Polyconjugated chains

Modification and functionalisation of natural polyenes, the carotenoids, is an efficient way for the molecular engineering of polyenic chains. Terminal bis-pyridinium carotenoids, termed caroviologens, represent an approach to electron conducting molecular wires (5). Fitting polyconjugated chains with an electron donor group on one end and an electron acceptor on the other end yields push-pull systems of type 1 that may be considered as polarized, unidirectional (oriented) molecular wires and also possess marked NLO properties. 

Owing to the mechanism of the topochemical reaction the polyconjugated polymer chain is of exceptional purity and stereochemical regularity. Polydiacetylene crystals are thus ideally suited to study the inherent optical and electrical properties of polyconjugated chains. These unique features have attracted considerable attention and in recent years the topochemical polymerization of diacetylenes has developed to... 

G. Zotti, G. Schiavon, S. Zecchin, A. Berlin, G. Pagani and A. Canavesi, Mixed-valence conduction in redox-substituted polythiophenes. Enhancement of redox electron-exchange rate by polyconjugated chains, Synth. Met, 76, 255-258 (1996). 

Polythiophenes, 3-substituted by bipyridyl [268], benzoquinone [269], viologen [270], ferrocene [271], and tetrathiafulvalene [272], have been reported. The redox group is generally apparent in the voltammetric response of the polymers obtained, while the response of the polyconjugated chain is not, an indication of degradation of the backbone. Polymers of better quality with ferrocene and viologen pendants were later electrodeposited from bi- and terthiophenes [273]. 

The butadiyne thermopol3rmer structure is characterized by IR, UV and ESR spectroscopy as having a polyconjugated chain structure with pendant terminal acetylinic functional groups. 

In the process of radical polymerization a monomolecular short stop of the kinetic chain arises from the delocalization of the unpaired electron along the conjugated chain and from the competition of the developing polyconjugated system with the monomer for the delivery of rr-electrons to the nf-orbitals of a transition metal catalyst in the ionic coordination process. Such a deactivation of the active center may also be due to an interaction with the conjugated bonds of systems which have already been formed. 

In the following we shall consider the effect of polyconjugation and configuration of the polyene chain on the equilibrium dissociation of polyconjugated polyelectrolytes40, 41 45 264, such as PPA. The comparison of pAa and Z(energy of... 

Commonly, the increase in the conjugation chain length leads to the bathochromic shift of the absorption bands. The optical and photoelectrical properties analysis needs to take into account not only formal polyconjugation following from the molecule chemical structure but effective conjugation defined by sterical factors too. 

Reucroft et al. 37>38 reported photoconductivity of polymers with polyconjugation in the chain, prepared by polycondensation of 3,3 -diaminobenzidine and 3,3, 4,4 -benzophenone tetracarboxylic acid dianhydride39, pyrrone polymers ... 

Molecules can also function as resistors. Organic chemists will tell us that saturated straight-chain alkanes will conduct less well than unsaturated polyalkenes or polyconjugated aromatic hydrocarbons indeed, by studying... 

If a carbonyl group in a side chain is not directly conjugated to an aromatic ring, the double bonds of a polyconjugated system are not attacked. This fact was used in the synthesis of vitamin A from the corresponding aldehyde.348... 

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