Using Lifetime and Quenching Rate Constant to Determine Optimal Quencher Concentration

Area of Science:

• Photochemistry
• Chemical Kinetics

Background:

• Excited state quenching is crucial for energy or electron transfer in photochemical reactions.
• Efficient quenching necessitates high quencher concentrations for optimal reaction quantum yields.
• Current methods for determining quencher concentrations often rely on empirical trial and error.

Purpose of the Study:

• To develop a predictive model for determining optimal quencher concentrations.
• To establish a relationship between photosensitizer lifetime, quenching rate constant, and required quencher concentration.
• To evaluate quencher concentrations used in acridinium-based photoredox catalysis against theoretical predictions.

Main Methods:

• Utilized kinetic modeling to derive a predictive relationship for quencher concentration.
• Calculated the concentration needed to quench 90% of excited states.
• Compared predicted concentrations with those employed in published photoredox reactions.

Main Results:

• A simple kinetic model successfully predicts the required quencher concentration for 90% excited state quenching.
• Many reported photoredox reactions using acridinium photocatalysts employ quencher concentrations below the predicted optimum.
• This discrepancy suggests potential inefficiencies in reported reaction quantum yields.

Conclusions:

• Kinetic modeling offers a rational approach to determine quencher concentrations, moving beyond trial and error.
• Suboptimal quencher concentrations in many photoredox studies may lead to reduced quantum yields.
• Optimizing quencher concentration is essential for efficient photochemical reactions, potentially reducing reaction times and light intensity requirements.