Internal Conversion and Vibrational Energy Redistribution in Chlorophyll A

Area of Science:

• Photochemistry
• Molecular Dynamics
• Quantum Chemistry

Background:

• Chlorophyll A (ChlA) is crucial for photosynthesis.
• Understanding excited state relaxation is key to photochemistry.

Purpose of the Study:

• Investigate the role of intramolecular vibrations in ChlA's nonradiative relaxation.
• Identify specific vibrational modes involved in excited state decay pathways.

Main Methods:

• Computational study using nonadiabatic excited state molecular dynamics.
• Analysis of excited state trajectories and normal mode velocities.
• Calculation of nonadiabatic coupling vectors (NACRs).

Main Results:

• A small subset of medium-to-high frequency normal modes actively participate in relaxation.
• Two distinct relaxation pathways with different timescales were identified.
• Active modes show high overlap with NACRs during electronic transitions.

Conclusions:

• Vibrational modes significantly dictate ChlA's excited state relaxation pathways.
• Identified active modes and pathways provide insights for computational modeling.
• This approach can simplify identifying key vibrational coordinates for mixed quantum-classical methods.