ELECTRON STORAGE AND TRANSFER IN ORGANIC REDOX SYSTEMS WITH MULTIPLE ELECTROPHORES

The chapter focuses on “dimeric” or (low molecular weight) “oligomeric” redox systems with identical, electronically decoupled electrophores A. The chapter presents the biselectrophore A-1- A, where 1 represents a saturated spacer. Injection of an electron into one subunit A under formation of a radical anion raises the immediate question of whether the electron will tend to localize in the original subunit or whether it will undergo a degenerate electron transfer to the neighboring unit. In the terminology of electron-transfer kinetics such electron hopping between identical redox groups is termed self-exchange. Depending upon the rate of this process, one will observe an “effective delocalization” over two or more units within the timescale of the experiment, or a localization of charge on one unit. The chapter also focuses on the tailoring of the redox behavior of organic compounds— that is, the optimization of such systems for electron storage and electron hopping. While the emphasis is on the reduction and thus on anion formation, it has been shown on many occasions that oxidative cation formation leads to analogous conclusions. It should be emphasized that the approach is a purely empirical one: knowledge of the structural dependence of the charge-storage capacity and of intra-molecular electron-hopping processes might enable us specifically to design dimers, oligomers, and polymers in which the electron-transfer rate, and thus the resulting charge distribution, can be controlled precisely. © 1993, Academic Press Limited.