic process. These results provide a deeper understanding of the intermediate transition states in the gel under ultrasound irradiation.3. Gelation induced reversible syneresis via structural evolution.1) We reported here a tremendous volume changes in a cholesterol based low weight molecular gel system in the presence of multiamine. Meanwhile, the gelling solvents dissociated from the gel in a dynamic manner.2) This capability can be restored and recycled by gel-sol transformation. Thus, the gel may serve as a dynamic solvent pump that can be controlled by subtle changes in parameters, solvent composition or gel composition.3) A structural evolution from lamellar vesicles to a more compact hexagonal structure was observed accompanied by the solvent release. This report clearly shows how a practical actuator gel can react to external effects, and thus provides a strategy for the development of spontaneous-release soft materials and raises the possibility of stimulus-responsive organogels as new gel-based systems for applications such as drug delivery and other active ingredients.4. Self-assembly of peptide-based multi-color gel triggered by up-converting rare earth nano-particles.1) The self-assembly of dipeptide 1a and tripeptide 1b molecules are accelerated through physical interaction with UCNPs (NaYF₄) in polar solvent, which facilitates the self-assembly processes and leads to the formation of hydrid multi-color organogels.2) The dipeptide 1a and tripeptide 1b are locked by hydrogen bond and van der Waals forces to realize disperse of UCNPs in gel networks. The individually dispersed UCNPs are significantly aligned within the peptide gel, thereby reinforcing the peptide supramolecular tapes.3) UCNPs may also act as physical crosslinks between the tapes, thus enhancing gel stability. This new strategy to make UCNPs-peptide hybrid multi-color gels allows the UCNPs to retain their nanophosphor properties in the gel state.