The Fluorescence Quenching of Lysozyme by Iodide and Acrylamide

Luminescence is the emission of photons from electronically excited states. The electron in the in the lowest excited singlet state (S1), has the opposite spin orientation as the second electron in the lower ground state (S0) orbital. The ground state and excited state electrons are said to be paired. Fluorescence is the emission which results from the return to the lower orbital of the excited electron. Such transitions are quantum mechanically allowed and the rate is typically near 10 s. The lifetime, the average period of time a fluorophore remains in the excited state, is therefore typically 10 s (10 ns). Most often, there are competing nonradiative processes which return the electron from the excited singlet state to the ground state. Substances which display fluorescence generally have delocalized electrons present in conjugated double bonds. The systems are usually polycyclic planar aromatics. Some familiar examples of fluorescence are the blue glow, Fig 1, from quinine observed when a gin and tonic is in sunlight, whitening agents in clothes, minerals under "black" lights at a natural history museum, the green glow of fluorescein in antifreeze, and the blue glow in gasoline from aromatic hydrocarbons.