Completing a Charge Transport Chain for Artificial Photosynthesis

Area of Science:

• Artificial photosynthesis
• Molecular electronics
• Photochemistry

Background:

• Photosystem II utilizes tyrosine for efficient electron transport.
• Mimicking natural processes in artificial systems is key for renewable energy.
• Understanding electron transfer dynamics is crucial for designing efficient devices.

Purpose of the Study:

• To synthesize a novel ruthenium polypyridyl complex with triarylamine substituents.
• To model the function of tyrosine in the photosystem II electron transport chain.
• To investigate electron injection and transfer dynamics at a TiO2 electrode surface.

Main Methods:

• Synthesis of a ruthenium polypyridyl chromophore with triarylamine substituents.
• Adsorption of the complex onto a TiO2 electrode surface.
• Spectroscopic analysis to study electron transfer kinetics and lifetimes.
• Electrochemical oxidation of hydroquinone using the generated radical cation.

Main Results:

• Successful synthesis of the target molecule.
• Efficient electron injection from the Ru(II) Metal-to-Ligand Charge Transfer (MLCT) excited state to TiO2.
• Rapid intramolecular electron transfer from triarylamine to Ru(III) at ~10^10 s^-1.
• Formation of a long-lived triarylamine radical cation (τ = ~165 μs).
• Demonstrated oxidation of hydroquinone to quinone.

Conclusions:

• The synthetic complex effectively models tyrosine's role in electron transport.
• Electron transfer dynamics at the semiconductor interface are controllable.
• The long-lived radical cation intermediate shows potential for catalytic applications.