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Determination of the Photoisomerization Quantum Yield of a Hydrazone Photoswitch

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Published on: February 7, 2022

Dispersion-Controlled Excited-State Dynamics in Azobenzene Photoisomerization.

Torben Sassmannshausen¹, Nils Oberhof², Marcel A Strauss³

¹Institute of Physical and Theoretical Chemistry, Goethe University, Frankfurt 60438, Germany.

Journal of the American Chemical Society

|December 30, 2025

Summary

This summary is machine-generated.

London dispersion forces significantly impact molecular photoreactions. Increased dispersion interactions prolong excited-state lifetimes, altering azobenzene photoisomerization dynamics and opening new research avenues.

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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.