Novel photo-responsive crystal compounds melt under ultraviolet light

Japanese researchers have made a fascinating discovery regarding a unique material that can melt when exposed to ultraviolet light instead of heat. This groundbreaking finding involves a type of crystal compound known as “heteroaromatic 1,2-diketones.” The researchers from Osaka University recently published their findings in Chemical Science on April 20, shedding light on the remarkable properties of these photo-responsive crystals.

When subjected to light irradiation, the crystals in these materials undergo a remarkable transformation, transitioning from a solid state to a liquid state. This phenomenon, termed photo-induced crystal-to-liquid transition (PCLT), offers immense possibilities for various applications. For instance, it opens up the potential for developing light-controlled, reversible adhesives with wide-ranging uses.

Notably, only a limited number of materials have exhibited the ability to undergo this crystal-melting process. Therefore, the discovery of a novel class of PCLT materials marks a significant advancement in this field of research.

During their characterization of this newly discovered class of materials, the scientists identified a particular member called the diketone SO. This compound stands out due to its unique luminescent properties during the melting process triggered by irradiation. Lead author Mao Komura explained that the diketone SO is the first organic crystal known to exhibit an evolution in luminescence as it melts, showcasing changes in both intensity and color—specifically shifting from green to yellow.

Real-time observation of crystal melting with luminescence evolution. Credit: Osaka University

The changes observed in the luminescence of the material, specifically how it absorbs and emits light, indicated that the compound SO underwent significant molecular-level transformations during the process of photo-induced crystal-to-liquid transition (PCLT). Building upon previous research on luminescent molecules, the team of researchers realized that by investigating these molecular-level changes, they could gain a deeper understanding of the phenomenon of crystal melting.

Senior author Yosuke Tani explained that the alterations in luminescence were a result of a sequential series of processes involving the loosening of the crystal structure and conformational changes that occurred prior to melting. These visual indicators of the various steps in the PCLT process provided valuable insights into the molecular-level mechanisms of crystal melting.

To gain further insights into the behavior of this new PCLT material, the researchers employed techniques such as single-crystal X-ray analysis, thermodynamic property analysis, and theoretical calculations. These methods allowed them to probe the underlying mechanisms governing the material’s behavior and revealed that a disordered layer within the crystal played a crucial role in the PCLT process for this class of materials.

The discovery of this novel PCLT material, combined with the comprehensive characterization conducted by the researchers, not only enhances our understanding of the molecular-level mechanisms involved in crystal melting but also paves the way for the development of PCLT materials with diverse applications. These applications include photolithography, thermal energy storage, and light-induced adhesion, among others.

Source: Osaka University

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