Polythiophene conformation

Nilsson KPR, Rydberg J, Baltzer L, Inganas O (2003) Self-assembly of synthetic peptides control conformation and optical properties of a zwitterionic polythiophene derivative. Proc Natl Acad Sci 100 10170-10174... 

Nilsson et al. designed an experiment to test the ability of a polymer to directly detect conformational changes within peptide/protein structure [27]. Using the zwitterionic polythiophene derivative, POWT, they succeeded in detecting the distinct conformations of synthetic peptides. The mechanism was concluded to be based on the polymer side chains charged interactions and hydrogen bonding with the proteins. 

Nilsson KPR, Andersson MR, Inganas O (2002) Conformational transitions of a free amino-acid-functionalized polythiophene induced by different buffer systems. J Phys Condens Matter 14 10011-10020... 

Aslund A, Herland A, Hammarstrdm P, Nilsson KPR, Jonsson BH, Inganas O, Konradsson P (2007) Studies of luminescent conjugated polythiophene derivatives enhanced spectral discrimination of protein conformational states. Bioconjug Chem 18 1860-1868... 

Against this background of infusible conducting polymers, the development of the soluble polythiophenes is most interesting. Glass transition temperatures have been reported as 48 °C for poly(3-butylthiophene) and 145 °C for poly(3-methyl-thiophene) 261). These polymers also show crystallinity in films and can be crystallized from solution. Solution studies indicate that there are two chain conformations 262) and the availability of a non-conjugated conformation may be a key to the low transition temperatures and solubility, when compared to the stiff-chain conjugated polymers. 

The soluble polythiophenes are the first conducting polymers that can be taken above their glass transition without decomposition and it will be interesting to study morphology-property relationships. Heeger et al.262) have recently described conformational changes in solutions of poly-3-hexylthiophene which seem to involve a coil-helix transformation as the temperature is decreased or a poor solvent is added. 

Interest in the chemistry of polythiophenes has stemmed from their potential as organic conducting polymers . The simplest polythiophenes are bithienyls, which are 2 -16 ( = 0), 2,3 -32, or 3,3 -33. Furthermore, the molecules can rotate round the intermolecular C-C bond and thus each isomer can possess various conformations. 

The reversible thermochromic effect observed here and in the solid state is associated with enhanced order of the alkyl side chains with decreasing temperature, facilitating coplanar conformers in the polythiophene backbones, with the attendant enhancement in the 7t-7t -transition of the thiophene ring electronic absorption spectra and improvement in electronic conduction of the doped film. 

The colour of ICPs can also be sensitive to temperature. Substituted polythiophenes, in particular, show a marked blue shift of the highest wavelength absorption band when films or solutions are heated [7-9]. These reversible colour changes have been attributed to a twisting of the polymer backbone to a less ordered non-planar conformation. Less dramatic thermochromic effects have also been reported for polyanilines [3,10,11] where circular dichroism studies of... 

Polythiophenes 126 and 127 having chiral side groups have been synthesized, and their conformation has been studied by means of CD absorption and fluorescent spectra.214 215 For example, polymer 126... 

Grage MML, Pullerits T, Ruseckas A, Theander M, Inganas O, Sundstrom V (2001) Conformational disorder of a substituted polythiophene in solution revealed by excitation transfer. Chem Phys Lett 339( 1—2) 96—102... 

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... 

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