| Abstract |
The utilization of solar energy is an issue that has always concerned mankind. The beneficial effect of the Sun has been recognized for thousands of years, with humans developing even more imaginative and functional mechanisms over the centuries to benefit from it. However, the ever-increasing energy demands of human society make the need to find modern and efficient methods of harvesting solar energy imperative. According to extensive research, the energy that the Sun offers to the Earth is not only inexhaustible, but also particularly powerful, as it is sufficient to exclusively cover the energy demand required for the daily activities of the entire planet. In an attempt to invent ways to produce energy from renewable sources, the research community is actively engaged in exploiting incident solar radiation. Attempts to convert solar energy into other, readily usable forms, the most prevalent of which are electrical and chemical energy, have proven to be particularly attractive. The immediate link between light and electricity are photovoltaic devices, which are setups capable of converting solar radiation directly into electrical current. Significant progress has been made in the field of manufacturing such devices, but the high cost remains an obstacle to their mass use. In recent years, considerable emphasis has been placed on the construction of Dye-Sensitized Solar Cells (DSSCs), in which a chromophore entity is added, responsible for the easier capture of sunlight. A second and equally useful process is to use the Sun as a springboard to carry out reactions that lead to the formation of substances that are capable of being stored and releasing energy, such as fuels. The overall process is called "photocatalysis" and involves the conversion of solar energy into chemical energy. Molecular hydrogen (H2) is in full agreement with this description, as it can be produced by photocatalytic reduction of water, the most abundant compound on the planet. In photocatalysis, a dye-containing system is involved in order to capture the solar photons. In the present Master Thesis, the design, synthesis and characterization of systems based on pigments, which can be used in the two applications mentioned above, are presented. Porphyrin derivatives were chosen as chromophores in both cases, due to their significant ability to absorb visible light. The first part of this work deals with the synthesis of porphyrins for study in DSSC-type photovoltaic cells. Three new porphyrin derivatives were successfully synthesized, which were differentiated by the existence of electron-donating or -accepting groups, with one of them bearing no functional groups, so that their power conversion efficiency could be compared and a pattern regarding the effect of the substituents could be determined. Although fundamental physicochemical tests were performed on the final products, photovoltaic measurements are still ongoing. In the second and final part of this research, the aim is the development of molecular photocatalysts for H2 evolution. More specifically, the successful synthesis of a dinuclear complex of molybdenum(II) (catalyst) and a series of three porphyrins (photosensitizers) was confirmed, in order to construct catalyst-photosensitizer catalyst triads and test their ability to produce H2. A few basic photocatalytic studies were performed on one of the three systems designed, providing encouraging results but requiring further investigation.
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