New Class of Materials Made of Crystal Compounds Respond to Light Irradiation, Show Changes in Luminescent Properties

In Japan, a group of scientists from Osaka University discovered a type of material that melts by ultraviolet light instead of heat. The research, published in the Royal Society of Chemistry, used a material belonging to a new class of crystal known as heteroaromatic 1,2-diketones. This novel compound responds to light irradiation in a phenomenon called photo-induced crystal-to-liquid transition (PCLT).

Bringing Light to Materials Science

Scientists discovered that one member of this class of PCLT materials, the diketone SO, changes intensity as it melts. Its luminescent color also transformed from green to yellow. These changes in luminescent properties reveal the tendency of SO to undergo shape changes at the molecular level during the PCLT process.

According to lead author Mao Komura, "This is the first organic crystal we know of that exhibits a luminescent evolution during crystal melting, showing changes in intensity and color, from green to yellow."

This study applies the analysis of single-crystal X-ray and thermodynamic properties to investigate the mechanisms that affect the behavior of the new PCLT material. From their research, the scientists conclude the role of the disordered layer in the crystal is an important factor for PCLT in this material class.

Scientists are hopeful that the discovery and characterization of the novel PCLT material will help them understand the process of crystal melting and can also be applied to the photolithography industry, where precise patterns on surfaces must be created using UV light. It can also be used in heat energy storage, requiring materials that can store and release heat. Aside from it, the discovery of the novel material can also provide an understanding of the process of light-induced adhesion.

Some materials are proven to have crystal-melting properties. Scientists are aware of the significant effects of PCLT in changing the properties of materials. However, only a limited amount of study has been conducted regarding the diversity of compounds that exhibit this property. The discovery of novel PCLT materials is considered a major breakthrough in materials science.

Light-Induced Crystal Melting

The ability of light to induce melting is different from how heat does. Under light irradiation, photo energy is exposed out of the electromagnetic waves. Since light sources can have different ranges of wavelength emission, the rate of a chemical reaction can be affected. It is a straightforward process involving the absorption of non-ionizing radiation energy in the form of light stimuli. The energy of the reactant's molecule is elevated to a level required for the chemical process. The absorbed energy is used to propagate chemical reactions.

Crystal melting by photo-induced crystal-to-liquid transition is attributed to photoexcitation that leads to changes in the molecular structure of the crystal. The process of transducing light energy from the change in the molecular structure enabled scientists to express their fundamental interest in investigating PCLT. Material properties with high spatiotemporal resolution can dramatically change crystal melting by light irradiation.