Researchers observed a hidden state triggered by light forming within 30 femtoseconds.
A pulse of light sent a metal-organic framework into a hidden electronic state in just 30 femtoseconds. By watching the transformation almost as it happened, researchers uncovered a fleeting intermediate stage that appears to guide the material into its new state.
The work was conducted by researchers at the Institute of Science Tokyo, Tohoku University, and Nagoya Institute of Technology, Japan. Combining ultrafast laser spectroscopy with theoretical calculations allowed them to identify the transient electronic state and clarify its role in the rapid transition. The results could improve efforts to control material properties using light.
Light can briefly push materials into states that behave differently from their ordinary forms. These photoinduced states give researchers a way to alter electronic and optical properties without relying only on heating or cooling. Revealing how they develop is important for designing advanced optical technologies and materials that respond predictably to light.
Ultrafast pulses expose the transition
The challenge is speed. The earliest stages of photoinduced state formation unfold on the femtosecond (fs) timescale (a millionth of a billionth of a second), making them exceptionally difficult to observe directly.
Assistant Professor Tadahiko Ishikawa of the Department of Chemistry, School of Science, Institute of Science Tokyo (Science Tokyo), Japan, led the investigation with then doctoral student Samiran Banu (currently a Special Postdoctoral Researcher at RIKEN). They collaborated with researchers from Tohoku University and Nagoya Institute of Technology, Japan.
Their focus was a metal-organic framework (MOF), a material constructed by connecting metal ions with organic molecules. The researchers wanted to reconstruct the sequence through which light drives the material into a hidden state. Their findings were published in Physical Review Letters.
“We found that the photoinduced hidden state forms within 30 fs through a previously unknown intermediate electronic state,” says Ishikawa.
To follow that transition, the researchers used time-resolved reflectance spectroscopy with laser pulses lasting only six fs. The technique measures how the light reflected by a material changes immediately after the material absorbs a laser pulse, providing a rapid view of its evolving electronic structure.
Within 30 fs, the MOF’s reflectance spectrum shifted sharply and developed features linked to a new optical absorption band. Those changes indicated that the hidden photoinduced state had formed.
A transient state drives atomic change
The experimental measurements showed when the transition occurred, but theoretical calculations were needed to explain the underlying sequence.
Immediately after absorbing light, the material briefly entered an electronic state in which bonds between neighboring sites alternated between stronger and weaker arrangements. This temporary configuration is called a bond-order wave state.
Small changes in the positions of atoms followed that electronic reorganization. Together, the changing bond pattern and atomic movement carried the material into the photoinduced hidden state.
The calculations also indicated that the final state may be polar, meaning positive and negative electrical charges are distributed unevenly across the material. Light-induced polar states could provide a way to adjust electronic behavior without permanently changing the material.
“By revealing intermediate states, our method could help design materials that can be efficiently controlled using light,” explains Ishikawa.
Light control could reach new materials
The findings provide a clearer view of how light can produce temporary material states through a rapid sequence of electronic and atomic changes. Understanding those intermediate steps could help researchers create more precise methods for switching or tuning material properties with ultrashort laser pulses.
Such control may support future photoresponsive materials for high-speed electronics, optoelectronic devices, and other technologies that depend on carefully managed electronic behavior. Applying the same experimental and theoretical approach to additional materials could reveal whether similar hidden transitions occur elsewhere and guide the design of new light-controlled systems.
Reference: “Ultrafast Formation of a Photoinduced Hidden State Driven by a Bond-Order Wave in a Metal-Organic Framework” by Samiran Banu, Tatsuya Amano, Takahisa Kato, Kou Takubo, Yoichi Okimoto, Shinya Koshihara, Yohei Kawakami, Hirotake Itoh, Wataru Kosaka, Hitoshi Miyasaka, Shinichiro Iwai, Akira Takahashi and Tadahiko Ishikawa, 22 July 2026, Physical Review Letters.
DOI: 10.1103/x43y-61c1
Never miss a breakthrough: Join the SciTechDaily newsletter.
Follow us on Google and Google News.