This course seeks to introduction students to the chemistry of the excited state and the consequences of absorption of light by molecules and extensions into the photochemistry of biological system. View in the perspective of a physical organic chemistry course, it will allow students to reasonably evaluate the reactivity of an excited state and to analyze its monomolecular fate (photophysics), as well as, its bimolecular interactions. It will also provide an understanding of principles underlying photochemical reactions such as photosynthesis, and an appreciation of light – initiated chemical processes, fluorescence, phosphorescence, and quantum yields and applications of photochemistry to organic systems.