Synthesis, Properties, and Redox Behavior of Tetracyanobutadiene and Dicyanoquinodimethane Chromophores Bearing Two Azulenyl Substituents

Acetylene derivatives with an azulenyl group at both terminals have been prepared by palladium-catalyzed alkynylation under Sonogashira–Hagihara conditions. These alkynes reacted with tetracyanoethylene and 7,7,8,8-tetracyanoquinodimethane in a formal [2 + 2] cycloaddition–retroelectrocyclization reaction to afford the corresponding new tetracyanobutadienes (TCBDs) and dicyanoquinodimethanes (DCNQs), respectively, in excellent yields. Intramolecular CT absorption bands were found in the UV–vis spectra of the novel chromophores, and CV and DPV showed that they exhibited a reversible two-stage reduction wave, due to the electrochemical reduction of TCBD and DCNQ moieties. Color changes were also observed during the electrochemical reduction

Synthesis of 2‑Methyl-1-azulenyl Tetracyanobutadienes and Dicyanoquinodimethanes: Substituent Effect of 2‑Methyl Moiety on the Azulene Ring toward the Optical and Electrochemical Properties

We describe the comparative study of optical and electrochemical properties of tetracyanobutadienes (TCBDs) and dicyanoquinodimethanes (DCNQs) with a 2-methyl-1-azulenyl group and their derivatives with a 1-azulenyl substituent examined under the same conditions. TCBDs and DCNQs with a 2-methyl-1-azulenyl substituent have been prepared by the Sonogashira–Hagihara alkynylation of the 2-methyl-1-iodoazulene with arylalkyne derivatives, followed by the formal [2+2] cycloaddition–retroelectrocyclization (CA–RE) reaction with tetracyanoethylene and 7,7,8,8-tetracyanoquinodimethane. The optical properties of the TCBDs and DCNQs with a 2-methyl-1-azulenyl group were investigated through the comparison with those of TCBDs and DCNQs with a 1-azulenyl substituent by employing the UV/vis spectroscopy and theoretical calculations. The electrochemical properties of the TCBD and DCNQ derivatives were also examined by cyclic voltammetry and differential pulse voltammetry experiments, which elucidated their multistep redox properties. Furthermore, noticeable spectral changes of these chromophores were identified by the spectroelectrochemical measurements