Towards the Preparation of Electrochromic Materials with Strong Absorption in the Near‐Infrared Region: Synthesis and Redox Behavior of Azulene‐Substituted Enediyne Scaffolds Connected by a 9,10‐Anthracenediyl Spacer

Enediyne scaffolds connected by a 9,10‐anthracenediyl spacer as a redox‐active substructure with 6‐azulenyl groups as π‐electron‐accepting groups in their periphery ( 3a and 3b ) have been prepared by a one‐pot reaction involving repeated Pd‐catalyzed alkynylation of 6‐haloazulenes 7b and 7c with bis(enediyne) derivative 6 . The azulene‐substituted bis(enediyne)s 3a and 3b exhibited two reversible one‐step, two‐electron reduction properties upon cyclic voltammetry (CV) attributable to the formation of dianionic and tetraanionic species. The electrochemical reduction of 3a and 3b led a strong absorption in the near‐IR region corresponding to the formation of the stabilized dianionic species 3a RED 2– and 3b RED 2– . An electrochromic analysis revealed the lower stability of the tetraanionic species 3a RED 4– ·· and 3b RED 4– ·· , although the CV exhibited good reversibility. The mono(enediyne) systems 11a and 11b were also prepared for comparison. The electrochemical reduction of 11a and 11b did not exhibit good electrochemical reversibility by CV, but the electrochemical reduction led to a strong absorption in the near‐IR region, similar to the formation of the stabilized dianionic species 3a RED 2– and 3 b RED 2– in the bis(enediyne) systems. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)