{
  "id": 11513525,
  "title": "Ultrafast X-rays reveal how the light-responsive molecular switch azobenzene changes shape",
  "url": "https://urgent.news/2026/10/02/ultrafast-x-rays-reveal-how-the-light-responsive-molecular-switch",
  "topic": "science",
  "section": "Science",
  "published": "2026-10-02T20:00:06.000Z",
  "source": {
    "name": "Phys.org",
    "slug": "phys-org",
    "url": "https://phys.org/news/2026-10-ultrafast-rays-reveal-responsive-molecular.html"
  },
  "original_language": "en",
  "account": "An ultrafast X-ray study has revealed how the light-responsive molecule azobenzene alters its structure following absorption of light. Azobenzene, renowned for its ability to switch between two forms triggered by light, had its dynamic changes in the first few picoseconds (trillionths of a second) following light absorption remained unclear for nearly 50 years.\n\nLed by Hyotcherl Ihee from KAIST's Department of Chemistry and IBS Center for Advanced Reaction Dynamics, the research team has shed light on this mystery. Their findings, published in Nature, show that in the initial stage of the reaction, azobenzene undergoes a coordinated motion where the two nitrogen atoms at its core move together, while its two benzene rings stay largely in place.\n\nThis coordinated movement of the nitrogen atoms, akin to the pedaling of a bicycle, represents the first step in the transformation from the trans form (with rings on opposite sides of the nitrogen linkage) to the cis form (with rings on the same side). The central nitrogen linkage's motion, rather than significant rotation of the large benzene rings, drives the overall shape change.\n\nThis discovery is crucial as it clarifies the pathway azobenzene follows when moving from one form to another, a detail that had previously eluded researchers due to the fleeting nature of these structures. The ultrafast X-ray measurements, conducted at the Pohang Accelerator Laboratory's X-ray free-electron laser, allowed the team to observe these ultrafast molecular motions.\n\nThe study's implications extend beyond just understanding azobenzene's behavior; it lays the groundwork for designing light-responsive materials and molecular-scale machines. By identifying the precise molecular choreography during the light-induced transformation, researchers can better predict and manipulate the properties of such materials. The research highlights that the reaction rate remains relatively stable even in more viscous liquids, as the localized motion around the central nitrogen atoms requires less displacement of the surrounding solvent compared to a full ring rotation.",
  "summary": "Azobenzene is one of the best-known molecules that can be switched between two forms by light. However, the question of how the molecule moves in the first few picoseconds (trillionths of a second) after it absorbs light has remained unresolved for nearly 50 years.",
  "key_points": [
    "Azobenzene's shape change revealed in ultrafast X-ray study",
    "Nitrogen atoms coordinate motion in initial reaction stage",
    "Discovery aids light-responsive material design"
  ],
  "editors_take": null,
  "illustration": null,
  "coverage": {
    "outlets": 1,
    "also_reported_by": []
  },
  "ai_generated": true,
  "disclaimer": "Summaries, key points and the editor’s take are written by software from other outlets’ reporting and may contain errors — always check the linked original."
}