Quantum Coherence Enhances Electron Transfer Rates to Two Equivalent Electron Acceptors.

Area of Science:

• Photochemistry
• Quantum Dynamics
• Molecular Interactions

Background:

• Electron transfer (ET) is fundamental in chemical and biological processes.
• Quantum coherence can influence ET rates, particularly in systems with multiple acceptors.
• Donor-acceptor (D-A) compounds provide a platform to study these phenomena.

Purpose of the Study:

• To investigate the effect of quantum coherence on photodriven electron transfer rates.
• To compare ET rates in donor-acceptor systems with one versus two acceptors.
• To elucidate the role of temperature on ET dynamics in these systems.

Main Methods:

• Synthesis of donor-acceptor compounds linking anthracene (An) donor to 1,4-benzoquinone (BQ) acceptors.
• Ultrafast spectroscopic techniques to measure subpicosecond electron transfer rates.
• Variable temperature studies (room and cryogenic) to probe temperature-dependent effects.

Main Results:

• Electron transfer from anthracene to two benzoquinones is approximately 2.4 times faster than to one benzoquinone at room temperature.
• At cryogenic temperatures, the ET rate to two benzoquinones becomes approximately 5 times faster than to one.
• A factor of 2 increase in rate enhancement at low temperatures is observed.

Conclusions:

• Quantum coherence plays a crucial role in enhancing electron transfer rates in multi-acceptor systems.
• The observed rate enhancement is attributed to a transition from single-site ET to coherent ET involving a superposition state.
• Correlated system-bath fluctuations at low temperatures further contribute to the enhanced ET efficiency.