This chemical is a fluorophore, containing many aromatic groups and having the ability to absorb light and re-emit a new photon (fluorescence). There are other types of fluorescence that allow re-emission of light at higher energies or even the same energy but in this case the re-emitted light is at a lower energy. Because it is under a UV light, it absorbs the UV and the light that it re-emits will be visible to human eyes. Sadly, what we can see is only a very narrow band of the spectrum, still pretty awesome!
House on the outskirts of Brussels with plant-covered wall by French botanical artist Patrick Blanc
via Dezeen
