Photochemistry is the study of chemical reactions involving light energy. This field investigates how light drives chemical transformations, focusing on the absorption of photons and the subsequent energy transfer and electron excitation that initiate chemical change. Key processes include photooxidation, photoisomerization, and photochemical reactions, which are fundamental to understanding natural systems like photosynthesis and the mechanisms of light-sensitive biological molecules. The principles of photochemistry are applied across various disciplines, leading to the development of advanced photodynamic therapies in medicine and novel materials for solar energy capture and data storage.