Photochemistry is the branch of chemistry that studies chemical reactions and processes caused by light (usually ultraviolet, visible, or infrared radiation).
In simple terms, it explains what happens to molecules when they absorb light energy — how their electrons get excited, how bonds break or form, and how entirely new substances can be created.
Key Points about Photochemistry:
- Basis: It deals with the interaction of photons (light particles) with atoms and molecules.
- Principle: Light provides energy to start reactions that may not occur under normal conditions.
- Processes:
- Excitation of electrons to higher energy levels.
- Bond breaking or bond formation.
- Emission of light (fluorescence, phosphorescence).
- Examples in Nature:
- Photosynthesis in plants (light → glucose + oxygen).
- Vitamin D formation in skin under sunlight.
- Vision in the human eye (light triggers changes in retinal molecules).
- Applications:
- Photography (silver halide reactions).
- Solar cells (light absorption for energy conversion).
- Lasers and optical devices.
- Environmental chemistry (formation of photochemical smog).
- Medicine (photodynamic therapy).
In short: Photochemistry is the science of how light energy drives chemical change, with huge importance in nature, technology, and daily life.