Poly conjugate

The formation mechanisms and the nature of chromophores in PET are still a matter of discussion. Postulated chromophores are polyenaldehydes from the aldol condensation of acetaldehyde [73] and polyenes from polyvinyl esters [69], as well as quinones [74, 75], Goodings [73] has proposed aldol condensation as forming poly conjugated species by subsequent reactions of acetaldehyde molecules (Figure 2.16). 

Polymers with saturated bonds, heteroatoms, heterostructures and poly-conjugated ones are available now as photosensitive materials. Really one cannot expect a single mechanism to be reponsible for photoconductivity in so many diverse systems. However, there are a lot of verified factors which permit us to explain the main features of the photoconductive processes in polymers. The status and prospects of the application of polymeric photoconductors as prospective new electronic materials will be also analyzed for various types of photoconductors. 

This unexpected result may be related to the increase in TOC on fraction G3 and may be further evidence of the polymerization phenomenon discussed earlier. However, this hypothesis must be carefully considered because of our limited knowledge of pyrolysis mechanisms. The possibility of phenol formation during the thermal fragmentation process from elimination reactions followed by cycliza-tion of poly conjugated chains has been suggested by Bracewell (22) and should be investigated. 

Davydov, B. E. and Krentsel, B. A. Progress in the Chemistry of Poly conjugated Systems. 

I. Polymers with Poly conjugated Systems of Multiple Bonds... 

Among the first poly conjugated polymers found to display an internal photoeffect were polyquinazones such as polyacenequinone radicals and aniline black21 ... 

No studies have been reported on the action of this acid on dienes, but in view of the effectiveness of trichloroacetic acid on cyclopentadiene " one would expect an even easier catalysis by the stronger trifluoro derivative. Furan polymerises in the presence of fairly hi concentration of trifluoacetic acid giving rise to poly-conjugated products. The stmcture of these prdymers has been analysed in det but the mechanian of initiation and the nature of the chain carriers vdiich produce them remain unexplored, particularly in the early stages of the reaction. 

The paramagnetic properties of the polymer clearly establish a poly-conjugated system and rule out the polyspirocyclo-butanedione structure suggested (32) for the polymer. 

All electronic and electro-optic applications of poly-conjugated systems require the preparation of polymers with high chemical and structural homogeneity. Several optical and electrical properties of conjugated polymers such as their quantum efficiency of electroluminescence or maximum conductivity after doping can be correlated with the concentration of conjugation breaking defects introduced to the polymer upon its preparation. 

Acetaldehyde also engaged in other conjugate additions with poly-conjugated substrates, such as nitrodienynes and nitroenynes. Interestingly, only 1,4-additions were observed and no 1,6- or 1,8-addition occurred. The utility of the products was demonstrated by the enantioselective total synthesis of (- -)-a-lycorane (Scheme 8.2). ... 

The guided tour, presented here, for the stepwise analysis of the vibrational data recorded for trans-PA, can be and has been, equally applied for the interpretation of the spectra and the structural analysis of other poly conjugated polymers such as polyparaphenylene [44], polypyrrole [45], poly thiophene [46] and their alkyl derivatives [47]. For these substances, more experimental data are needed. Moreover, additional theoretical problems must be considered, due to the fact that the electron delocalisation depends on the torsional angle between the aromatic rings. Moreover, these systems cannot sustain solitonic excitation, but only polarons or bipolarons can be formed with the generation of "quinoid structures."... 

Thanks to their unique architecture, chirahty, supramolecular properties, and photophysical features, thiahelicenes are surely among the most versatile poly-conjugated systems for which a huge number of appHcations have been envisaged and investigated. In many cases these explorations have... 

Wegner, G., The structure of poly conjugated macromolecules, Macromol. Ghent. Suppi, 4, 155-175 (1981). 

Figure 2 shows some of the reactions of aromatic amines that contribute to their activity as antioxidants and to their tendency to form highly colored poly-conjugated systems. 

The most relevant fact is that while the Gr matrix is certainly truncated at the -fl and -1 units in the Fr matrix the distance of interaction of the zero-th unit with its s-th neighbour is yet unknown since the so-called delocalization length needs to be determined [41-43], The truncation at the site s of the long ribbon of interaction submatrices is then arbitrary, Many ab initio calculations are at present dealing with this essential problem which is common to all poly-conjugated chains presently available. 

The truncation of the sum in Eq. (3-45) is then arbitrary, thus affecting the validity of the physical conclusions which may be derived. It follows that any addition or variation of terms or extension of the interactions (increase of delocalization length) will affect the numerical values of the elements of the Fr(dispersion curves [41, 42], It is apparent that the shape of the dispersion curves is a direct consequence of the electronic properties of the poly-conjugated chains [58] (Figure 3-5). 

Vercelli B, Zecchin S, Comisso N, Zotti G, Berlin A, Dalcanale E, Groenendaal LB (2002) Solvoconductivity of poly-conjugated polymers the roles of polymer oxidation degree and solvent electrical permittivity. Chem Mater 14 4768-4774... 

The most apparently true model of electric conductivity in materials with the system of double conjugated bonds seems to be the change transfer in the ranges of poly conjugation possessing metal conductivity and jump conductivity between poly conjugation spheres [6]. 

Polyacetylene the simplest example of this class of poly-conjugated systems was synthesized in 1958 by Natta et al.(77) as the trans form by means of typical Ziegler catalysts. Cis and trans configurations of polyacetylene were reported first by Watson, McMordie and Lands (78) in 1961. Shirakawa and Ikeda (79 81) synthesized an all-cis and an all-transpolyacetylene and pointed out the cis-transoid(IV)and trans-transoid(V)structure of these polymers. 

In this chapter frequency correlations are discussed only marginally. We report the state of the art of frequency and intensity spectroscopy, which can help in the understanding of the electronic phenomena in poly-conjugated low band gap molecules that form the basis for relevant macroscopic electrical and optical properties. 

A nonnegligible advantage in the treatment of the vibrational problem of poly conjugated systems derives from the fact that for a very large class of compounds it is possible to extract a unique and well-defined nuclear coordinate as the only one necessary to describe the coupling between nuclei and tt electrons. It can be shown that this simplification is a consequence of the fact that it is possible to obtain a correct description of the electronic properties of these systems under the assumption that only one excited electronic state is relevant. 

The optical and vibrational spectra of PA in its two modifications (c/s-PA and trans-PA) have been the subject of many experimental and theoretical studies for a long time, and their interpretation has laid the ground for the understanding of the physics of the whole class of poly-conjugated materials. Most of the peculiar features of the IR and Raman spectra listed above are indeed observed in the case of trans-PA, which has become the prototypical system, seemingly the simplest and the one tackled first in all theoretical and/or experimental studies. 

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