Photochemistry

Photochemistry is the branch of chemistry that studies the chemical reactions initiated by the absorption of light. When a molecule absorbs a photon, typically in the ultraviolet or visible spectrum, it is promoted to a higher-energy "excited state," enabling it to undergo unique chemical transformations—such as dissociation, isomerization, or reaction with other species—that would not occur in its ground state. This fundamental process is crucial to a vast array of natural and technological systems, driving everything from photosynthesis and vision to the atmospheric formation of ozone and the industrial curing of polymers.

1. Introduction to Photochemistry
   1. Definition and Scope
      1. Definition of Photochemistry
      2. Relationship to Physical Chemistry
      3. Relationship to Organic Chemistry
      4. Relationship to Biochemistry
      5. Relationship to Materials Science
      6. Interdisciplinary Nature
   2. Historical Development
      1. Early Observations of Light-Induced Reactions
      2. Discovery of Photography
      3. Grotthuss-Draper Law
      4. Stark-Einstein Law
      5. Development of Quantum Theory
      6. Modern Photochemistry Era
      7. Key Contributors and Milestones
   3. Comparison with Thermal Chemistry
      1. Energy Sources in Chemical Reactions
      2. Activation Mechanisms
      3. Reaction Pathways
      4. Product Selectivity
      5. Reaction Conditions
      6. Unique Features of Photochemical Processes
   4. Significance and Applications
      1. Role in Biological Systems
      2. Industrial Applications
      3. Environmental Processes
      4. Technological Innovations
      5. Future Prospects