| Self-assembling processes are common throughout nature and technology. Self-assembled materials, such as liquid crystals and organogels, formed by non-covalent bonding have attracted much attention because they are good candidates for the next generation of materials, for which dynamic function, environmental benignity, and low energy processing are required. Hydrogen bonding was most commonly used to direct the self-assembling process among those non-covalent interactions. Many low molecular weight organogels and liquid crystalline materials, containing, for example, amide and urea groups have been reported respectively, and where the intermolecular hydrogen bonding was considered to be the driving force. However, it is relatively rare to find low molecular compounds capable of both gelling solvents and exhibiting thermotropic mesomorphic behaviors.On the other hand, it was reported that non-symmetric liquid crystal dimers often exhibit intercalated smectic phases, in which specific molecular interactions between the two different mesogenic units account for this specific phase behavior. However, if we introduce lateral intermolecular hydrogen bonding into non-symmetric liquid crystal dimers, along with the interaction between the identical mesogenic units in non-symmetric dimers, do they still exhibit intercalated smectic phases dimers?In this thesis, two series of low molecular compounds, wedge-shape dihydrazide derivatives and hydrazide-based non-symmetric liquid crystal dimers, were designed. Through studying the effect of lateral hydrogen bonding and molecular structures on the self-assemble ability, we focused on understanding the nature and mechanism of the self-assemble processes, which can provide new route to design functional supra-structures.1. Synthesis and self-assembly behaviour of wedge-shape molecules containing dihydrazide groupsThree series of wedge-shape dihydrazide derivatives have been designed and synthesized, namely N-(3, 4, 5- alkoxybenzoyl)-N'-(4'-nitrobenzoyl) hydrazine {Rn-NO2 (n=3, 6, 8, 12, 16)}, N-(3, 4, 5- alkoxylbenzoyl)-N'-(4'-amidobenzoyl) hydrazine {Rn-NH2 (n=3, 6, 8, 16)} and 3, 4, 5-tris (hexadecyloxy)-N, N'-dimethyl-N'-(4-nitrobenzoyl) benzohydrazide (Me-R16-NO2). The molecular structures were confirmed by 1H NMR, FT-IR and Elemental Analysis. The self-assembly behaviors in temperature and solvent field were investigated through employing polarizing optical microscopy (POM), differential scanning calorimetry (DSC), variable temperature X-ray diffraction, variable temperature FT-IR, and scanning electron microscopy (SEM) et al.Notably, the compounds Rn-NO2 and Rn-NH2 with long terminal chains show thermotropic mesophase and strong gelation ability in organic solvents. (1) Liquid crystalline behaviour of wedge-shape molecules containing dihydrazide groupsIn compounds Rn-NO2 (n=3, 8, 12, 16), no mesophase was observed in R3-NO2 and R8-NO2, whereas the compounds R12-NO2 and R16-NO2 with long terminal chains showed enantiotropic hexagonal and rectangular columnar liquid crystalline phase respectively. Hydrogen bonding between the C=O and N–H groups was confirmed to exist in the mesophase and played an important role in stabilizing the liquid crystals by variable temperature FT-IR.No mesomorphic phase was observed in Me-R16-NO2, Tm = 97℃.In compounds Rn-NH2 (n=3, 6, 8, 16), no mesophase was observed in R3-NH2, the compounds R6-NH2 and R8-NH2 showed enantiotropic rectangular columnar liquid crystalline phases, whereas R16-NH2 showed enantiotropic rectangular columnar mesophases and cubic phases with primitive cubic lattices (Pm3n). Weak C=O…H-N intermolecular hydrogen bonding was confirmed to exist in the mesophase.The effect of both the length and number of the terminal chains on the liquid crystalline properties was discussed. For example, the compound R12-NO2 and R16-NO2 with long terminal chains shows enantiotropic columnar phase; however, no mesophase was observed in R3-NO2 and R8-NO2 with short terminal chains. On the other hand, the compounds R16-NO2 and C16-NO2 with same length terminal chains showed different liquid crystalline phases, the rod-like molecule C16-NO2 showed smectic phase, whereas wedge-shape molecule R16-NO2 showed columnar mesophase. This might be explained as the increase of the length and number of the terminal chains increased the micro-segregation effect by enhancing the incompatibility between the hydrogen bonded rigid aromatic rings and flexible alkoxy chains, and this leads to an increase in the volume fraction of the lipophilic aliphatic region and finally leads to mesophases with curved interfaces, such as columnar and cubic mesophases.The polarity of substituent group of wedge-shape molecules plays an important role in stabilizing the mesophase. For example, the mesophase range of R16-NO2 and R16-NH2 with different group polarity of substituent is 24℃and 102℃respectively.The effect of lateral hydrogen bonding on the liquid crystalline properties was also discussed. We reduced hydrogen bonding of R16-NO2 through substitute the hydrogen atom of N-H groups with–CH3 (Me-R16-NO2), melting point of Me-R16-NO2 decreased compared to that of R16-NO2 and no mesomorphic phase was observed in Me-R16-NO2. So the conclusion can be drawn that lateral intermolecular hydrogen bonding played an important role in stabilizing the mesophase.The study of the mixing of structurally related compounds R16-NH2 and C16-NH2 confirmed that without any solvent by mixing of two structurally related low molar mass molecules can exhibit different mesophase morphologies as pure compounds, hence, by gradually changing the average volume fractions of incompatible molecular fragments.