title: Violene/cyanine hybrids as electrochromics part 2: tetrakis(4-dimethylaminophenyl)ethene and its derivatives
abstract: The general structure of violene/cyanine hybrids (see below) is exemplified by tetrakis(4-dimethylaminophenyl)ethene 1(RED) its vinylogue 2(RED) and its diazavinylogue 3(RED). As judged from their cyclic voltammograms and spectroelectrograms, oxidation occurs perfectly reversible by loss of two electrons creating closed shell systems 1-3(OX)+2 with strong bathochromic shifts (Michlers hydrol blue moieties). ESR spectra indicate only minor amounts of radical cations. At much higher potentials by another reversible loss of two electrons (-->1-3(OX)+4) the long wavelengths absorptions are replaced by shorter ones. In system 4, containing two 4-dimethylaminophenyl units only, the violene character is better preserved since oxidation occurs stepwise by single electron transfer up to 4(OX)+4. These results are backed by theoretical calculations for 1-4, demonstrating the strong geometrical differences between the various oxidation levels. Besides, new types of cyclic structures for 1-4(OX)+4 are indicated by these calculations: For systems 1-3 cyclic structures for tetracations have been found to be more stable by 3-20 kcalmol(-1) than acyclic structures, whereas for system 4 the acyclic structure is more stable by about 22 kcalmol(-1). The redox behavior of systems 1-4 is of general importance for electrochromic systems.
authors.affiliation: Institut fur Organische Chemie der Universitat Wurzburg, Germany. huenig@chemie.uni-wuerzburg.de
authors.initials: S
authors.lastname: Hunig
authors.initials: M
authors.lastname: Kemmer
authors.initials: H
authors.lastname: Wenner
authors.initials: F
authors.lastname: Barbosa
authors.initials: G
authors.lastname: Gescheidt
authors.initials: IF
authors.lastname: Perepichka
authors.initials: P
authors.lastname: Bauerle
authors.initials: A
authors.lastname: Emge
authors.initials: K
authors.lastname: Peters