The concept of "aggregation-induced emission" (AIE) effect has induced a great deal of attention these days. Now, exploration of new AIE-active molecular system and multiple high technique applications for AIE materials are the two research hotspots. Cyanostilbene, as a classical structural unit in photoelectric functional materials, also exhibited this unique luminescence behavior. The research background was illustrated in Chapter 1, which mainly introduced the development of this subject. In this project, Chapter 2 and Chapter 3 presented two classes of functionalized AIE-active molecules based on cyanostilbene moiety, and their applications were investigated, while Chapter 4 demonstrated a series of donor-acceptor (D-A) molecules with highly emissive unit, and their photophysical properties were studied.;In Chapter 2, four different donor-substituted cyanostilbene-based dipyrrins were synthesized and characterized. The investigation of photophysical properties confirms that these molecules are AIE-active, which should be attributed to the cyanostilbene moiety. The introduction of different donor groups showed little impact on their luminescence. Furthermore, the emission properties of these molecules were found to be sensitive to Zn2+, that is, addition of Zn2+ enormously enhanced its fluorescence in THF. The titration experiments proved they showed good selectivity and sensitivity for Zn2+ detection with relatively low limit of detection. Job's curve and spectral studies of their corresponding zinc complex indicated that the ratio for dipyrrins and Zn2+ is 2:1, which suggested the formation of zinc complex by chelation-enhanced fluorescence (CHEF) effect should be the reason of the enhanced fluorescence. By combining dipyrrin with typical AIE-active moiety tetraphenylethylene (TPE), an AIE-active TPE-based dipyrrin was prepared. The studies of its fluorogenic Zn2+ detection confirmed that the CHEF effect together with AIE effect are responsible for the intense fluorescence, indicating the potential application as a Zn2+ detector in aqueous media.;In Chapter 3, the cyanostilbene backbone was functionalized with a terpyridine unit to construct four terpyridine-based cyanostilbene molecules with different donor substitutents. The investigation of their photophysical properties confirms that they are AIEE-active. With the effect of different electron-donating groups, their solid-state fluorescence color was adjusted from blue to orange-red successfully. According to the calculation results of their frontier molecular orbitals, terpyridine has little impacts on their luminescence, but would influence their solid-state emission obviously owing to its large steric hindrance. This class of molecules displayed higher luminescence efficiency in solid state than in their dissolved state. The twisted molecular conformation in single crystal, which effectively avoids close π-π stacking, was assumed to be responsible for the high luminescence efficiency in solid state. This kind of molecules show distinct switched fluorescence by stimuli of acid/base vapors, and this phenomenon derives from the protonation effect of nitrogen atoms in the terpyridine unit. Moreover, three of these molecules exhibit good electroluminescence properties. Especially, the crystal of non-donor substituted molecule show amplified spontaneous emission (ASE) properties, indicating this blue-emissive material can be used in multiple areas such as chemical sensor, organic light emitting diodes (OLEDs) and organic laser media.

No description available.

No description available.

No description available.

No description available.

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

The overall goal of this research is to characterize the potential-dependent structure and composition of the alcohol-Ag electrochemical interface. The approach involves the use of a variety of electrochemical and spectroscopic tools to arrive at a consistent model for a series of straight-chain alcohols (methanol, ethanol, 1-propanol, and 1-pentanol) at Ag electrodes. There are essentially four areas of investigation presented in this dissertation. The first portion of this work has been directed at the development of charge coupled device detection in Raman spectroscopy so that many of the interface investigations could be performed. The advantages and limitations of these detectors in Raman spectroscopy are addressed. The second area involves the characterization of in-situ alcohol-Ag electrochemical interfaces using Raman spectroscopy and associated surface selection rules for the evaluation of solvent orientation and bonding. Since the series of alcohols offers a systematic variation in solvent properties, these studies provide substantial insight regarding some of the chemical interactions which can dictate orientation. The development of emersed electrode technologies is also presented as a means to improve selectivity for surface molecular species over bulk molecular species. The utility of this approach is demonstrated for a variety of straight-chain alcohols at both rough and smooth Ag electrodes. Conditions for emersing the molecular interface, intact, under potential control are presented. Finally, double layer capacitance measurements are performed to offer additional insight regarding alcohol solvent structure and interfacial composition as a function of electrode potential. In addition, capacitance-potential plots are used along with the Hurwitz-Parsons analysis to determine absolute surface coverage of Br⁻ as a function of electrode potential. These results are correlated with the Raman spectroscopic results to obtain a consistent model for the structure and composition of the alcohol-Ag electrochemical interface.

No description available.

A dissertation submitted to the Faculty of Engineering, University of the Witwatersrand, in fulfillment of the requirements for the degree of Mastel' of Science in Engineering Johannesburg 1998 / Impala's Minerals Processing Plant in the Rustenburg Area, South Africa, uses flotation to beneficiate precious metal bearing ores from the Bushveld Complex. Pyrrhotite is one of the sulphide minerals that is targeted but it is the least amenable to current flotation conditions having the lowest recovery. Electrochemical techniques (mixed potential measurements, cyclic voltammetry and current transient techniques) were used to study the relevant reactions on the surface of pyrrhotite mineral electrodes. Aspects investigated included the oxidation of the mineral in aqueous alkaline solutions, activation by copper sulphate, kinetics of oxygen reduction and the adsorption of isobutyl xanthate. Mixed potential measurements of mineral electrodes were taken in batch flotation test work. In addition a novel qualitative measure of hydrophobicity was investigated. The oxidised surface of pyrrhotite is likely to be covered with iron hydroxides and a sulphur rich sub-lattice. No direct evidence was found for the activation of pyrrhotite by copper sulphate in alkaline solutions. It was shown however that activation could be achieved in mildly acidic media and that the surface remained activated if subsequently exposed to alkaline conditions. When achieved under acidic conditions activation was observed to enhance the degree of interaction between the mineral and the xanthate collector. Also copper sulphate appeared to aid the formation of a more hydrophobic surface (as indicated by the hydrophobicity tests). Copper activation conducted in acidic media did not significantly enhance the kinetics of oxygen reduction, a reaction seen as crucial to the adsorption of xanthate. No evidence was found for the initial chemisorption of xanthate onto the mineral surface. However evidence was found for the oxidation of xanthate to dixanthogen at sufficiently anodic potentials. It Was concluded that the relatively poor flotation performance of pyrrhotite could be combated by minimising the extent of the oxidation, adding reagents as soon as possible before the mineral becomes extensively oxidised and by removing surface hydroxides through lowering the pH during conditioning. / MT2017