Construction of Redox-type Photochromic Systems Based on Photoinduced Electron Transfer Reactions in Crystalline State

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The research project is intended to construct the novel redox-type photochromic systems based on the photoinduced electron transfer reactions of electron-donor-acceptor complexes in the crystalline state. In order to realize such an idea it is essential to develop a new type of redox molecules exhibiting bistability. Thus, the redox pairs were designed so as to undergo reversible C-C bond formation and cleavage upon electron transfer. The research started from examining the interconversion hexaphenylethane derivatives 1 and dicationic bis (triarylmethane) dyes 2. It has been found that they constitute the dynamic and reversible redox pair showing vivid change in color and drastic structural change upon electron transfer. They surely are the promising candidate for the present purpose. Unfortunately, however, attempts to obtain the CT crystal of 1 with a variety of electron donors have been unsuccessful, preventing me from realizing my initial proposal. Next, the biphenyl-type electron acceptors having dicyanovinyl moieties were investigated. 2,2'-Disubstituted derivative was found to undergo C-C bond formation upon two-electron reduction. By combining the further isomerization of the reduction product, the latter system constitute a prototype of the novel electrochromic system with "write protect" option.