Violenes structure

Electrochromism is observed in reversible redox systems, which exhibit significant color changes in different oxidation states. Violenes, whose general structure is represented in Figure 1, are typical examples that exhibit electrochromism (1). 

Figure 3. General structure of Hiinig s violene-cyanine hybrid. One or two of the moieties X=C-Y represent cyanines, oxonols, or merocyanines.

We have established the conversion between the two colored species by electrochemical reaction utilizing the concept of a Wurster type violene-cyanine hybrid. Dications 222+ and 232+ showed significant changes in their absorption spectra in different oxidation states. Therefore, dications 222+ and 232+ could function as new violene-cyanine hybrids, in which the four end groups (X and Y) in the general structure are azulenes (Figure 4). 

Synthesis of novel polyelectrochromic materials with the new structural motif utilizing stabilized carbocations has been demonstrated by several examples. The Wurster type violene-cyanine hybrid systems (22z+ and 232+) exhibit the presumed two color changes. The new cyanine-cyanine hybrid system (24 ) with a cyanine unit at the one terminus exhibits three color changes. 

The report will emphasize mainly type A with a radical cation SEM ( violene ) as the intermediate oxidation level. Structural types B and C will be dealt with essentially for the sake of completeness and for comparison. 

Variations on the theme of the tetrathiafulvalene structure have been investigated. Thus, the violene radical 156 has been characterized polaro-graphically and by electronic absorption spectra s 157, the phenylog of 154, has been reported the p-phenylenebis(tetrathiafulvalene) 158 gives an ESR spectrum upon oxidation which implies three equivalently coupling protons i.e., it behaves as a monosubstituted 153. ° There have been various attempts to incorporate the tetrathiafulvalene structure into polymeric materials, but with limited success in producing conducting polymers. i- ... 

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