Conjugated polymers aromatic ring structures

The innovations in materials science boost the development of polymer solar cell. Considering the four aspects mentioned previously, three methods have been developed accordingly (Li, 2012), namely side chain engineering, donor-acceptor (D-A) copolymerization and large fused aromatic ring structure. Some of the representative high performance conjugated polymers are displayed in Fig. 5.2B. 

Similar structures will occur in conjugated polymers such as polypyrroles and polythiophenes prepared from monomers with one or more different substituents at the positions on the aromatic ring not involved in the polymerisation, see Fig. 1.5. The reactivity of one particular site in the monomer usually predominates, so that the effect is relatively small. A 1 % head-to-head content may, however, seriously upset crystallisation. 

Pyrrole offers two positions that can be substituted to obtain soluble polymers, the N- and the 3-/or 4-positions on the aromatic ring. In general, N-substitution lowers the conductivity caused by the loss of conjugation due to steric interactions, which leads to a torsion of adjacent pyrrole units the advantage of the N-substitution is the improved environmental stability and the more straightforward structural characterization [155]. For the preparation of N-substituted and ring-substituted PPys oxidative chemical and electrochemical... 

As the title of this article suggests, the material covered will deal with the electronic structure of conductive conjugated polymers in relation to their physicochemical properties. This subject is so broad that the theme is confined herein to polyacetylene and other conjugated systems having aromatic rings. The research in this area, however, is rapidly developing and, on reflection, yielding fruitful results that have wide applications and ramifications in quantum chemistry. 

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."... 

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