Luciferin

Luciferin (from Latin lucifer 'light-bearer') is a generic term for the light-emitting compound found in organisms that generate bioluminescence.

[1] Luciferins are a class of small-molecule substrates that react with oxygen in the presence of a luciferase (an enzyme) to release energy in the form of light.

[5] Bacterial luciferin is two-component system consisting of flavin mononucleotide and a fatty aldehyde found in bioluminescent bacteria.

[6] Coelenterazine is found in radiolarians, ctenophores, cnidarians, squid, brittle stars, copepods, chaetognaths, fish, and shrimp.

[10] This reaction and the luminescence produced is useful for imaging such as detecting tumors from cancer or capable of measuring gene expression.

This is a space-filling model of firefly luciferin . Color coding: yellow= sulfur ; blue= nitrogen ; black= carbon ; red= oxygen ; white= hydrogen .
This structure of firefly luciferin is reversed (left to right) from the space-filling model shown above
Latia luciferin
Bacterial luciferin (FMN)
Coelenterazine
Luciferin of dinoflagellates (R = H) resp. of euphausiid shrimps (R = OH). The latter is also called Component F .
Vargulin (cypridinluciferin)
3-hydroxy hispidin from N. nambi