Q-Band relaxation in chlorophyll: new insights from multireference quantum dynamics

Area of Science:

• Biophysics
• Quantum Chemistry

Background:

• Photosynthetic light-harvesting relies on ultrafast relaxation within chlorophyll's Q-bands.
• This critical process remains incompletely understood despite extensive research.

Purpose of the Study:

• To investigate chlorophyll's Q-band relaxation using non-adiabatic wave packet dynamics.
• To identify key vibrational modes involved in non-adiabatic coupling.

Main Methods:

• Constructed reduced-dimensional coordinate spaces using normal modes.
• Analyzed wave packet dynamics on XMS-CASPT2 potential energy surfaces.
• Addressed computational challenges related to Q-band energy gap overestimation.

Main Results:

• Identified specific vibrational eigenstates participating in relaxation.
• Demonstrated that Q- and Q- potential energy surfaces do not cross in accessible regions.
• Showcased ultrafast population transfer facilitated by non-adiabatic coupling.

Conclusions:

• Chlorophyll's Q-band system is strongly coupled, enabling easy population transfer between x- and y-polarized states.
• Both orientations likely contribute to electron transfer in photosynthetic reaction centers.