MEH-CN-PPV中Z/E的构型

用Knoevenagel方法,合成了MEH-CN-PPV,通过对其¹H-核磁共振(¹H-NMR)谱的研究,在MEH-CN-PPV的1H-NMR谱中发现烯键的Z/E两种构型的信号,通过积分面积初步估算E构型占15%,Z构型占85%。并且合成了模型化合物——齐聚物(E,E)-1,4-二(1-氰基-2-苯乙烯基)-2-(2-乙基己氧基)-5-甲氧基苯,其发生异构时,¹H-NMR谱的变化与MEH-CN-PPV的Z/E两种构型在1H-NMR谱中的信号吻合。

Z/E Configuration in MEH-CN-PPV

CN-PPV is one of the important series of PPV and its derivatives, demonstrating very high quantum efficiency of over 4% in a two-layers device, ITO/PPV/CN-PPV/Al. It is widely known that the defects in the polymer backbone can affect the properties of the device. The main structural defects in PPV-type conjugated polymers involve the "tetrahedral" structural segments and the E-double bone configurations. In order to achieve a better understanding to the structure of MEH-CN-PPV, the model compound (8a) (Z,Z-configuration) was synthesized. The Z/E-isomerization of the vinylene moiety with cyano group happened easily under the influence of visible and UV light. (8a) dissolved in chloroform was irradiated in daylight for 2 days under purging nitrogen. Its NMR spectrum become more complex, which showed the occurrence of the Z/E-isomerization. Through a careful separation for this mixture by column chromatography (silica gel, cyclohexane/ dichloromethane 2:5) in the dark, two new compounds (8b) (a green solid) and (8c) (yellow oil) were obtained. According to the ¹H-NMR spectra, the configuration of (8b) was E,E and that of (8c) was Z,E. In the ¹H-NMR spectrum of the copolymer MEH-CN-PPV, the main signals were similar to (8a), which indicated that the configuration of the copolymer MEH-CN-PPV was mainly Z. Some feeble signals at 6.47×10^-6 and 3.32 ×10^-6 were similar to the signals of the protons on the vinylene bond and OCH related with the E-configuration in (8b) and (8c). Hence these signals can prove the presence of the E-configuration in MEH-CN-PPV backbone. The ratio between the signal (d) and the signal (a) was 0.09. The contents of the Z/E-configuration could be estimated: for Z-configration was 85% and 15% for E-configration.