Förster resonance energy transfer, including transient coherent effects

Area of Science:

• Theoretical Chemistry
• Quantum Dynamics
• Spectroscopy

Background:

• Förster resonance energy transfer (FRET) theory traditionally models energy transfer in molecular systems.
• Existing models often require strong system-bath coupling, limiting their applicability.
• Calculating ultrafast non-linear responses in molecular systems remains a challenge.

Purpose of the Study:

• To develop a generalized Förster resonance energy transfer theory.
• To enable accurate calculation of ultrafast non-linear responses in molecular systems.
• To extend the validity of FRET theory to regimes with weak system-bath coupling.

Main Methods:

• Formally exact factorization of the time-dependent molecular statistical operator.
• Generalization of the traditional Förster master equation to a complete master equation for the reduced statistical operator.
• Derivation of a time-nonlocal Förster-type master equation.

Main Results:

• The derived master equation is valid even for vanishing system-bath coupling.
• A rapid initial coherent evolution of populations is predicted due to a transient coherence-dependent term.
• This term induces an initial condition 'slippage' that influences subsequent energy transfer.

Conclusions:

• The generalized FRET theory offers significant improvements over traditional formulations.
• The theory accurately predicts ultrafast non-linear responses and initial coherent dynamics.
• The study delineates the range of validity for the new theoretical framework.