Polythiophenes molecular structure

Different color transitions are obtained by simply changing the molecular structure of the polythiophene and then oxidizing or reducing it. Figure C. p. 93. shows the different colors obtained by taking the neutral form... 

Figure 3.12. Molecular structure of the amphiphilic polythiophene derivative discussed in the text.

Molecular self-organization in solution depends critically on molecular structural features and on concentration. Molecular self-organization or aggregation in solution occurs at the critical saturation concentration when the solvency of the medium is reduced. This can be achieved by solvent evaporation, reduced temperature, addition of a nonsolvent, or a combination of all these factors. Solvato-chromism and thermochromism of conjugated polymers such as regioregular polythiophenes are two illustrative examples, respectively, of solubility and temperature effects [43-45]. It should therefore be possible to use these solution phenomena to pre-establish desirable molecular organization in the semiconductor materials before deposition. Our studies of the molecular self-assembly behavior of PQT-12, which leads to the preparation of structurally ordered semiconductor nanopartides [46], will be described. These PQT-12 nanopartides have consistently provided excellent FETcharacteristics for solution-processed OTFTs, irrespective of deposition methods. 

Some conjugated polymers, such as polythiophene and polyaniline were synthesized already in the last century [8a,b], It is not surprising that, for example, polyaniline has played a major role in research directed toward synthetic metals because it possesses a relatively stable conducting state and it can be easily prepared by oxidation of aniline, even in laboratories without pronounced synthetic expertise (see section 2.6). It is often overlooked, however, that a representation of, for example, polypyrrole or polyaniline by the idealized structures 1 and 2 does not adequately describe reality, since various structural defects can occur (chart 1). Further, there is not just one polypyrrole, instead each sample made by electrochemical oxidation must be considered as a unique sample, the character of which depends intimately on the conditions of the experiment, such as the nature of the counterion or the current density applied (see section 2.5). Therefore, one would not at all argue against a practical synthesis, if the emphasis is on the active physical function and the commercial value of a material, even if this synthesis is quick and dirty . Care must be exercised, however, to reliably define the molecular structure before one proceeds to develop structure-property relationships and to define characteristic electronic features, such as effective conjugation length or polaron width. 

FIGURE 8.1 Molecular structures of some common conjugated polymers and small molecules (a) poly(p-phenylene vinylene), (b) polythiophenes, (c) MEH-PPV, (d) P3HT, (e) copper phthalocyanine, and (f) pentacene. 

The refractive index and the rugosity, i.e. the roughness of the sample, were studied by optical transmission in the transport region of unsubstituted and j8-alkyl substituted a6T [222]. The refractive index is n= 1.904 for a6T, n= 1.763 for diethyl-substituted 6T, and n= 1.688 for didecyl-substituted a6T, the rugosity of 6T is determined as 44.1 run which is much higher than in amorphous silicon with 16.9 nm. The latter is attributed to the large thickness of the film (1.4 pm) and to the microscopic molecular structure in the film. The differences of the refractive index can be simply explained by the lower density of the alkyl-substituted films. This is also a valid explanation for the lower refractive index of polythiophene and the higher one of amorphous Si. 

Figure 1. Molecular structure of I) poly(paraphenylene vinylene), PPV II) poly[2-methoxy-5-(2 -ethyl-hexoxy)-paraphenylene vinylene], MEH-PPV III) poly(paraphenylene), PPP IV) poly(2-decyloxy-paraphenylene), DO-PPP V) polythiophene.

During the last decade, there have been countless studies devoted to the synthesis of different thiophene-based polymers and oligomers for photovoltaic applications and various photoconversion efficiencies ranging from 0.1 to 5 % have been reported for devices based on such materials. We have chosen some references that cover a small part of the literature on polythiophene-based [40-54] and oligothiophene-based [55-60] devices with relatively successful photovoltaic performance. Figure 18.3 shows the molecular structures of some of the most successful materials, and their optical bandgaps and PCE are given in Table 18.1. 

Because of the strong coloration of PT, especially in the partly and fully oxidized state, resonance Raman spectroscopy has been employed suceessfully to elucidate the molecular structure and changes thereof as a function of applied electrode potential and other experimental parameters [930]. Resonance Raman and infrared spectra of polythiophene obtained ex situ under various, frequently unsatisfactorily defined experimental conditions have been reported [931-935]. These early results were, in part, inconsistent. In particular, the assignment of bands not found in the thiophene monomer to modes of the newly created polymer was repeatedly contradictory. 

Figure 7. Polaron in a polythiophene chain. Top geometrical change of the molecular structure. Bottom associated localized levels in the forbidden gap.

Figure 3.2 (a) Molecular structure of polythiophene diblock copolymers, and... 

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