The quantum yield (Φ) is calculated by dividing the number of molecules that react or the amount of product formed (P) by the number of photons absorbed (n) by the sample.
$$Φ = \frac{P}{n}$$
The quantum yield can range from 0 to 1, where a quantum yield of 1 indicates that every absorbed photon results in a chemical reaction, while a quantum yield of 0 indicates that no reaction occurs despite photons being absorbed. A quantum yield greater than 1 is possible in certain cases, such as chain reactions where a single photon can initiate a series of reactions, amplifying the product formation.
Factors affecting quantum yield:
- Light intensity: Higher light intensity generally increases the quantum yield until a plateau is reached, beyond which the rate of reaction becomes limited by other factors.
- Wavelength of light: The quantum yield can be wavelength-dependent due to the specific absorption characteristics of the reactants and intermediates involved in the photochemical reaction.
- Temperature: Temperature can influence the quantum yield by altering the rates of competing reactions and the stability of intermediates.
- Presence of inhibitors or catalysts: Impurities, inhibitors, or catalysts can affect the quantum yield by interfering with the reaction pathway or altering the efficiency of photon utilization.
The quantum yield provides valuable information about the efficiency of a photochemical reaction and is used in various fields such as photochemistry, spectroscopy, and photosynthesis research to study the fundamental mechanisms and optimize the efficiency of light-driven processes.
