Pyrene, a Test Case for Deep-Ultraviolet Molecular Photophysics

Area of Science:

• Ultrafast spectroscopy
• Photochemistry
• Molecular dynamics

Background:

• Pyrene's excited-state dynamics are crucial for understanding photophysical processes.
• Conical intersections play a key role in the rapid decay of excited states.

Purpose of the Study:

• To elucidate the complete relaxation dynamics of pyrene from its second bright state.
• To investigate the role of conical intersections in excited-state decay pathways.

Main Methods:

• Broadband heterodyne-detected transient grating spectroscopy.
• Two-dimensional photon echo (2DPE) spectroscopy with 6 fs pulses (250–300 nm).
• Combined experimental and theoretical approaches.

Main Results:

• Identified multiple lifetimes associated with a cascade of electronic states.
• Observed rapid population transfer to the lowest excited state followed by vibrational cooling.
• Demonstrated that population transfer efficiency is linked to kinetic energy and conical intersection geometry.

Conclusions:

• The study provides a detailed picture of pyrene's ultrafast relaxation dynamics.
• The findings highlight the importance of conical intersections in mediating excited-state decay.
• The developed methodology is applicable to studying deep-ultraviolet-absorbing biochromophores.