Fluorescence

Fluorescence

1. Example of luminescence

   • This is emission of light from an excited state of a molecule
   • Phosphorescence
     • Different quantum number T1 -> S0
     • Has longer wavelength because there's less energy
     • Lifetime: 10-4 to 10^2s because there is a change in the spin quantum numbers

2. Emission of a photon during a transition between states

   • SAME quantum number
     • S1 -> S0

3. Lifetime: 10-8 to 10-4s

4. Highly sensitive

5. Highly specific as a small number of compounds fluoresce

   • QUININE

6. Useful 2nd detector to HPLC, UV is primary

7. Technique used for quantative analysis

   • Emission intensity is directly proportional to concentration over a limited concentration range
   • To perform analysis, you need to specify both the excitation and emission wavelengths

8. Problems

   • Intensity can be pH dependent
   • Can be affected by other compounds in solution
     • These are QUENCHERS e.g. Iodide, Oxygen
       • A decrease in intensity, usually by temperature/pressure