Thesis (Ph.D.)--Hong Kong University of Science and Technology, 2005. / Includes bibliographical references. Also available in electronic version.

Thesis (M.Sc.)--City University of Hong Kong, 2004. / At head of title: City University of Hong Kong, Department of Physics and Materials Science, Master of Science in materials engineering & nanotechnology dissertation. Title from title screen (viewed on Sept. 1, 2006) Includes bibliographical references.

Thesis (M.S)--Ohio University, March, 2005. / Title from PDF t.p. Includes bibliographical references (p. 94-96)

Thesis (M.Phil.)--Hong Kong University of Science and Technology, 2007. / Includes bibliographical references. Also available in electronic version.

The photophysics and thermal properties of a series of seven novel triarylamine (TAA) dyes are described. Fluorescence characteristics have been studied in solvents of various polarities at room temperature and at 77 K. High molar extinction coefficients of the magnitude of 3.0-4.0(+/-0.50)x104 M-1cm-1 were obtained for most compounds, and relatively short radiative lifetimes were observed. Fluorescence quantum yields of the dyes at room temperature in cyclohexane were found to be between 0.34-0.57 increasing to 0.67-0.95 at 77 K. It has been shown that while at room temperature, solvent shell relaxation around the excited state can occur, and emission is from an equilibrium excited state to a twisted ground state, at 77 K in a rigid matrix environment solvent shell relaxation cannot occur and emission is from a Franck-Condon excited state to a planar ground state. The TAAs studied have excellent thermal properties for possible use in devices with thermal decomposition temperatures of greater than 300 °C, they also do not crystallise readily. Three poly (9,9-bis[N,N-(trimethylammonium)hexyl] fluorene-co-l,4-phenylene), fluorescent cationic conjugated polymers (CCP), of average chain lengths- 6, 12 and 100 repeat units, and their interaction with DNA and guanine are reported. Fluorescence microscopy and atomic force microscopy have been utilised to visualise the interaction between the polymers and DNA. Results show both efficient compaction of DNA induced by the polymer and linking and bridging of DNA/polymer aggregates. CCPs are known to aggregate in water, and for the CCPs studied here this is reflected in a decrease in fluorescence. These aggregates can be broken up by mixtures of solvents, e.g. acetonitrile/water. Steady state and ps time resolved techniques have been used to study: (i) aggregation of CCPs in various acetonitrile/water mixtures, and (ii) fluorescence quenching by single and double strand DNA, and guanine. All CCPs are extremely sensitive to quenching by DNA or guanine, with sensitivity increasing with chain length of both the CCP and DNA. Stem-Volmer plots are sigmoidal and have initial quenching rates constants far in excess of the diffusion controlled limit. The results have been analysed in terms of energy migration and trapping within and between polymer chains. Quenching seems best analysed in terms of an equilibrium in which a CCP/DNA aggregate complex is formed which brings polymer chains into close enough proximity to allow interchain excitation energy migration and quenching at aggregate or DNA base traps. We also report preliminary results of modelling time resolved data, of both the aggregation and quenching, using a kinetic model in which energy migration and trapping are represented as a series of energy transfer steps between neighbours.

Organic light-emitting diode (OLED) technology has found multitudinous applications in the development of solid-state lighting, flat-panel displays and flexible screens. Nowadays, the phosphorescent OLEDs based on metallophosphors can reach sufficiently high efficiencies for practical application. Recently, red, green and blue (RGB) platforms of highly efficient phosphorescent emitters have been achieved and OLEDs TV is now commercialized in the marketplace. However, the design and synthesis of innovative emitter materials play an important role in commercialization of the OLED technology. The basic concept of OLED is herein discussed in chapter 1 putting main focus on phosphorescent iridium(III) complexes. In chapter 2, a series of cyclometalated iridium(III) complexes containing 2-(4-benzylphenyl)pyridine have been synthesized and different electron-donating and electron-withdrawing substituents were attached on the pyridyl ring in the ligand. The device D6 doped with 8 wt% B4 gave the excellent OLED performance with a peak of external quantum efficiency (ext) of 21.4%, power efficiency (P) of 51 lm/W and current efficiencyL) of 76.3 cd/A, which is much higher than that of commercial available fac-Ir(ppy)3 under the same operation condition. These findings draw our attention to the fact that a weak electron-donating benzyl group could alleviate intermolecular aggregation in the solid state, thus improving the device performance. The bulky moiety introduced on 2-phenylpyridine through a CH2 spacer in the ligands could suppress the triplet-triplet annihilation in their metal complexes. Cylcometalating ligands and their respective metal complexes have been fully characterized by 1H and 13C NMR spectroscopy and matrix-assisted laser desorption inoization-time of flight (MALDI-TOF) mass spectrometry. In chapter 3, a series of thiazole-based iridium(III) complexes have been synthesized and characterized. It is considered that the thiazole moiety is infrequently used for organic semiconducting materials. To have a better understanding on this functional unit, different hole-transporting groups (eg, carbazole or fluorene) are attached to the thiazole ring in the cyclometalating ligands in order to tune the HOMO and LUMO levels of the complexes. Device D29 doped with 8 wt% T2 gave the highest L of 35.8 cd/A and ext of 11.1%. This result implied that thiazole moiety is an alternative option to afford a new class of cyclometalating ligands for OLED research. In chapter 4, a series of cationic iridium(III) complexes bearing diimine ligand have been synthesized and characterized. The diimine ligands were decorated with the sterically bulky groups. As self-aggregation could deteriorate the device efficiency, this molecular design strategy can diminish the aggregation-caused quenching problems, which has been supported by the aggregation-induced emission enhancement present in complexes E2 and E3. In Chapter 5, a series of bis-tridentate iridium(III) complexes have been synthesized and characterized. Our challenging is to design two types of tridentate chelates (ie. monoanionic and dianionic ligands) for balancing the charge on the metal center. Besides, these chelates should be a good cyclometallate to coordinate with the iridium metal. Four compounds with different dianionic tridentate chelates were designed to achieve distinct color emission. Compound K4 exhibited extremely high quantum yield of 85.5%. This finding revealed that the metal complex featuring two tridentate chelates is a promising phosphorescent dye in OLED. Lastly, the concluding remarks and the experimental details of all the compounds in the previous chapters were included in Chapters 6 and 7.

