Electrochemical Oxidation Mechanism of Photochromic Switches: Electrodimerisation, Ring Closure or Ring Opening?

Christophe Coudret,^a,* Iluminada Gallardo,^{b, *} Gonzalo Guirado , ^b,* Jean-Pierre Launay ^a,*

^aNanoSciences Group, CEMES-CNRS, 29 rue Jeanne Marvig, BP 94347, F-31055 Toulouse Cedex 4, France

^bDepartament de Química, Universitat Autònoma de Barcelona 08193-Bellaterra (Barcelona), Spain

 

 

Abstract

Simple photochromic dithienylethylenes with either perfluoro or perhydro cyclopentene ring, and a variety of substituents have been prepared and their electrochemical behavior explored by cyclic voltammetry. All present two electron irreversible oxidation waves in their open form, but the radical cation of the open isomers can follow three different reaction pathways: dimerisation, ring closure, or ring reopening. Whereas the chloro derivative follows a dimerisation mechanism (EC₂E mechanism), the phenylthio substituted compound displays an efficient oxidative ring closure (ECE or DISP1 mechanism). Interesting electrochromic behavior is associated with this compound, a redox process occurring in the range 0.5-1.5V is observed by monitoring the absorption species changes (colored species) in function of the applied potential. Furthermore, electrochromic properties are also found in the corresponding ring closed isomers. Depending on the substituents on the thiophene ring and the perfluro or perhydro cyclopentene ring, open isomers can be obtained from oxidation (chemical or electrochemical) of the corresponding ring closed isomers via EC mechanism. These observations should be taken into account for the potential design of three-state conjugated systems and photoelectrical molecular switching.

Keywords: diethienylethylenes, cyclic voltammetry, electrochemical oxidation mechanism, molecular switches, isomerization kinetics

 

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*Corresponding authors. E-mail addresses: coudret@cemes.fr, launay@cemes.fr, Iluminada.Gallardo@uab.es, Gonzalo.Guirado@uab.es