Self-Organization of Bilayr-Forming Crystals

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The purpose of this research project is to understand the fundamental aggregation principle when amphiphile molecules organize spontaneously in solution by themselves. To do this, the relationship between chemical structures and bilayr structures of azobenzene-containing amphiphiles C_nAzoC_mN^+Br^- were thoroughly investigated by the systematic change of alkyl chain lengths, m and n.Following results were obtained. (1) For the compounds with m-n<greater than or equal>2, azobenzene chromophores are parallely arranged in a side by side fashion and amphiphile molecules from both sides of a bilayr interdigitate each other. This packing mode was called "H-aggregate" structure. Especially, the compounds with m-n=2 were crystallized and their structures were analyzed precisely. Although cast films of compounds with m-n<greater than or equal>2 showed H-aggregation structure, their stability decreased with the increase of the difference (m-n) from 2. (2) In the case of compounds with m=5, azob … More enzene chromophores are arranged in a head to tail fashion and amphiphile molecules tilt by about 30ﾟ to the bilayr surface. This packing mode was called "J-aggregate" structure. This group of compounds was easy to crystallize and every specimen was analyzed to get precise bilayr structures. (3) Every compound with different m and n showed a crystal-crystal transition at elevated temperature and their structures at higher temperature seemed to be similar to the J-aggregation structure, independent on their original aggregation structures. (4) From the above experimental results the following conclusions were obtained. The cross-section balance between the hydrophobic part and the hydrophilic part is most important as a driving force in the formation of bilayr structures. The bilayr structure was controlled by changing the number of carbon atoms in the tail (n) and the spacer (m) part. Moreover, in the case of H-aggregation state, small structural differences could be controlled by the odd or even Less