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| Research Domain：Materials for Nonlinear Optical Applications |
Country：[CN] |
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Current trends suggest that light, rather than electricity, will increasingly be used in the area of information technology, with potential in optical communications, data storage and computer systems. Although materials being studied are diverse, they are usually "off-the-shelf" compounds selected by the physicists and engineers active in this area, so that there are many areas in which chemists can make important contributions by rational synthesis of designed candidate molecules for the optical technology industry.
Materials whose optical properties depend on the intensity of the incident light are termed non-linear optical (NLO) materials. Organic compounds that are asymmetrically polarizable e.g. through conjugated p systems, have been shown to produce large NLO responses. We are interested in both organic and organometallic materials. Organometallic complexes combine the advantage of organic materials (fast NLO responses) with the design flexibility of inorganic complexes (variation in oxidation state, coordination number, coordination geometry, and co-ligands, and intense MLCT transitions). Initial work has focussed on metal acetylide complexes. These are usually thermally robust and oxidatively stable, and accessible in high yields by well-established synthetic methodologies. We have systematically varied molecular components in order to derive structure-NLO property relationships to facilitate organometallic NLO materials design and produced complexes have the largest quadratic and cubic nonlinearities for organometallic complexes thus far.
These studies have utilized hyper-Rayleigh scattering and electric field-induced second harmonic generation (experimental molecular quadratic nonlinearities), semi-empirical ZINDO (computational molecular quadratic nonlinearities), Kurtz powder (bulk second-order susceptibilities), and degenerate four-wave mixing and Z-scan (molecular cubic nonlinearities) measurements.
Our ongoing studies are involved with extending these small molecule-based studies into the macromolecular realm to afford useful and processable materials. There has been an explosion of interest in dendrimers (hyperbranched oligomers) recently, with the current move to prepare functional dendritic materials. We are currently investigating the NLO properties of arylalkynyl metal-based dendrimers with a variety of core units, branching groups and spacers. For example, our Ru9 species pictured has been shown to have the largest cubic nonlinearity for an organometallic complex thus far.
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| Research Domain：Our current research involves two areas of interest, both related to materials with potential use in optical technology: |
Country：[CN] |
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Nanotechnology has been recognized as a priority area of research world-wide, and has been defined as "the creation and utilization of functional materials, devices and systems with novel properties and functions that are achieved through the control of matter atom by atom, molecule by molecule or at the macromolecular level." (National Science Foundation, USA)
Dendrimers are hyperbranched nanomolecules prepared by sequential addition of simple branched monomer building blocks to a central core. Their step-wise synthesis allows the preparation of precise chemical structures which can be easily and systematically varied to manipulate their physical properties. Dendritic molecules have been shown to mimic the bioactivity of enzymes and proteins, or to produce previously unknown or significantly improved physical and chemical properties, compared to traditional linear polymers. As a consequence, dendrimers are considered to be one of the prime building blocks for the construction of nanoscale objects, molecular devices, advanced drug-delivery systems, etc.
We are looking at oligomeric and dendritic assemblies with potential in nonlinear optical applications for emerging photonics technologies.
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Materials based on incorporating metal complexes into processable organic-based polymeric backbones i.e. metallic polymers. These materials have potential as "optical limiters", affording optical device protection which is of potential use in both laboratory and military applications.
