{"id":9521,"date":"2025-06-23T12:49:00","date_gmt":"2025-06-23T10:49:00","guid":{"rendered":"https:\/\/serwisnaukowy.uw.edu.pl\/en\/?p=9521"},"modified":"2026-06-23T12:49:45","modified_gmt":"2026-06-23T10:49:45","slug":"a-chemical-chameleon-materials-that-respond-to-light","status":"publish","type":"post","link":"https:\/\/serwisnaukowy.uw.edu.pl\/en\/a-chemical-chameleon-materials-that-respond-to-light\/","title":{"rendered":"A chemical chameleon: Materials that respond to light"},"content":{"rendered":"\n

Advances in physicochemistry of materials<\/strong><\/h3>\n\n\n\n

The ability of a material to instantly change its properties \u2013 for example, under the influence of light \u2013 is more than just intriguing; it is one of the most exciting developments in modern physicochemistry of materials. Despite rapid progress, many of the underlying mechanisms are still not fully understood. Gaining better control over how light interacts with matter could unlock a wide range of applications \u2013 from advanced displays and data storage to smart electronic systems that quietly power everyday technology.<\/p>\n\n\n\n

It is hard to imagine daily life without smartphones or flat-screen TVs. Even lighting has changed dramatically \u2013 LEDs have largely replaced traditional bulbs. And storage technologies? Floppy disks (like the once-ubiquitous 3.5-inch, 1.44 MB version) are long gone, replaced by compact USB drives that can hold thousands of times more data.<\/p>\n\n\n\n

What is a spin-crossover process?<\/strong><\/h3>\n\n\n\n

To understand spin-crossover, we first need to clarify what spin actually is. Spin is a quantum property of elementary particles \u2013 such as electrons or protons \u2013 that has no direct counterpart in the macroscopic world of everyday objects like balls or stones. It can be loosely compared to angular momentum, a physical quantity describing \u201ca kind of rotation,\u201d or \u201ctwisting motion.\u201d<\/p>\n\n\n\n

An electron always has a spin of \u00bd, which can take two orientations: \u201cup\u201d or \u201cdown,\u201d indexed by physicists as +\u00bd and \u2212\u00bd. This property plays a key role in spin-crossover process because changing the spin of one or more electrons can alter the behavior of an entire atom \u2013 and even the properties of a whole material.<\/p>\n\n\n\n

\u201cTwo electrons can occupy the same position in space (for example, within an atomic orbital), but in that case their spins must have opposite signs. In addition, electrons generally prefer to occupy orbitals singly when possible. This means that, given a set of electrons and available orbitals, only certain configurations are allowed. Spin-crossover (SCO) processes involve a rearrangement of electrons within a metal ion in response to changes in the surrounding environment (such as temperature) or external stimuli (such as a light pulse),\u201d explains Prof. Katarzyna Jarzembska at the Faculty of Chemistry, University of Warsaw.<\/p>\n\n\n\n

From a molecular perspective, iron-containing compounds with metal centers such as Fe\u00b2\u207a or Fe\u00b3\u207a are particularly fascinating. These iron cations are atoms that have lost two or three electrons, respectively, and they can adopt different spin states. For instance, the same iron center, Fe\u00b2\u207a, can exist either in a high-spin (HS) or a low-spin (LS) state.<\/p>\n\n\n\n

In the high-spin case, it has four unpaired electrons with \u201cup\u201d spin, whereas in the low-spin state it has none, as all electrons are paired. According to the Pauli exclusion principle, electrons with the same spin must occupy different regions of space; as a result, the Fe\u00b2\u207a ion in the HS state is larger than in the LS state. A spin-crossover transition is precisely the transformation between the HS and LS states, which can be induced, for example, by temperature or a light pulse.<\/p>\n\n\n\n

In addition to changes in geometry, spin-crossover transitions primarily affect the physical properties of a material, such as its color. Iron is especially important in this context because it is abundant on Earth, relatively easy to extract, and a fundamental component of materials such as all steels. It is difficult to imagine modern civilization without it.<\/p>\n\n\n\n

\"Investigating
Investigating spin-crossover phenomena using modern methods that allow us to probe molecular structure. Source: Nature Communications<\/figcaption><\/figure>\n\n\n\n

Tracking the chameleon\u2019s changes<\/strong><\/h3>\n\n\n\n

The study employed two advanced techniques: ultrafast electron diffraction (UED) and pump\u2013probe experiments using a free-electron laser (FEL) in the X-ray range (XFEL). In the latter experiments, Prof. Katarzyna Jarzembska\u2019s team from the University of Warsaw played a significant role.<\/p>\n\n\n\n

An FEL is a unique type of laser that uses a beam of free electrons to produce extremely intense electromagnetic radiation. When it operates in the X-ray range \u2013 then called an XFEL \u2013 it allows scientists to examine the structure of matter with extraordinary precision, even tracking how atoms move. Together, these methods make it possible to capture and analyze these phenomena with remarkable precision on ultrafast timescales.<\/p>\n\n\n\n

\u201cThe most surprising thing for me was the ultrafast timescale of the geometric change around the iron ion induced by the spin transition, and the fact that we were able to distinguish two stages of this process \u2013 first, an elongation of the bonds between the iron center and the surrounding atoms, and then their rotation. It is remarkable how much information can be extracted from such subtle changes in a diffraction pattern. The XFEL itself has come a long way \u2013 from an ambitious idea to a 3.4-kilometer-long facility. We have finally reached a point where research dreams are becoming reality,\u201d says Prof. Jarzembska.<\/p>\n\n\n\n

