Directed Electron Transfer

Electron-transfer processes play key roles in chemical reactions, energy-storage systems and contemporary devices for information transfer. Such reactions are driven by thermodynamics and, given the choice between several partners, electron transfer will generate a thermodynamically stable distribution of products. Selectivity is acquired only by way of proximity and reduction potential. Here, we set out to devise rational ways to direct an electron along one particular pathway when several seemingly identical routes are available. In this case, selectivity is obtained by the choice of excitation wavelength. Low energy excitation of the main chromophore causes electron transfer to a proximal acceptor. Higher energy excitation into the same chromophore causes energy transfer to a secondary chromophore, which subsequently transfers an electron to a distal acceptor. The redox products differ in terms of spin and/or chemical identity. The ultimate achievement within this programme refers to directed electron transfer around a ring. Thus, low energy excitation causes clockwise electron flow but higher energy illumination causes electrons to move around the ring in an anti-clockwise direction.