Synthesis and properties of azulene-substituted donor-acceptor chromophores connected by arylamine cores

1-Ethynylazulenes connected by several arylamine cores reacted with tetracyanoethylene (TCNE) and 7,7,8,8-tetracyanoquinodimethane (TCNQ) in a formal [2+2] cycloaddition-cycloreversion reaction to afford the corresponding tetracyanobutadiene (TCBD) and dicyanoquinodimethane (DCNQ) chromophores, respectively, in excellent yields. The intramolecular charge-transfer (ICT) characters between the donor (azulene and arylamine cores) and acceptor (TCBD and DCNQ units) moieties were investigated by UV/Vis spectroscopy and theoretical calculations. The redox behavior of the new TCBD and DCNQ derivatives was examined by cyclic voltammetry (CV) and differential pulse voltammetry (DPV), which revealed their multistep electrochemical reduction properties. Moreover, significant color changes were observed by visible spectroscopy under the electrochemical reduction conditions. 1-Ethynylazulenes connected by several types of arylamine cores reacted with TCNE and TCNQ in formal [2+2] cycloadditions to afford corresponding tetracyanobutadiene and dicyanoquinodimethane chromophores, respectively. Cyclic voltammetry of the chromophores revealed their multistep reduction properties; significant color changes were also visible during electrochemical reduction.