Professor, Division of Molecular Materials Science
Research Center for Low Temperature and Materials Sciences, Kyoto University
Development and analysis of functional conducting organic materials
Since 2002, our research center has performed two missions: the stable supply of cryogens in Kyoto University and our own original scientific research. The facilities for the former purpose are being set up, while those for the research are not yet organized. Although all of the scientific works have been carried out with the help of other departments, the investigations in our center are highly original.
Our division investigates functional materials based on low molecular weight organic molecules. Focusing mainly on the conducting properties, structural and physical properties have been investigated to develop new materials and new concepts. For example, the study on ethylenedioxytetrathiafulvalene (EDO-TTF) is presented below.
An investigation aimed at the partial suppression of the self-assembling nature of bis(ethylenedioxy)tetrathiafulvalene (BEDO-TTF), from which complexes with stable metallic states have been afforded almost exclusively. The analogue EDO-TTF did not show the ability to self-assemble. Instead, a peculiar metal-insulator transition associated with a distinct molecular deformation was observed for (EDO-TTF)2PF6 at around 280 K. The mechanism was interpreted as cooperation among Peierls, charge ordering, and anion ordering transitions (Fig. 1). Such a concept of mechanism mixing has been rarely considered. From the viewpoint of multi-instability, the photo-induced phase transition (PIPT) was examined in cooperation with other research groups. A pulsed weak laser light was used to stimulate the insulating phase, and ca. 500 donor molecules were converted into the highly conducting metastable state within 1.5 ps (Fig. 2). The ultra-fast and highly efficient conversion can be used as the basis of optoelectronics materials in the future as well as the seeds for basic sciences. It is noteworthy that other research groups have also examined the PIPT for conducting charge-transfer complexes after our reports were published. At present, cooperative work is underway to elucidate the dynamics of the PIPT. Also, new materials are being explored under the working hypothesis that flexible and strongly correlated π-electron systems will provide conductors having multi-instabilities.
