The research in my group is focused on the design and synthesis of novel organic functional materials targeting a broad range of environmental, energy and biological applications, such as gas separation/storage (e.g., carbon capture), hybrid nanocomposite fabrication, light harvesting, and nanomedicine. Our efforts in developing novel materials frequently lead us to explore new synthetic tools, particularly in the area of dynamic covalent chemistry (DCC) (e.g., metathesis reactions), which enable efficient materials synthesis.
SHAPE-PERSISTENT 2-D AND 3-D MOLECULAR ARCHITECTURES
In recent years, there has been intense interest in organic shape-persistent molecular architectures, including 2D macrocycles and 3D cages, which have been playing important roles in nanomaterials and nanotechnology development. Conventionally, these rigid molecules are mainly prepared via irreversible cross-coupling reactions, which are under kinetic control and usually provide very low yields of target compounds. Our group has successfully applied thermodynamically controlled, dynamic covalent chemistry (DCC) to the synthesis of various 2-D and 3-D molecules. In our approach, provided a large energy gap between the target species and other possible products, DCC is capable of generating the desired molecular architecture in high yield from readily available simple building blocks. DCC is one of the main synthetic tools in my group, and we are developing novel dynamic covalent reactions and catalysts that would enable fast reversible covalent bond formation.
ORGANIC POROUS MATERIALS
Recently, organic porous materials have rapidly emerged as promising materials for gas storage/separation. These new materials are composed of only relatively light elements (e.g. C, H, B, N, O) that are connected by strong covalent bonds, offering great thermal and chemical stability. To date, preparation of these porous materials has generally focused on synthesizing amorphous organic polymers with non-ordered structures or densely packed polymers having crystalline structures. However, these approaches usually yield insoluble polymers, and solution-processable porous materials for certain applications (e.g., membrane fabrication for gas separation) have not yet been realized. In this project, we have explored well-defined, shape-persistent, 3-D organic molecules (prepared through highly efficient DCC) as soluble organic porous materials for gas adsorption and separation. Our group also developed "cage-to-framewok" strategy to construct novel organic porous materials using well-defined 3-D cages as building blocks. Our "cage-to-framework" strategy would enable efficient encoding of both dimensional (pore size/distribution) and functional information (guest recognition, sensing, catalysis, etc.) within the individual cage molecule into the final frameworks, enabling control over their pore size/distribution and chemical nature of the surface area.
Covalent network polymers, which offer robust mechanical properties, generally lack the ability to be recycled. There has been a great deal of research effort to incorporate reversible cross-links into network polymers in order to obtain mechanically tough materials with self-healing properties. Our group is interested in developing covalent network polymers with silica-like malleability by introducing dynamic covalent bonds into the polymer backbone and crosslinks. Recently, our group developed the first malleable network polymer which can be reprocessed by application of either heat or water. This inexpensive, catalyst-free network polymer can be recycled from a fine powder to a strong polymeric structure of any shape by simple molding using heat or water. This represents an ideal system for do-it-yourself prototyping of cross-linked polymeric solids, which will retain intrinsic value as the polymer can easily be recycled.
NANOMATERIALS FOR BIOMEDICAL RESEARCH
Nanomedicine has been emerging as an active and promising research area with emphasis on exploiting the unique properties of nanomaterials for therapeutics and targeted drug delivery. In searching for nanocages that are compatible with biological systems, we discovered a subset of COPs that are fluorescent and enter mammalian cells efficiently. In this project, we aim to develop novel nanohybrid materials using 3D shape-persistent organic molecular cages that can potentially be translated clinically for non-invasive delivery of therapeutic agents, diagnostics imaging and testing the efficacy of targeted therapeutic agents in vitro and in vivo.