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Related Experiment Video

Updated: Feb 8, 2026

Light-driven Molecular Motors on Surfaces for Single Molecular Imaging

Light-driven Molecular Motors on Surfaces for Single Molecular Imaging

Published on: March 13, 2019

Double Molecular Photoswitch Driven by Light and Collisions.

James N Bull¹, Michael S Scholz¹, Eduardo Carrascosa¹

¹School of Chemistry, University of Melbourne, Parkville, Victoria 3010, Australia.

Physical Review Letters

|June 16, 2018

Summary

Collision-induced isomerization of Congo red (CR) dianions drives a cascade to the lowest-energy form. Photon absorption allows reversible E/Z switching of CR azo groups, influencing energy states.

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Area of Science:

Photochemistry
Chemical Physics
Molecular Dynamics

Background:

Molecular shape and configuration are crucial for chemical function.
Isomerization, the transformation between molecular shapes, can be triggered by external stimuli like light or heat.
Congo red (CR) dianion, with its two azo groups, serves as a model for studying complex isomerization processes.

Purpose of the Study:

To investigate the mechanisms of isomerization in the isolated Congo red (CR) dianion induced by collisions and photons.
To differentiate between collision-induced and photon-induced isomerization pathways.
To elucidate the role of conical intersections in the photoisomerization of CR dianions.

Main Methods:

Experimental investigation of isolated CR dianions using mass spectrometry and spectroscopy.
Controlled collisional activation to induce isomerization.
Photon irradiation across a specific wavelength range (270-600 nm) to induce photoisomerization.
Computational analysis of statistical isomerization rates and potential energy surfaces.

Main Results:

Collisional activation of CR dianions results in a directed ZZ→EZ→EE isomerization cascade, favoring the lowest-energy isomer.
Single-photon absorption can reversibly switch either azo group (E to Z or Z to E), leading to changes in CR dianion energy.
Photoisomerization in the gas phase proceeds via conical intersection seams, connecting excited and ground electronic states.

Conclusions:

Collision-induced and photon-induced isomerization pathways for CR dianions are distinct.
Photon absorption provides a versatile method for controlling CR dianion configurations and energy states.
Gas-phase photoisomerization of CR dianions involves excited-state dynamics through conical intersections, not solely ground-state isomerization.