| Research Abstract |
Although pi-conjugated molecules will small to medium size have been studied extensively, those with larger pi-systems have remained much to be explored and studied probably owing to increasing difficulties in the synthesis, handling, and structural characterization. The primary purpose of this project is to design, synthesize, and elucidate the structure-property relationship of novel extended pi-systems. The following results have been obtained in these two years.
(1) Following to our first synthesis of several triquinarenemethane di-ions, we have succeeded in the synthesis of hexacyanotriquinarenemethane dianion 1, a stable and highly tetrapolar substance, and triquinarenemethane di-ions having aromatic ion moieties at the terminals. These di-ions show strong absorptions in the visible to near-infrared region.
(2) For the synthesis of 1 we have developed a versatile synthon which is widely applicable to the synthesis of a variety of dicyanoquinodimethanes. As the first examples we synthesized and studied a number of dicyanodiarylquinodimethanes 2 whose dipolarity largely changes by the electronic nature of para-substituents.
(3) Taking electron-withdrawing nature of boron atom into account, we designed and synthesized sterically protected boraquinodimethanes 3 and a triquinarenemethane analogue having a boron atom at the center. Compounds 3 show appreciable solvatoshromism and further studies are undergoing.
(4) We have also synthesized dendrimer-type hexacations based on hexa-substituted benzene skeleton 4, tetrakis (2-thienyl) quinodimethanes 5, and a new dibenzoterquinone derivative 6. Compounds 4 are the first example of hydrocabon haxaxation, quinodimethanes 5 show good amphoteric redox properties, and the extended quinone 6 undergoes a highly reversible photochemical and thermal isomerization between quinone and diradical form involving conformational change. This property of 6 represents a switch function.
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