Study On Rational Design, Syntheses, Characterization Of Functional Supramolecular Gels Self-Assembled By Hydrogen Bonding Between Urea Based Gelators Containing Photoresponsive Azobenzene Mesogens

Supramolecular gels with various ordered structures are constructed from the self-assemblies of low-molecular-weight gelators (LMWGs) in some sovlent driven by non-covalent interactions (such as hydrogen bonding, π-π interactions, hydrophobic effects, etc). As an effective hydrogen-bonding group, the urea based gelators are of broad interest and intensively studied. Some urea-based functional supramolecular gels with fast reponse to external stimuli are highly promising candidates for a diverse range of applications such as smart gels, nanodevices and drug delivery. In this thesis, three series of gelators based on bis-urea containing photoresponsive azobenzene groups were designed and synthesized. The gel-forming ability and morphologies of formed gels and some bulk materials for contrast were preliminarily studied by FTIR, SEM and polarized optical microscopy (POM). The whole thesis contains several parts as following.1) With 4-acetamino phenol as the starting reagent, through Williamson etherification, diazonium reaction and the Gabriel’s primary amine synthesis that transforming primary alkyl halides into primary amines using potassium phthalimide and hydrazine hydrate reduction, bis-urea precursors containing photoresponsive azobenzene were synthesized and their composition and structures were confirmed using NMR, FTIR and elemental analysis.2) By reaction of the primary amino precursors with different diisocyanates HDI, MDI and IPDI, a series of six bis-urea gelators containing azobenzene groups, that is LCm-Azo-n(HDI), LC8-Azo-10(MDI) and LC8-Azo-4(IPDI), were synthesized and characterized. Also a contrast bis-urea gelator G18(MDI) was synthesized from MDI and octadecyl amine.3) The gelation performance of LC8-Azo-4(HDI)、LC8-Azo-10(HDI) and LC1-Azo-1(HDI) were preliminarily examined. Their solubility was quite poor in most common organic solvents, so no reversible gels were formed. With mixing less than 20 wt% LC8-Azo-10(MDI) with the gelator G18(MDI), the bicomponent mixture LC8-Azo-10(MDI/G18(MDI) exhibited good reversible sol-gel transformation in toluene.4) Due to the cooperative or synergetic effects of π-π stacking of azobenzene mesogens, strong hydrogen bonding between bis-urea units and van der Waals interactions among long alkyl chains, these bis-urea compounds containing azobenzene mesogens of high regular and symmetrical structure showed poor solubility and strong tendency to crystallize, no real reversible gels could formed by a single component of them.For further study, an optimized molecular structure design and photo-responsiveness of the bicomponent mixture gelators and some more functional gels and their applications will be explored.