Highly ordered structures of amphiphilic polythiophenes in aqueous media

Aqueous dispersions of a regioregular polythiophene, bearing enantiomerically pure oligo(ethylene oxide) side chains, are obtained by injecting small volumes of a THF solution of the polymer into water. The interplay of hydrophilic and hydrophobic interactions accounts for the unprecedented formation of hexagonal platelets, as well as other aggregates. Electron microscopy and selected area electron diffraction revealed that the platelets show diffraction patterns typical for single crystals. The relative amount of these highly ordered structures reaches 30% of all aggregates, in case of dispersions containing 10% (v/v) of THF in water. The effect of the organic solvent in controlling the formation of highly ordered assemblies is also investigated by means of UV-vis spectroscopy, where the occurrence of main chain organization gives rise to a distinct red-shifted absorption band. In the fluorescence spectra, the same situation accounts for quenching of the emission located at higher wavelengths with respect to the one in pure THF. The chiral information in the side chain is expressed at the supramolecular level in the highly ordered states, as revealed by CD spectroscopy. Notably, the intensity of the bisignated Cotton effect reaches its maximum at 10% (v/v) of THF, which coincides with the highest amount of single crystals in TEM. Thermochromic experiments show high thermal stability of the chiral assemblies in water.