| Improvements in organic electronic materials could lead to novel device applications, ranging from large-area, flexible displays to light weight, plastic electronics. Progress on these applications would benefit from development of low-cost, aqueous, solution-based fabrication techniques for organic semiconductors. Supramolecular self-assembly enables molecules to organize in complex structures through non-covalent interactions. The nanoscale structure and aggregation of organic semiconductors influence conductivity, charge mobility and luminescence. We developed three approaches to enhance the performance of organic semiconductors through molecular self-assembly. The first uses a liquid crystalline (LC) template to mediate electrochemical polymerization of poly(3,4-ethyldioxythiophene) (PEDOT), a conducting polymer used for hole injection in organic light emitting diodes (OLED). Monomers were polymerized in the cylindrical, hydrophobic cores of a hexagonal, lyotropic LC formed by a non-ionic amphiphile in water, The templated, conducting polymer films exhibited anisotropic optical properties and increased conductivity as a direct result of the nanoscale, self-organized structure of the template. Another approach was used to control molecular order by preparing organic semiconductors that are themselves liquid crystalline. We developed a novel series of triblock oligo(phenylene vinylene) (OPV) amphiphiles that form thermotropic and lyotropic LC mesophases. The self-organized, layered structure of these mesophases influences aggregation of OPV, enhancing fluorescence in the liquid crystalline state compared with disordered films. These OPV-amphiphiles are the first example of a water-soluble oligo(phenylene vinylene) that can self-organize into aligned, well-ordered, highly fluorescent films. In a third system, a triblock, dendron rod-coil (DRC) molecule containing a quaterthiophene segment was prepared and its self-assembly and electronic properties investigated. In non-polar solvents, this molecule formed high aspect ratio, supramolecular nanowires containing stacked oligo(thiophene) segments. These self-assembled nanowires formed conductive films that were aligned by an electric field. Using these three systems, we demonstrate how nanoscale templating and self-assembly can enhance the performance of thiophene- and phenylene vinylene-based organic semiconductors. |
