Two-dimensional Fourier transform electronic spectroscopy at a conical intersection.

Area of Science:

• Physical Chemistry
• Quantum Dynamics
• Spectroscopy

Background:

• Silicon naphthalocyanine (SiNc) is a model system for studying ultrafast electronic processes.
• Jahn-Teller conical intersections play a crucial role in the dynamics of excited states in molecules.
• Understanding electronic coherence and decoherence is vital for controlling photochemical reactions.

Purpose of the Study:

• To measure and model two-dimensional (2D) electronic spectra of SiNc in benzonitrile.
• To investigate the role of Jahn-Teller conical intersections and vibrational dynamics in electronic decoherence.
• To elucidate the mechanisms behind ultrafast electronic anisotropy decay in SiNc.

Main Methods:

• Femtosecond two-dimensional electronic spectroscopy (2DES) was employed to capture ultrafast dynamics.
• Full non-adiabatic calculations were performed to model coupled electronic and vibrational dynamics.
• Analytical response functions were used to incorporate damped and Franck-Condon active modes.

Main Results:

• Experimental 2D spectra show loss of electronic coherence on a ~100 fs timescale.
• Conical intersection dynamics alone could not fully explain the observed coherence loss.
• Totally symmetric vibrational dynamics and an asymmetric solvation mode were necessary to match experimental data, including anisotropy decay.

Conclusions:

• Vibrational dynamics, particularly totally symmetric modes, significantly contribute to electronic decoherence in SiNc.
• The interplay between conical intersection passage and vibrational motion governs ultrafast dynamics.
• Accurate modeling requires considering both non-adiabatic electronic transitions and vibrational coherences/decoherences.