Mechanism of the Non-Kasha Fluorescence in Pyrene

Area of Science:

• Quantum chemistry
• Spectroscopy
• Photophysics

Background:

• The high-energy shoulder in pyrene's gas-phase fluorescence spectrum is a known instance of non-Kasha emission.
• Understanding non-Kasha emission is crucial for accurately modeling molecular excited states.

Purpose of the Study:

• To comparatively assess vibronic perturbation theory and nonadiabatic dynamics for predicting pyrene's gas-phase fluorescence spectrum.
• To elucidate the strengths and weaknesses of each method in explaining non-Kasha phenomena.

Main Methods:

• Computational modeling using vibronic perturbation theory.
• Computational modeling using nonadiabatic dynamics simulations.
• Comparative analysis of spectral prediction accuracy and physical interpretation.

Main Results:

• Both vibronic perturbation theory and nonadiabatic dynamics qualitatively reproduce the non-Kasha emission in pyrene.
• The methods exhibit differences in computational cost, predictive accuracy, and the underlying physical insights provided.
• Vibronic perturbation theory offers a more direct interpretation of spectral features, while nonadiabatic dynamics captures the time-evolution of excited states.

Conclusions:

• Vibronic perturbation theory and nonadiabatic dynamics are valuable, complementary tools for studying non-Kasha fluorescence.
• A combined two-step approach leveraging both methods can provide a more comprehensive understanding of non-Kasha emission.
• These findings aid in selecting appropriate computational strategies for complex photophysical processes.