Synthesis, Optical Properties, and Microstructure of a Fullerene-Terminated Poly(3-hexylthiophene)

End-functionalized, regioregular poly(3-hexylthiophene) (P3HT) was synthesized by a combination of a controlled polymerization technique and postpolymerization functionalization. Both ends of the polymer chains were terminated with fullerene units to create an internal electron accepting-donating-accepting molecule, methylfulleropyrrolidine-poly(3-hexylthiophene)-methylfulleropyrrolidine (C-60-P3HT-C-60). The molecular properties of the polymer were characterized using (HNMR)-H-1 spectroscopy, size exclusion chromatography (SEC), ultraviolet-visible (UV-vis) absorption spectroscopy, and fluorescence spectroscopy. These results show that the fullerene units are covalently bound to the polymer chain ends. Differential scanning calorimetry (DSC), wide-angle X-ray scattering (WAXS), and small-angle X-ray scattering (SAXS) were used to determine the bulk microstructure of the polymers. In addition, atomic force microscopy (AFM) was used to examine spun-cast thin films. These experiments revealed that microphase separation occurs between the main polymer chain and the fullerene end groups and suggests the creation of two distinct semicrystalline regimes in C-60-P3HT-C-60 that are similar to those seen in a compositionally similar blend of P3HT and C-60. This comparable domain formation, coupled with the possibility of enhanced charge transfer associated with an internal donor-acceptor material, makes C-60-P3HT-C-60 a promising candidate as a material in bulk heterojunction organic photovoltaics.