The entry of molecular species into the lattice of an electroactive polymer during its dissolution

Molecular details obtained from quantum chemical DFT calculations on 3-methylthiophene oligomers are used in a molecular dynamics (MD) investigation of the solution-interface region of the soluble polymer poly(3-alkylthiophene) in its oxidized (electroactive) form. The MD shows that the presence of the solvent interface results in conformational changes in the polymer main chains in that region from all-trans to largely cis. The entry of BF4− ions and solvent molecules (chloroform) across the interface from the solvent to the positively charged polymer is anisotropic (particularly for the ions), entry occurring most readily along the direction of the main chains. Both BF4− solute ions and CHCl3 solvent molecules occupy specific sites in the polymer, but those of the BF4− ions are the better defined. A temperature study of the incursion of the two species into the polymer shows that the entry of the ions has a small activation energy.