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:
Quantum Yield (Φₓ)
Definition: The ratio of the number of photons emitted to the number of photons absorbed.
Formula:
Influence: Higher quantum yields indicate more efficient fluorescence.
Molecular Structure
Conjugation: Extended π-electron systems enhance fluorescence.
Rigidity: Rigid structures reduce non-radiative decay pathways.
Functional Groups: Electron-donating groups can increase fluorescence intensity.
Solvent Effects
Polarity: Polar solvents can stabilize excited states differently than ground states, affecting energy gaps.
Viscosity: Higher viscosity reduces molecular motions, potentially increasing fluorescence.
Hydrogen Bonding: Can alter electronic energy levels and fluorescence properties.
Temperature
Effect: Increased temperature enhances molecular collisions, promoting non-radiative decay and decreasing fluorescence.
pH
Ionization States: Protonation or deprotonation can change electronic structures, influencing fluorescence.
Applications: Useful in studying pH-dependent fluorescence of compounds.
Concentration
Self-Quenching: At high concentrations, interactions between fluorophore molecules can lead to quenching.
Inner Filter Effect: Reabsorption of emitted light by other molecules in the sample reduces observed fluorescence.
Presence of Quenchers
Oxygen: A common quencher due to its paramagnetic nature.
Halide Ions: Heavy atoms can enhance intersystem crossing, reducing fluorescence.
