How do excited electrons in proteins produce fluorescence?

[retupmoc]

What is fluorescence and how does it arise?

Is it just a spontneous de-excitation after the electron in the molecule (protein) has been excited. This is a 6 mark question in last years Chemistry-2 exam and i don't really know how to go about answering it. Any suggestions?

 

[Monique]

Fluorescence arises when a molecule absorbs light of a certain frequency, which brings electrons from a ground to an excited state. These excited electrons can fall back to their ground state by the loss of energy. There are several ways by which this energy can be lost, like through vibrational energy. Fluorescent compounds have very rigid structures though, so they are unable to vibrate and the electron returns to the ground state through the emittion of a photon. Some of the energy of the photon will already have been lost, so the wavelength has changed to a longer one.