Fluorescence is the emission of light by a substance that has absorbed light. Several factors can influence the intensity, duration, and efficiency of fluorescence.
Here are the primary factors affecting fluorescence:
1. Nature of the Molecule:
Not all molecules fluoresce. The molecular structure, including the presence of conjugated systems, plays a role in determining if a molecule is fluorescent.
2. Excitation Wavelength:
The intensity of fluorescence can depend on the wavelength of the exciting light.
Each molecule has an optimal excitation wavelength that produces the maximum fluorescence emission.
3. Quantum Yield:
Refers to the efficiency of the fluorescence process.
It's the ratio of the number of photons emitted to the number of photons absorbed.
4. Environmental Factors:
pH: The acidity or basicity of the environment can affect the protonation state of the molecule, influencing its fluorescence.
Temperature: Higher temperatures generally reduce fluorescence due to increased non-radiative processes.
Viscosity: In more viscous environments, molecular rotation and vibration might be restricted, which can influence fluorescence.
Solvent: The polarity and nature of the solvent can affect fluorescence. Some solvents can enhance while others can quench fluorescence.
5. Concentration:
At high concentrations, self-quenching can occur where molecules absorb the emitted fluorescence of neighboring molecules.
6. Presence of Quenchers:
Some molecules can reduce or quench fluorescence when present. Oxygen is a common quencher.
7. Lifetime of the Excited State:
The longer the excited state lasts, the higher the chance for non-radiative processes to de-excite the molecule, reducing fluorescence.
8. Intersystem Crossing:
This is the process where the molecule moves from a singlet excited state to a triplet state.
Since fluorescence occurs from the singlet state, intersystem crossing to the triplet state reduces the yield of fluorescence.