Inhaltszusammenfassung

In this thesis, small molecule organic semiconductors (SMOS) containing electron donor and acceptor moieties have been designed as metal-free, visible light-active and stable photocatalysts for organic transformation reactions as a promising alternative to the traditional transition metal complexes. First, a general structural design principle of the small molecule organic semiconductor-based photocatalysts has been established following crucial requirements: (i) visible light absorpti...In this thesis, small molecule organic semiconductors (SMOS) containing electron donor and acceptor moieties have been designed as metal-free, visible light-active and stable photocatalysts for organic transformation reactions as a promising alternative to the traditional transition metal complexes. First, a general structural design principle of the small molecule organic semiconductor-based photocatalysts has been established following crucial requirements: (i) visible light absorption; (ii)sufficient photoredox potential; (iii) long lifetime of photogenerated excitons. Using a C-H functionalization reaction between electron-rich heteroaromates and malonate derivatives as the model reaction, the structural design principle of the SMOSs was demonstrated.A mechanistic study focusing on the variation of the photoredox potential of the catalysts and sacrificial reagents was conducted. It could be demonstrated that the catalytic efficiency of the small molecule organic semiconductor were absolutely comparable with the state-of-the-art photocatalytic systems consisting of transition metal complexes. Second, an important issue for photo-redox reactions, i.e. the mandatory use of electron donating sacrificial reagents, has been addressed. Here, a new conceptual study using a double photocatalyst system made of cooperative organic semiconductor couples was conducted. By the cooperative photocatalyst design, an extra intermolecular electron transfer could occur between the OSs, leading to enhanced photo-generated electron/hole separation and thereby more stable reductive and oxidative species which can give out one electron to the diethyl bromomalonate or get one electron back from the intermediate directly.The C-H functionalization reaction between electron-rich heteroaromates and malonate derivatives can be conducted successfully without triphenylamine as sacrificial reagent. Advanced photophysical studies illustrate the excitons separation process between OS couples in a direct way. Precisely tuning the energy levels of the photocatalysts will improve the excitons separation process, further influence the reaction rate. Aromatic carbon-carbon bond formation reactions could be successfully conducted via the reductive dehalogenation of various aryl halides by a designed OS with a high reduction potential of -2.04 V vs. SCE. An additional study for light-controlled atom transfer radical polymerization using organic semiconductor photocatalysts was carried out. The living nature of the polymerization process was confirmed by the controllable growth of the molecular weight in a light “on-off” cycle, successful synthesis of the chain extension anddi-block copolymer and the defined molecular weight distribution of the polymer chain.» weiterlesen» einklappen

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DDC Sachgruppe:
Chemie