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)
- Release Date
- 01 Dec, 2009
- BL02B2 (Powder Diffraction)
- BL44B2 (RIKEN Materials Science)
RIKEN
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. Publication: |
<Figure>
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
Triphenylene derivatives 1-3 are composed of triphenylene (pink), imidazolium ions (blue), alkyl side chains (hydrocarbon chains, black), and ion pairs (BF4, PF6, (CF3SO2)2N).
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.
Diffraction intensity
Fig. 4 Phase transition behavior of triphenylene derivatives 1-3
The phase of triphenylene derivatives 1-3 depends on temperature and has a three-dimensional charge transport path when a bicontinuous cubic phase is expressed. Triphenylene derivative 114 has the most stable bicontinuous cubic phase.
Glass phase, Bicontinuous cubic phase, Hexagonal columnar phase, Isotropic liquid phase
<Glossary>
*1 Liquid crystalline
A liquid crystalline material is flowable; however, its molecules are aligned. This is an intermediate phase that exhibits the properties of both crystal and liquid.
*2 Discotic molecules
This refers to molecules with a disc-shaped structure.
*3 Organic electronics
Organic electronics is a research field particularly aimed at the development of lightweight flexible electronic components using organic and polymer materials. Representative organic electronic devices include organic electroluminescence devices, organic solar cells, and organic transistors.
*4 Triphenylene
Triphenylene is a type of discotic polycyclic aromatic hydrocarbon, in which four benzene rings are linked to form a structure similar to a triangular geometry (Fig. 2).
*5 Bicontinuous cubic phase
Two continuous layers are three-dimensionally entangled to form a bicontinuous cubic phase. Unlike common liquid crystals, those in this phase are optically isotropic and exhibit no birefringence.
*6 Columnar phase
This is a column-shaped phase. Molecules are unidirectionally aligned to form columns that are arrayed on the two-dimensional plane to form a columnar-phase assembly. There are hexagonal, rectangular, square, and orthorhombic columnar phases, for example.
|
For more information, please contact: or |
- Current article
- 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)