不对称三环偶氮苯甲酸液晶的合成、光敏性及电化学性质

Synthesis,Photosensitive and Electrochemical Properties of Asymmetric Liquid Crystals Based on Tri-ring Azo-benzoic Acid

以4-烷基环己基甲酸（C1~C3）、4-烷基苯甲酸（C1~C5）和对羟基偶氮苯甲酸为主要原料,通过室温一步酯化反应,合成了2个系列8个不对称酯基偶氮苯甲酸类多官能团液晶化合物.目标产物的结构、液晶性及光敏性采用红外光谱（IR）、核磁共振谱（NMR）、质谱（MS）、元素分析、示差扫描量热分析（DSC）、热台偏光显微镜（HS-POM）和紫外-可见光谱（UV-Vis）等表征.利用循环伏安法（CV）测定了目标分子的前线轨道能级.测试结果表明,8个化合物均有液晶性,在甲醇溶液中显现出光敏性,在液晶态也观察到光顺反异构化.端烷基碳原子数对化合物紫外吸收峰Ⅱ（偶氮结构π-π＊带）、HOMO能级、LUMO能级和能隙Eg存在奇偶效应影响.烷基为奇碳数化合物的Eg低于相邻烷基为偶碳数化合物.这与目标分子紫外光谱变化趋势相吻合,即Eg较小的化合物在紫外光谱中峰Ⅱ的吸收波长较长（能量较低）,反之亦然.

Eight new asymmetric liquid crystals based on azo benzoic acid of two series were prepared,in which 4-alkyl（Me,Et or n-Pr） cyclohexyl carboxylic acid（3a—3c） or 4-alkyl（Me,Et,n-Pr,n-Bu or n-Pe）ben-zoic acid（3d—3h） were esterified with 4＇-hydroxy azo benzoic-4-acid.A simple one-step reaction was developed to esterify only the hydroxyl of 4＇-hydroxy azo benzoic-4-acid to synthesize target compounds at room temperature.The structure characterizations of all related products were performed using infrared spectrometer（IR）,1H-nuclear magnetic resonance（1H NMR）,mass spectrometer（MS） and elementary analysis.The liquid crystalline and photosensitive properties were investigated by differential scanning calorimeter（DSC）,hot stage polarizing optical microscope（HS-POM） and ultraviolet-visible spectrophotometer（UV-Vis）.The HOMO,LUMO energy levels and the energy gaps（Eg） of the compounds were calculated by cyclic voltammetry（CV）.All the 8 compounds had liquid crystalline properties and exhibited photosensitivities in methanol solution and in mesophase by irradiation of UV-light.There is an effect of odd-even carbon number alkyl chains on the second peak（π-π＊band of azo） in UV spectra and on energies of frontier molecular orbital was observed.The compound with odd carbon number alkyl chain has lower Egthan its neighboring ones with even carbon number alkyl chain.The result showed that the change tendencies of Egwere in excellent agreement with these of the absorption wavelength in UV spectra.The less was the Eg,the longer was the absorption wavelength（lower energy） of the second peak,and vice versa.