Liquid Crystalline Poly(3-hexylthiophene) Solutions Revisited: Role of Time-Dependent Self-Assembly

Abstract

Poly(3-hexylthiophene) (P3HT) in trichlorobenzene solution self-assembles and exhibits liquid crystal ordering when confined to rectangular capillaries. The relative proportion of polymer assemblies increases with time, as determined by UV–vis spectroscopic analysis. Polarized optical microscopy (POM) reveals development of birefringence and monodomainlike long-range ordering. Micro-Raman spectroscopy was used to calculate the orientational order parameters, ⟨P2⟩ and ⟨P4⟩, of the liquid-crystalline P3HT solutions. The order parameter ⟨P2⟩ increased with time up to 0.35, indicating increased anisotropy. The calculated depolarization ratio (ρv) from depolarized dynamic light scattering measurements points to the time-dependent formation of highly ordered P3HT nanostructures, whereas cryogenic transmission electron microscopy was employed for the direct visualization of the rodlike assemblies. POM shows that the observed anisotropy can be preserved in P3HT films drawn from aged solutions. These results suggest that P3HT self-assembly leads to a liquid-crystalline solution of conjugated polymer aggregates, which may lead to a viable approach for optimization of processes for organic electronic device applications. Such ordered and oriented conjugated polymer assemblies have many desirable attributes for high-performance device applications, where the ability to control nano- through macroscale molecular ordering is required.