Electrochemical switching fluorescence emission in rhodamine derivatives

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Electrochemical switching fluorescence emission in rhodamine derivatives, Electrochimica Acta 260 (2018) 589-597

Combination of electrochemistry with spectroscopic techniques is a powerful tool in the fields of analytical chemistry, biophysics and chemical physics. Especially electrofluorochromism, in which fluorescence of molecules can be modulated electrochemically, is becoming a very attractive approach in analytical and bioanalytical chemistry since many analytes are redox active and can be detected and/or mapped with high sensitivity through fluorescence. Even though electrochemical fluorescence modulation is becoming a promising approach, only a few systems based on single fluorescent molecules, molecular dyads, or polymers have been described. The use of intrinsically switchable fluorophores appears to be the most straightforward strategy as the fluorophore can behave both as the light emitter and the redox switch.

 

 

The photophysical and electrochemical properties of various rhodamine 101 derivatives have been investigated. The commercially available Rh101 (1), used as a reference model, was first examined. Contrary to its parental molecule, the electrogenerated radical form of Rh101 was found to be nonfluorescent. It was shown that the electrochemical fluorescence switching between the starting fluorescent Rh101 compound and its corresponding non-fluorescent radical form could be achieved. This result prompted us to modify the Rh101 molecule with an alkyne moiety and investigate the electrochemical fluorescence properties of the new derivative 2. Subsequently, it was used for the synthesis of the triazole derivative 3. While the reversibility of electrochemical fluorescence switching in compound 2 was not as efficient as in compound 1, fluorescence of compound 3 could be restored electrochemically, a most interesting feature for rhodamine-based compounds obtained by click chemistry. This work proved that rhodamine 101 derivatives can act both as light emitters and redox switches, opening new perspectives in the development of these fluorophores as practical probes, namely in fluorescence confocal microscopy.

 

Pour plus d'information,consultez le communiqué de presse associé à cet article : L’électrofluorochromisme : quand l’électrochimie rencontre la fluorescence !

 

Résumé: 

Electrochimica Acta 260 (2018) 589-597

 

Three rhodamine derivatives exhibiting electrofluorochromic properties were investigated by cyclic voltammetry and UVeVis/fluorescence spectroelectrochemistry. Rhodamine 101 (Rh101, compound 1) was used as a reference model. In compound 2, the carboxylate anion of Rh101 was replaced by an alkyne moiety to allow further functionalization. The compound 3 was prepared from 2 by conversion of the alkyne to a triazole group bearing an alkyl chain with an alcohol function. These three rhodamine derivatives exhibited similar electrochemical behaviors. Their mono-electronic reductions produced the corresponding radical species which were stable on the time-scale of cyclic voltammetry. Additional reduction of electrogenerated radicals produced unstable anions which underwent subsequent chemical reaction, most likely protonation. Based on cyclic voltammetry investigations, absorption and fluorescence spectroelectrochemistry were then performed on compounds 1, 2, 3 and their parent reduced radicals 1a, 2a, 3a. UVeVis spectroelectrochemistry, combined with TD-DFT calculation, confirmed the formation of radicals upon mono-electronic reduction of starting rhodamines. Fluorescence spectroelectrochemistry showed that, contrary to their parent molecules, electrogenerated radicals were non-fluorescent. Electrochemical fluorescence extinction was successfully achieved with all studied compounds. Moreover, compound 1 underwent on/off switching between fluorescent and nonfluorescent states repeatedly. Also, recovery of fluorescence in compound 3 was observed, which open interesting opportunities for the development of versatile rhodamine-based probes.

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Electrochemical switching fluorescence emission in rhodamine derivatives

 

Martina Cízkova, Laurent Cattiaux, Jean-Maurice Mallet, Eric Labbé, Olivier Buriez

 

Electrochimica Acta 260 (2018) 589-597

 

doi : 10.1016/j.electacta.2017.12.104