Dispersion-Controlled Excited-State Dynamics in Azobenzene Photoisomerization

Area of Science:

• Chemical Physics
• Photochemistry
• Molecular Dynamics

Background:

• Weak interactions, particularly London dispersion forces, were traditionally considered important mainly for large molecular systems.
• Recent studies highlight their role in chemical reactivity, but their influence on excited-state photoreactions remains largely unexplored.
• Azobenzene, a well-known photoswitch, serves as a model system to investigate these phenomena.

Purpose of the Study:

• To elucidate the impact of London dispersion forces on the excited-state behavior of azobenzene.
• To understand how dispersion interactions influence the outcome of azobenzene photoreactions.
• To explore the concept of
• dispersion-controlled excited-state dynamics
• for ultrafast processes.

Main Methods:

• Computational modeling and simulation of azobenzene and its derivatives.
• Analysis of excited-state lifetimes and potential energy surfaces.
• Investigation of conical intersection pathways.

Main Results:

• Increased London dispersion interactions between substituents demonstrably prolong the excited-state lifetimes of azobenzene.
• Dispersion forces impede direct access to the conical intersection, a critical step in photoisomerization.
• This alteration in dynamics significantly modifies the Z to E photoisomerization pathway.

Conclusions:

• London dispersion forces play a crucial role in controlling excited-state dynamics in photochemical reactions.
• These forces can be harnessed to steer ultrafast processes by influencing excited-state lifetimes and reaction pathways.
• The findings suggest a new paradigm of "dispersion-controlled excited-state dynamics" with broad implications for photochemistry.