X-ray liquidography resolves the atomic steps of azobenzene switching
5 October 2026
The Nature paper of 30 September 2026 used femtosecond time-resolved X-ray liquidography to watch azobenzene turn from its trans form to its cis form in solution.
Two transient intermediates, called I1 and I2, were identified on the path from the Franck-Condon state to the cis product.
The three steps carry time constants of 0.4 ps, 2.7 ps and 14 ps.
The sequence begins with C-N torsion and is followed by N-N rotation, rather than a single concerted twist.
A method the authors call PEPC separated the weak solute signal from the far larger solvent background, and CASPT2 quantum chemical calculations were used to check the structures.
The team was led by Hyotcherl Ihee, with Jungmin Kim and Hosung Ki among the authors.
In plain words
Azobenzene azobenzene — A molecule with two benzene rings joined by a nitrogen-nitrogen double bond that flips shape when it absorbs light.
Isomerization isomerization — A change in the arrangement of a molecule's atoms without any change in its formula.
ps picosecond — One million millionth of a second.