Scientists unveiled two intermediate structures formed during light-induced trans-cis isomerization of azobenzene, a common molecular photoswitch, using a technique called femtosecond time-resolved X-ray liquidography (TRXL). Previously proposed mechanisms for the transformation, which occurs within roughly 10 ps, or trillionths of a second, have been contentious. But now researchers have recorded a frame-by-frame visualization of the process as it occurs in a liquid. The work deepens understanding of molecular dynamics and reveals that azobenzene conserves volume as it isomerizes. The study also supports TRXL’s use as a tool for peering into the reactions of light-atom organic solutes (Nature 2026, DOI: 10.1038/s41586-026-11068-4).
X-ray crystallography, to which liquidography is analogous, has yielded countless molecular maps. “But a crystal is not where most chemistry happens. Most chemical and biological reactions take place in liquids,” says Hyotcherl Ihee, director of the Center for Advanced Reaction Dynamics at the Institute for Basic Science and the leader of the study. “A tightly packed lattice can restrict or even prevent the large-scale motions of a reaction,” he adds.
