generally yield
product in an
electronically excited state producing visible light.
As a general rule, only quite exothermic reactions
can generate the required energies. Therefore, most
CL reactions use oxygen, hydrogen peroxide, or
similar potential oxidants. As a principle in bioluminescence
and CL reactions, at least two reagents,
A and B react to form a product C, some fraction
of which is present in an electronically excited state,
C*, which may subsequently relax to the ground
state emitting a photon: