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, ⟨P 2 ⟩ and ⟨P 4 ⟩, of the liquid-crystalline P3HT solutions. The order parameter ⟨P 2 ⟩ increased with time up to 0.35, indicating increased anisotropy. The calculated depolarization ratio (ρ v ) 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 nanothrough macroscale molecular ordering is required.

Collapse Transition‐Assisted Crystallization in P3HT Solution

“…It is widely reported that P3HT can undergo a liquid crystal (LC) transition both in the melt and in solutions at room temperature . Incorporation of liquid‐crystalline functionality would induce long‐range ordering that can be reserved and transferred into the condensed film and thus enhance the electric performance of the film greatly .…”

“…Increasing the solubilizing strength (i.e., the size and branching) of the alkyl chains may allow conjugated polymers to be fully soluble in nonpolar solvents. P3HT has shown lyotropic liquid crystallinity in chlorobenzene solutions after extensive aging, whereas the research on the order–disorder transition of P3HT and possible LC formation in toluene solution is still unclear.…”

Optical-based spectroscopic methods for measuring chemical, optical, and physical properties of thin polymer waveguide films

“…59 Other polymer waveguide applications include biological 60,61 and environmental 62,63 sensors, as well as non-plasmonic devices for Raman scattering enhancement (e.g., waveguide Raman spectroscopy). 64,65 The theory underlying optical waveguides, both irradiative and leaky, has been presented in several papers.…”

“…47,48,[57][58][59][60] Extensive work on P3HT aggregation has been reported by Grey et al 61,62 They classify P3HT films with a ratio of the peak intensities for aggregated and unaggregated chains (I1450 cm -1 /I1470 cm -1 ) greater than 1.5 as highly aggregated chains with correlated planarity and an average intrastack chain-to-chain spacing of approximately 3.8 Å. Table III presents measured parameters for the P3HT carbon-carbon double bond peak at 1450 cm -1 for films prepared in the absence of an external electric field, or with an electric field oriented in the noted directions.…”

Exploitation of Self‐Assembly Phenomena in Liquid‐Crystalline Polymer Phases for Obtaining Multifunctional Materials

“…Very recently, Kleinhenz et al demonstrated that poly(3-hexylthiophene) in trichlorobenzene solution is able to self-assemble and shows liquid crystal ordering when confined to rectangular capillaries [29]. UV-Vis spectroscopy clearly indicated that the relative proportion of poly(3-hexylthiophene) assemblies increases with time; in addition, polarized optical microscopy measurements demonstrated the development of birefringence and monodomain like long-range ordering within the assembled structures.…”