Tuning Metastability of Poly(3-hexyl thiophene) Solutions to Enable in Situ Atomic Force Microscopy Imaging of Surface Nucleation

Molecular-level periodic arrays of long-chain poly(3-hexylthiophene-2,5-diyl) driven by an electric field

Two-dimensional (2D) periodic arrays of conductive polymers represent attractive platforms for wiring functional molecules into the integrated circuits of molecular electronics. However, the large-scale assembly of polymer periodic arrays at the molecular level faces challenges such as curling, twisting, and aggregation. Here, we assembled the periodic arrays of long-chain poly(3-hexylthiophene-2,5-diyl) (P3HT, Mw = 65 k) at the solid-liquid interface by applying an electric field, within which the charged chain segments were aligned. Atomic force microscopy (AFM) imaging revealed that individual P3HT chains assemble into monolayers featuring face-on orientation, extended chain conformation and isolated packing, which is thermodynamically more stable than folded chains in 2D polycrystals. The assembly process is initiated with the formation of disordered clusters and progresses through voltage-dependent nucleation and growth of extended-chain arrays, wherein continuous conformational adjustments along the nucleation pathway exhibit dependence on the cluster size.

Dynamics of Poly(3-hexylthiophene) Monolayers at Solution/Graphite Interfaces

We have studied the dynamics of poly(3-hexylthiophene) (P3HT) monolayers at the interfaces between highly oriented pyrolytic graphite (HOPG) and P3HT solutions in 1,2,4-trichlorobenzene, using scanning tunneling microscopy (STM). Real-time STM observation at room temperature reveals that P3HT molecules adsorbed on graphite are substantially mobile even in densely packed conditions, causing significant fluctuations of the self-organized monolayer of P3HT. We find that in the monolayers, the orientational order is limited to a short range comparable to the polymer chain length. We show that our observations can be understood based on a 2D semiflexible lattice polymer model by performing kinetic Monte Carlo simulations.

Hybrid conjugated polymer/magnetic nanoparticle composite nanofibers through cooperative non-covalent interactions

Hybrid organic-inorganic composites possessing both electronic and magnetic properties are promising materials for a wide range of applications. Controlled and ordered arrangement of the organic and inorganic components is key for synergistic cooperation toward desired functions. In this work, we report the self-assemblies of core-shell composite nanofibers from conjugated block copolymers and magnetic nanoparticles through the cooperation of orthogonal non-covalent interactions. We show that well-defined core-shell conjugated polymer nanofibers can be obtained through solvent induced self-assembly and polymer crystallization, while hydroxy and pyridine functional groups located at the shell of nanofibers can immobilize magnetic nanoparticles via hydrogen bonding and coordination interactions. These precisely arranged nanostructures possess electronic properties intrinsic to the polymers and are simultaneously responsive to external magnetic fields. We applied these composite nanofibers in organic solar cells and found that these non-covalent interactions led to controlled thin film morphologies containing uniformly dispersed nanoparticles, although high loadings of these inorganic components negatively impact device performance. Our methodology is general and can be utilized to control the spatial distribution of functionalized organic/inorganic building blocks, and the magnetic responsiveness and optoelectronic activities of these nanostructures may lead to new opportunities in energy and electronic applications.