\"A
A free-electron laser (FEL) generates highly intense electromagnetic radiation using free electrons. In the X-ray range, it is known as an XFEL. Pictured: the main tunnel of the European XFEL accelerator. Source: XFEL press materials<\/figcaption><\/figure>\n\n\n\n

Using the studied phenomena in practice<\/strong><\/h3>\n\n\n\n

The impact of spin-crossover transitions on a material\u2019s physical properties \u2013 including, for example, its magnetization, color, dielectric constant, and electrical resistance \u2013 is of considerable importance in the physicochemistry of materials. <\/p>\n\n\n\n

\u201cPotential practical applications of spin-crossover materials, which exploit their switchable properties, include optical displays and data storage devices (with pixels made of SCO materials whose color or dielectric constant can be switched, for example, by localized heating or cooling, or by light exposure); switches in electronic circuits (where spin changes can trigger different functions within such systems); electroluminescent devices; and pressure sensors, where spin changes would indicate variations in the environment. The switchable paramagnetism of spin-crossover compounds may also be used in temperature-sensitive contrast agents administered during magnetic resonance imaging,\u201d the scientist notes. <\/p>\n\n\n\n

The researchers stress that real-world applications of spin-crossover materials are still some way off. Even so, research on new systems is moving fast worldwide, and we may soon see reports of these molecular switches being used in prototype devices \u2013 in practice. <\/p>\n\n\n\n

\u201cOur work is among the first to investigate the behavior of spin-crossover (SCO) materials on an ultrafast timescale. I hope it will contribute to a better understanding of the mechanisms behind these processes, as well as to future applications of SCO materials. Importantly, we also demonstrate the capabilities of molecular-structure probing methods \u2013 combining UED and XFEL \u2013 in advancing our understanding of the ultrafast dynamics of photoswitchable and, more broadly, photoactive materials,\u201d Prof. Jarzembska concludes. <\/p>\n\n\n\n

\"The
The European XFEL facility in Hamburg and Schenefeld (as of January 2025). This 3.4-kilometer-long X-ray laser operates mostly underground. Three sites (marked in orange) are located in Hamburg (DESY\u2013Bahrenfeld and Osdorfer Born) and in the southern part of the city of Schenefeld. Source: XFEL press materials.<\/figcaption><\/figure>\n\n\n\n

The text was originally published in Polish on the Serwis Naukowy UW <\/em>website <\/em><\/a>on June 6, 2025.<\/em><\/p>\n\n\n\n

<\/p>\n","protected":false},"excerpt":{"rendered":"

Chameleons are known for changing color in the blink of an eye \u2013\u00a0but nonliving matter can do something similar. Spin-crossover (SCO) materials can rapidly switch their electronic configuration when exposed to light, altering properties like color, magnetism, or conductivity \u2013\u00a0within femtoseconds, or quadrillionths of a second. An international team led by Dr. Yifeng Jiang (European XFEL) and Dr. Maciej Lorenz (University of Rennes, France) captured one of the first ultrafast \u201csnapshots\u201d of this process, with contributions from researchers at the University of Warsaw, including Prof. Katarzyna Jarzembska, Dr. Rados\u0142aw Kami\u0144ski, and PhD student Piotr \u0141aski.<\/p>\n","protected":false},"author":10,"featured_media":9524,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[244],"tags":[1386,577,1774,1776,574,573,570,1775,1777,1387,578],"class_list":["post-9521","post","type-post","status-publish","format-standard","has-post-thumbnail","category-chemistry","tag-faculty-of-chemistry","tag-free-electron-laser","tag-photoswitchable-materials","tag-physicochemistry-of-materials","tag-sco","tag-spin","tag-spin-crossover","tag-structural-dynamics-research-group","tag-ultrafast-electron-diffraction","tag-university-of-warsaw","tag-xfel"],"acf":[],"_links":{"self":[{"href":"https:\/\/serwisnaukowy.uw.edu.pl\/en\/wp-json\/wp\/v2\/posts\/9521","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/serwisnaukowy.uw.edu.pl\/en\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/serwisnaukowy.uw.edu.pl\/en\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/serwisnaukowy.uw.edu.pl\/en\/wp-json\/wp\/v2\/users\/10"}],"replies":[{"embeddable":true,"href":"https:\/\/serwisnaukowy.uw.edu.pl\/en\/wp-json\/wp\/v2\/comments?post=9521"}],"version-history":[{"count":2,"href":"https:\/\/serwisnaukowy.uw.edu.pl\/en\/wp-json\/wp\/v2\/posts\/9521\/revisions"}],"predecessor-version":[{"id":9528,"href":"https:\/\/serwisnaukowy.uw.edu.pl\/en\/wp-json\/wp\/v2\/posts\/9521\/revisions\/9528"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/serwisnaukowy.uw.edu.pl\/en\/wp-json\/wp\/v2\/media\/9524"}],"wp:attachment":[{"href":"https:\/\/serwisnaukowy.uw.edu.pl\/en\/wp-json\/wp\/v2\/media?parent=9521"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/serwisnaukowy.uw.edu.pl\/en\/wp-json\/wp\/v2\/categories?post=9521"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/serwisnaukowy.uw.edu.pl\/en\/wp-json\/wp\/v2\/tags?post=9521"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}