Chemistry Technology

Compound Transforms From Liquid to Solid when Exposed to Heat and Light

liquid to solid

A research group at Kobe University led by Professor Mochida Tomoyuki and PhD student Funasako Yusuke from the Tokyo University of Science have created a compound which is made up of metal. The compound holds the ability to transform into a solid upon being exposed to light and when it is heated turns back into its liquid form. The substance holds promise in the photolithography technology world and may be used in fabricating printed circuits as well as many other applications.

Such coordination polymers research has increased in recent years, with scientists developing a number of ways to synthesize them. Most of the methods require chemical reactions in order for the solutions to change form. This latest research marks the first time where coordination polymers were caused to change simply by exposing the liquid to light.

Creating materials that can be used in electronics requires techniques that can control the properties of materials through extraneous stimulation. Materials that turns to solids when in direct contact with light are used in the creation of printed circuits but these types of materials are not generally something that can be used more than one time.

The chemical structure (above) and outlook (below) of the ionic liquid and coordination polymer.
The ionic liquid is clear, but when exposed to UV light, the bonds between benzene rings and ruthenium are disconnected and replaced by a structure in which cyano groups link with the ruthenium ions, converting it into a yellow solid. This solid reverts back to the ionic liquid when exposed to heat. (Image credits: Kobe University)

The research group led by Professor Mochida suggested that if they could find a way to control the binding process which takes place between metal ions and organic molecules with heat and light, then they would be able to build a material that changes properties when exposed to external stimuli. The group succeeded in becoming the first in the world to create an ionic liquid from a ruthenium complex with cyano groups. This particular liquid is clear, colorless, extremely stable and does not freeze even when temperatures fall below negative 50 degrees Celsius. If ultraviolet light is applied to the liquid for a matter of hours, the substance changes from an amorphous coordination polymer and after it is heated for 60 seconds at 130 degrees Celsius, it turns back into its original ionic liquid form.

This is how the group realized they had uncovered a reversible transformation between an ionic liquid and a solid coordination polymer. This amazed the group as the two substances are made up of completely different structures as well as chemical properties.

Due to these newest findings, it is now possible to create a photocurable liquid that is completely reusable, which holds promise for applications in printed circuit boards, 3D printing and even adhesives. Professor Mochida says the team plans to continue their research with a more in-depth approach towards the molecular design of the substance. They want to reduce response time and figure out how to create more functions for the polymer.

The complete study was published in Chemical Communications Journal on May 7th, 2016.