Selective anion-induced helical aggregation of chiral amphiphilic polythiophenes with isothiouronium-appended pendants

An optically active isothiouronium-attached polythiophene 1 poly has been prepared for the first time by oxidative polymerisation of (S)-3-(3-(N-(2-(2-methoxyethoxy)ethyl)-N-(1-phenylethyl)-S-isothiouronio)propoxy)-4-methylthiophene 1 with FeCl3. The analysis carried out using gel-permeation chromatography allows us to estimate the number average molecular weight (M n ) and the polydispersity index as 5.53 × 105 and 1.4, respectively. Although the polymer showed an absorption band at 420 nm with circular dichroism (CD) silence in H2O–MeOH (1:1, v/v) at 25°C, the addition of anions as a chemical stimulus was found to cause not only a bathochromic shift but also a split-type-induced CD (ICD) in the π–π* transition region. This phenomenon is anion selective; the most enhanced ICD spectra were obtained when hydrophobic anions such as were added to the solution. As inferred from field emission-scanning electron microscopy observation, the anion-ICD spectra arose from chiral aggregation of the polymer, which was effected by solvophobic effect via the exchange with hydrophobic anions at isothiouronium pendants. Solvent polarity and temperature dependencies on the chirality induction were investigated, the obtained results suggested that the dynamic helical aggregation of the polythiophene backbone is based on planar interchain interactions.