新型光学活性含氰基三联苯液晶聚噻吩合成与分子构象

合成了一种含有长柔性间隔基和氰基三联苯液晶基元的发光性聚噻吩衍生物{—thiopheneyl—CH2—COO—(CH2)6—O—terphenyl—CN]n—, PT(6)TPhCN}. 利用傅里叶变换红外(FT-IR)光谱、核磁共振(1HNMR)、差示扫描量热(DSC)仪、偏光显微镜(POM)、紫外-可见(UV-Vis)吸收光谱和荧光(PL)光谱对单体和聚合物的结构及性质进行了表征. 单体都呈现出良好的液晶性能, 由于长间隔基的存在, 聚合物PT(6)TPhCN也呈现出良好SmAd相. 氰基三联苯的存在还赋予了聚合物良好的光致发光性能, 同时, 长间隔基也有效地降低了分子间的相互作用, 进一步增强了聚合物的发光性能. 另外, 研究发现, 在未引入任何手性元素的情况下, 聚合物主链在圆二色(CD)光谱中还呈现出明显的Cotton 效应, 这可能是由于大体积液晶基元的位阻效应和取向作用, 液晶基元环绕主链进行取向的同时诱导聚噻吩主链在长程范围内呈螺旋取向.

Synthesis and Helical Conformation of New Optically Active Liquid Crystalline Polythiophene Containing Cyanoterphenyl Mesogen Pendant

A novel liquid crystalline(LC)polythiophene bearing cyanoterphenyl mesogenic pendants with a long flexible spacer{-thiophene-CH_2-COO-(CH_2)_6-Oterphenyl-CN]_n-,PT(6)TPhCN} was designed and synthesized.Structures of the monomer and the polymer were characterized by nuclear magnetic resonance(NMR)and Fourier transform infrared(FT-IR)spectroscopy while the liquid crystalline and other properties were evaluated with thermo-gravimetry,differential scanning calorimetry(DSC),polarized optical microscopy(POM),ultraviolet visible(UV-Vis)spectroscopy,and photoluminescence(PL).The monomer shows enantiotropic smectic phases during the heating and cooling processes.Because of the long flexible spacer,the polymer PT(6)TPhCN exhibits a colorful SmA_d mesogenic phase texture.The cyanoterphenyl group results in the polymer having good photoluminescence.The spacer length also greatly influences the UV absorption and photoluminescence behavior of the polymers.A longer spacer may better segregate the backbone,which effectively enhances the stronger photoluminescence emission.More interestingly,without introducing any chiral groups,the polymer exhibits an obvious Cotton effect on the circular dichroism(CD) spectra,which results from the predominant screw sense of the backbone.This is probably due to the heavy bulky mesogenic pendant rotating around the polythiophene backbone and producing a backbone with a helical conformation in the long wavelength region.