Figure 1.

Schematic illustration on the mechanism of endogenous biological chemiluminescence during germination of a seedling. Hydroxyl radical can oxidize all types of biomolecules such as nucleic acids, lipids, and proteins to produce initial radicals of biomolecules. Other oxidation processes can also form biomolecule radicals. During the further reactions, high-energy intermediates such as dioxetane (ROOR) and tetroxide (ROOOOR) can be generated. This high-energy intermediates can be decomposed to electronically excited species such as triplet excited carbonyl or singlet oxygen. Electronically excited species can further react, emit a photon or (in case of triplet excited carbonyl) transfer the excitation energy to a donor - another chromophore which can serve as an emitter at longer wavelengths. Reaction scheme adopted from².