Self-organized supramolecules of π-conjugated rodlike polymers

This thesis concerns fundamental self-organized aspects in π-conjugated polymers. Self-organization is the central issue in nanotechnology of soft condensed matter. The thesis focuses on the design and control of supramolecular hairy-rodlike molecules which are characterized by a thermotropic and preferentially aligned nanoscale structure. The major emphasis is on polypyridine, polyaniline, and polyfluorene. Because of their rodlike chain the formation of supramolecules is nontrivial. The understanding of the structure-property relations of this class of materials is vital in the development of organic high-performance opto-electronic devices. Throughout this work, synchrotron radiation and X-ray diffraction techniques have been extensively used and combined with the photophysical methods. In the first part, the ways to form hierarchic, highly ordered, and aligned lamellar smectic supramolecules of poly(2,5-pyridinediyl) complexed with dodecylbenzenesulfonic, methanesulfonic or camphorsulfonic acid and pentyl- or hexylresorcinol, octyl gallate, or octyl phenol have been developed and perfected. They have been characterized in the solution, in bulk and – in particular – in aligned films. Several new phases have been discovered and detailed structural description is given. When side groups are introduced microphase separated phases reveal a regular axial repeat but have different degrees of lateral packing regularity between molecules, varying from crystalline to liquid. Depending on composition they exhibit an order-order and then an order-disorder transition to isotropic phase. Liquid crystallinity allows facile overall alignment and results in the opto-electronic anisotropy as revealed by dichroism and polarized photoluminescence. In particular, it is shown that the hierarchic supramolecular structure of poly(2,5-pyridinediyl), camphorsulfonic acid and octyl phenol comprises of a higher level head-to-head structure of polymer and lower lamellae, stacked, and monomer related structure levels in normal, equatorial, and meridional directions, respectively. By choosing the exact components and tuning the composition a coherence length as high as 800 Å along the smectic axis has been achieved. By contrast to covalent side chains, the supramolecular side chains can be cleaved from the aligned materials, which render aligned pristine polymer and high photoluminescence quantum yield of pure polymer. The structure and phase equilibria have been designed between theory and experiment. The compilation of the results has been presented as a phase diagram in the melt state in the high polymer fraction limit. The study shows that the recent theoretical model highlights the most important mechanisms responsible for the observed phenomena and gives trends in which direction the developed system has to be adjusted to achieve the desired effects. In the second part, the thickness dependent triaxial texturing in poly(9,9-bis(2-ethylhexyl)-fluorene-2,7-diyl) thin film on the rubbed polyimide has been identified, when thermotropic alignment has been applied. The polymer is 5/2 helix as proposed by Lieser and coworkers. It has three chain unit cell and the hexagonal-like cells of helical polymers are flattened in the direction of the surface normal and reveal two kinds of coexistent crystallites, a multiple orientation, where the greater proportion of the crystallites have a crystal axis a perpendicular to the substrate surface and where a smaller proportion is aligned with the crystal axis a parallel to the surface. This has been found to depend on the temperature and the film thickness. The overview shows a selection of unpublished results, reviews the trends in the supramolecular science discusses and reviews widely the characterization methods. In addition, a selection of further clarifications of the publications is reported. An unambigous experiment showing a hexagonal (cylindrical) supramolecular hairy-rodlike structure of polyaniline complexed with camphorsulfonic acid and hexylresorcinol is presented. A comb-shaped supramolecule of poly(4-vinylpyridine) complexed with methanesulfonic acid and octyl gallate is found to form a white lamellar self-organized structure. Characteristics in the fluid state are discussed.reviewe