Internal Conversion (IC):
Definition: A non-radiative process where an excited molecule transitions between electronic states of the same spin multiplicity without emitting a photon.
Mechanism: Energy is dissipated as vibrational energy to the surrounding environment (solvent or lattice).
Effect on Fluorimetry: Reduces fluorescence intensity by providing a pathway for the excited state to relax without emission.
External Conversion (EC):
Definition: A non-radiative process involving the transfer of energy from an excited molecule to another molecule (quencher) in the vicinity.
Mechanism: Energy is transferred to another molecule, which dissipates it as heat or undergoes its own transitions.
Effect on Fluorimetry: Also reduces fluorescence intensity by competing with the radiative emission process.
Comparison:
Internal Conversion: Involves transitions within the same molecule.
External Conversion: Involves energy transfer between different molecules.
Role in Fluorimetry:
Both internal and external conversions are pathways that decrease the quantum yield of fluorescence, affecting the sensitivity and accuracy of fluorometric measurements.