"This is one of the most important works that this research group has done in its history, and that is saying a lot", especially in a team that is able to characterize and synthesize its own carbon nanostructure materials, which has made it one of the most important groups "not only in Europe, but also internationally". This is what Nazario Martín León, professor in the Department of Organic Chemistry and director of the Organic Molecular Materials group, says when he explains the pioneering work published in Nature Synthesis, in which the chirality of a graphene fragment has been controlled, which opens the door to the possibility of scaling it up and developing materials with new properties.
Starting with the most basic: ¿ What is chirality - The best example to explain it is our own hands, which are mirror images, which cannot be superimposed on each other, and if we want to join our nails together, each hand looks to one side. Chirality, according to Nazario Martín "is inherent to nature and, above all, inherent to life". We ourselves, humans, have a type of amino acids, a type of sugars, that only have one type of chirality, towards one of the two sides. This is fundamental for the development of drugs that are not harmful, and the emblematic example is thalidomide, which, if it had one type of chirality, was useful for reducing the symptoms of pregnant women, but if it had the other chirality, it caused cancer and malformations.
Explained in a more scientific way, it can be said that "drugs are compatible and effective if they are enantioselective, i.e. if they present only one of the enantiomers of a substance, an enantiomer being each of the two isomeric forms that are non-overlapping images with their mirror image".
The pharmaceutical industry has already succeeded in producing drugs with a specific chirality, but accessing chiral materials in enantiopure forms is still a challenge in chemistry, and even more so in some materials such as graphene, which is a completely flat sheet. In fact, it was something that had not been achieved until the doctoral thesis of Manuel Buendía, from the Faculty of Chemical Sciences, which has been reflected in the article published in Nature Synthesis.
It should be remembered that graphene, formed only by carbon atoms and hexagons, reminiscent of a honeycomb, is a flat surface of atomic thickness, i.e., its thickness is only one carbon atom. The work of the Complutense group has managed to create chirality from this flat surface by introducing a defect in it, which makes it lose its planarity in a controlled manner, thus giving rise to one of the two possible enantiomers, being able to choose the one desired in a process of asymmetric or enantioselective synthesis.
Martín León adds that this is "the first time in history that this graphitization reaction has been carried out in an enantioselective manner, and this reaction has been known since 1910". Thanks to the method designed by the Complutense group, the two chiral structures can be extracted from a fragment of graphene at will, in a defined and designed manner.
Manuel Buendía recognizes that it has been a hard work, but satisfactory for the results, which has taken him three years, "where sixty or seventy conditions have been used, with different catalysts, to finally reach one of the precursors that gave the appropriate synthetic route". The author of the doctoral thesis also points out the work of Salvatore Filippone and Jesùs Manuel Fernández-García, "who have been a key player". Nazario explains that before the synthesis, a design of the synthesis must be made, and "this important work has been done by Filippone and Fernández-García; while the X-ray diffraction has been done by Josefina Perles, from the Universidad Autónoma de Madrid".
Fernández-García recognizes that "the conditions used are clearly reproducible, and also scalable", which is ideal for industrial use, and although it is true that this is the first time that this concept has been used in nanographene chemistry, "that is, it is the first time that a nanographene has been made enantioselectively, this opens the door for other research groups, with imagination, to make similar structures. Here we describe the technique, the way to make them, and other groups can design their own routes to make theirs based on this pioneering work".
Nazario Martín makes it clear that "this is an important achievement in the chemistry of carbon nanostructures, which should be included in the field of advanced materials". And although they are at a very early stage of research, the fact of being able to control at will the chirality in a fragment of graphene is a very important leap.
Little by little, different properties are being discovered and they have designed, for example, "molecular bilayers, which are molecules genuinely from the UCM group, which have practically been developed here, and if they connect, on one side that is also chiral, a helicene that goes up in one direction or another, they can act in many ways, they can be spin filters, for quantum computing for example, or they can modify paramagnetic surfaces. That is, they have free electrons, and these can be organized in some way". With respect to this, some measurements are already being made by a physicist in Germany and "he is enthusiastic about the result he sees when putting chiral molecules of this type on surfaces that are also chiral".
They are also designing smaller molecules, which due to the effect of electronic confinement, allow the electrons to move in a confined space and new properties appear, new electronic levels, and that makes them have luminescent properties. "We can now play with a luminescent molecule that is also chiral, where the luminescence is polarized, without forgetting that they are only pure carbon molecules, and that is what is interesting, that, although they are only carbon, they show photophysical and chiroptic properties". Martín León clarifies that "organic molecules usually have functional groups, such as oxygen and nitrogen, but this is pure carbon, they are fragments of graphene to which a defect is induced and molecules are obtained that are luminescent, but also circularly polarized, thanks to the presence of this defect that has been introduced".
The future is open to multiple applications, from LEDs to sensors, field effect transistors of organic nature or the aforementioned quantum computing, and, as the publication of this work shows, this group of researchers from the Faculty of Chemical Sciences of the Complutense University will certainly be involved in this future, "a group of very enthusiastic young people who are working on a subject that excites them all, and that they are spreading to each other".
