Reversible signal regulation system of ¹⁹F NMR by redox reactions using a metal complex as a switching module

We present here the reversible signal regulation of ¹⁹F NMR using the transition metal complex as a switching module. Water-soluble fluorinated dendrimers containing ferrocene were synthesized as a probe, and the signal intensities of ¹⁹F NMR of the probes were monitored by changing the valence state of the ferrocene moiety. By oxidation of the ferrocene moiety, the relaxation of the nearby fluorine atoms was accelerated via the paramagnetic relaxation enhancement, as a result the ¹⁹F NMR signal from the probe was significantly decreased. The reduction of the ferrocenium cation of the probe recovered the signal intensity. Finally, in combination with the difference of the fluorescence quenching ability between ferrocene and ferrocenium cation, we constructed the multimodal ¹⁹F NMR/fluorescence probe based on the redox switching system.