Photophysics of uracil: an explicit time-dependent generating function-based method combining both nonadiabatic and...

Area of Science:

• Computational Chemistry
• Photochemistry
• Quantum Mechanics

Background:

• Non-radiative decay processes like internal conversion (IC) and intersystem crossing (ISC) are crucial for understanding molecular photophysics.
• Accurate theoretical calculation of these rates remains a challenge, particularly for complex molecular systems.
• Existing methods often treat IC and ISC separately, limiting a unified approach.

Purpose of the Study:

• To develop a unified computational framework for calculating both internal conversion (IC) and intersystem crossing (ISC) rates.
• To explicitly compute non-adiabatic coupling (NAC) and spin-orbit coupling (SOC) constants within a single model.
• To validate the framework's applicability and accuracy for molecular systems like azulene and uracil.

Main Methods:

• A stationary-state approach utilizing a time-dependent generating function based on Fermi's golden rule.
• Explicit computation of non-adiabatic coupling (NAC) and spin-orbit coupling (SOC) constants.
• Application of Duschinsky rotation matrices, displacement vectors, and NAC matrix elements for detailed analysis.

Main Results:

• The framework successfully computed internal conversion (IC) rates for azulene, showing good agreement with experimental and previous theoretical results.
• Simulated photophysical rates for uracil corroborated experimental observations, highlighting the method's accuracy for complex photodynamics.
• Qualitative explanations of the Fermi's golden rule based method's suitability were provided using single-mode potential energy surfaces.

Conclusions:

• The developed composite framework provides a robust and unified approach for calculating non-radiative deactivation rates (IC and ISC).
• The method demonstrates significant potential for accurately simulating the photophysics of complex molecules.
• The study validates the use of Fermi's golden rule based calculations for understanding molecular deactivation pathways.