Berlepsch Hans v, Ludwig Kai, Böttcher Christoph
Forschungszentrum für Elektronenmikroskopie, Institut für Chemie und Biochemie, Freie Universität Berlin, Fabeckstraße 36a, D-14195 Berlin, Germany.
Phys Chem Chem Phys. 2014 Jun 14;16(22):10659-68. doi: 10.1039/c4cp00967c.
The aggregation behaviour of the cationic pinacyanol chloride in aqueous solution is investigated using absorption and linear dichroism spectroscopies, optical microscopy and cryogenic transmission electron microscopy (cryo-TEM). The investigations are focused on solutions in a concentration range from 50 μM up to 1 mM. At a concentration of 0.7 mM H-aggregates are detected that are characterized by a broad absorption band centred at ∼511 nm. The aggregates possess a tubular architecture with a single-layer wall thickness of ∼2.5 nm and an outer diameter of ∼6.5 nm. Linear dichroism spectroscopy indicates that the molecules are packed with their long axis parallel to the tube axis. These H-aggregates are not stable, but transform into J-aggregates on the time scale of weeks. The kinetics of J-aggregation depends on the dye concentration and the route of sample preparation, but can also be enhanced by shear stress. J-aggregates possess a split absorption spectrum composed of two longitudinally polarized J-bands and one H-band that is polarized perpendicular to the aggregate axis. The J-aggregates are ∼9 nm wide and several micrometer long fibrils consisting of stacked pairs of ribbons with a dumbbell-shaped density cross-section. Upon aging these ribbons laterally stack face-to-face to form tape-like aggregates.
使用吸收光谱和线性二色光谱、光学显微镜以及低温透射电子显微镜（cryo-TEM）研究了阳离子氯化藻红在水溶液中的聚集行为。研究重点是浓度范围从50 μM到1 mM的溶液。在浓度为0.7 mM时，检测到H聚集体，其特征是在约511 nm处有一个宽吸收带。这些聚集体具有管状结构，单层壁厚约为2.5 nm，外径约为6.5 nm。线性二色光谱表明分子以其长轴平行于管轴的方式堆积。这些H聚集体不稳定，但在数周的时间尺度上会转变为J聚集体。J聚集的动力学取决于染料浓度和样品制备途径，但也可通过剪切应力增强。J聚集体具有由两个纵向极化的J带和一个垂直于聚集体轴极化的H带组成的分裂吸收光谱。J聚集体是宽度约为9 nm、长度为几微米的纤维，由成对堆叠的带组成，具有哑铃形密度横截面。随着时间推移，这些带会面对面横向堆叠形成带状聚集体。
