Design And Synthesis Of Organic Dyes And Their Applications In Dye-Sensitized Solar Cells And Colorimetric Chemodosimeter

As a new type of solar-to-electricity conversion system, dye-sensitized solar cells (DSSCs) based on mesoporous TiO2 electrodes have attracted extensive interest. While ruthenium polypyridyl complexes still represent the most efficient sensitizers so far, metal-free organic chromophores are increasingly applied in DSSCs by virtue of their high molar extinction coefficient, easy preparation, low cost, as well as their rich structures. The rich structures lead to diverse photophysical, photochemical, and electrochemical properties, which stimulate the continuous exploration of new types of organic dye molecules for DSSC application.The low-molecular mass aminothiols, including cysteine, homocysteine, cysteine-glycine, and glutathione, play important roles in biological systems. Cyanide ion is one of the most toxic inorganic anions one can find, but cyanide or hydrogen cyanide are used in many industries. Thus, their colorimetric and fluorescent chemosensors have been the focus of numerous research efforts.In this dissertation, four new azulene-based and one oligothiophene-based organic photosensitizers for DSSCs, and one near-infrared croconium dye-based colorimetric chemodosimeter for biological thiols and cyanide anion were designed and synthesized. The detailed results are summarized as follows:1. Four new azulene-based dye molecules were synthesized and their photoelectrochemical properties were studied in DSSCs. All of them exhibit, in the visible region, a strong absorption band coming from the S0–S2 transition and a very weak band coming from the S0–S1 transition, and the transition assignments are supported by theoretical calculations using time-dependent density functional theory (TD-DFT) at the B3LYP/6-31G* level. In sensitization of DSSCs, reducing their adsorption amount on the TiO2 surface (by co-adsorption with deoxycholic acid) mitigates dye aggregation and improves their photoelectric conversion efficiency greatly. Also, extending the conjugated side chain not only shifts their photoelectric response to longer wavelengths and therefore enhances the short-circuit photocurrent, but also increases the open-circuit photovoltage significantly. Moreover, it was found that the electron injection efficiencies varied remarkably with excitation wavelength, suggesting direct electron injection from the S2 state of these dye molecules.2. An electron-withdrawing group, 2-cyano-2-carboxyl-vinyl, was attached onto the 5 position of 2,2':5',2"-terthiophene and the photophysical and the photoelectrochemical properties of the resultant compound, 3T-CCV, was studied. Density functional theory (DFT) calculation confirms the efficient intramolecular charge separation of 3T-CCV upon excitation. Under irradiation of simulated sun light (AM1.5, 70 mW cm-2), 3T-CCV based dye-sensitized solar cell presented an overall photoelectric conversion efficiency of 3.25%.3. A croconium dye, CR-1, was utilized as a colorimetric chemodosimeter for nucleophiles, which exhibits responses in both visible and NIR regions. In aqueous ethanol solutions buffered at pH 5.7, CR-1 selectively probe the presence of cysteine, homocysteine, and cysteine-glycine. In aqueous ethanol solutions buffered at pH 9.0, CR-1 can also be used to selectively detect the cyanide anion over other common anions when other nucleophilic molecules such as thiols are not present. Besides the response in NIR region, CR-1 also shows higher sensitivity than the corresponding squarylium dye, SQ-1, in the same solution and at the same pH.