Charge Transfer through Redox Molecular Junctions in Nonequilibrated Solvents

Area of Science:

• Physical Chemistry
• Molecular Electronics
• Condensed Matter Physics

Background:

• Molecular conduction in dielectric solvents typically uses Marcus theory for electron transfer kinetics.
• This theory assumes solvent equilibrium, which may not hold for successive charge transfer events.
• Nonequilibrium solvent dynamics significantly impact charge transfer processes at the molecular level.

Purpose of the Study:

• To generalize Marcus theory by incorporating solvent nonequilibrium effects in molecular junctions.
• To investigate the influence of dynamic polarizable solvents on charge current and its fluctuations.
• To explore methods for controlling solvent damping effects in molecular conduction.

Main Methods:

• Developed a generalized theory for molecular junctions with donor-acceptor systems in polarizable solvents.
• Solved diffusion equations in strong- and weak-friction limits to determine nonequilibrium solvent distributions.
• Calculated charge current and its fluctuating behavior under nonequilibrium conditions.

Main Results:

• Charge transfer statistics transition from Poissonian (no solvent or fast relaxation) to correlated behavior due to dynamic solvents.
• Observed a Kramers-like turnover in nonequilibrium current as a function of solvent damping.
• Demonstrated that solvent dynamics introduce correlations absent in equilibrium models.

Conclusions:

• Solvent nonequilibrium is crucial for accurately describing molecular conduction and charge transfer statistics.
• The dynamic solvent response introduces correlations and a turnover in current, deviating from equilibrium predictions.
• Geometrical control of solvent dielectric response in nanostructured channels offers a method to tune solvent damping.