Long-lived charge separation and applications in artificial photosynthesis

Area of Science:

• Artificial Photosynthesis
• Electron Transfer (ET) Systems
• Photocatalysis

Background:

• Replicating photosynthetic reactivity is a long-standing research goal.
• Marcus theory is applied to design synthetic electron-transfer systems.
• Mimicking long-lived charge separations in photosynthetic reaction centers is key.

Purpose of the Study:

• To rationally design electron-transfer control systems based on photosynthetic reaction center models.
• To achieve long-lived charge-separated states using synthetic donor-acceptor systems.
• To develop efficient organic photocatalysts for various chemical reactions.

Main Methods:

• Utilized Marcus theory to design electron-transfer systems.
• Employed porphyrins as electron donors and fullerenes as electron acceptors.
• Engineered donor-acceptor dyads with controlled distances, redox potentials, and geometries.
• Incorporated components like terminal donors, mediators, and acceptors.
• Assembled systems on gold nanoparticles and within mesoporous silica-alumina.

Main Results:

• Achieved long-lived charge-separated states by selecting components with small reorganization energies.
• Located driving force for back electron transfer in the Marcus inverted region.
• Developed the 9-mesityl-10-methylacridinium ion (Acr(+)-Mes) system with extremely slow back ET.
• Observed structural changes during photoinduced ET via X-ray crystallography.
• Demonstrated enhanced lifetimes in isolated Acr(+)-Mes molecules within silica-alumina.

Conclusions:

• Rational design of electron-transfer systems can mimic photosynthetic charge separation.
• Controlling electron transfer in the Marcus inverted region is crucial for long-lived states.
• Acr(+)-Mes and related compounds are effective organic photocatalysts for diverse reactions.