Compound switches between liquid and solid states when exposed to light or heat

A group of researchers from the Kobe University Graduate School of Science and Tokyo University of Science, Yamaguchi, has developed a metal-containing compound which transforms into a solid when exposed to light and returns to liquid form when heated. This substance could potentially be used for photolithography technology, such as fabricating printed circuits, among other applications.

Coordination polymers are solids with various useful applications. In recent years, research into coordination polymers has increased, and scientists have developed many ways to synthesise them, but most of these methods rely on chemical reactions in solutions. This is said to be the first example of a method that creates coordination polymers by exposing liquids to light.

Techniques that can control the properties of materials through external stimuli such as light and heat are important in creating materials for use in electronics. For example, materials which solidify when exposed to light (photosensitive resins) are used in creating printed circuits, but it is difficult to reuse these materials.

The researchers proposed that if they could control the binding process between metal ions and organic molecules using heat and light, they could create a material that drastically changes its properties when exposed to external stimuli. The group became the first in the world to develop an ionic liquid from a ruthenium complex with cyano groups. This liquid is colourless, clear, non-volatile, and does not freeze, even at -50°C. When ultraviolet light is applied to the liquid for a few hours, it changes into an amorphous coordination polymer, and if this solid it is then heated for one minute at 130°C, it returns to its original ionic liquid form.

In this way, by applying light and heat, the group realised a reversible transformation between an ionic liquid and a solid coordination polymer — two substances with completely different structures and different chemical properties.

This research has led to the successful creation of a reusable photocurable liquid. It can potentially be applied to printed circuit boards, 3D printing, and adhesives. Mochida Tomoyuki, professor of Materials Chemistry and Inorganic Chemistry at Kobe University, said: “We plan to continue research on the molecular design of this substance, to reduce its response time, and look into creating more functions for this coordination polymer.”

Author
Tom Austin-Morgan

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