Design And Synthesis Of D-π-A Organic Dyes And Their Applications To Dye-Sensitized Solar Cell And Chemical Sensor Of Metal Ions

As a novel renewable and clean solar energy conversion system, dye-sensitized solar cell (DSSC) has attracted extensive interest due to the high efficiency at low cost. D-Ï€-A type organic chromophores are increasingly applied in DSSC by virtue of their high molar extinction coefficient, easy preparation and purification, low cost, as well as their rich structures. However, the open-circuit photovoltages of organic dye-based DSSCs were generally lower than those based on ruthenium polypyridyl complexes, mainly resulting from the charge recombination. To restrict the charge recombination between the conduction band electrons and electrolyte or between the conduction band electrons and oxidized dyes, D-Ï€-A organic dyes containing either long saturated alkyl chains or multiple aromatic amine units were designed and synthesized, and their photosensitization behaviors in DSSC were studied.In the above mentioned D-Ï€-A dyes bearing long alkyl chains, the electron acceptor group (A) is rhodanine acetic acid, which contains N, O, and S atoms, and therefore had found important applications in heavy metal detection. In this work, we obtained the aggregates of such kind of dyes in DMSO/H2O mixed solvents, and compared the absorption and fluorescence spectrum responses of the monomer and the aggregates towards 10 kinds of transitional metal ions.The main results are summarized as follows.1. Six D-Ï€-A organic dye molecules (R-2, R-M-2, R-8, R-M-8, R-16, and R-M-16) bearing saturated alkyl chains of different lengths, were synthesized and applied as photosensitizers to DSSC. It was found that the longer alkyl chains may improve the open-circuit voltage. The co-sensitization by fatty acid may enhance the sensitization abilities of the photosensitizers further, and the improvement extents depended on the match between the length of the fatty acids and the size of the photosensitizers.2. Three D-Ï€-A organic dyes (C1, C2, and C3) bearing one, two, or three aromatic amine units, respectively, were synthesized and applied as photosensitizers to DSSC. It was found that C2 exhibited the highest open-circuit photovoltage among the three dyes, probably because that the hole generated in C2 upon electron injection may delocalize to the site farther away from the TiO2 surface than the case of C1. However, C3 showed the worst efficiency, most likely due to the large molecular size, which decreased remarkably the loading amount of C3 on TiO2 surface.3. The aggregates of different aggregation extent or even mode of R-16 were facilely obtained in DMSO/H2O solvent by varing the content of H2O. It was found that the monomer and the aggregates exhibited different absorption and fluorescence spectrum responses towards 10 kinds of transitional metal ions (Fe²⁺, Fe3+, Co²⁺, Ni²⁺, Zn²⁺, Cd²⁺, Hg²⁺, Cu²⁺, Ag+, Pb²⁺). The aggregate formed at high H2O content can interact with the metal ions that have no effects on R-16 monomer or R-16 aggregate obtained at low H2O content, suggesting the cooperation effect of R-16 in the aggregate.