Thiophene, polythiophene, oligothiophenes

Yamamoto et a. [60-62] and Kurata et al [63] prepared polythiophene layers by vacuum evaporation. To ensure the deposition of poly- and not oligothiophenes, they removed low molecular weight material ( < 15-17) by Soxhlet extraction with CHCI3, The evaporated material is assumed to consist of poly-thiophene with a molecular weight of about 1500-2000 and 20-25 thiophene units. The X-ray and electron diffraction data of Yamamoto et al. point to a (partially) crystalline film with the polymer axes oriented perpendicular to a carbon or gold substrate plane if sub = 423 K. At lower substrate temperatures, the orientation and crystallinity are worse. This behaviour is not only true for the first deposited layer, but at least up to 10 layers, i.e, 100 nm. On polyimide substrates, however, the molecules lie on the substrate plane and orient along the rubbing direction of the polyimide [61]. 

Bauerle, R, and S. Scheib. 1995. Synthesis and characterization of thiophenes, oligothiophenes and polythiophenes with crown ether units in direct tr-conjugation. Acta Polym 46 124—129. 

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...

We are aware of only two reviews (book chapters) devoted solely to the theoretical smdy of oligothiophenes and polythiophenes [2, 3]. Since these were published in 1998 [2] and 1999 [3], the present chapter covers mostly research published after 1998. Due to the significant number of pubiications over the last 10 years that include theoretical studies on thiophene-containing compounds, we have not attempted to write a comprehensive review and to cover all available publications. Rather, our aim is to provide an overview of the field. We decided to concentrate on representative case studies of thiophene-containing compounds and not necessarily on the deepest or most comprehensive studies hence some other important studies are not covered in this review. Most theoretical studies were performed on oligomers however, where polymer calculations are available, they are also included in this review. We note that, since around 1996-99, density functional theory (DFT) has become the most popular computational tool in chemistry in general and in material chemistry in particular. Earlier reviews, published before 2000, concentrated... 

FET applications of thiophene-based materials have a two-decade history. Pioneering work was conducted by Koezuka and co-workers [33], The device utilized electrochemically synthesized polythiophene as the channel layer, its mobility being 10 cm V s . This work was followed by Garnier and co-workers [13], who used sexithiophene as the channel layer and recorded an enhanced mobility of 10 cm s . Akimichi et al. [14] made FET devices using alkyl-capped oligothiophenes and mentioned that the alkyl substitution not only improves the chemical stability of the oligothiophenes but also enhances the mobility. A similar substitution effect was also observed with other oligomers [34, 35]. 

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