| Research Abstract |
In order to develop novel organic functional materials with different responding units to outer stimuli, such as light, heat, electric field, the following efforts were made in the last three years.
The preparation of several organic photo-responsive materials was carried out to tune their physical properties, such as magnetic property, conductivity, or liquid crystalline property, being based on the structural change evoked by the outer stimulus of light. Although so far no organic photo-responsive conductors or liquid crystalline materials could be obtained in spite of our efforts, several organic photo-responsive spin systems could be prepared. A couple of naphthopyran derivatives with aminoxyls were found to show the changes of their intermolecular magnetic interactions with Curie-Weiss model by irradiation and the intermolecular spin-spin interactions of an azobenzene with long alkoxy group and a TEMPO radical at an end were found to be switched by irradiation from weak ferromagnet
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ic interactions with Curi-Weiss behavior to relatively strong antiferromagnetic interactions with singlet-triplet behavior and vice versa.
During the course of our studies to prepare organic heat-responsive materials, a couple of spin systems with heat responsive property could be obtained. The intermolecular magnetic interactions of a heptylbiphenyl derivative with N-methylamido-TEMPO substituent was found to be changed from singlet-triplet behavior to Curie-Weiss one by merely heating over the thermal phase transition temperature, while, on the contrary, the original Curie-Weiss behavior of a cyanobiphenyl derivative with long alkoxy and a TEMPO group was coverted to singlet-triplet one by heating. Several biradical compounds with a naphthalene, biphenyl, azobenzene or azoxybenzene core and long alkoxy as well as TEMPO substituents at both their ends were found to show fairly large interermolecular magnetic interactions based on singlet-triplet model and the interactions were suggested to be originated from the unique supramolecular structural features according to their X-ray analyses.
Several radical catin salts containing TEMPO radicals in anionic part and TTF derivatives in cationic part were prepared and, among them, a BEDT-TTF salt with TEMPO-sulfonate showed semi-conductive property with relatively high conductivity at room temperature together with weak ferromagnetic behavior based on 1-D Heisenberg model and their structure-property relationship could be clarified based on the X-ray crystal structure analysis. Less
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