As in many other scientific applications, photochemical reactions face challenges when scaling up to industrial volume and performance. Maximizing resources in this industry is a must while ensuring the highest quality and purification standards. Equally, understanding the scientific basis of this powerful catalysis is key to troubleshoot common issues in the photochemical field relating to yields, by-products, and waste streams.
Light has been used as a catalyst for the last two centuries, throughout which basic principles have been established, commonly known as the laws of photochemistry. These provide a strong foundation to understand the innovative and technological needs of the chemical industry today.
The first law states that light must be absorbed by a molecule in order for photochemistry to occur. This concept refers to the exclusivity of molecule-wavelength mechanisms. Light absorption is substance specific, where different molecules will absorb distinct types of wavelengths. Therefore, determining the peak wavelength for a reaction can have a great impact on efficiency.
When a molecule absorbs a UV or visible photon, its distribution of electrons surrounding the nuclei change, moving the molecule into an electronically excited state. This effect causes changes in the chemical and physical properties of the substance, which is the underlying principle of light acting as a catalyst.
The chemical industry today lacks understanding of wavelength-specific mechanisms and therefore many major photochemical reactions don’t reach their full potential. In addition, the most widespread light source used (powered by Mercury) today simultaneously emits light of different wavelengths. This not only loses productivity in the reaction but gives rise to unwanted by-products that lower yields.
With quantum theory came the second law of photochemistry, stating that only one photon of light is absorbed by each molecule undergoing a photochemical reaction. There is a one-to-one correspondence between the number of absorbed photons and the number of excited species. Being able to accurately determine the number of photons leading to a reaction allows engineers to calculate reaction yields.
Given this, power or intensity play an enormous role in an industrial scale photochemical reaction. Light sources with greater intensity increase the number of photons emitted and thus absorbed by the species, which in turn produces higher yields.
How do LEDs solve problems in the photochemical industry?
With 2 key solutions: monochromatic light and increased power.
As opposed to other sources, LEDs emit light close to the monochromatic range. With only ONE wavelength, no secondary reactions will take place, leading to ONE single product. This mechanism allows for 3-10*x yields, decreasing the cost associated with excessive raw materials or handling of undesired byproducts.Through this process, company profits exponentially increase.
*While yield increases are not guaranteed and highly dependent on the specific reaction and existing reactor system; most applications will benefit yield-wise from the use of LEDs
In addition, LEDs have proven to have the greatest power in the industry at every wavelength and have a wide variety of wavelengths available, as shown here:
Since 2019, Phoseon Technology has worked with chemical manufacturers to effectively enhance their photochemical processes through LEDs and have recently released the KeyReact™ line.