Electrochemical Switch‐On of Nonlinear Optical Response in a Nitro‐Functionalized Arylimido‐Polyoxometalate

Electrochemical switch‐on of second‐order non‐linear optical (NLO) responses ( β ) has been demonstrated in a polyoxometalate (POM) based chromophore (POMophore) for the first time. Reduction of the POM in a POM‐imidoaryl‐NO 2 derivative invokes an up to 15‐fold off/on switchable increase in intensity of scattered frequency‐doubled light, and the highest “on” state β yet reported for a redox‐cyclable POMophore. Computational and spectroscopic studies show that in the oxidized state, directionally opposed charge transfer (CT) transitions to POM and ─NO 2 result in a low net β . Upon reduction, the POM becomes a much weaker CT acceptor, resulting in more dipolar imido‐aryl to nitro CT, and thus enhanced NLO response.