Luminous light ‘created’ by researchers

Scientists at the University of Vermont in the US have discovered a method to artificially create luminescence that could have a range of potential applications such as medical dyes and LED bulbs.

Along with researchers at Dartmouth College in New Hampshire, they discovered that when molecular rotors (molecules shaped like kayak paddles) were placed in high viscosity liquids, they emitted a vivid green colour.

Morgan Cousins, a doctoral student and co-author from the University of Vermont, said: “The compound we found is very bright, and due to its viscosity sensitivity, may have a multitude of applications. We see uses for these kinds of molecules from industrial materials to new kinds of LEDs to biomedical imaging.”

When the same molecular rotors were in a less viscous liquid they emitted a weak, reddish glow. After further investigation the scientists realised these rotors broke a long standing chemistry law called Kasha’s Rule. It states luminescent molecules will only emit the same colour of light, regardless of the colour of light it absorbs.

After absorbing light, the rotors then attempt molecular relaxation —rapidly vibrating, stretching and releasing heat —to get to their lowest energy excited state. However, the more viscous liquids prevents the rotors from being able to vibrate fully to reach that stage and so green light is emitted.

Liptak said: “We found a new way that the universe works that we didn't understand before. It’s an exception to the rule.” The researchers are looking for other bio-compatible compounds that could be used in a medical dye to understand more about the differing viscosities of the human cell.

The research was published in Nature Chemistry.