Synthesis of donor-acceptor chromophores by the [2+2] cycloaddition of arylethynyl-2H-cyclohepta[b]furan-2-ones with 7,7,8,8-tetracyanoquinodimethane

Arylethynyl-2H-cyclohepta[b]furan-2-ones reacted with 7,7,8,8-tetracyanoquinodimethane (TCNQ) in a formal [2 + 2] cycloaddition reaction, followed by ring opening of the initially formed cyclobutene derivatives, to afford the corresponding dicyanoquinodimethane (DCNQ) chromophores in excellent yields. The intramolecular charge-transfer (ICT) interactions between the 2H-cyclohepta[b]furan-2-one ring and DCNQ acceptor moiety were investigated by UV/Vis spectroscopy and theoretical calculations. The redox behavior of the novel DCNQ derivatives was examined by cyclic voltammetry (CV) and differential pulse voltammetry (DPV), which revealed their multistep electrochemical reduction properties depended on the number of DCNQ units in the molecule. Moreover, a significant color change was observed by visible spectroscopy under electrochemical reduction conditions.