Vibronic Quantum Beating between Electronic Excited States in a Heterodimer.

Area of Science:

• Quantum chemistry
• Molecular dynamics
• Spectroscopy

Background:

• Energy transfer in multichromophoric molecules is influenced by electronic and vibrational couplings.
• Coherent electron-vibrational dynamics can persist at room temperature on subpicosecond timescales.
• Vibrations can actively modulate wave-like electronic motion during intermolecular energy transfer.

Purpose of the Study:

• Investigate the role and mechanism of coherent energy transfer in multichromophoric systems.
• Utilize a rigid synthetic heterodimer as a simplified model system.
• Compare surface hopping (SH) and Ehrenfest (EHR) simulation approaches.

Main Methods:

• Nonadiabatic excited state molecular dynamics simulations.
• Application of both surface hopping (SH) and Ehrenfest (EHR) methods.
• Photoexcitation of the synthetic heterodimer at room temperature.

Main Results:

• Ehrenfest simulations show ultrafast electronic population beating between the two lowest electronic states at room temperature.
• These oscillations, absent at low temperatures, originate from vibrations.
• The observed coherent dynamics and population beating could not be reproduced by the SH approach.
• Vibrations near-resonant with the energy difference between the lowest electronic states significantly contribute to the observed coherent dynamics.

Conclusions:

• Coherent electron-vibrational dynamics play a critical role in energy transfer within multichromophoric systems.
• The Ehrenfest method is more adept at capturing these ultrafast coherent phenomena compared to surface hopping.
• Vibrational modes are essential modulators of electronic energy transfer pathways.