Hierarchical organization of photoresponsive hydrogen-bonded rosettes
Hierarchical organization of photoresponsive hydrogen-bonded rosettes
复制标题
DOI：
10.1021/ja052645a
复制
发表时间：
2005-08-10
影响因子：
15
通讯作者：
Kitamura, A
中科院分区：
文献类型：
--
作者：
Yagai, S;Nakajima, T;Kitamura, A
通过 H-1 NMR 和 UV/vis 光谱、动态光散射、脂肪族溶剂中的凝胶行为和块状液晶行为，研究了由偶氮苯连接的三聚氰胺和巴比妥酸盐或氰尿酸盐组成的氢键盘状聚集体（玫瑰花结）的层次结构和光响应行为。在块状状态下，巴比妥酸盐组分中具有空间庞大的三十二烷氧基苯基取代基的玫瑰花结以偏移排列方式堆叠，形成矩形柱状中间相，而在脂肪族溶剂中，它不会分层组织成更高阶的柱状聚集体。通过将巴比妥酸盐组分更换为空间要求更高的N-十二烷基氰脲酸酯组分，可以改善该缺点。由此产生的新玫瑰花结以面对面排列方式堆叠，形成块体状态的六方柱状中间相，并在环己烷中分层组织成细长的纤维聚集体，最终形成有机凝胶。柱状聚集体在环己烷中的紫外照射的动态光散射和紫外可见实验表明，柱状聚集体的解离和重组可以通过偶氮苯部分的反式-顺式异构化来控制。分子模型表明，具有顺式偶氮苯侧链的玫瑰花结失去了平面性。利用这种光诱导玫瑰花结的形态变化，首次使用盘形超分子创建了光响应有机凝胶。
Hydrogen-bonded disk-shaped aggregates (rosettes) composed of azobenzene-appended melamine and barbiturate or cyanurate are investigated in view of their hierarchical organization and photoresponsive behavior by H-1 NMR and UV/vis spectroscopies, dynamic light scattering, and gelation behavior in aliphatic solvents and liquid crystalline behavior in bulk state. In the bulk state the rosette possessing a sterically bulky tridodecyloxyphenyl substituent in the barbiturate component stacks in an offset arrangement to form a rectangular columnar mesophase, whereas in aliphatic solvents it does not hierarchically organize into higher-order columnar aggregates. This drawback is improved by exchanging the barbiturate component into a more sterically nondemanding N-dodecylcyanurate component. The resulting new rosette stacks in a face-to-face arrangement to form a hexagonal columnar mesophase in the bulk state and hierarchically organizes into elongated fibrous aggregates in cyclohexane, which eventually leads to the formation of organogel. Dynamic light scattering and UV-vis experiments upon UV-irradiation of the columnar aggregates in cyclohexane revealed that the dissociation and the reformation of columnar aggregates can be controlled by the trans-cis isomerization of the azobenzene moiety. Molecular modeling indicates that the rosette possessing cis-azobenzene side chains loses its planarity. Using this photoinduced morphological change of the rosette, photoresponsive organogel is created by the use of a disk-shaped supramolecule the first time.