Dynamic Covalent Nanocrystal Building Blocks

The discovery of how to make nanoparticles from a range of materials has been one of the most important areas of chemical research over the past 20 years. These tiny but uniform fragments (about 0.000001 mm across) often display new and exotic properties. Yet, for many potential applications, nanoparticles must be assembled in an orderly fashion and integrated with other components (e.g., with molecules, electrical contacts, or other nanoparticles). We currently lack the synthetic chemistry techniques that would allow us to achieve this with generality and precision.
Commonly, inorganic nanomaterials such as semiconductor nanocrystals or metallic nanorods are stabilized by a single layer of organic molecules on their surface. Existing approaches for connecting nanoparticles to other objects have generally focused on forming bonds to these surface molecules using rather rudimentary reactions. Although sometimes fast and high-yielding, these approaches offer poor control over the final products. This proposal aims to develop a fundamentally different approach by extending some of the more sophisticated techniques that we already use to assemble materials from atoms and molecules, and apply them to the manipulation and assembly of nanomaterials.
To achieve this, we aim to exploit a class of bond-forming processes known as dynamic covalent reactions. Under suitable conditions, dynamic covalent bonds can form and break many times over. Conferring this ability on nanoparticles will allow them to 'self-assemble' into extended ordered arrays: by repeatedly forming, breaking and re-forming bonds with their neighbours, nanoparticles will be able to gradually arrange into ordered structures even if disordered aggregates are formed initially. As the nanoparticles are linked by strong covalent bonds, the final structures should be very stable. Tuning the linking molecules will allow control over the distance between the nanoparticles and the arrangements into which they pack; it will also allow the introduction of other features into the final product using the full range of synthetic chemistry at our disposal. Each of these capabilities will facilitate fine-tuning of the end material properties. Furthermore, the dynamic covalent reactions can be used to attach nanoparticles to specific components under one set of conditions, but break apart the assemblies under other conditions.
We propose to demonstrate and characterize the first example of dynamic covalent reactions taking place on the surface of nanocrystals. We will study the parameters that govern such reactions and will probe how these vary with changes to the molecular and nanocrystal structure. Subsequently we will explore the scope of this approach to: (a) reversibly alter the properties of nanoparticles; (b) join several nanoparticles together in a controlled manner to create assemblies of pre-determined design that can then be broken apart; (c) assemble nanoparticles into larger arrays and ordered materials where the arrangement is governed by the design of the surface-bound molecules.
By promising improved control over structure, diversity of building blocks and process reversibility, we predict that the concept of dynamic covalent nanocrystal building blocks will represent an entirely new and very powerful approach to manipulating and exploiting the remarkable nanomaterials that have been prepared over the past two decades.

This research aims to develop the new synthetic concept of dynamic covalent nanocrystal building blocks that will allow objects from different size regimes (i.e., molecules and nanocrystals) to be combined in a self-assembly process, with the aim of producing designer nanoconstructs and materials. This is high quality fundamental science with many potential follow-on impacts, both for the research community and ultimately for the exploitation of nanomaterials in end-user products.
The outcome of this work will be a new synthetic approach that will allow nanoparticles to be manipulated in much the same way as molecular building blocks can be today. This will afford the ability to create a range of designer and responsive nanoconstructs, aggregates and materials displaying new and unique properties. As virtually every potential application of nanomaterials requires them to be integrated with other components, the potential impact of transformative synthetic advances that facilitate this goal is huge. Yet, current solutions only offer rudimentary control, or specific solutions that are hard to generalize.
In the short to medium term, the techniques developed by this project will impact research and development involving nanomaterials in a variety of fields - from chemistry to bioengineering; from materials science to optical physics - and in both academic and industrial environments. It will allow control, with molecular precision, of nanoparticle assembly to form dynamically responsive aggregates or ordered materials and will provide a new route to interface nanoparticles with other components such as surfaces, electrodes or biomolecules. For example, a general method for switching nanomaterial properties such as solubility, in a mild and reversible procedure by attaching a dynamic covalent modifier, would have significant benefits for nanomaterial handling and processability, both on the laboratory and the industrial scale.
In the longer term, it is anticipated that new materials made possible by this synthetic technique will display unique emergent properties - as already indicated by the relatively simple nanoparticle-based materials created to date. Such materials have intrinsic interest for the insights they will bring to the understanding of how matter behaves at the nanoscale. Ultimately however, the unique properties of novel nanoparticle-based materials have the potential to impact a very wide range of industries. Oligonucleotide-based NC functionalization and assembly has already led to commercial successes in the biomedical field. It is to be expected that alternative non-biological linking strategies that can exploit the full gamut of synthetic molecular chemistry will be key to unlocking the potential of NC assemblies for a much wider range of application areas, including telecommunications, microelectronics and photonic circuitry.
Finally, it is also imperative that modern synthetic chemists have the training and experience to work with nanomaterials, as such skills will be in high demand in both the academic and industrial R&D sectors in the future. This project aims to combine molecular, supramolecular and nanochemical synthetic principles and as such the researchers working on this project will develop a strong skill set that ideally places them to be leaders in exploiting nanomaterials in the future.