A diffusional alternative to the Marcus free energy gap law.

Area of Science:

• Photochemistry
• Electron Transfer Reactions
• Physical Organic Chemistry

Background:

• Electron transfer reactions are fundamental in chemistry and biology.
• The Marcus theory describes electron transfer rates based on free energy changes.
• Perylene and tetracyanoethylene are common molecules used in electron transfer studies.

Purpose of the Study:

• To estimate the Stern-Volmer constant for perylene quenching by tetracyanoethylene.
• To investigate the role of double channel electron transfer in quenching dynamics.
• To compare experimental results with theoretical models like the Marcus theory and Rehm-Weller plateau.

Main Methods:

• Precise kinetic fitting of experimental data.
• Analysis of electron transfer from excited perylene to tetracyanoethylene in acetonitrile.
• Estimation of the Stern-Volmer constant for perylene quenching.

Main Results:

• The Stern-Volmer constant for perylene quenching was found to be equal to the diffusional height of the Rehm-Weller plateau.
• This suggests the quenching process substitutes the exergonic wing of the Marcus free energy gap law.
• Single channel transfer was observed to be fast enough for diffusion control at high exergonicity.

Conclusions:

• The Rehm-Weller plateau height accurately predicts the Stern-Volmer constant in this system.
• Electron transfer quenching can be diffusion-controlled even at high exergonicity.
• The findings provide insights into the mechanisms of electron transfer reactions.