Discovery of Liquid Crystal Structure Bifurcated in Form of Ant Colony -Serving as a new motif of liquid crystalline organic semiconductors with three-dimensional charge transport path (Topic)
01 Dec, 2009
RIKEN and Japan Synchrotron Radiation Research Center have succeeded in developing a liquid crystalline organic semiconductor with a three-dimensional charge transport path at room temperature.
Japan Synchrotron Radiation Research Center
Key Research Achievements
• Discovery of bicontinuous cubic phase comprising discotic molecules at room temperature
• Formation of three-dimensional charge transport path in liquid crystalline triphenylene derivatives
• Realization of sub-millisecond lifetime of photon carriers, two orders of magnitude longer than those of previous photon carriers
RIKEN (Ryoji Noyori, President) and Japan Synchrotron Radiation Research Center (JASRI; Tetsuhisa Shirakawa, President) have succeeded in developing a liquid crystalline*1 organic semiconductor with a three-dimensional charge transport path at room temperature.
Liquid crystalline organic semiconductors composed of aromatic molecules (discotic molecules*2) have attracted attention as a constituent element of organic electronics.*3 Discotic molecules are generally laminated to form a unidirectional column and therefore exhibit a high electrical conductivity along the column direction. If such a column formed by discotic molecules can be laminated as a three-dimensional network, it becomes possible to realize a liquid crystalline organic semiconductor that exhibits excellent charge transport characteristics in all directions.
A research group involved in the project of "Creation and Application of Electronic Nanospace by Molecular Programming" (project leader: Takuzo Aida, professor at The University of Tokyo) as part of the Exploratory Research for Advanced Technology and Solution Oriented Research for Science and Technology (ERATO-SORST) by the Japan Science and Technology Agency (JST; Koichi Kitazawa, President), in collaboration with a research team led by Masaki Takata a chief scientist at RIKEN, analyzed in detail the laminated structure of liquid crystalline triphenylene*4 derivatives bearing ionic sites using the synchrotron radiation X-rays at SPring-8. They clarified that the molecules form a bicontinuous cubic phase*5 over a wide temperature range. It was also demonstrated that this liquid crystal is composed of triphenylene columns, which three-dimensionally develop in the form of an ant colony, and exhibits a high electrical conductivity equivalent to that of a unidirectional columnar phase*6 formed by similar molecules. These observations unveiled for the first time the existence of bicontinuous cubic liquid crystalline materials with a three-dimensional charge transport path, providing a new motif of liquid crystalline organic semiconductors.
The results of this research were published online in Journal of the American Chemical Society on 10 August 2009, prior to publication in the printed version, with the image of the discovered liquid crystal structure appearing on the cover on 16 December 2009.
""Bicontinuous Cubic" Liquid Crystalline Materials from Discotic Molecules: A Special Effect of Paraffinic Side Chains with Ionic Liquid Pendants"
Md. Akhtarul Alam, Jin Motoyanagi, Yohei Yamamoto, Takanori Fukushima, Jungeun Kim, Kenichi Kato, Masaki Takata, Akinori Saeki, Shu Seki, Seiichi Tagawa and Takuzo Aida.
Journal of the American Chemical Society, published online 10 August, 2009
Fig. 1 Schematics of columnar phase (left) and bicontinuous cubic phase (right)
Pink sections represent columns composed of discotic molecules and blue sections represent layers composed of side chains and ion pairs.
Fig. 2 Molecular structure of triphenylene derivatives 1-3
Fig. 3 X-ray diffraction pattern of triphenylene derivative 110 at room temperature
The abscissa shows diffraction angle measured when X-rays are irradiated onto the triphenylene derivative. The phase of the derivative is determined from diffraction angle and intensity.
Glass phase, Bicontinuous cubic phase, Hexagonal columnar phase, Isotropic liquid phase