Exploring the Chemical Doping of a Water-Soluble Cylindrical Micelle-Forming Conjugated Polyelectrolyte.

The chemical doping of water-soluble conjugated polyelectrolytes (CPEs) offers a promising pathway for the direct printing of semiconducting polymer films by using environmentally friendly solvents. In this study, we explored the chemical doping of the cationic cylindrical micelle-forming CPE poly(cyclopentadithiophene-alt-thiophene) (PCT-NBr) in aqueous solution using two Fe(III)-halide dopants, FeCl3 and FeBr3. Treatment with nonoxidizing salts (KCl and KBr) showed that polymer micelles preferentially interact with Br- ions over Cl- ions, resulting in a more rigid micelle and spectroscopic evidence of Br- ion accumulation around the polymer. Doping with both FeCl3 and FeBr3 was followed using UV-visible-near IR absorption spectroscopy, which indicated that the polymer micelles could be stably doped with both iron compounds. FeCl3 was shown to be a stronger dopant due to differences in the lability of Cl- and Br- ligands in water. Compared at similar concentrations, FeCl3 induces higher doping levels, while FeBr3 generates more delocalized charge carriers, as evidenced by spectral shifts in the polaronic bands, likely due to weaker counterion Coulombic trapping. Small-angle X-ray scattering was used to confirm that a micellar structure was preserved at all doping levels of PCT-NBr, but the data also indicate increased structural disorder in doped polymer micelles, likely due to partial loss of the polymer's amphiphilic character and ion-polymer interactions. Films spin-cast directly from FeBr3-doped polymer solutions exhibited a stable conductivity of 1.0 S/cm, demonstrating the viability of using doped micellar CPE solutions as a route to single-step deposition of conductive polymer films.