The effective condensation of organic π-electron systems in crystal

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The compound (1) that is made by introducing a tricyanoethenyl group into a novel π-electron system, 1-aryl-2,5-di(2-thienyl)pyrrole, gave stable crystals with gold-like metallic luster. We investigated this phenomenon from a point of basic view that the metallic luster is based on the effective condensation of organic π-electron systems in crystal. We also made its practical application and, as a result, the following results have been gained.1)Basic and Theoretical Investigation of the Origin of the Metallic Luster : Starting from the parent π-systems, 1-aryl-2-(2-thienyl)-5-(5-tricyanoethenyl-2-thienyl)pyrroles and 1-aryl-2,5-bis(5-tricyanoethenyl-2-thienyl)-pyrroles, their derivative that have an arene ring or a furan ring instead of the thiophene were synthesized. These derivatives were found to form crystals with gold-like or greenish metallic luster. The relationship between metallic color and crystal structure was investigated in detail to show that the kind of metallic color is attributable to how the π-systems interact to each other.2)Utilization of the Present π-System for Nanoscopic Materials : It was found that introduction of a long alkyl chain into the parent π-system changes artificially the arrangement of the π-molecules in the crystal under keeping the condensation of the π-systems, which is important to the emergence of metallic luster, to develop a novel nanoscopic materials.3)The Application to Electron-conducting Materials : It had been shown that the compounds (1) exhibit electric conductivity under doping with an electron acceptor. In the present research, the introduction of an electron-donating group such as methoxyl or diphenylamino group at their terminal thiophene increases electric conductivity.