Reversible redox switching of chromophoric phenylmethylenepyrans by carbon-carbon bond making/breaking

Abstract : Electrochromic organic systems that can undergo substantial variation of their optical properties upon electron stimulus are of high interest for the development of functional materials. In particular, devices based on radical dimerization are appropriate because of the effectiveness and speed of the carbon-carbon bond making/breaking. Phenylmethylenepyrans are organic chromophores which are well suited for such purpose since their oxidation leads to the reversible formation of bispyrylium species by radical dimerization. In this paper, we show that the redox and spectroscopic properties of phenylmethylenepyrans can be modulated by adequate variation of the substituting group on the para position of the phenyl moiety, as supported by DFT calculations. This redox switching is reversible over several cycles and is accompanied by a significant modification of the UV-Vis spectrum of the chromophore, as shown by time-resolved spectroelectrochemistry in thin layer conditions.