Molecular Endofullerenes: Nanoscale dipoles, rotors and oscillators

Lead Research Organisation: University of Nottingham
Department Name: Sch of Physics & Astronomy

Abstract

Fullerenes are football-shaped cages of carbon atoms, for the discovery of which the British scientist Harry Kroto won the Nobel prize in 1996. Inside the cage is an empty space. Chemists and physicists have found many ingenious ways of trapping atoms or molecules inside the tiny fullerene cages. These encapsulated compounds are called endofullerenes.

A remarkable method was pioneered by the Japanese scientists Komatsu and Murata, one of whom is a project partner on the current proposal. They performed "molecular surgery". First, a series of chemical reactions was used to open a hole in the fullerene cages. A small molecule such as water (H2O) was then inserted into each fullerene cage by using high temperature and pressure. Finally, a further series of chemical reactions was used to "sew" the holes back up again. The result was the remarkable chemical compound called water-endofullerene, denoted H2O@C60.

Our team has succeeded in developing a new synthetic route which requires milder conditions and has improved yield for the production of H2O@C60. In addition we will encapsulate other small molecules in the fullerene cage, including ammonia (NH3) and methane (CH4).

Molecules of ordinary water have two forms, which are called ortho and para-water, which are distinguished by the way the magnetic hydrogen nuclei point: in opposite sense for para-water, and in the same sense for ortho-water. In ordinary conditions, these two forms interconvert rapidly, and cannot be isolated. However, by trapping water molecules inside fullerene cages, the two forms are isolated and may be studied separately.

We recently observed that these two forms of water have different electrical properties. At low temperatures, the two forms interconvert over a period of tens of hours. We will study the interconversion of the two forms of water, and develop a theory of why this conversion changes the electrical properties.

In order to understand how these molecules behave, we will use several techniques. These methods include nuclear magnetic resonance (which involves a strong magnet and radiowaves), neutron scattering (in which the material is bombarded with neutrons from a nuclear reactor) and infrared spectroscopy (which involves the absorption of low-energy light waves). By combining the information from these different techniques, we will build up a complete picture of the quantum-mechanical behaviour of the trapped molecules.

Since ortho and para-water have different electrical properties, we expect to distinguish between single H2O@C60 molecules in the ortho and para states, by measuring the electrical response of single molecules. This will be done scanning over a surface loaded with the fullerenes, using a very sharp tip. In this way, we hope to observe the ortho to para transition of single molecules - something that has never been done before.

Although most of this project concerns basic science, this project could lead to technological and even medical advances in the future. For example, the ortho and para states of the individual H2O@C60 molecules could allow the storage of one bit of information inside a single molecule, without damaging it in any way. This might lead to a new form of very dense data storage. Since a single gram of H2O@C60 contains about 10^19 molecules, this single gram could in principle store 1 million terabytes of information, sufficient to store the DNA sequences of everyone on the planet (although it will be very difficult to store and retrieve this information). In addition, the quantum behaviour of the encapsulated molecules is expected to give rise to greatly enhanced magnetic resonance signals, leading to the possibility of greatly enhanced MRI images, with considerable medical benefits.

Publications

10 25 50
 
Description The key findings resulting from this project thus far are as follows: (i) A detailed understanding of the extent to which quantum mechanics underpins the behaviour of small molecules (HF, H2O, H2) trapped inside fullerenes (i.e. nanoscopic carbon cages); (ii) analysis of the role of the spin state of the encaged molecule on the dielectric properties of a bulk endofullerene sample; (iii) determination of the role that the external environment (e.g. adsorption on a solid surface) has on the encaged molecule.
Exploitation Route Our findings thus far reveal key aspects of how delicate quantum systems can both be protected from, and 'communicate' to, the external world.
Sectors Education,Electronics

URL https://www.youtube.com/watch?v=tWWyAklkYqM
 
Description A key non-academic impact is the "Anatomy of a Physics Experiment" series of videos for the Sixty Symbols YouTube channel: https://www.youtube.com/watch?v=tWWyAklkYqM . (Links to the other videos are in the information section at that YT upload). This has reached an audience nearing 100,000 and, if YT metrics can be taken at face value (which is always problematic), has been well-received.
First Year Of Impact 2017
Sector Education
Impact Types Cultural,Societal

 
Description Collaboration with King's College London 
Organisation King's College London
Department Department of Physics
Country United Kingdom 
Sector Academic/University 
PI Contribution This project is a collaborative effort between Nottingham and King's College London, where KCL (Prof. Lev Kantorovich et al.) carries out the theoretical calculations used to support and inform the experimental work at Nottingham.
Collaborator Contribution Density functional theory calculations.
Impact A large number of publications have resulted from the Nottingham-KCL collaboration. These are listed as part of the outputs for each project. The Nottingham-KCL activity has also fed directly into a number of videos for the Sixty Symbols YouTube channel. Again, those outputs are listed for each of the relevant grants.
Start Year 2009
 
Description Anatomy of a Physics Experiment -- YouTube video 
Form Of Engagement Activity Engagement focused website, blog or social media channel
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Public/other audiences
Results and Impact "Anatomy of a Physics Experiment" is one of a "triology" of videos made for the Sixty Symbols YouTube channel [1]. At the time of writing, the video has attracted 94,557 views across an international audience. (It should be noted, however, that for YouTube videos, view counts very often do not correlate with quality..!) The video describes X-ray standing wave experiments carried out at the Diamond synchrotron as part of the "Molecular Endofullerenes" project.
Year(s) Of Engagement Activity 2017
URL https://www.youtube.com/watch?v=tWWyAklkYqM