Polythiophenes anisotropy

Synthesis, Characterization and Properties of Regioregular Polythiophene-based Materials 191 2.6.5 Anisotropy... 

The conductivities parallel to the rubbing direction (a//) increased by 5-15-fold compared with those of random orientation and the ratios of parallel to perpendicular conductivities (polythiophene derivatives show fiuorescence in the range 530-540 nm. This suggests that they might be useful for novel luminescent materials with optical anisotropy when they are macroscopically aligned. 

Note that /// and I are perpendicular and parallel to the main chain, respectively. The aligned films exhibit a linear dichroism in the fluorescence band around 550 nm due to the uniaxially aligned polythiophene chain, giving a dichroic ratio (/ ////) of 3.8. The iodine-doped aligned Aims exhibited an anisotropy of about 8 in electrical conductivity, although the absolute value of the conductivity was very low, e.g. of the order of 10 -10 Scm ... 

The most attractive feature of a-6T and a-8T crystals is undoubtedly the access that they provide to optical dichroism (absorption and luminescence) and charge transport anisotropy (carrier mobility) so that comparison can be made with what is currently observed in polycrystalline thin films and disordered polythiophenes. Beside a-6T and a-8T, a few studies have also been done on doped Q -4T(Q -Me)2 single crystals. 

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