During his Ph. D. course, Dr. Sang-Kee Choi studied the synthesis of organic small molecules. He usually focused on the synthesis organic fluorescent materials, which is based on Aggregation-Induced Emission (AIE) and tetrazine click chemistry tools.  The organic molecules can understand the biological processes that can discover complex systems of biology. Fluorescent probes help to visualize the cell, protein, and even DNA that can be easy to illuminate the target molecule, monitor it, and analyze the effect of the drug or delivered molecules with it. Also, the modification of special moiety, substituent, or linker to the molecule can lead the novel applications with biological effect.  The click chemistry is having a great attention to apply on diverse area and its potential on biorthogonal chemistry. Among the click chemistry tools, he focused on synthesizing diverse tetrazine derivatives, fusing the tetrazine as a moiety, and applying on the novel linker systems to deliver specific molecules to induce click chemistry. With those skills, he wants to discover and understand the systems of biology and at the end, tries to develop novel strategies that can use in analysis and treatment of diverse diseases.