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| Research Domain：Single Molecule Electroluminescence. |
Country：[CN] |
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We have created the first electroluminescent single molecules/nanoclusters at room temperature. The discrete energy levels of these 2-20 atom nanoclusters yield molecular emission with color being indicative of nanocluter size. Employing negative differential resistance-like behavior in the EL, we have created single molecule LEDs, single nanocluster logic gates, and even a full adder constructed from only two nanoclusters. We are currently studying the charge injection into different nanoclusters to characterize the interfaces crucial to all nanoscale/molecular electronics and optoelectonics devices |
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| Research Domain：Molecules in Polymeric Environments |
Country：[CN] |
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Single molecules in polymeric matrices exhibit surprising rotational mobility and spectral dynamics. Since each molecule interacts slightly differently with its surroundings, great diversity is observed in molecular behaviors. Photophysical properties of individual dyes are used to probe both random and enclosed structures to provide a better understanding of polymeric systems. |
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| Research Domain：Single Molecule Biophysics |
Country：[CN] |
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Having observed orientation-dependent interactions of fluorescently labeled single proteins, precise studies of biological mechanisms are performed. Unfortunately, standard fluorescent labels are often unsuitable for long-time single molecule imaging, especially in living systems. Thus, in order to make single molecule methods moreaccessible, we are developing Au and Ag nanoclusters as a new class of fluorescent labels in biology. These high brightness, robust nanomaterials should enable direct labeling of proteins to image live cells, study protein-protein interactions, and potentially watch individual proteins as they fold to their native conformations. Au and Ag nanoclusters exhibit discrete excitation and emission due to being composed of only a few atoms. Consequently, with size-tunable optical properties and absoprtion comparable to semiconductor quantum dots, but with improved photstability, these nanoclusters offer new opportunities in biological labeling. For, example, the extremely small size will be less invasive, noble metals are not toxic, and their discrete energy levels enable energy transfer experiments to be performed, all with weak mercury lamp illumination on the single molecule level. Much brighter and more robust than organic dye molecules, these advanced inorganic nano-materials are being utilized both as optical memory elements and as photo-activated biological labels. |
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| Research Domain：Molecular and cellular analysis of the aquaporin water channels |
Country：[CN] |
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Water is the most abundant component of all living organisms, however cells and tissues are remarkably different in their ability to absorb or release water. Water selective channels had long been suspected to provide rapid water permeation of certain tissues, however the molecular identity of these membrane proteins remained unknown until the serendipitous discovery of Aquaporin-1 by young scientists in our lab. Based upon this, efforts of several research laboratories around the world have now defined more than 200 different aquaporins in tissues from mammals, invertebrates, microorganisms, and plants. Current research in our laboratory is devoted to the structural and functional characterization of aquaporins from humans, bacteria, and yeast. For example, we are studying the anion conductance which we recently discovered in an intracellular aquaporin. We are also studying aquaporin gene regulation, and we are searching for disease phenotypes which may result from mutations or perturbation of specific aquaporins--a list which now includes diseases ranging from renal concentration defect, loss of a major blood group antigen, cataracts, renal tubular acidosis, Sjogrens syndrome, and brain edema. Collaborative efforts with laboratories in Denmark and Switzerland are yielding the details of tissue and developmental expression of aquaporins as well as the high resolution structure of several mammalian and microbial aquaporins.
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| Research Domain：Generalized kinetic sorption model in natural wate |
Country：[CN] |
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Many previous kinetic sorption models for natural waters treat a sorption reaction as a first order, reversible reaction. In fact chemical reaction cannot be regarded as the sole rate-limiting step since various diffusion steps could be much slower than the former steps. We have recently proposed a “generalized kinetic sorption model”, which may describe complex sorption processes when sorption is controlled by liquid film diffusion, chemical reaction, intra-particle diffusion and shell progressive diffusion (Pan, G, 1999). None of the previous models (numerical models) with less than 4 empirical parameters can describe the ‘two phase’ kinetic sorption behavior typically found in natural waters/sediments. With the generalized kinetic sorption model (analytical equation), it is possible to describe the two-phase kinetic sorption behavior with only two parameters. The generalized model can also cover many existing equations in textbooks and literatures.
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| Research Domain：Phosphorus geochemistry in marine and fresh waters |
Country：[CN] |
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Nutrient limitation is one of the core topics in biogeochemistry in natural waters. More than 70% of the world’s fresh waters are P limited, while only very few seawater, such as East Mediterranean, are P limited. Little is known why East Med. is P limited and why there is such contrast biogeochemical behavior between fresh and sea waters. We have recently develop a new phosphate sorption-desorption model from MEA hypothesis which can explain many of the environmental questions that would be otherwise impossible in the past (Environ. Sci. & Technol., 36, 3519). |
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| Research Domain：Re-define the concept of chemical equilibrium cons |
Country：[CN] |
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Partition coefficient (Kd) is one of the basic parameters used in geochemistry and environmental chemistry. However, there is strong evidence that significant misleading environment assessment can be made based on the conventional method of Kd. This project is to establish a new method/parameter, based on the MEA hypothesis, to replace the current practice of Kd in environmental assessment, geochemistry and environmental chemistry. Large number of experiments simulating various environmental conditions (metals, nutrients, organic pollutants in fresh/sea waters, aerobic/anaerobic sediments and soils) will be used to experimentally map the ‘inconstancy problem’ of Kd in different systems and to verify whether the problem can be systematically solved by the new methodology. |
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| Research Domain：. Toxic algal blooms/eutrophication controls in co |
Country：[CN] |
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The method is to use a cost-effective clay-microorganism powder (environmental friendly) to sink algal cells (by flocculation) and dissolved toxins and nutrients (by adsorption) down to the bottom sea/lake. In addition to the technical side, we are also studying the biogeochemical effects of the method on the circulation of P, N, Fe, Mn, O2 and CO2 in the waters and/or across the sediment as well as air-sea interfaces. |
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