Liquid Crystal Containing Dihydrazide Groups: Synthesis And Two-Dimensional Correlation Spectroscopy Study

Polymer science and engineering has experienced a rapid development and the theory became more and more complete since Staudinger proposed that the polymer is constituted of long-chain molecules, which inaugurated the field of polymer chemistry field in 1920s. After that Prof. Lehn proposed the concept of supramolecular chemistry. He and other scholars sparkpluged supramolecular chemistry and it became another new the field of chemistry.The chemistry, which people are familiar with, is about the synthesis, structure, character and transform rule of the moleculars combined with covalent bonds. Supramolecular chemistry is the one that molecular aggregates based on non-covalent bonds. The key question concerned is the interactions among the molecules. According to the strength, tropism and the degree of the dependence of distance and angle, it could be classified to coordination bond of the metal ions, hydrogen bond,π-πstacking, electrostatic interaction and hydrophobic interaction, etc. Both the supramolecular polymer science and the traditional covalent-bond polymer science build up the whole world of polymer science and engineering together.Supramolecular liquid crystal is based on non-bonded interactions, such as hydrogen bonding, ionic, charge transfer, hydrophobic, and Van der Waals force, among which hydrogen bonding is most crucial to construct ordered supra-structures because of its strength and directionality. Lots of structure and function of biological tissue is owing to the supra-structures based on the hydrogen bonding, such as double helix chain structure of DNA. In recent years, supramolecular self-assembly material based on the hydrogen bonding, such as liquid crystals, organogels and hydrogels has aroused concern of academe. Generally, spectroscopy methods are very sensitive to the hydrogen bonding interaction. In the traditional spectroscopy the spectrogram is always two dimension graph. It is composed of abscissa figures some variable (such as wavelength and wavenumber) and coordinate figures some spectroscopy character corresponding with the variable (such as absorbency and Light intensity). This kind of traditional 1-D spectroscopy has many shortcomings such as the low distinguishability. As a new spectrum technique developed recently, two-dimensional correlation spectroscopy has the ability of distinguishing the overlapping apices and providing the change order of structure induced by physical variables. It shows special advantage in studying supra-molecular liquid crystals.We consider the change of spectrum intensity y (ν, t) caused by the disturbance variables t between and in two-dimensional correlation spectra. The dynamic spectrum is the spectrum change corresponding with the interaction to variable outside, which is defined as follows: Through the Fourier Transform the complex two-dimensional correlation strength X (ν1 ,ν2) of the intension change ( y ( v1 , t ) and y ( v2 , t )) of dynamic spectrum of some spectrum variable (ν1 and v2) is calculated as follows:The real partΦ(ν1 ,ν2) and the imaginary partΨ(ν1 ,ν2)are called as the intensity of a synchronous 2D correlation spectrum and the intensity of an asynchronous spectrum, respectively.Φ(ν1 ,ν2) represents the simultaneous or coincidental changes of two separate spectral intensity variations during the interval.Ψ(ν1 ,ν2) represents sequential or successive, but not coincidental, changes of spectral intensities. Besides, we can judge the order of groups change.In this dissertation, we synthesized a series of the liquid crystal molecules (Cn-NO2) containing dihydrazide group. In order to study the effect of hydrogen bonding on the phase transitions, temperature dependent FT-IR was performed on C16-NO2 in the temperature range of 40-240℃. It was observed that the group of N-H and C=O move to high wavenumbers during heating process which indicated the existence of hydrogen bonding. Moreover, to get more information from the IR spectra, the 2D correlation spectra study was carried out on C16-NO2 in the temperature range of 60-175℃and 175-240℃, respectively. It is affirmed that there are two kinds of hydrogen bonding of different strength in the crystalline and only one in the liquid crystalline state. We also figure out the order of groups change during both heating and cooling process.(1) During the heating process of 60-175℃the order of groups change is as follows: Alkyl chain changes in the low temperature firstly. Then the stronger hydrogen bonding becomes weaker and the inferior one fractures. Finally, the C=C of phenyl ring changes. We consider that in the low temperature alkyl chain changes firstly because of its higher freedom.(2) During the cooling process of 175-60℃the order of groups change is as follows: The C=C of phenyl ring changes in the high temperature firstly. Then free N-H forms inferior hydrogen bonding with the electron donor. With the temperature descending, inferior hydrogen bonding become stronger and another different stronger hydrogen bonding appears. Finally, alkyl chain changes. The whole process just reversed.(3) During the heating process of 175-240℃the order of groups change is as same as the process in the scope of 60-175℃. Alkyl chain changes firstly. Then the hydrogen bonding becomes weaken and fractures. Finally, the C=C of phenyl ring changes.