Laser Induced Fluorescence of Quinine Sulfate and the Kinetics of Cl - Induced Quenching of the Fluorescence

In this experiment you will be concerned with the decay kinetics of the fluorescence of quinine sulfate in water solutions and the physical processes that effect these. Quinine is used as a fluorescence standard because the fluorescence is not quenched (decreased) by oxygen but can be quenched in a controlled manner by adding atomic anions (F-, Cl-, Iand Br-) to the solution . Many molecules re-emit some of the light energy they have absorbed as light, but delayed in time and at a different energy than the absorbed light. This is usually referred to as fluorescence or phosphorescence. As shown in Figure 1, fluorescence is the emission of light by a molecule in the same electronic state it was initially photoexcited into (usually S1), whereas phosphorescence is the emission of light from a molecule in a different electronic state (usually T1). Phosphorescence usually has a longer average time between photon absorption and emission than fluorescence. For a more detailed discussion of these phenomena see any standard physical chemistry text. The Notes on Electronic Spectroscopy should be consulted for this experiment.