Modeling time-coincident ultrafast electron transfer and solvation processes at molecule-semiconductor interfaces

Area of Science:

• Physical Chemistry
• Materials Science
• Quantum Mechanics

Background:

• Standard kinetic models (Fermi's Golden Rule) assume fast nuclear relaxation relative to electron transfer.
• This assumption fails for electron transfer on the 100-fs timescale.

Purpose of the Study:

• Develop a more accurate perturbative model for photoinduced electron transfer.
• Capture the interplay between electron transfer and nuclear relaxation at short timescales.
• Provide a framework for analyzing ultrafast dynamics at molecule-semiconductor interfaces.

Main Methods:

• Developed a fourth-order perturbative kinetic model.
• Model parameters derived from spectroscopic measurements and first-principles calculations.
• Applied the model to a donor molecule coupled to a single acceptor and a TiO2 density of states (DOS).

Main Results:

• The fourth-order model captures simultaneous electron transfer and nuclear relaxation.
• Second-order theories fail when the DOS has narrow peaks near the molecular excited state energy.
• Demonstrated model's applicability to realistic molecule-semiconductor systems (e.g., TiO2).

Conclusions:

• The fourth-order rate formula provides a rigorous framework for ultrafast electron transfer.
• This model is essential for understanding dynamics on the 100-fs timescale.
• Offers an intuitive approach for analyzing complex photoinduced processes.