Synthesis And Characterization Of Fluorescent Sensors For Palladium Ions Detection

In the last decades, fluorescent sensors have been widely utilized as popular tools to monitor environment pollution, such as mercury ions and lead ions. However, along with the rapid advancement of technology, new type of pollutants begins to appear in environmental water, and the toxicity of pollutants hasn’t been fully recognized. As a result, design and develop a new fluorescent sensor for new type of pollutants such as palladium ions is crucial for evaluation of environment and human health. Today, palladium as a transition metal lies in its wide spectrum of applications, such as in the electrical and electronic industries, dental appliances, fuel cells, jewelry, and catalysts. Palladium is predominantly used as oxidizing reagents and pre-catalysts for many cross-coupling reactions in organic chemistry. A large number of organic reactions, such as Heck, Sonogashira, and Suzuki-Miyaura reactions are usually performed by palladium or platinum catalysts, leading to the formation of carbon-carbon bonds and they play a significant role in medicinal chemistry. Palladium is capable of eliciting a series of cytotoxic effects which may cause severe primary skin and eye irritations. Platinum can also cause DNA alterations, cancers, autoimmune disorders, respiratory, hearing problems, and damages to organs, such as the intestine, kidney, and bone marrow. In view of potential biotoxicity, the recommendations from the European Agency for the Evaluation of Medicinal Products (EMEA) for the allowable level account for a specification that palladium metals must below the limit suggested (5ppm for oral dosage forms). Conventional analytical methods can be used for the detection of palladium in environmental samples. However, these methods often require sophisticated and time-consuming sample preparation procedures or expensive equipments. Fluorescent chemosensor methods for detecting palladium are expected to be more desirable because they exhibit more advantages, such as relatively easier and cheaper, less labor-intensive, and highly sensitive. Therefore, design of new fluorescent sensor for palladium detection is urgently desired for human health and the environmental pollution protection. This dissertation includes four parts as follows:1. Synthesis and characterization of a fluorescent polymer P-1containing2,6-bis(2-thienyl) pyridine moieties as a highly efficient sensor for Pd2+detection. The UV-Vis absorbance and fluorescence spectra have been investigated in THF. A selective chromogenic behavior towards Pd2+can be observed by naked eye. The absorbance at426nm is linearly proportional to the amount of Pd2+in the range of1μM-100μM. Pd2+ion can effectively quench the fluorescence of the polymer with an excellent selectivity. The polymer sensor possesses an excellent selectivity. The transitional metal ions such as Hg2+and Ag+almost don’t cause any fluorescence quench of the polymer. The Stern-Volmer data of polymer sensor demonstrates that polymer possesses the desired much higher sensitivity than small molecules due to signal amplification effect. All the results demonstrate the polymer sensor can be used as an efficient sensor with a high sensitivity and an excellent selectivity for Pd2+detection, and has potential applications in the human health and environmental protection.2. Three conjugated polymers P-A, P-B and P-C have been designed and successfully synthesized via Sonogashira coupling reaction. The Polymers formation was confirmed both by GPC, NMR spectrum, and elemental analyses. The fluorescence quenching degrees of the three polymers P-A, P-B and P-C upon the addition of transition metal ions have been investigated. It was found that the fluorescence intensity of P-A obviously decreased upon the addition of Pd2+or Pt4+ions, the other metal salts have negligible or virtually no effect on the fluorescence of P-A. Moreover, the fluorescence quenching degree of P-A for Pd2+is very close to Pt4+, and this provides a potential way to detect the total amount of Pd2+and Pt4+ions regardless of their ratio. P-B exhibits different selectivity for palladium and platinum ions. It’s attributed to that the more restricted thiophene group in TPP units of P-B and the different coordination spaces constituted by polymer chains lead to different sensing properties P-C exhibits almost no response to all the transition metal ions detected due to the steric hindrance effect from two meta-linked benzene groups can’t provide any coordination points to bind metal ions.The UV-Vis absorbance and fluorescence spectra of P-A have been investigated and the results showed that the polymer displays a highly selective chromogenic behavior towards Pd2+and Pt4+ions, which can be observed with the naked eye. And meanwhile, Pd2+and Pt4+ion can effectively quench the fluorescence of the polymer with an excellent selectivity. When binding to Pd2+or Pt4+, an approximately80%reduction of the fluorescence intensity was observed with a detection limit of1×10-6M in aqueous solution.The mechanism of fluorescent quenching and the interaction fashion between metal ions and TPP units of polymer chains has been discussed. The fluorescence anisotropy proved that interchain binding-induced aggregation is the major reason causing the fluorescence quenching. Through demonstrating the feasibility of varying the polymer structures to match the molecular spatial dimension for controlling the metal ion selectivity, this work provided an amplified fluorescence assay based on aggregation-induced fluorescence quenching mechanism for detection of the sum of palladium and platinum ions in aqueous medium.3. We designed and synthesized a chemical reaction-based ratiometric ESIPT fluorescent sensor POF specific for palladium species with a large Stokes’shift of more than150nm. The results demonstrate that sensor POF exhibits a high sensitivity and an excellent selectivity for Pd2+detection in aqueous solution, whose detection limit can be down to～87nM (15.4ppb). Moreover, the ratios of the fluorescent intensities are linearly proportional to the amount of PdCl2from0to30μM. Obvious ratiometric responses are observed towards all the oxidation states of palladium among other transition metal ions without additional reagents. This work provides a new mild and promising strategy for the detection of Pd species in biological and environmental systems.4. We utilized a simple dosimeter array, consisting of three fluorescent dosimeters POF, AOF, and HF, to successfully achieve the detection and discrimination of palladium species by using pattern recognition analysis. AOF showed great sensitivity and selectivity towards all the oxidation states of palladium species, whose detection limit can be down to10nM. We calculated the chromaticity of dosimeters POF, AOF and HF via CIE1931chromaticity diagram towards different palladium species, and the color change in a column was unique pattern. This is the first time the fluorescence dosimeter array has been used for discrimination of palladium species. It offers a convenient and efficient example for the other metal ion analysis. The successful recognition and detection of various palladium species is particularly important for human health and the environmental safety.