Design, synthesis, and properties of self-organizing dyes

点击翻译按钮获取中文摘要

Our research group develops new materials based on self-organizing dyes and other compounds (e.g. liquid crystals), and nanostructured materials based on polymers and nanoparticles as well as their composites. Natural and synthetic dyes are ubiquitous in our environment and new dyes with improved properties for specific technologies are constantly in demand. In this proposal we shall develop new design criteria for organic dyes that (i) self-organize into columnar stacks and (ii) form one molecule thick films (mono-layers) of defined structure. All proposed projects emphasize properties that are critical for potential applications in organic electronics, though we are aware that developments in this area have a diverse range of applications from colorants and fluorescent probes to discotic liquid crystal based high pressure lubricants. It is well established that columnar stacks of aromatic dyes function as anisotropic organic semiconductors that have achieved charge transport properties superior to presently used organic semiconductors. However, the utilization of columnar phases as organic semiconductors in electronic devices has stalled because their processing is too complex for industrially targeted low cost devices that are mainly manufactured by printing technologies. We identified the attachment of lateral side-chains, a design concept common to almost all known columnar phases, as the root cause for their main deficiencies as organic semiconductors for commercial device applications. The main objective of the first project is the development of organic semiconductors based on columnar phases that do not contain lateral side-chains. Specifically, we will target materials properties required for organic semiconductors in bulk-heterojunction organic solar cells as we believe columnar phases of dyes have some unique advantages over conventional organic semiconductors due to their self-organizing properties that should aid the formation of the required nanostructures. Fabrication and testing of solar cells will be conducted in collaboration with both academic and industrial partners. The vertical alignment of molecules between the electrodes to form columnar structures is essential for organic devices with semiconductor properties since charge conduction is only high along the columnar stacks. Yet this packing motif, which is necessary for organic light emitting and photovoltaic devices, is particularly difficult to achieve. Our second set of proposed projects directly addresses this problem through the preparation of insoluble, unimolecular dye films that exhibit flat-on orientations of the dye molecules with regard to the substrate. These films are expected to function as the first vertical alignment layer for the many columnar phases that presently cannot be aligned vertically on substrates. The proposed approaches further advance technology we recently developed on the alignment of dye molecules in thin films and their cross-linking to thermally and chemically robust films. Applications of cross-linked dyes with flat-on orientation, however, are not limited to their use as alignment layer for columnar phases. Our long term objectives include the application of these films as robust coatings for chemical and electronic modification of electrode surfaces as well as the development of 2-dimensionally conjugated films and 3-dimensionally conjugated bulk materials of dyes based on this alignment and cross-linking methodology. Especially the characterization of modified electrode surfaces, an important option for the optimization of interfaces between inorganic electrode materials and organic semiconductors, will require collaborations with expert groups and afford excellent opportunities to enhance the training of HQP.