Conical Intersections at Interfaces Revealed by Phase-Cycling Interface-Specific Two-Dimensional Electronic...

Area of Science:

• Photochemistry
• Surface Science
• Molecular Dynamics

Background:

• Conical intersections (CIs) are crucial for controlling molecular photochemical reactions.
• Characterizing CIs at interfaces and surfaces is currently challenging.
• Understanding interfacial molecular dynamics is vital for chemical processes.

Purpose of the Study:

• To develop a novel tool for characterizing CIs at the air/water interface.
• To investigate the nonadiabatic dynamics of molecules at interfaces using advanced spectroscopy and modeling.
• To compare interfacial and bulk photochemical reaction pathways.

Main Methods:

• Developed phase-cycling interface-specific two-dimensional electronic spectroscopy (i2D-ES).
• Integrated phase-locked pump pulse pairs with an interface-specific electronic probe.
• Employed advanced computational modeling to explore nonadiabatic dynamics.
• Studied an interface-active azo dye molecule at the air/water interface.

Main Results:

• Demonstrated distinct kinetic pathways for nonadiabatic transitions at the interface versus bulk water.
• Identified two conical intersections: S2-S1 and S1-S0.
• Found differences in ground-state molecular conformations at the interface.
• Observed slower nonadiabatic dynamics at the interface due to excited-state configurations.
• Noted significantly longer S1 dark state to S0 ground state transitions at the interface.

Conclusions:

• Molecular orientation at interfaces significantly influences photochemical reaction pathways.
• The developed i2D-ES technique is effective for characterizing CIs at interfaces.
• Interfacial environments lead to altered nonadiabatic dynamics compared to bulk phases.
• Understanding these interfacial effects is key for controlling chemical reactions on surfaces.