Internal and external conversions

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.

Internal and external conversions

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.