The Photochemistry of Sunscreens.
To understand how sunscreens work, one must understand how molecules interact with light energy. Absorption of light by a molecule is associated with the part of its structure called a chromophore, which may or may not encompass the whole molecule. For organic molecules the chromophores that are responsible for the absorption of ultraviolet light are generally associated with delocalised p-electrons in conjugated systems.
Once
in the excited state the molecule has several different pathways that it can
take:
The
molecule can emit a photon and return to its ground state.
The
molecule can return to its ground state by emitting the energy thermally through
a series of vibrational transitions.
The
molecule can undergo some type of reaction from the excited state, which is
generally termed photochemistry.
The favored path will be the one which is most rapid.
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