Azulene-Based Donor-Acceptor Systems: Synthesis, Optical, and Electrochemical Properties

We describe the synthesis and properties of azulene-substituted 1,1,4,4-tetracyanobutadienes (AzTCBDs) and heteroazulenyl TCBDs. TCBD derivatives were prepared in good to excellent yields through reaction of the corresponding 1-ethynylazulenes with tetracyanoethylene (TCNE). In contrast, the reaction between propargyl alcohols and the 1-azulenyl group in TCNE generated 2-aminofuran derivatives, which were transformed into 6-aminofulvenes with a 1-azulenyl substituent upon treatment with several amines. The optical and electrochemical properties of the AzTCBDs were clarified by UV/Vis and voltammetry. The AzTCBD derivatives exhibited electrochromism, showing a multi-step color change under electrochemical redox conditions. The multistage redox properties of AzTCBDs could be useful for the development of novel organic electronic materials.