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Poly(3-hexylthiophene)(P3HT) in trichlorobenzene solution self-assemblesand exhibits liquid crystal ordering when confined to rectangularcapillaries. The relative proportion of polymer assemblies increaseswith time, as determined by UV–vis spectroscopic analysis.Polarized optical microscopy (POM) reveals development of birefringenceand monodomainlike long-range ordering. Micro-Raman spectroscopy wasused to calculate the orientational order parameters, ⟨P2⟩ and ⟨P4⟩, of the liquid-crystallineP3HT solutions. The order parameter ⟨P2⟩increased with time up to 0.35, indicating increased anisotropy. Thecalculated depolarization ratio (ρv) from depolarizeddynamic light scattering measurements points to the time-dependentformation of highly ordered P3HT nanostructures, whereas cryogenictransmission electron microscopy was employed for the direct visualizationof the rodlike assemblies. POM shows that the observed anisotropycan be preserved in P3HT films drawn from aged solutions. These resultssuggest that P3HT self-assembly leads to a liquid-crystalline solutionof conjugated polymer aggregates, which may lead to a viable approachfor optimization of processes for organic electronic device applications.Such ordered and oriented conjugated polymer assemblies have manydesirable attributes for high-performance device applications, wherethe ability to control nano- through macroscale molecular orderingis required. [ABSTRACT FROM AUTHOR]

We report here on our investigations of structure−property correlations in soluble organic semiconductors. To develop formulations for mass printing of semiconductor films, a series of alkoxy- and alkyl- disubstituted symmetric phenylene thiophene co-oligomers (disubstituted-PTTP) were systematically synthesized to achieve high solubility in common organic solvents. Solubilities of up to 40% by weight in tetrahydrofuran at room temperature were achieved by introducing branching at various positions on the terminal chains, and by silyloxy or hydroxy functionalization of the chains. Concomitant with the solubility increase, however, mobilities and Ion/Ioffratios of these materials in TFT devices fall several orders of magnitude. X-ray diffraction of the semiconductor films reveals increasing tilt of the molecular orientation on the substrate with an increase in steric crowding near the PTTP core. This indicates that -stacking of these molecules along the channel between the source and drain is hampered and leads to the observed inverse interdependence of solubility and the field effect mobility. [ABSTRACT FROM AUTHOR]