Reversible Redox Switching of Chromophoric Phenylmethylenepyrans by Carbon–Carbon Bond Making/Breaking

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 carbon–carbon bond making/breaking. Phenylmethylenepyrans
are organic chromophores which are well suited for such purposes 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.