No description available.

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The structural design, synthesis and characterization of luminogens with aggregation-induced emission (AIE) properties are studied in this thesis. The remarkable emission properties, thermal stability and biocompatibility of the AIE-active materials demonstrate the promising applications in bioimaging and organic light-emitting diodes (OLEDs).;Chapter 1 introduces the existence of aggregation-caused quenching (ACQ) effect in most conventional organic dyes as well as phosphorescent transitional metal complexes. Discovery of AIE and its mechanical study allow further exploration of usage in organic luminescent materials. This chapter also gives some examples and the applications these AIE-active compounds.;In Chapter 2, a series of cyanostilbenes with simple electron donor (D)-p-electron acceptor (A) structure are presented and synthesized. They exhibit remarkable AIE effect as well as deep red emission peak in 95 % water fraction in THF. These results indicate that attachment of these electron acceptors provides alternative strategy for designing highly emissive AIE-active materials.;In Chapter 3, strongly emissive cyanostilbenes with phenothiazine unit are designed and synthesized. This chapter also investigates the effect of substituents in phenothiazine and terminal cyanostilbene on the photophysical properties and AIE effect. The results suggest that they are AIE-active with different sizes in nano-aggregates. Furthermore, these dyes exhibit clear and strong fluorescence in live cell imaging with excellent biocompatibility.;In Chapter 4, a series of AIE-active phosphorescent Pt(II) complexes made up of C^N^C tridentate ligands are designed and synthesized. They exhibit different morphologies and emission properties upon aggregation in 90 % water in acetonitrile although similar tridentate ligands are applied. One of the complexes in this chapter show nano-rod formation with the highest quantum efficiency in aggregated state, suggesting that rapid self-assembly process occurs to prevent non-radiative decay and oxygen quenching.;In Chapter 5, a series of bis-cyanostyryl fluorophores are designed and synthesized. They are emissive in solid state with colour range from orange to NIR region. Furthermore, they are AIE-active and some of them may contain hybridized local and charge transfer (HLCT) excited state to achieve highly efficient emission upon solvatochromic investigation. Some bis-cyanostyryl thiophenes are fabricated in OLED devices show deep-red to NIR emission, indicative of a promising way to design solid-state NIR-emissive compounds using bis-cyanostyryl derivatives.;Finally, Chapter 6 and 7 present the concluding remarks and the experimental details of the work in Chapters 2 to 5, respectively.

Vitamin D is a fat-soluble vitamin that has proven to be extremely important for human health. Vitamin D has important functions that regulate calcium and phosphate absorption from the gastrointestinal tract. The regulation of calcium and phosphorus metabolism is extremely important for the maintenance of the structural integrity of the human skeleton, neuromuscular function and a wide variety of metabolic processes. A major source of vitamin D for most children and adults if exposure to sunlight. During sun exposure 7-dehydrocholesterol in the epidermis and dermis absorb solar ultraviolet B radiation with wavelengths of 290-315nm. This results in it being converted to previtamin D. Once formed, the thermodynamically unstable previtamin D is isomerized to vitamin D. Vitamin D is then hydroxylated in the liver and the kidneys to its active form before it can act as a homeostatic regulator of calcium and phosphorus metabolism. There are certain patients who do not respond well to vitamin D supplements because they suffer from fat malabsorption syndromes such as cystic fibrosis, Crohn’s disease and ulcerative colitis. In addition, gastric bypass patients have difficulty in absorbing dietary and supplemental vitamin D. One approach for treating vitamin D deficiency in these patients is to recommend that they be exposed to artificial UVB radiation either from a tanning bed or from a Sperti vitamin D producing lamp. Novel ultraviolet emitting light emitting diodes (LED) have emerged as a promising solution because of their size, efficiency, and ability to use narrow band UV radiation. A LED has been developed to emit narrowband UVB radiation with a peak wavelength of that 295nm. This thesis provides evidence that this novel UVB-LED is able to cause the photo-conversion of 7-deyhdrocholesterol to previtamin D3 in vitro, using 7-dehydrocholesterol containing borosilicate ampoules as positive controls, as well as produce vitamin D3 in surgically obtained type II human skin. Results from this study suggest that vitamin D producing LEDs can be developed for the treatment of vitamin D deficiency, especially in patients with fat malabsorption syndromes.