Oligothiophene Model Structure

Figure 1,7 DFT-calculated structures of syn-cycio [l4]thiophene and anti-cycio [30]thiophene. Reproduced with permission from S. 5. Zade and M. Bendikov, Cyclic oligothiophenes novel organic materials and models for polythiophene. A theoretical study, J. Org. Chem., 71, 2972-298 (2006). Copyright 2006 American Chemical Society...

Figure 8.7 Example orbital plot. A contour plot of (FTF)2 in the perfect dimer model. The molecular orbital contour plot reveals the overlap in charge density. Reprinted with permission from 5. E. Koh, B. Delley, J. E. Medvedeva, A. Facchetti, A. J. Freeman, T. J. Marks and M. /. Ratner, Quantum chemical analysis of electronic structure and n- and p-type charge transport in perfluoroarene-modified oligothiophene semiconductors, j. Phys. Chem. B, 110, 24361 -24370 (2006), Copyright 2006 American Chemical Society...

Conversely, due to the defined structure of a-oligothiophenes it was quickly realized that they constitute interesting models of the electronic properties of polythiophene [32]. The first spectral characterization of oligothiophene radical cations and dications in 1989 [32c, 33] and the use of a-sexithiophene 6 as active component in an a//-organic electronic device one year later [34] have triggered a renaissance of interest and intensive research work in the synthesis and characterization of these materials that had been neglected for so many years [35]. 

The early synthesis and characterization of ohgothiophenes entailed an immense number and variety of derivatives and related compounds. Due to their structural variabihty, stability, and well-balanced properties, it seems likely that oligothiophenes have developed to be ideal model compounds for the corresponding conjugated polymers. This chapter intends to give an overview of the synthesis of various classes of oligothiophenes. They will be arranged by the diflferent methods... 

The crystal structure of the model compound a-4T(/0-Me)4 (Scheme 11) has been investigated by Barbarella et al. [86] in comparison with its conformation in solution [87]. Crystals of a-4T(/0-Me)4 grown in hexane are monoclinic with a P2ic space group and Z = 2. As it can be seen in Figure 8, the molecules are stacked in parallel layers along the a axis similarly to unsubstituted oligothiophenes. 

Oligothiophenes with well defined structures have recently received a great deal of attentions not only as a model eompoimds for conducting polymers, but also as anew class of functional r-electron systems [153], Since the initial discovery of organic compounds showing metallic conductivity, for which 2000 Nobel prize in chemistry was awarded [154-156], oligo- and polythiophenes have attracted much attention as advanced molecules with practical use in electronic devices [157-160] and their potential application in field-effect transistors [161], photovoltaic devices [162] and organic electroluminescent devices [163],... 

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