Biochemistry - Chemical Reactions in Living Cells, Volume 3 - D. Metzler 1980

Light in Biology
Fluorescence and Phosphorescence
Triplet States

One of the pathways for removing singlet excitation is intersystem crossing, As a result of which the molecule transitions into a triplet state. Since Selection rules forbid transitions between the excited triplet and the ground singlet states, the lifetime of the triplet state turns out to be quite long. Partly for this reason, photochemical reactions predominantly involve molecules that are specifically in the excited triplet state. The unusually high reactivity of molecules in the triplet state is also due to its biradical character. Despite the prohibition, a radiationless transition from the excited triplet state to the ground singlet state is also possible, which is why for many compounds phosphorescence is observed only at low temperatures when the solvent transitions into an immobilized Glass-like state.



Last update: 06/08/2026

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