| With the increasing of global pollution, the issue of environment has been a matter of great concern during the past few years. As a common polluting gas, Hydrogen Chloride (HCl) has a serious galvanising impact on eyes and respiratory mucosa. Exposing to concentrated HCl vapor for a long time can cause chronic bronchitis, gastrointestinal dysfunction or tooth acid corrosion, etc. In addition, plants also have limited endurance capacity for HCl vapor. Once exceeding the critical concentration, the cells and tissues of plants will be damaged. Furthermore, concentrated HCl vapor in air may also result in acid rain, which can cause acidification of soil, corrosion of construction and so on. In conclusion, the accurate detection of HCl vapor in air is extremely urgent. High purity reagents have been widely used in laboratory and industry. The key process to produce high purity reagents is dehydration. Therefore, the detection of the trace amount of water in organic solvents is of great importance. Nomatter the detection of HCl vapor in air or a trace amount of water in organic solvents, various methods have been developd. Fluorescence methods possess a number of advantages among all the approaches, such as great sensitivity, high selectivity, reference-free, and abundant signals, etc. Compared to low molecular-mass compounds, conjugated polymers (CPs) possess several superior features:(1) high molar extinction coefficient (106 M-1cm-1), (2) the backbone of CPs enabling the rapid propagation of an exciton throughout the individual polymer chain, which is the so-called "molecular wire effect", (3) super-fast photo induced electron transfer or energy transfer between CPs and analytes (in several hundred femtoseconds), which leads to "super-quenching effect". Hence the potential of CPs based fluorescent sensors is great.Based on the discussions above and research progress in our lab, cholesterol, which is a natural compound, and is a commonly used unit for creation of supramolecular building blocks due to its rigid skeleton, several sterogenic centers, and the strong tendency to form aggregates via van der Waals interactions, was deliberately introduced to the side chains of 1,4-bis(phenylethynyl)benzene (OPE). The resulting compound was taken as a core structure to design and derive two fluorescent sensors. Specifically, three charpters were listed in this dissertation.In charpter one, the design idea and detection mechanism of fluorescent sensors were presented. Also, the state of the art of fluorescent sensors especially OPE-based fluorescent sensors was summarized.In charpter two, a OPE derivative (C2) with two cholesteryl residues in the side chains and two glucono units in the head and tail positions was designed and synthesized. As a control, compound C1 was also prepared. The only difference between C1 and C2 is that the hydroxyl groups in the glucono residues of C1 are fully acetylated. Studies of the fluorescence behaviors of the two compounds in solution revealed that both the profile and the intensity of the fluorescence emission of the compounds, in particular C2, are dependent on the concentration of them and on the nature of solvents employed. Presence of HCl also alters the emission of the compounds in solution. Based on the studies, three fluorescent films were prepared, and their sensing performances to HCl in vapor state were studied. Specifically, Film 1 and Film 3 were fabricated via physical coating, separately, of C2 and C1 on glass plate surfaces. As another comparison, Film 2 was also fabricated with C2 as a fluorophore but at a much lower concentration if compared to that for the preparation of Film 1. As revealed by SEM and fluorescent microscopy studies, Film 1 and Film 2 exhibit well-defined microstructures, which are spherical particles and spherical pores, respectively, while Film 3 is characterized by irregular aggregates of C1. Fluorescence measurements demonstrated that Film 1 and Film 3 both display an aggregation emission, of which the emission from Film 1 is supersensitive to the presence of HCl vapor (Detection Limit: 0.4 ppb, a lowest value reported in the literatures). For Film 3, however, its emission is insensitive to the presence of the vapor. Similarly, the emission from the non-aggregated state of C2, a characteristic emission of Film 2, is also insensitive to the presence of the vapor. Furthermore, the sensing process of Film 1 to the vapor is highly selective and fully reversible, which lays foundation for its real-life uses. As for C2 studied, the results from solution studies and those from film studies demonstrate clearly that introduction of auxiliary structures with opposite properties onto a typical fluorophore is a good strategy to develop fluorescent supramolecular motifs with rich assembly prOPErties and great potential of applications.In chapter three, a OPE derivative modified with both cholesterol and nitrobenzoxadiazole (NBD) was designed and synthesized. In the design, OPE and NBD were specially chosen as an energy donor and an acceptor, respectively. Fluorescence studies revealed that fluorescence energy transfer did take place from OPE to NBD. Solvent effect study demonstrated that the efficiency of fluorescence energy transfer varies from the polarity of solvents employed. Furthermore, the fluorescence emission of the compound is sensitive to the trace amount of water in some organic solvents, especially 1,4-dioxane. Further studies are in progress. |
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