How can ultraviolet light produce free radicals in chemical solutions?

When solutions containing organic substances are irradiated with ultraviolet light, the molecules absorb sufficient energy to disrupt their chemical bonds. This absorption of energy leads to the homolytic cleavage of these bonds, resulting in the formation of free radicals.1

In chemistry, this process is a fundamental aspect of many photochemical reactions, which are widely considered to involve free-radical intermediates. Because these radicals are highly reactive and transient, researchers often use techniques such as flash photolysis—which employs an intense, momentary flash of light—to produce and study high concentrations of these species in solution.1

Beyond direct bond disruption, ultraviolet light can also facilitate the production of reactive species through photosensitization. In this process, a photosensitizer absorbs a photon and transfers that energy to other molecules, such as molecular oxygen, converting them into highly reactive excited states that can subsequently participate in further chemical reactions.2