Thiophene dendrons and dendrimers: Design, synthesis, and characterization.

摘要

Oligothiophenes have been considered as very promising materials for applications in organic and molecular electronics. On the other hand, dendrimers have emerged as one of the most interesting materials because of their potential applications in materials and life science. This dissertation details the design, synthesis, and applications of the thiophene dendrimers, a new class of dendrimers based on oligothiophenes. Two unique features of these thiophene dendrimers are (1) a very broad and strong absorption in the UV region, a feature particularly suited to light-harvesting purposes; (2) supramolecular self-assembly into regular 2D structures and one-dimensional nanowires. Based on these two features, a series of thiophene dendrons and dendrimers were designed and synthesized for potential applications in catalysis, light-harvesting, and supramolecular assembly.; First, two different approaches to use thiophene dendrons in the synthesis of nanoparticles for catalytic applications were demonstrated. Thiophene dendrons were used to functionalize the periphery of poly (amido amine) dendrimer generation 4 (PAMAM G4), and the resulting functionalized dendrimer was used as template for the synthesis of Cu, Au, and Pd nanoparticles. Very uniform aggregates of Pd hybrid nanoparticles were obtained for potential electrocatalytic applications in fuel cells. Also, thiophene dendrons were functionalized at the focal points with alkanethiols and then were used directly, in contrast to the indirect use in the first approach, for the synthesis of Au nanoparticles. Energy transfer from thiophene dendrons to the gold nanoparticle core was studied for potential applications as optoelectronic devices.; Then, a series of thiophene dendrons and dendrimers with terminal functional groups were designed and synthesized because the absence of terminal functional groups has limited the applications of thiophene dendrons and dendrimers. Two more synthetic methodologies of using these thiophene dendrons and dendrimers with terminal groups as important building blocks and scaffolds were demonstrated.; Finally, two light-harvesting systems were designed based on two important photosynthetic model systems: ruthenium polypyridines and porphyrins. Ruthenium polypyridine thiophene dendritic complexes showed a unique photophysical property: fluorescence in the near IR region. On the other hand, porphyrin thiophene dendrimers were found to form both H- and J-aggregates in organic solution, very unusual behavior for typical water-insoluble free base porphyrins.