11.12.2017 change 11.12.2017

Nanographenes: Lego bricks in the nano scale

A model of crown-like  hydrocarbon with bound chloride. Fig. Marcin Majewski A model of crown-like hydrocarbon with bound chloride. Fig. Marcin Majewski

Nanographenes change their properties depending on the shape and method of joining the rings. The structure affects their interaction with light and chemical molecules. In the future, they may be used in electronics, drug transport and gas storage.

CROWN, BAGEL, BOWL...

Nanographenes are carbon compounds composed of properly connected five or six-membered rings. This structure influence their way of interacting with different types of light. Marcin Majewski, PhD student at the University of Wrocław creates and characterises new materials based on these molecules. He specialises in crown-shaped nanographenes.

"In my work, I synthesize the crown-like nanographenes, i.e. particles of the order of a millionths of a meter, looking like crowns or bagels. Figuratively speaking, I create very small +Lego+ bricks, which I then use to build larger structures" - explained the scientist in an interview with PAP.

According to Majewski, graphene-like structures can be both flat and spatial. To illustrate them, Marcin Majewski proposes a paper sheet model: if we cut out stripes or polygons from a flat sheet, we can spatially manipulate them by deforming individual fragments. For example, bending all the corners of a square upwards creates a bowl, and bending them alternately (up-down) results in a saddle shape.

In addition to various shapes, nanographenes can have variable sizes. This factor also affects their properties, the way they interact with the environment. According to Majewski, depending on the shape and size, nanographenes can absorb and emit light in different ways - in both visible and other ranges. This is a desirable property of materials in electronics. Thanks to strictly defined optical parameters, devices for specific applications can be constructed on their basis.

On the other hand, these materials can be used to interact with smaller molecules that enter the centre of the rim - the so-called "guest-host" interactions. As a result of the project, the researcher obtained a compound that in appropriate conditions binds with chloride ions, such as the ones found in table salt. It is the first hydrocarbon known in the literature that shows the properties of an anion receptor.

DESIGNING HAND TO HAND WITH SUPERCOMPUTER

Chemistry of nanographenes is a dynamically developing field, and research in this field is conducted in many of the best research centres in the world. For now, it is mainly basic research, but in the future the gathered knowledge will allow engineers to design new materials more easily and anticipate their desirable properties.

"Not 15 years has passed since the synthesis and description of graphene, and it already is considered by many to be the future of the whole material chemistry field. It is hundreds of times more durable than steel, it conducts electricity and heat well, it is practically transparent. We can imagine its use in mobile phones, displays, solar panels" - the researcher told PAP.

His work is largely based on computer modelling. Completely new compounds are developed in the laboratory and it is often difficult to predict how they will behave in reality. Majewski performs synthetic research, that is building compounds and forming them into appropriate shapes, at the Faculty of Chemistry of the University of Wrocław as part of a doctorate in the Organic Synthesis Team under the supervision of Prof. Marcin Stepień. ProfStępień is also responsible for modelling; for this purpose, he uses the resources of supercomputing centres in Poznan and Wroclaw.

"Computational aspect is very important in modern chemistry. By creating virtual models of future designed molecules and simulating some of their properties we can save a lot of time. It allows us to find out what direction a synthetic project should be going to achieve the goals" - said Majewski.

He noted that this is a complex process. First, he models his nanographene compound, then he figures out with what smaller elements - the mentioned "Lego" bricks - it can be built. Then he must make them in the laboratory and then work out how the individual bricks should be connected.

FROM A SCIENTIFIC CURIOSITY - A COMMERCIAL PRODUCT

The researcher admitted that there are many dead ands in his work, and the characterization of the obtained material usually requires cooperation with specialists in various fields of science, often also from other research centres. In the described project, some of the calculations, as well as description of certain electrochemical and luminescent properties of the obtained compounds was possible thanks to the researchers from the Yonsei University in Seoul (South Korea).

"The equipment available at the university allows us to study the magnetic properties of compounds, among other things. The basic technique for me - as an organic chemist - is nuclear magnetic resonance (NMR) spectroscopy, a modified version of which we know from hospitals under the name of magnetic resonance. Our spectrometer is designed to study a variety of chemical molecules. UV-Vis spectroscopy that tests the interaction of these compounds with visible and ultraviolet light is also helpful" - said the chemist.

Although graphene is still not cheap material, scientists and engineers can buy it without a problem. From a scientific curiosity it has become a commercially available product. However, as the researcher emphasised, laboratory scale production, which is many times smaller than industrial one, requires considerable resources, including laboratory equipment and chemical reagents. In this context, scientific grants become the basic form of research funding.

Marcin Majewski received funds from the National Science Centre and a START scholarship from the Foundation for Polish Science. He emphasised that in modern technologies the cost is considered differently and often one successful investment at the implementation level is enough to cover the costs of ten other, non-commercialised projects.

PAP - Science in Poland, Karolina Duszczyk

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