-Abstract- The selective transformation of ubiquitous but inert C-H bonds (C-H activation) not only represents an important and long-standing goal in chemistry, but also has far-reaching practical implications. We believe that such a C-H activation enterprise is extremely important as it will not only streamline the state-of-the-art synthesis of useful molecules, but also unlocks opportunities for markedly different strategy in the construction of organic molecules. For example, C-H activation allows rapid synthesis and identification of bio-functional molecules. More recently, rapid and site-selective π-extension by C-H activation has emerged as an ideal methodology for preparing organic π-materials and molecular nanocarbons. In this talk, I will introduce some of our recent C-H activation catalysts and their applications to develop new small molecules that can control plant growth and mammalian biological clocks. The applications toward developing new nanocarbon materials will be also presented.