Design,Synthesis, And Self-assemble Behaviors Of Rod-like Molecules With Lateral Hydrogen Bonding

Supra-molecular liquid crystals are based on non-bonded interactions, such as hydrogen bonding, ionic, change transfer, hydrophobic, and vander vals interactions. Among which hydrogen bonding is crucial to construct ordered supera-structures, because of its strength and directionality. However, in the field of calamitic thermotropic liquid crystals, many efforts was restricted in generating desired mesophase with the hydrogen bonding along with the long molecular axis. Lateral intermolecular hydrogen bonding has not been extensively investigated, except a few reports which claimed that it can stabilize the smectic layer structure. In this thesis, through studying the effect of lateral hydrogen bondding and molecular structures on the self-assemble ability, we aimed to understanding the nature and mechanism of the self-assemble processes, which can provide new route to design functional supra-structures. In order to introduce lateral hydrogen bonding,three series of dissymmetrical dihydrazide derivateives have been designed and sythesized, namely N-(4-alkoxybenzoyl)-N'-(4'-nitrobenzoyl)hydrazine(Cn-NO₂), N-(4-alkoxyben-zoyl)-N'-(4'-biphenylcarbonyl)hydrazine(Cn-Ph), and N-(4-alkoxybenzoyl)-N'-(4-amino-benzoyl)hydrazine(Cn-NH2). The molecular structures were confirmed by 1H NMR, FT-IR, and Elemental Analysis. the self-assemble 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.. The results are summarized as following: Cn-NO(2n=3,6,12,16)and Cn-Ph (n =12, 16) exhibited enantiotropic smectic A phase with fan-shaped texture, and was further assigned to be SmA1 based on the WAXD results. The isotropic enthalpies of Cn-NO2 varied from 6.32 to13.9 kJ mol-1, while that of Cn-Ph is 3.53⁵.92 kJ mol-1. The melting temperature decreased, while the clearing point rose with the elongating terminal alkoxy chain (n≤12). This can be understood that enhanced vander waals interactions by elongating the alkoxy chains can stable the mesophase,so the clearing points rised, and the range of mesophase broaded. Cn-NH2 ( n=6,12,16 ) exhibited enantiotropic SmC phase in the higher homologues (n=12,16). Fan-shaped and schlieren textures co-presented. the results of WAXD and FT-IR suggested that bilayer structures was formed, with hydrogen bonding existing in both inter-sublayers and intra-sublayers. Additionally, lateral intermolcular hydrogen bonding between O=C-NH-NH-C=O groups was confirmed through variable temperature FT-IR, dilution 1H NMR, varialbe temperature 1H NMR study and crystal structure analysis.The crystal structure determination from the powder diffraction data was carried out using Materials Studio.All the diffraction peaks can be indexed as the monoclinic structure, and the unit cell contains two molecules. It belongs to P121 space group and the lattice parameters are a = 17.179(5) ?, b = 3.319(2) ?, c = 16.692(8) ? and β= 92.533(8)°. The density calculated was 1.20 g cm-3. The final Rietveld refinement gave Rwp = 7.38% and Rp = 5.45% (110 reflections, 1627 data points). The effect of substitution on the liquid crystalline properties was disscussed. The mesophase range of C16-NO2,C16-Ph, and C16-NH2 is 114.3℃,66℃and 21.72℃, respectively. The most stable mesophase was observed in the compounds that bears electron withdrawing substituent (-NO2). It is because that the dipole of -NO2 group along the long molecular axis can make the molecules take anti-parallel arrangement, which is in favor of the orientational packing of molecules. The effect of lateral hydrogen bonding on the liquid crystalline properties was also disscussed. Hydrogen bonding was confirmed to exist in the mesophase play an important role in stabilizing the smectic phases by variable temperature FT-IR and DSC analysis. In addition, we reduced hydrogen bonding through substitute the hydrogen atom of N-H groups with –CH3 (D16-NO2) or change the amide unit (O=C-N-H)to schiff base (CH=N) (E16-NO2) and found that D16-NO2 is non-mesomorphic, E16-NO2 showed SmA1 phase but with quite lower clearing point, smaller transition enthalpy and mesophase range (146.3℃to158.64℃) than C16-NO2. So the conclusion can be drawn that lateral intermolecular hydrogen bonding played an important role in stabilizing the mesophase.