For the first time, scientists at ETH Zurich have utilized extremely brief, rotating bursts of light to analyze and modify electron movements in mirror-image molecules. They demonstrated that the chirality of molecules is both a structural and an electronic phenomenon. The study was published in the journal Nature.
When rotating light hits chiral molecules, electrons are emitted preferentially in the forward or backward direction. Attosecond pulses (blue) and infrared pulses (red) can manipulate and reverse the direction. Image Credit: Alexander Blech / FU Berlin
From an early age, we recognize that our left and right hands are anatomically the same, yet shaped as mirror images. That’s why a glove made for the left hand won’t fit the right: it looks similar, but it’s not interchangeable.
This concept of "handedness" also exists in chemistry. Many molecules come in two mirror-image forms that appear nearly identical but are fundamentally different. Chemists refer to this phenomenon as chirality.
The contrast between right and left-handed chiral compounds is critical in biology, chemistry, and the pharmaceutical business. Many of life’s building blocks, including DNA, amino acids, and proteins, are chiral, meaning they only exist in left- or right-handed versions. Depending on their handedness, chiral medicines can be beneficial, useless, or even dangerous.
Chirality is often considered to be a structural characteristic.
Recently, however, there has been growing evidence that the adoption of the structural approach is not sufficient to fully understand chiral phenomena.
Hans Jakob Wörner, Professor, Physical Chemistry, ETH Zurich
What has received little attention until now is how electrons, the tiniest and fastest building components of atoms, behave differently in chiral molecules depending on whether they are left- or right-handed. For the first time, a team of researchers led by Wörner discovered a mechanism to visualize and modify the emission of electrons from chiral molecules in real time.
Processes on the Attosecond Scale
Wörner and his team explored an interesting effect that happens when chiral molecules are exposed to circularly polarized light, which rotates in a spiral like a corkscrew. An electron is expelled from the molecule immediately following light excitation.
The essential point here is that, depending on the chirality of the irradiated molecule and the direction of rotation of the light, the electron is expelled either in the same direction as the incoming light beam or in the opposite direction.
In their study, the researchers not only measured this phenomenon, known as photoelectron circular dichroism (PECD), but also amplified it, manipulated it in time, and even reversed it.
This measurement was made possible by a new electron flash device known for its exceptional precision. It produces circularly polarized attosecond pulses—bursts of light with a time resolution as short as a billionth of a billionth of a second .
This level of precision is necessary to observe electron dynamics on their natural attosecond timescale. For the first time, researchers have identified the handedness of electron motion in these light pulses based on the direction of their own rotational orientation.
Together with a temporally superimposed, circularly polarized infrared light beam, the researchers were able to control the direction in which an electron preferentially moves based on the chirality of the sample, the direction of rotation of the light beams, and their phase shift. They were also able to measure the time it takes for an electron to be expelled from a chiral molecule following light excitation.
Fundamental Research with Application Potential
The results make it possible to embrace a novel strategy for chirality:
We no longer understand chirality solely as a static feature of molecular structure but also as the dynamic behaviour of electrons in chiral systems.
Meng Han, Study First Author and Former Postdoctoral Researcher, ETH Zurich
Prior to this, chirality had only been suspected as a controllable electrical phenomenon; nevertheless, the requisite technology prevented it from being experimentally accessible.
In the future, attosecond flashes might be used to more accurately assess the chirality of medical agents and to answer basic concerns about the origins of chirality in life.
The approach also offers new opportunities for time-resolved research of chiral processes at the electronic level, which might lead to advances in information processing, spintronics, molecular machines, and biosensor technology.
Journal Reference:
Han, M., et al. (2025) Attosecond control and measurement of chiral photoionization dynamics. Nature. doi.org/10.1038/s41586-025-09455-4.