New Material Captures Light Energy

By Iva Fedorka

With nature as their inspiration, researchers at Pacific Northwest National Laboratory (PNNL) and Washington State University have created a new material that can capture light energy. The material produces a light-harvesting system that has potential for photovoltaics and bioimaging. The results of this study were published in the May 14, 2021 issue of Science Advances.

Bones, teeth, and other naturally occurring hierarchical structured hybrid materials are made from components that have structure themselves.  Artificially creating similarly strong and durable organic-inorganic hybrid materials has been a challenge, and this work may help to overcome some of those hurdles.

Created by PNNL materials scientist Chun-Long Chen and his collaborators, this new material mimics the structural and functional complexity of natural hybrid materials. It combines protein-like synthetic molecules with complex silicate-based nanoclusters to form a new class of nanocrystals. They programmed this two-dimensional (2D) material to create an efficient light-harvesting system.

"The sun is the most important energy source we have," said Chen. "We wanted to see if we could program our hybrid nanocrystals to harvest light energy — much like natural plants and photosynthetic bacteria can — while achieving a high robustness and processability seen in synthetic systems."

Big Dreams, Tiny Crystals

Though hierarchically structured materials are exceptionally difficult to create, Chen's multidisciplinary team of scientists combined their expertise to synthesize a sequence-defined molecule that could form a similar material. They created an altered protein-like structure, called a peptoid, and attached a silicate-based cage-like structure (abbreviated POSS) to one end. Under the right conditions, these molecules could be induced to self-assemble into perfectly shaped crystals of 2D nanosheets. This formed a layer of a cell-membrane-like substance while also retaining the stability and mechanical properties of the individual molecules.

Designing Bio-Inspired Materials

When they had successfully created these POSS-peptoid nanocrystals and demonstrated their unique properties, the team set out to explore other uses. They programmed the material to include special functional groups at specific locations and intermolecular distances. Programming options are endless since the nanocrystals can be combined with multiple and many varieties of peptoid building blocks.

The scientists then created a system that captures light energy much like plant pigments do. They added pairs of special "donor" molecules and cage-like structures that could bind to "acceptor" molecules at precise locations in the nanocrystal. The donor molecules absorb a specific wavelength of light and transfer the energy to the acceptor molecules, which emit light at a different wavelength. This system exhibited an energy transfer efficiency above 96%, one of the most successful light-harvesting systems reported to date.

Using POSS-Peptoids for Light Harvesting

To demonstrate its potential, the researchers inserted the nanocrystals into live human cells to create a biocompatible probe for live cell imaging. When light of a certain color shines on cells in which acceptor molecules are present, the cells emit a light of a different color. No color change is observed when acceptor molecules are absent. While this is the only applications tested so far, it may be the first of many.

"Though this research is still in its early stages, the unique structural features and high energy transfer of POSS-peptoid 2D nanocrystals have the potential to be applied to many different systems, from photovoltaics to photocatalysis," said Chen.