Yao Hiroshi, Isohashi Takeshi, Kimura Keisaku
Graduate School of Material Science, University of Hyogo, Ako-gun, Hyogo, Japan.
J Phys Chem B. 2007 Jun 28;111(25):7176-83. doi: 10.1021/jp070520h. Epub 2007 May 25.
Countercation size specificity is presented for the electrolyte-induced aggregation of 3,3'-disulfopropyl-5,5'-dichloro-9-methyl thiacarbocyanine (TCC) dye in aqueous solution. Addition of electrolytes having a small monovalent cation (Na+, NH4+, or Cs+) induced pure H aggregates of TCC, whereas J aggregates were preferentially promoted by electrolytes with a large monovalent cation ([N(CH3)4]+ or [N(C2H5)4]+). The electrolyte-induced H aggregate (HS aggregate) differed spectroscopically from that spontaneously self-assembled in aqueous solution. Mesoscopic structure of the HS aggregates was revealed via polarized-light microscopy and atomic force microscopy; a rodlike morphology of 50-70 nm wide and tens to hundreds of micrometers long with very strong negative birefringence. A simple structural model based on semiempirical molecular orbital calculations can explain the aggregation behaviors: The anionic TCC monomer shows a considerable planar geometry between two benzothiazole end groups when it involves a sodium cation, which favors the H-type molecular arrangements in a face-to-face orientation. On the other hand, the TCC dye has a twisted conformation when it implicates a large tetramethylammonium cation, resulting in the formation of the J aggregates.
本文介绍了在水溶液中，抗衡阳离子大小特异性对电解质诱导的3,3'-二磺丙基-5,5'-二氯-9-甲基硫代碳菁（TCC）染料聚集的影响。添加具有小的单价阳离子（Na+、NH4+或Cs+）的电解质会诱导TCC形成纯H聚集体，而具有大的单价阳离子（[N(CH3)4]+或[N(C2H5)4]+）的电解质则优先促进J聚集体的形成。电解质诱导的H聚集体（HS聚集体）在光谱上与在水溶液中自发自组装形成的聚集体不同。通过偏光显微镜和原子力显微镜揭示了HS聚集体的介观结构；其呈现出棒状形态，宽度为50 - 70 nm，长度为数十至数百微米，具有非常强的负双折射。基于半经验分子轨道计算的简单结构模型可以解释这种聚集行为：当阴离子TCC单体与钠阳离子结合时，在两个苯并噻唑端基之间呈现出相当大的平面几何结构，这有利于H型分子以面对面的方向排列。另一方面，当TCC染料与大的四甲基铵阳离子结合时，会具有扭曲的构象，从而导致J聚集体的形成。
