Molecular Design And Synthesis Of Metal-Free Organic Sensitizers For The Application Of Solar Energy Conversion

Hydrogen generation from water under solar irradiation includes homogeneous and heterogeneous catalytic systems, and is regarded as one of the Holy Grails of 21 st century chemistry, being one route to a fuel that is not derived from fossil fuels and a potential source of clean and renewable energy to satisfy the rising global energy.DSSCs, often known as Gratzel cells, have garnered significant attention as promising low-cost alternatives for the photovoltaic conversion of solar energy. A crucial issue in solar hydrogen production and DSSC design is the choice of photosensitizers used to capture the solar energy. Complexes of ruthenium and other noble metals(Ir, Pt) as light absorbers remain dominant in the most successful systems. However, noble-metal complexes are rare and expensive, limiting their practical application.As an alternative to noble-metal complexes, organic dyes are becoming more and more attractive due to many advantages, such as diversity of molecule structures,high extinction coefficients leading to great light harvesting abilities, simple synthesis as well as low cost and environmental issues. However, organic dyes have been examined as optical absorbers in the conversion of solar energy on a limited basis.Thus, the search for new, highly efficient based-organic dyes remains an active aspect of solar hydrogen generation and DSSC development.In this paper, A series of boron dipyrromethene(BODIPY) dyes(B1-B9) were synthesized and characterized. These organic dyes were applied for investigating the relationship between the BODIPY structure and the effectiveness of homogeneous and heterogeneous visible-light-driven hydrogen production as well as dye-sensitized solar cells(DSSCs). For the homogeneous photocatalytic hydrogen production systems, Under the best optimized conditions, B5 containing two I atoms and an ortho-COOH anchoring group was the most active one(TONs = 197). A reductive quenching pathway in the photochemically driven step is possible for the hydrogen production, as evaluated from the electrochemical and photophysical data as well as theoretical calculations. For the heterogeneous hydrogen production systems, B3 having two core iodine atoms and a para-COOH group with TONs of 70 excelledother BODIPYs. In the case of DSSCs, The B1-Ti O2 system showed the best cell performance. The differences between dye-sensitized hydrogen-generating systems and DSSCs may be due to rates of electron transfer and the dye aggregation tendency.In the meanwhile, a novel metal-free D-π-A-π-A based organic photosensitizer D2 featuring carbazole as donor residue and benzothiadiazole and cyanoacrylic acid residues as acceptor units has been synthesized and applied to the development of solar energy conversion. Compared with the traditional D-π-A photosensitizer D1, the D-π-A-π-A photosensitizer D2 exhibits improved stability and efficiency in light-to-electricity(η = 3.50% vs 1.14%) and light-to-fuel conversion(TON = 1450 vs 100) via increased light capture and effective charge transfer.