Development of organic superconductors and multifunctional supramolecules based on new π-elecfron systems

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In this research project, development of new organic conductors and superconductors based on new molecular design that is destabilization of stable molecular metals as seen in TTP(tetrathiafulvalen) and TTP(tetrathiapentalene) conductors has been conducted. For this purpose, new π-electron donors whose π-electron systems are reduce compared with those of the previous TTF and TTP donors have been designed and synthesized. Structures and physical properties of the conducting radical salts prepared from such π-reduced electron donors have been investigated and a new superconductor, (DODHT)_2BF_4・H_2O, was discovered. By investigating the insulating phase at ambient pressure of the pressure-induced superconductor, (DODHT)_2PF_6, by X-ray diffraction and magnetic susceptibility measurements, the insulator phase was a charge ordering state with stripe type charge pattern. Furthermore, measurement of the transport properties of this material under pressure more precisely, particularly around … More the boundary between superconducting and insulator phases, leads to the pressure-temperature phase diagram ; In the phase diagram, the superconducting and normal resistive states coexists above the pressure of 13 kbar, and the insulator phase exists immediately above the superconducting phase between 13.2 and 15.1 kbar. Because the clear insulator transition was observed in the transport measurement up to 8 kbar, the charge ordering insulator might spread over high pressure region at least 8 kbar. These results suggested that the charge fluctuation might be crucial to the superconductivity in this material and the present material will seive as a simple tool for the investigation of the universality of the interplay between superconductivity and charge fluctuation.With studying the molecular conductors, development of multifunctional supuramolecular materials and their application to the organic devices have been carried out. For such materials, donor-acceptor linked molecules, such as C_<60>-TTF dyads, were newly prepared and an obvious intramolecular charge transfer interaction was observed unlike the previously reported C_<60>-TTF systems. The life time of the photo-induced charge separated state of the C_<60>-TTF dyad was revealed to be extremely short by the photo-physical study of the excited states, which is disadvantageous for the organic devices such as an organic solar cell. In order to overcome this situation, C_<60>-TTF dendrimers were prepared and the solar cell property was observed in spite of the low efficiency. Less