Hydrogen-bond-assisted control of H versus J aggregation mode of porphyrins stacks in an organogel system.
Hydrogen-bond-assisted control of H versus J aggregation mode of porphyrins stacks in an organogel system.
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DOI：
10.1021/jo0341822
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发表时间：
2003-05
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通讯作者：
Michihiro Shirakawa;Shin‐ichiro Kawano;Norifumi Fujita;K. Sada;S. Shinkai
中科院分区：
文献类型：
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作者：
Michihiro Shirakawa;Shin‐ichiro Kawano;Norifumi Fujita;K. Sada;S. Shinkai
为了深入了解有机凝胶体系中结构与聚集模式之间的关联关系，我们合成了以卟啉为一维聚集单元、以酰胺基团为外围氢键中心的凝胶剂2a-4a。在本文测试的23种溶剂中，在中位苯基的4位含有酰胺基团的凝胶剂3a和3b被归类为多功能凝胶剂，分别凝胶化10种和14种溶剂。相反，分别在3，5-位和3-位含有酰胺基团的胶凝剂2a和4a被归类为劣胶凝剂。用光谱学方法(UV-Vis、ATR-FTIR、XRD等)进行检测。结果表明，在有机凝胶相中，3a中的卟啉采用H聚集模式，而2a和4a中的卟啉采用J聚集模式。对单晶的X射线分析表明，实际上3b具有可归类为H-聚集体的卟啉部分的柱状堆积，而2a则形成二维a-b平面，其中的卟啉部分排列在J-聚集体中。非常有趣的是，扫描电子显微镜观察到的宏观聚集形态的差异很好地反映了H和J聚集模式的差异：3A+环己烷凝胶导致一维聚集的纤维结构，而2A+环己烷凝胶导致二维片状结构。这些结果表明，卟啉的H-J聚集模式可以由外围的氢键相互作用控制，宏观的扫描电子显微镜观察结构很好地反映了微观的氢键网络结构。
To obtain insights into a correlation relationship between the structure and the aggregation mode in an organogel system, we synthesized gelators 2a-4a bearing a porphyrin moiety as a one-dimensional aggregation unit and amide groups as peripheral hydrogen-bonding sites. Gelators 3a and 3b bearing the amide groups at the 4-position of the meso-phenyl groups are classified as versatile gelators, gelating 10 and 14 solvents, respectively, among 23 solvents tested herein. In contrast, gelators 2a and 4a bearing the amide groups at the 3,5-positions and 3-position, respectively, are classified as poor gelators. Examination by spectroscopic methods (UV-vis, ATR-FTIR, XRD, etc.) revealed that in the organogel phase porphyrins in 3a adopt the H aggregation mode whereas those in 2a and 4a adopt the J aggregation mode. X-ray analysis of the single crystals established that in fact 3b features a columnar stack of porphyrin moieties that can be classified as the H-aggregate, whereas 2a results in a two-dimensional a-b plane, in which porphyrin moieties are arranged in the J-aggregate. Very interestingly, the difference in the H versus J aggregation mode is well-reflected by the difference in the macroscopic aggregate morphology observed by SEM: 3a + cyclohexane gel results in a one-dimensionally aggregated fibrillar structure, whereas 2a + cyclohexane gel results in a two-dimensional sheetlike structure. These findings indicate that the H versus J aggregation mode of porphyrin stacks can be controlled by the peripheral hydrogen-bonding interactions and the microscopic hydrogen-bonding network structure is well-reflected by the macroscopic SEM-observed structure.