1. Fluorescence Spectroscopy

2. What factors control whether a molecule will fluoresce?
Quantum Yield
f = ________kf______________
kf + ki + kec + kic + kpd + kd
kf = rate constant for fluorescence
ki = “ “ for intersystem crossing
kec = “ “ for external conversion
kic = “ “ for internal conversion
kpd = “ “ for pre-dissociation
kd = “ “ for dissociation

3. What factors control whether a molecule will fluoresce?
B. Structure:
1.) Aromatic
2.) Rigid structures exhibit more
3.) Heavy atoms will decrease fluorescence
4.) Fluorescence will increase when molecule is adhered to surface

4. What factors control whether a molecule will fluoresce?
C. Temperature and Solvent Effects
1.) Lower temperature increases fluorescence
2.) Solvent contains heavy atoms will decrease fluorescence but increase phosphorescence

5. Effect of Concentration on Fluorescence
F = k’Po2.303ebc
F = Fluorescence
k’ = constant depending on quantum efficiency
Po = incident power
For high concentrations linear relationship no longer holds due to self quenching
What is self quenching? Excited molecules collide and radiationless transfer of energy occurs

6. Instrument Design for Fluorimeters
Important considerations for fluorimeters
1. Must have intense source, D2 & W not intense enough so use Xe or Hg
Fluorescence is not as strong as absorbtion so need more sensitive detectors like PMT
3. Cells transparent on 4 sides detection usually at right angles of source
4. Phosphorescence measurements may be made on fluorimeters w/ 2 differences
Irradiation + time delay + measurement
Cooled 77K to prevent collisional deactivation

7. Applications of Fluorescence
Fluorescence and phosphorescence are one of the most sensitive techniques available!