The radiative surface hopping (RSH) algorithm: Capturing fluorescence events in molecular systems within a...

Area of Science:

• Computational Chemistry
• Photochemistry
• Molecular Dynamics

Background:

• Modeling excited-state deactivation in molecules is crucial for understanding photophysical processes.
• Semi-classical non-adiabatic molecular dynamics often neglects radiative processes like fluorescence.
• Accurate simulation of fluorescence requires integrating radiative and non-radiative decay pathways.

Purpose of the Study:

• To introduce and validate a novel radiative surface hopping algorithm.
• To model the photodeactivation dynamics of trans-4-dimethylamino-4'-cyanostilbene (DCS) including fluorescence.
• To provide a comprehensive molecular movie of excited-state deactivation.

Main Methods:

• Developed a radiative surface hopping algorithm within a semi-classical non-adiabatic molecular dynamics framework.
• Employed a semi-empirical quantum mechanical/molecular mechanical (QM/MM) Hamiltonian.
• Simulated dynamics for hundreds of picoseconds in both gas and solution phases (isopropyl ether).

Main Results:

• Successfully captured initial fluorescence events in DCS.
• Reproduced experimental fluorescence lifetime and quantum yield, particularly in polar solvents.
• Analysis of emissive species geometry ruled out a twisted intramolecular charge transfer (TICT) state as the cause of dual emission.

Conclusions:

• The radiative surface hopping algorithm enables accurate modeling of fluorescence in molecular dynamics.
• The method provides insights into excited-state deactivation pathways and photophysical properties.
• This approach facilitates theoretical studies of early fluorescence events in molecular systems.