Azulenyl structures

We have therefore been able to prepare the highly stable tetracation 254+ salt despite the presence of four positive charges in the structure. However, this first example for a cyanine-cyanine hybrid with cyanine units at both two termini did not demonstrate the presumed multiple color changes during electrochemical reduction. However, the tetracation 254+ exhibited multiple-electron transfer as a function of the substituted di(l-azulenyl)methylium units and also showed color change during the electrochemical reduction. 

The synthesis and characterization of a series of azulenyl-substituted cations (223) showed468,469 that these are extremely stable ions, which is attributed to the dipolar structure of the azulene rings. 

Probably to circumvent the former Hoechst AG s strong patent position on bisindenyl-type ansa-metaUocenes, alternative structures were developed by Mitsubishi Chemical Corporation [23, 52] and by former Montell [14, 56], based on azulenyl and heterocenyl ligands, respectively. 

With the ability of stabilizing both cations and anions due to its polarized structure, azulene can in principle be used as a building block for the construction of redox-active molecules, such as polyelectrochromic materials, which respond to different potentials with a variety of colors. In this context, Ito and coworkers synthesized a series of 6-azulenyl-substituted benzenes (4-7) [9-11] and 6-azulenylethynyl-substituted benzenes (8-11) [12], as shown in Figure 4.3, and investigated their redox behaviors. 

Figure 4.3 Structures of 6-azulenyl-substituted benzenes 4-7 and 6-azulenylethynyl-substituted benzenes 8-11.

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