How is light absorbed by matter?

Matter may come in many forms such as gas, liquids, crystals or solids. Common to all forms of matter is that it is built of , themselves built of nuclei and electrons. The atoms may be bound together into , the basis of chemistry.

When molecules are exposed to light, which is a sort of energy, they may absorb it under certain conditions. Thus the energy of the light is transferred to the electrons which now behave in a new way. Photochemists call this new energy state of the molecule an Excited Electronic State. An excited electronic state cannot contain any arbitrary amount of energy but only certain discreet values (this is described by quantum physics). Therefore, a molecule can only absorb photons with the corresponding quantum of energy.

An important property of molecules is that the energy of the photons they can absorb may depend on their environment, e.g. if this is a water solution, or an organic solvent such as hydrocarbon, ethanol etc.

TREL, the molecule, travels freely in space, enjoying his favourite violet photons. But when diving into the swimming pool his taste is up to red photons. Later he, unfortunately, finds himself covered in petrol he goes for green photons.

Many TRELs, lying close to each other, are strongly coupled. Therefore, if a photon strikes the group, it is absorbed collectively by several TRELs. But even a slight motion may bring all the energy onto a single TREL