Two-dimensional electronic-vibrational spectroscopic study of conical intersection dynamics: an experimental and...

Area of Science:

• * Physical Chemistry
• * Spectroscopy
• * Chemical Dynamics

Background:

• * Triphenylmethane dyes (e.g., crystal violet, malachite green) are widely used and exhibit complex excited-state dynamics.
• * Understanding excited-state relaxation pathways is crucial for controlling photochemical processes and designing new materials.
• * Previous studies have lacked detailed insights into the ultrafast evolution of nuclear and electronic states during relaxation.

Purpose of the Study:

• * To investigate the excited-state relaxation dynamics of crystal violet and malachite green using two-dimensional electronic-vibrational (2DEV) spectroscopy.
• * To elucidate the role of intramolecular charge transfer and conical intersection passage in the relaxation process.
• * To analyze the interplay between electronic and vibrational degrees of freedom, influenced by solvent dynamics and molecular dipole moment changes.

Main Methods:

• * Two-dimensional electronic-vibrational (2DEV) spectroscopy was employed to track excited-state dynamics.
• * Excitation was performed at the absorption maxima of the dyes.
• * Analysis involved monitoring the C=C aromatic stretch and utilizing electronic structure calculations to interpret spectral features and wavepacket evolution.

Main Results:

• * Detailed mapping of nuclear wavepacket evolution on the excited state potential energy surface (PES), including diffusion and passage through a conical intersection.
• * Observation of intramolecular charge transfer occurring while the wavepacket resides on the excited state PES.
• * Quantification of the influence of solvent motions and molecular dipole moment fluctuations on the electronic-vibrational coupling, evidenced by center line slope analysis.

Conclusions:

• * 2DEV spectroscopy is a powerful tool for visualizing nuclear wavepacket motion after photoexcitation.
• * The study reveals a detailed mechanism for excited-state relaxation in triphenylmethane dyes, involving charge transfer and conical intersection dynamics.
• * The findings highlight the significant impact of the solvent environment on ultrafast molecular dynamics and electronic-vibrational coupling.