A Zero-Background Fluorescent Probe For Hg²⁺ Designed Via The "Covalent-Assembly" Principle And Research On Properties Of The Coumarin Fluorescent Dyes With Large Hindrance Steric

There are two parts in my dissertation:Part 1,The detection of ions and neutral small molecules by fluorescent probes has an important applications in biomedical and environmental sciences. With respect to sensitivity, a very important parameter of probe, low background signal greatly facilitates the sensitive detection of a weak fluorescence signal, therefore "turn-off" and "turn-on" probes are highly desired in research. Especially the "off-on" probes has superior sensitivity with reducing of the fluorescence intensity of unreacted probe. "Covalent-assembly" is such a principle that warrants a zero background signal and represents a viable addition to the field of fluorescent probe development. Detection of Hg2+ is necessary in consideration of its’high toxicity on central nervous system and endocrine system, and the detection with fluorescent probe is more convenient and efficient. In this manuscript, we have developed a novel fluorescent probe (Hg57O) for Hg2+ via the "covalent-assembly" principle. Presence of Hg2+ triggers a cascade, which ultimately furnishes a push-pull backbone of Pyrinin B which contains a highly absorbing and emitting. The probe has outstanding advantages on low limitation of detection, low cytotoxicity and good metal selectivity. In addition, Hg570 can quantitatively react with the substrates, to achieve a significant signal changes from colorless to pink. On the other hand, because probe Hg570 possesses no charged functionalities, so it is easier to pass through the cell membrane.Part 2, Chemical stability and light stability of dye is closely related to the practical application potential. The skeleton of push-pull electronics dye always contains either positive or some negative charges alternately, therefore the dye can react with nucleophiles and electrophilics, which will destroy the chemical stability of dye. Meanwhile, when extending the light exposure time, the dye will degrade irreversibly. This process is also known as photobleaching and will destroy the light stability of dye. Aggregation of dye based on π-π stacking always result in fluorescence quenching. So the enhancing of the stability and the prevention of aggregation is of great significant for the fluorescent dyes. To improve the steric hindrance,which can reduce the chance of the photobleaching and the chance of fluorescent dye interacts with other substrates. This can improve the chemical stability, we have developed a method which is introducing large steric hindrance groups into the dye skeleton. In this manuscript, we have synthesized some coumarin fluorescent dyes with some simple alkanes (-Mc-Et、-Pr、-Bu) and determined the fluorescence quantum yield and molar extinction coefficient of these compounds, futher tests about other properties are still on the way.