Directed assembly of optoelectronically active alkyl-<i>π</i>-conjugated molecules by adding <i>n</i>-alkanes or <i>π</i>-conjugated species

Supramolecular assembly can yield ordered structures by taking advantage of the cumulative effect of multiple non-covalent interactions between adjacent molecules. The thermodynamic origin of many self-assembled structures in water is the balance between the hydrophilic and hydrophobic segments of the molecule. Here, we show that this approach can be generalized to use solvophobic and solvophilic segments of fully hydrophobic alkylated fullerene molecules. Addition of n-alkanes results in their assembly--due to the antipathy of C60 towards n-alkanes--into micelles and hexagonally packed gel-fibres containing insulated C60 nanowires. The addition of pristine C60 instead directs the assembly into lamellar mesophases by increasing the proportion of π-conjugated material in the mixture. The assembled structures contain a large fraction of optoelectronically active material and exhibit comparably high photoconductivities. This method is shown to be applicable to several alkyl-π-conjugated molecules, and can be used to construct organized functional materials with π-conjugated sections

Engineering the Multi-Length Scale Structure of Self-Assembled Conjugated Polymer Networks

Thesis (Ph.D.)--University of Washington, 2014Conjugated polymers are a Nobel Prize winning class of materials known for their intrinsic semi-conducting properties and have been used in applications as diverse as organic-based solar cells, transistors, light emitting diodes, sensors and thermoelectric devices. These applications have varying, but optimized, structure and property requirements which often include an interconnected network of conjugated polymers to transport charge. In this work, self-assembly and gelation are explored as a platform to engineer the multi-length scale structure of conjugated polymer networks. A detailed understanding is developed through structural characterization of each stage of the self-assembly process: dissolved polymer, semi-crystalline fiber, fibrillar branching and percolated network formation. Variations in self-assembly conditions were utilized to develop multi-length scale structure-property relationships. Furthermore, a new method to directly incorporate these fibrillar network structures into thin films for organic electronics is discussed. This dissertation will demonstrate our work towards understanding the mechanisms behind conjugated polymer self-assembly in order to provide robust design parameters that can be tuned to generate specific structures, occurring on multiple length scales, and relevant properties for a diversity of applications

Electrical, Mechanical, and Structural Characterization of Self-Assembly in Poly(3-hexylthiophene) Organogel Networks

An electrically percolated network structure of conjugated polymers is critical to the development of organic electronics. Herein, we investigate the potential to rationally design an interconnected network of conjugated polymers using the gelation of poly­(3-hexylthiophene) (P3HT) as a model system. The three-dimensional network structure is evaluated through small-angle neutron scattering (SANS) and ultrasmall-angle neutron scattering (USANS). The analytical models used for data fitting provide relevant structural parameters over multiple length scales. Structural parameters include the fiber cross section (height and width), the specific surface area, and the network density (i.e., fractal dimension). Simultaneous rheological and conductivity measurements also provide insight into the development of the mechanical and electrical properties of organogels and allow us to propose a detailed gelation mechanism for P3HT. The fiber shape is found to be relatively independent of the solvent type, but P3HT organogels show distinct differences in conductivity, which can be directly linked to differences in the branching network structures. These results suggest that the gelation of fiber-forming conjugated polymers offers an excellent platform for designing electrically percolated networks that can be used for structural optimization in organic electronic devices