Polythiophenes unsubstituted

In all cases of electrochemicaHy or chemically polymerized unsubstituted polypyrrole, the final polymer is intractable in both the conducting and insulating forms. In contrast, a broad number of substituted polythiophenes have been found to be processible both from solution and in the melt. The most studied of these systems ate the poly(3-alkylthiophenes) (P3AT). 

Two Hell UPS spectra of poly(3-hexylthiophene), or P3HT, compared with the DOVS derived from VEH band structure calculations [83], are shown in Figure 5-14. The general chemical structure of poly(3-alkylthiophene) is sketched in Figure 5-4. The two UPS spectra, were recorded at two different temperatures, -h190°C and -60 °C, respectively, and the DOVS was derived from VEH calculations on a planar conformation of P3HT. Compared to unsubstituted polythiophene, the main influence in the UPS spectra due to the presence of the hexyl... 

Despite their low molecular weights, these unsubstituted polythiophenes are insoluble in THF and other common organic solvents, and are also infusible. Their poor processability has therefore led to extensive studies of alkyl- and alkoxy-sub-stituted polythiophenes in the hope of enhancing solubility in organic solvents and allowing melt processing. Synthetic approaches to these substituted polythiophenes are described in the following text. 

Electrochemically prepared alkylated polythiophenes have been investigated by Gamier and coworkers.90 91 When comparing polythiophene and monosubstituted polyalkylthiophenes, these workers found an increase in crystallinity of the substituted thiophenes in comparison to the unsubstituted poly thiophene. The degree of crystallinity was low (5%), but the crystal structure was assigned to a hexagonal cell... 

The him morphology of electrochemically prepared polythiophene has been shown in numerous studies to be almost identical to that commonly observed for polypyrrole (described in Chapter 2). A nodular surface is observed for both unsubstituted and 3-alkyl substituted thiophenes.92 As with PPy, the electrochemical preparation of PTh at higher current densities produced rougher surface morphologies. The similarity in morphologies suggest a similar growth mechanism for electrochemically polymerized PPy and PTh. 

FIGURE 8.9 Linear unsubstituted conjugated polymers poly(p-phenylene), poly(para-phenylene vinylene), polythiophenes, and polyfluorenes. 

The question about a helical configuration has often been raised, botli by theoi7 and experiment. The theoretical predictions for the most stable form of hithiopheiie is evidently dependent upon the set of basis functions used in the calculation, Wliereas Bredas et a . [9], and Cui and Kertesz [10] find that the planar form is stable, Samdal et a . [5] and Belletete et ai [11] find that twisted forms are most stable. For Unepolymeis Cui and Kertesz conclude that the planar fonn for unsubstituted polythiophene is slightly more stable than a twisted, helical form, and that the helical form is the most stable for the methyl-substituted polymer. 

Unsubstituted polythiophene (PT) is an intractable material because it is neither soluble nor fusible, although films electrochemically prepared under certain conditions may be stretch-deformed. Generally speaking PT prepared by purely chemical routes turns out to be more crystalline than their electrochemical counterparts, as will be discussed in the following. 

The problem of a. P (and possibly / -/ ) bonds existing in unsubstituted polythiophenes is practically non-existent in poly(3-alkylthiophenes) with bulky substituents. In this case coupling, other than a-a, is effectively eliminated due to steric reasons,... 

From the above presented cyclic voltammetry and spectroelectrochemical studies, it is clear that both unsubstituted polythiophene and poly(3-alkylthio-... 

The main PL-enhancing resonance observed in all polythiophenes studied to date, including unsubstituted, 3-hexyl, and 3-dodecyl derivatives, in films and... 

In the following, results obtained for thin films prepared from unsubstituted oligothiophenes, are reviewed in detail. The influence of substituents is briefly mentioned where it is important. Results of oligothiophenes in solution and on polythiophenes are... 

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