Nanohoops: A new approach to energize future devices

October 12, 2015 // By Paul Buckley
Researchers at the University of Oregon have shown that nanohoops can be made using a variety of atoms, not just those from carbon. The circular structures could be used to optimize the energy efficiency of solar cells, OLEDs or sensors.

The nanohoops - known chemically as cycloparaphenylenes - can be designed to efficiently absorb and distribute energy.

The research, led by Jasti's doctoral student Evan R. Darzi, was described in a paper placed online ahead of print in ACS Central Science, a journal of the American Chemical Society. The paper is a proof-of-principle for the process, which will have to wait for additional research to be completed before the full impact of the nanohoops can be realized.

The one-nanometer nanohoops offer a new class of structures - sized between those made with long-chained polymers and small, low-weight molecules - for use in energy or light devices, said Jasti, who was the first scientist to synthesize these types of molecules in 2008 as a postdoctoral fellow at the Molecular Foundry at the Lawrence Berkeley National Laboratory.

"These structures add to the toolbox and provide a new way to make organic electronic materials," explained Jasti. "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."

Nanohoops help solve challenges related to materials with controllable band gaps - the energies that lie between valance and conduction bands and is vital for designing organic semiconductors. Currently long materials such as those based on polymers work best.  

"If you can control the band gap, then you can control the color of light that is emitted, for example," said Jasti. "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."

To prove their approach could work, Darzi synthesized a variety of nanohoops using both carbon and nitrogen atoms to explore their behavior. "What we show is that the charged nitrogen makes a nanohoop an acceptor of electrons, and the other part becomes a donator of electrons," said Jasti.