Organic electronics have potential for low cost manufacturing based on the possibility of solution-processing deposition methods, such as inkjet or screen printing, and large-scale roll-to-roll processing. In order to realize these advantages, it is necessary to control the self-assembly behavior of organic materials in solution in order to influence solid state properties. Poly(3-hexylthiophene), (P3HT) is considered a model semiconducting material and has been widely studied for organic photovoltaic and transistor applications. To explore controlled solution-based self-assembly, two end-functionalized P3HT derivatives have been synthesized. The two end-groups were chosen to have different chemical functionalities, one hydrophobic and the other hydrophilic. The chemical properties of the end-group are shown to influence the polymer aggregation size in solutions of varying polarity.
Well-defined P3HT was synthesized via Kumada-coupling living polymerization such that a protected alkyne was introduced to the end of every polymer chain. End-functionalization was confirmed by 1HNMR spectroscopy and MALDI-TOF. After deprotection, azide derivatives of phenyl-C61-butyric acid methyl ester (PCBM) and sulforhodamine 101 dye were attached to the chain end of P3HT via azide-alkyne Huisgen cycloaddition to produce P3HT-C60 and P3HT-Dye respectfully. Characterization with UV-Vis absorption and dynamic light scattering elucidates the influence of the end-group on aggregation properties. From the dynamic light scattering data, we find that as the solvent polarity increases, the hydrodynamic radius of P3HT-C60 is greater than that of P3HT whereas the hydrodynamic radius of P3HT-Dye is smaller. This data, combined with differences in the absorption spectra, show the influence of the end-group on polymer aggregate size in methanol-containing solutions.