Reversible charge separation followed by exciplex formation

Area of Science:

• Photochemistry
• Chemical Kinetics
• Electron Transfer Theory

Background:

• Fluorescence quenching mechanisms are crucial for understanding photochemical processes.
• Reversible bimolecular ionization and exciplex formation are complex pathways.
• Spin dynamics play a significant role in radical-ion recombination.

Purpose of the Study:

• To investigate fluorescence quenching through reversible ionization and exciplex formation using integral encounter theory (IET).
• To analyze the influence of spin-conversion and radical-ion recombination on fluorescence quenching.
• To compare results obtained from pulse excitation and stationary fluorescence detection.

Main Methods:

• Application of integral encounter theory (IET) to model the quenching process.
• Incorporation of an incoherent (rate) model for spin-conversion.
• Analysis of ion recombination to excited triplet products.
• Comparison with experimental data and the free-energy gap (FEG) law.

Main Results:

• Calculations demonstrate distinct outcomes for pulse versus stationary fluorescence detection.
• The study quantifies the free-energy dependence of forward and backward electron transfer properties.
• Integral encounter theory successfully models the complex quenching mechanism.
• Deviations from the conventional free-energy gap law are observed.

Conclusions:

• The proposed mechanism involving reversible ionization, exciplex formation, and spin-conversion accurately describes fluorescence quenching.
• Integral encounter theory provides a robust framework for studying complex electron transfer processes.
• The distinction between pulse and stationary detection methods is critical for accurate interpretation.
• The findings offer insights into the limitations of the conventional free-energy gap law in certain scenarios.