Dynamic redox systems: Toward the realization of unimolecular memory

"Dynamic redox systems" is the name given to a certain class of compounds that can be reversibly converted into the corresponding charged species upon electron transfer (ET) but accompanied by drastic structural changes and/or covalent bond making/breaking. Although transformation between the neutral and charged species proceeds quantitatively in most cases, their electrochemical processes are irreversible owing to the chemical reactions followed by ET. This situation endows the "dynamic redox pairs" with very high bistability, which is a prerequisite in order to construct the molecular response systems. This chapter first describes the principle of the "dynamic redox properties", and then classifies the compounds into several categories from the viewpoint of the type of structrual changes. After the properties of representative molecules in each category have been described in detail, their expected use as unimolecular devices is commented on in the final part of the chapter.