Eco-friendly alternative to display luminescent materials using plant waste and amino acids

Scientists have devised a way to create an environmentally friendly alternative to light-emitting materials commonly used in televisions, smartphones and other display technologies.

The research, led by a team from Yale University’s Center for Green Chemistry and Green Engineering, with participation from Nottingham Trent University, aims to address the challenges of “photoluminescent” solid-state materials, which often rely on non-renewable resources and toxic metals.

These materials are often manufactured in multi-step processes that produce large amounts of hazardous chemical waste.

The study was published in the journal Chem.

Photoluminescent solid-state materials work by absorbing ultraviolet light and re-emitting it as visible light, providing the ability to emit light, making them ideal for a variety of applications, from display technology, lighting, sensors, security inks, and biomedical imaging to glow-in-the-dark toys.

The challenge for researchers was to develop these materials from sustainable resources that are environmentally friendly, with less waste and less risk.

As part of the study, the researchers discovered that by harvesting lignin, a natural substance found between and within the cell walls of plants and trees that is a byproduct of the wood pulping and paper industry, and combining it with the simple amino acid histidine, they can produce a variety of solid materials that fluoresce under ultraviolet light.

In addition to being able to easily tune the properties of the photoluminescent material, only green solvents in the form of water and acetone are used to prepare the material.

Fluorescence or lighting effects depend on specific parts of lignin, called phenolic groups, that become activated when they absorb light.

This energetic state releases protons to histidines within the solid structure. This is a process known as “excited state proton transfer” (ESPT).

As the lignin relaxes and returns to its normal state, it emits light that glows at room temperature. In some cases, the material continued to glow for a very short time even after the UV light was turned off.

“The concept of ESPT is not new and is well known for pure phenolic molecules,” said lead author Ho-Ying Tse, Ph.D., a researcher at Yale University’s Center for Green Chemistry and Green Engineering.

“However, what is interesting is that the natural phenolic structure of lignin, which is present throughout the polymer, may inherently support this type of photoacid behavior, yet this effect has rarely been investigated in this context.”

“This is a great example of green and sustainable chemistry,” said study co-author Dr Darren Lee, a researcher in sustainable chemistry at Nottingham Trent University’s School of Science and Engineering.

“Photoluminescent materials are essential for a variety of everyday and smart technologies, but most of them rely on toxic metals and non-renewable resources,” he said.

“In this work, we not only simplified the synthesis of these materials, but also harnessed an abundant waste stream to produce tunable materials in a safer way.”

“Computational modeling reveals how the molecular interactions between lignin and histidine enable this unique light-driven proton transfer,” said Dr Chi-Shun Yeung, who led the computational analysis at the University of Hong Kong.

“These mechanistic insights explain how biopolymers can achieve efficient light emission without relying on metals.”