February 20, 2025 -- Researchers based at the University of Cambridge have created a three-state (ternary) molecular switch controlled by light and temperature. Unlike materials such as silicon that switches between two states, the new complex material can act as a solid-state optical switch between three different molecular states. This provides a groundwork for future technologies like optical data storage, photonic circuits and quantum computing.

In our digital world, everything runs on binary logic—ON (1) and OFF (0)—which is the foundation of modern computing. Computers and smartphones rely on tiny transistors, made from materials like silicon, that switch between these two states. But what if we could add a third state to this logic? Imagine a world where computing and data storage could operate with three distinct states instead of just 0s and 1s, like having an additional gear in a car, giving more flexibility and power.

Now, scientists at the Cavendish Laboratory have managed to create a three-state (ternary) molecular switch made of a ruthenium-based complex with high purity, which could precisely be controlled by light and temperature. The study published in Nature Communications, describes a new method which only needs a visible green LED light and easily obtainable liquid-nitrogen temperature, roughly between  –175-185°C or 90-100 Kelvin to create this three-state optical switch.

“When exposed to green light and a specific temperature, the ‘ruthenium-based complex’ switches between three different states, or ‘isomers,’” said Professor Jacqui Cole, Professor of Materials Physics and Head of the Molecular Engineering Group at the Cavendish Laboratory. “Two things make the complex capable of acting as a three-state (ternary) molecular switch: its ability to undergo complete transition from one state to the other and most importantly the state being fully reversible under the right temperature.”

Previously, only partial conversion was achieved for similar complex materials which limited the usefulness of these complex materials. The ‘ruthenium-based complex’ is a single-crystal optical actuator.  Single crystals are uniform materials which offer a highly pure medium, ensuring that any structural changes using light are spread across the crystal. Hence, this newly developed ruthenium-based complex can undergo complete and controlled transitions, making it far more reliable. It undergoes 100% conversion (technically SO2-linkage photoisomerization) from one distinct (isomeric) state to another using the green LED light.

Importantly, the researchers have also been able to successfully demonstrate a fully reversible process, where  the material could be switched between three states with complete photoconversion. “These transformations are not random but precise and fully reversible,” said Cole. “The different states can be controlled with the right temperature and can be switched back and forth by adjusting temperature in a calibrated way - the complex can return to its original state upon heating and transition to another state upon cooling. What is more exciting is that each of these states is stable under appropriate conditions.”  

This useful property to precisely control  access between three different states and being stable under appropriate conditions enables the material to act as a three-state (ternary) molecular switch.

“The high level of control is significant as it offers a fresh approach to manipulating molecular states for technological applications. It opens new prospects for advancements in light-driven (or photonic) technologies, including micro-robotics, optical data storage, and for designing materials for futuristic quantum computing circuits,” concluded Cole.