‘Nanohoops’ could power future devices

Researchers from the University of Oregon have been creating tiny circular structures called nanohoops that could be used in the future to power a range of devices.

The structures – known chemically as cycloparaphenylenes – had previously only been made using carbon. But in the journal ACS Central Science, it is revealed how the Oregon team has been able to create nanohoops with a variety of atoms, opening up their potential use in solar cells, organic light-emitting diodes or as new sensors or probes in medicine.

Illustration of a cycloparaphenylene, or nanohoop, that has been doped with nitrogen atoms.
Illustration of a cycloparaphenylene, or nanohoop, that has been doped with nitrogen atoms.

“These structures add to the toolbox and provide a new way to make organic electronic materials,” said Ramesh Jasti associate professor at the university’s Department of Chemistry and Biochemistry and one of the paper’s lead authors.

“Cyclic compounds can behave like they are hundreds of units long, like polymers, but be only six to eight units around. We show that by adding non-carbon atoms, we are able to move the optical and electronic properties around.”

According to the researchers, nanohoops help solve challenges related to materials with controllable band gaps – the energies that lie between valance and conduction bands which are vital for designing organic semiconductors.

“If you can control the band gap, then you can control the color of light that is emitted, for example,” Jasti said. “In an electronic device, you also need to match the energy levels to the electrodes. In photovoltaics, the sunlight you want to capture has to match that gap to increase efficiency and enhance the ability to line up various components in optimal ways. These things all rely on the energy levels of the molecules. We found that the smaller we make nanohoops, the smaller the gap.”

Jasti’s early work with nanohoops was all carbon based, but the latest research combined nitrogen atoms with carbon atoms to give the structures new electronic and optical properties. While the potential of the work is significant, Jasti believes additional research needs to be completed before the full impact of these new nanohoops can be realised.

“We haven’t gotten very far into the application of this,” he said. “We’re looking at that now. What we were able to see is that we can easily manipulate the energy levels of the structure, and now we know how to exchange any atom at any position along the loop. That is the key discovery, and it could be useful for all kinds of semiconductor applications.”