Combined fluorescence and electrochemical microscopies using a single redox and fluorescent probe.

No abstract

Monolayers of tetrazine terminated alkyl chains have been grafted on ITO through siloxane functions. These monolayers are electroactive and display fluorescence with a maximum close to 560 nm when excited in the visible range. Potential step cycles have been applied and the fluorescence intensity drawn from background and bleaching corrected emission spectra was found to be switched off and on reversibly according to the applied potential. This demonstrates that the luminescence of grafted fluorophores can be electrochemically controlled as it is in solution and the emission intensity can be followed with a good signal to noise ratio even for a monolayer.

No abstract

The combination of Scanning Electrochemical Microscopy (SECM) and Time-Resolved Fluorescence Microscopy was successfully implemented to investigate the control of the fluorescence of a tetrazine derivative in solution according to its redox state, a phenomenon called electrofluorochromism. The normalized fluorescence intensity difference between the 'on' and 'off' states can be tuned by the tip potential and the distance between the polarized tip and the substrate. It is demonstrated for the first time that luminescence lifetime can be modulated as well, an evidence that a quenching process contributes to the fluorescence intensity drop. The experimental results demonstrate that this quenching is due to the electron transfer reaction between the excited fluorophore and the electrogenerated anion radical. A mixed dynamic and static quenching mechanism is considered to fit the variations of both luminescence intensity and lifetime ratios vs. the coulombic charge. The pertinence of a static quenching is validated by DFT calculations. Insulating (glass) and conductive (ITO) substrates have been tested and optical approach curves based on fluorescence lifetime modulation have been obtained in each case that are more sensitive than the electrochemical one based on the tip current. Finally, numerical simulations have been performed to fit these optical approach curves and validate the role of the electron transfer quenching in the variation of fluorescence intensity and lifetime.