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 F-19 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 F-19 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 F-19 NMR/fluorescence probe based on the redox switching system. (C) 2009 Elsevier Ltd. All rights reserved.