Two-photon absorption is the process in which a molecule absorbs two photons simultaneously. The two key advantages of two-photon processes over one-photon processes are the possibility of excitation of materials with high three-dimensional spatial resolution and deep light-penetration into absorbing materials. Based on bond-cleavage reactions activated by photon-induced intramolecular electron transfer, two-photon activatable acid and radical initiators and two-photon removable protecting groups have been successfully designed and synthesized for photopolymerization and three-dimensional microfabrication and for biomedical photo-triggers. The optical and chemical properties of synthesized molecules, such as quantum yield of acid generation, initiation efficiency of photopolymerization, and photolysis efficiency, have been studied by using a variety of physical and analytical techniques under one-photon conditions. The two-photon characteristics and applications of these molecules are being investigated in collaboration with other groups.