Reversible redox responses, electrochemical properties

Because of their rich redox properties, NLO chromophores featuring transition metal complexes are among the best candidates for the role of NLO molecular switches, and the majority of examples reported up to now concerns metal-based chromophores in which the NLO response is modified by a chemical (or electrochemical) oxidation/reduction sequence. Several examples of reversible proton- or photon-driven switching of 0 will also be discussed in the following. 

Since ferrocene derivatives may also be readily and reversibly oxidized to ferrocenium ions, this has been proposed and demonstrated as a means of electrochemically switching NLO responses. " Generally, the oxidized species is found to have a considerably lower hyperpolarizability, consistent with ferrocenium being a much poorer donor than ferrocene for example, HRS has been used to measure the second-order properties of a solution of 20 (Figure 4) through multiple redox cycles, the NLO response varying by a factor of >6 between 20 and [20]. ... 

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