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Research and development of fluorescence sensing properties of cholesteric modified OPE derivative films

Author: CuiHong
Tutor: FangYu
School: Shaanxi Normal University
Course: Physical and chemical
Keywords: Conjugated polymers Fluorescence sensing Cholic acid Cholesterol Self-assembling
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Type: Master's thesis
Year: 2013
Downloads: 8
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Abstract

Human’s life and security have been seriously threatened by environmental pollution, terrorism and food safety for the recent decades, with the development of science and technology. Thus, there is an enormous demand for developing high sensitive and efficient detection techniques. In comparison, film sensors have a large amount of advantages in terms of reversibility and reproducibility, no pollution to the detecting system and device implementation available. Additionally, fluorescent methods offer advantages in terms of high sensitivity and selectivity and particularly the multiple readout signals (e.g., spectra profile, fluorescence intensity, intensity ratio, lifetime, anisotropy, etc.). The development of fluorescent film sensors has been increasingly captivating the attention of scientists for many years. The conjugated polymers (CPs) have attracted increasing attention in the detection area due to their so-called "molecule wire effect" and "super-quenching effect". Conjugated polymers (CPs) have received a lot of attentions being a neoteric sensing element,which is used to manufacture and develop different kinds of chemical sensors. CPs processes several amount of advantageous, such as:high molar extinction coefficient (≥106M-1cm-1) and high fluorescent quantity, which is a very important factor as the sensing elements.In addition, the "molecular wire effecf" is another advantage. Moreover, fabrication of the fimls with this kind of compound possess good light stability and high detection sensitivity, which can be used in medical diagnosis, genetic testing, environmental monitoring, etc.On the basis of the introduction about the research progress on fluorescent sensing film based on cojugated polymer in Chapter One, we combine the advantages of Self-assembled Monolayer technique and the signal amplification effect of conjugated polymers to develop a new way to create novel fluorescent films.On the above disscusion and the research progress in our lab, cholic acid and cholesterol, the building blocks for supramolecular chemistry, were deliberately introduced as side chains to oligo(ρ-phenyleneethynylene)s (OPEs) separately, and be a core structure to design and fabricate two films sensors.In Chapter Two, a monolayer chemistry-based fluorescent film was created by chemical attachment of a cholic acid modified conjugated oligomer (CholA-OPE), onto a glass plate surface. Fluorescence studies revealed that the emission of the film is sensitive to the presence of trace amount of some inorganic acids in acetone, such as HCl, H2SO4, HNO3and H3PO4, etc. The quenching, however, has been attributed to the protonation of the imino groups next to the OPE units. The sensitivity of the emission of the film to the presence of HCl and the aerobic acids in acetone seems to be a combined result of the selective binding of the film to the compounds and proton transfer from the compounds to the imino groups within the OPE adlayer. A model was proposed to explain the sensing performances of the CholA-OPE functionalized film. This performance has been rationalized by considering presence or absence of a possible cavity, a substructure appearing above the OPE adlayer which is something like a dimmer of cholic acid formed at specific environment. The work as reported here shows again that introduction of side groups with special structures or properties to conjugated polymers/oligomers is a simple but effective way to create novel mono-layer chemistry-based fluorescent sensing films.In Chapter Three, the poly(pyrene-co-phenyleneethynylene) with cholesterol in its side chains was synthesised by copolymerization. And then the polymer had been casted onto the glass plate surfaces, which was chemically fabricated by cholesterol beforehand, to fabricate film, named film1. Film2was obtained in the same way, merely without any modification of the surface onto the glass substrate in advance. Fluorescence studies revealed that the emission of the film1is sensitive to the presence of trace amount of PYX in water, while film2had no obvious response. The difference should be a result of the high surface-area-to-volume ratio of nanoparticles, which containing the pendent cholesterol groups create the large cavity in polymer traps the analyte molecules that effectively cause fluorescence quenched.

Research and development of fluorescence sensing properties of cholesteric modified OPE derivative films

Abstract

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