Cui Yinan, Tao Daliao, Huang Xiaoyu, Lu Guolin, Feng Chun
Key Laboratory of Synthetic and Self-Assembly Chemistry for Organic Functional Molecules, Shanghai Institute of Organic Chemistry, University of Chinese Academy of Sciences , Chinese Academy of Sciences , 345 Lingling Road , Shanghai 200032 , People's Republic of China.
State Key Laboratory for Modification of Chemical Fibers and Polymer Materials , Donghua University , 2999 North Renmin Road , Songjiang, Shanghai 201620 , People's Republic of China.
Langmuir. 2019 Feb 26;35(8):3134-3142. doi: 10.1021/acs.langmuir.8b04127. Epub 2019 Feb 13.
The formation of chiral nanostructures from the self-assembly of achiral building blocks without external symmetry breaking inducing factors is believed to associate with the origin of chirality. Herein, we reported the synthesis and self-assembly of oligo( p-phenylenevinylene)- b-poly(ethylene glycol) (OPV- b-PEG, the subscripts represent the number of repeat unit of each block) in solution. We systematically examined the influence of solvent, heating temperature, and concentration of OPV- b-PEG on the self-assembly of OPV- b-PEG by UV/vis absorption and fluorescence spectrometry, circular dichroism technique, and transmission electron and atomic force microscopy. Interestingly, helical and twisted nanoribbons and nanotubes of a preferred handedness can be formed from achiral OPV- b-PEG in the mixture of water/ethanol (v/v = 1/1) and the solution showed an obvious exciton-coupled bisignated signal, which indicated that symmetry breaking occurred during the formation of these nanostructures without external inducing factors. Our results showed that the occurrence of symmetry breaking is subtle to the experimental factors including solvent, heating temperature, and concentration of OPV- b-PEG. The directional π-π stacking along with steric repulsion between PEG domains should be the driving force for the formation of these chiral nanostructures. The occurrence of statistical fluctuations in the initial stage of self-assembly led to an accidental excess of helical or/and twisted structures, that is, symmetry breaking. Subsequently, the autocatalysis effect resulted in the formation of helical or/and twisted nanoribbons with a preferred handedness.
在手性起源的研究中，人们认为由非手性结构单元自组装形成手性纳米结构，且无需外部对称破缺诱导因素。在此，我们报道了溶液中寡聚（对苯撑乙烯）-b-聚乙二醇（OPV-b-PEG，下标表示每个嵌段的重复单元数）的合成与自组装。我们通过紫外/可见吸收光谱、荧光光谱、圆二色技术以及透射电子显微镜和原子力显微镜，系统地研究了溶剂、加热温度和OPV-b-PEG浓度对OPV-b-PEG自组装的影响。有趣的是，在水/乙醇（v/v = 1/1）混合物中由非手性的OPV-b-PEG可以形成具有优先手性的螺旋状和扭曲的纳米带及纳米管，并且溶液显示出明显的激子耦合双信号，这表明在没有外部诱导因素的情况下，这些纳米结构形成过程中发生了对称破缺。我们的结果表明，对称破缺的发生对包括溶剂、加热温度和OPV-b-PEG浓度在内的实验因素很敏感。沿PEG域之间的空间排斥作用的定向π-π堆积应该是这些手性纳米结构形成的驱动力。自组装初始阶段统计涨落的出现导致螺旋状或/和扭曲结构的偶然过量，即对称破缺。随后，自催化效应导致形成具有优先手性的螺旋状或/和扭曲纳米带。
