Reactions between 1-ethynylazulenes and 7,7,8,8-tetracyanoquinodimethane (TCNQ): Preparation, properties, and redox behavior of novel azulene-substituted redox-active chromophores

[2+2] Cycloaddition/cycloreversion reactions between TCNQ and mono- or bis[2-(azulen-1-yl)ethynyl]benzene or -thiophene derivatives were examined: the corresponding TCNQ adducts, novel azulene-substituted redox-active chromophores, were produced in excellent yields. TCNE/TCNQ double adducts were also prepared both by stepwise and by one-pot cascade reactions. The redox behavior of these novel azulene-substituted chromophores was examined by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). Significant color changes in these azulene-substituted chromophores under electrochemical reduction conditions were observed by visible spectroscopy.