(2) Organogel properties of wedge-shape molecules containing dihydrazide groupsInterestingly, these wedge-shape dihydrazide derivatives showed strong gelling ability in organic solvents. The aggregation morphology and structure, of R12-NO2, R16-NO2 and R16-NH2 were fully characterized. And the driving force was discussed.In compounds Rn-NO2 (n=3, 8, 12, 16), only R12-NO2 and R16-NO2 with long alkyl chains and intermolecular hydrogen bonding showed strong gelation ability in organic solvents such as benzene, 1, 2-dichloroethane et al. No gelation is observed for compounds R3-NO2, R8-NO2 and Me-R16-NO2 in which the hydrogen of dihydrazide group of R16-NO2 were replaced by methyl groups. The SEM image of R12-NO2 and R16-NO2 xerogels from benzene that revealed a network structure composed of twist bundles of fibers, and the results of WAXD suggested that they have rectangular and hexagonal columnar packing respectively. Intermolecular hydrogen bonding between the dihydrazide groups and van der Waals interactions between the alkyl chains were demonstrated to be the major driving force for self-assembling process.Only R16-NH2 with long alkyl chains shows gelation ability in organic solvents such as ethanol, benzene, 1, 2-dichloroethane et al. No gelation is observed for R3-NH2, R6-NH2 and R8-NH2 with short alkyl chains. Interestingly, the morphological properties exhibited pronounced changes in different polar solvents. For example, the SEM image of a gel sample of R16-NH2 in benzene showed the surface-patterned, clumped, and textured spheroids; otherwise, the SEM image of a gel sample of R16-NH2 in ethanol formed elongated fibrous aggregates with different diameters. The results of WAXD suggested that they have hexagonal columnar packing both in benzene and ethanol xerogels. Intermolecular hydrogen bonding and van der Waals interactions between the alkyl chains were also demonstrated to be the major driving force for this self-assembling process.2. Synthesis and mesomorphic behaviour of non-symmetric liquid crystal dimers containing the dihydrazide groupsTwo series of non-symmetric liquid crystal dimers containing azobenzene and dihydrazide groups were designed and synthesized, namely 1-[4-(4'-Methoxyphenylazo)phenoxyl]-m- [(N-(4- alkoxybenzoyl) -N'-(benzoyl-4'-oxy)hydrazine)] alkylene {EmCn (m=3, n=1, 4, 6, 12, 16; m=5, n=16; m=6, n=12, 16)} and 1-[4-(4'-alkoxyoxyphenylazo)phenoxy]-m- [(N-(4- nitrobenzoyl) -N'-(benzoyl-4'-oxy)hydrazine)] alkylene {Ep-m-NO2 (p=1, m-5, 6, 10; p=12, m=5, 10)}. The molecular structures were confirmed by 1H NMR, FT-IR and Elemental Analysis. The liquid crystalline behaviour were investigated through polarizing optical microscopy (POM), differential scanning calorimetry (DSC), variable temperature X-ray diffraction, and variable temperature FT-IR et al.Notably, the monolayer smectic phases in these non-symmetric dimers were observed by introduced intermolecular hydrogen bonding into non-symmetric liquid crystal dimers.The results were summarized as following:The compounds E6C12 and E6C16 showed enantiotropic smectic C with schlieren textures; The compounds E3C12, E5C16 and E3C16 exhibited monotropic smectic C phase with schlieren textures and the broken fan-shaped texture (E3C16) respectively. The compound E3C1 showed monotropic nematic phase; however, no mesophase was observed in E3C4 and E3C6. Combining the results of WAXD and FTIR, we can propose that the molecules should have the ordering with alternating orientations of the mesogens, in which the azobenzene part can be considered more or less as a part of one of the tails, while the hydrazide-containing segment as the rigid core that is quite close to the center of the molecules.No mesophase was observed in E1-5-NO2, whereas E12-5-NO2 exhibited enantiotropic polygonal texture, E1-6-NO2, E1-10-NO2 and E12-10-NO2 all showed enantiotropic fan-shaped texture. The results of WAXD, POM and FTIR suggested that they have monolayer SmA phases.The effect of the length of terminal substitution on the liquid crystalline properties of non-symmetric liquid crystal dimers was discussed. For example, compounds E3Cn with long alkyl chain, such as, E3C12 and E3C16 exhibited monolayer SmC phase, whereas nematic phase for E3C1 and non-mesomorphic for E3C4 and E3C6. It is true that long terminal alkyl chains will favor the formation of layer structure.Both the length and the parity of the alkyl spacers have an important effect on the melting points, clearing points as well as liquid crystalline behaviour. For example, the melting points (147℃), clearing points (170℃) as well as the enthalpies (8.4 KJ/mol) from isotropic to liquid crystalline state of E5C16 are much lower than those of E6C16 (177℃, 199℃, 14.6 KJ/mol), which indicated the characteristic odd–even effect in EmCn.The effect of–NO2 substitution on the liquid crystalline properties was also discussed. E6C16 and E1-6-NO2 have the same molecular structure except the different substitution. The melting points (211℃) and clearing points (225℃) of E1-6-NO2 are much higher than those of E6C16 (188℃, 201℃), and the mesophase translates from the SmA of E1-6-NO2 to the SmC of E6C16. The monolayer SmA phase of E1-6-NO2 was due to the combined effect of the strong dipole interaction of -NO2 group along the long molecular axis and the lateral intermolecular hydrogen bonding, whereas the monolayer tilted SmC phase of E6C16 (weak dipole interaction of alkoxy) was due to the effect of the lateral intermolecular hydrogen bonding. The present results showed that it was possible to fine-tune the molecular arrangement through introducing specific intermolecular interactions (for example, the dipole interaction of -NO2 group along the long molecular axis and the lateral intermolecular hydrogen bonding) and controlling the balance among different interactions.So the conclusion can be drawn that intermolecular hydrogen bonding was demonstrated to be the major driving force for this self-assembling process, whereas molecular shape, intermolecular van der Waals interactions and effect of microphase segregation together determined the molecular arrangement.
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