1. Molecular Luminescence Spectrometry Chap 15

2. Three Related Optical Methods Fluorescence Phosphorescence Chemiluminescence } From excitation through absorption of photons Emission from an excited species formed in a chemical reaction

3. Fluorescence From atomic sodium vapor 3p → 3s transition at 589.6 and 589.0 nm 3p ʹ 3s 3p ʺ 3p ʹ 3s 3p ʺ Resonance fluorescence

4. Fluorescence excitation spectrum of the two sodium D-lines

5. FluorescencePhosphorescence Excited States Producing Fluorescence & Phosphorescence Electron Spins can be: “Paired” → diamagnetic “Unpaired” → paramagnetic (e.g., free radicals) Fig. 15-1

6. Energy Level Diagram for a Photoluminescent System Fig. 15-2 allowedforbidden

7. Rates of Absorption and Emission In general: Absorption:1 – 10 fs Fluorescence:1 – 100 ns Phosphorescence:0.1 us – 10 s or longer

8. Deactivation Processes Luminescence competes with: Vibrational Relaxation Internal Conversion External Conversion Intersystem Crossing

9. Deactivation Processes Vibrational Relaxation Result: Emission lines are Stokes shifted Longer λ ’s and lower v ’s

10. Energy Level Diagram for a Photoluminescent System Fig. 15-2

11. Deactivation Processes Internal Conversion Molecule passes to a lower energy electronic state without emission Bound State (e.g., S 2 → S 1 ) Unbound State: Predissociation Dissociation

12. Energy Level Diagram for a Photoluminescent System

13. Fluorescent Excitation and Emission Spectra of Quinine Fig. 15-3

14. Deactivation Processes External Conversion Excited state molecule collides with solute or another molecule Energy is transferred: collisional quenching

15. Energy Level Diagram for a Photoluminescent System Fig. 15-2

16. Deactivation Processes Intersystem Crossing Excited state electron spin flips S 1 → T 1 Common in molecules with heavy atoms: I, Br, etc.

17. Energy Level Diagram for a Photoluminescent System Fig. 15-2

18. Quantum Yield Method to express amount of luminescence Ratio of number of molecules that luminesce to total number of excited molecules Expressed in terms of rate constants: where k nr = k vib + k ic + k ec +k isc + k pd + k d varies from 0 to 1