Periodic Reporting for period 1 - NANOSPHERE (NANOStructure Photochemistry via Hot Electron driven REactions)
Reporting period: 2015-03-15 to 2017-03-14
The spacing between nanoparticles within an assembled nanoparticle structure ultimately determines the structures optical properties, as well as the strength of the optical near field that can be focussed between particles. It is therefore crucial that inter-particle spacing be controlled with utmost accuracy. Whilst synthetic routes for controlling nanoparticle size and shape have dramatically improved during the past two decades, the development of methods for controlling inter-particle spacing in assembled nanostructures has remained a fundamental scientific challenge.
Although nanoparticles and assembled nanoparticle structures offer orders of magnitude increases in performance in a wide variety of applications, such applications have not as-of-yet benefited from nanostructure incorporation due to the difficulty in assembling nanostructures reproducibly with accurate control of inter-particle spacing, despite intense research. This research proposal aimed to utilise the unique macrocyclic host-guest chemistry of cucurbit[n]urils in conjunction with metal nanoparticles to demonstrate a novel and malleable approach to nanoparticle self-assembly, resulting in structures that will be used in light-driven chemical reactions and advanced molecular sensing.
Furthermore, CB has been used to assembled hydrogel networks that incorporate CePO4 nanowires (NWs). It was demonstrated that the incorporation of wires into this system augments the rheological nature of the gel, and thus reinforcing it. The supramolecular hydrogel used was comprised of methyl viologen-functionalised poly(vinyl alcohol) (PVA-MV), hydroxyethyl cellulose with naphthyl moieties (HEC-Np) and CB macrocyclic hosts. It was demonstrated that gel structure can be effectively enhanced by the framework supporting effects of CePO4 NWs and additional hydrogen bonding interactions between the NWs and the PVA-MV/HEC-Np polymers. The high aspect ratio NWs serve as a “skeleton” for the network, providing extra physical crosslinks, resulting in a single continuous phase hybrid supramolecular network with improved strength, presenting a general approach to reinforce soft materials.
Thermo-responsive materials are generating significant interest on account of the sharp and tunable temperature deswelling transition of the polymer chain. Such materials have shown promise in drug delivery devices, sensing systems, and self-assembly. Incorporation of nanoparticles (NPs), typically through covalent attachment of the polymer chains to the NP surface, can add additional functionality and tunability to such hybrid materials. The Fellow has demonstrated that the aggregation of PNIPAm-coated AuNPs, and likely other such materials, relies on the size and concentration of unbound “free” PNIPAm in solution, contray to popular belief (Figure 1(d)). It is this unbound polymer that also leads to an increase in solution turbidity, a characteristic that is typically used to prove nanoparticle aggregation.
The Fellow has also applied CB[n] macrocycles to gas encapsulation, reduction chemistries via hot electron generation and chemical sensing applications and the details of these outcomes will be published in due course.
Furthermore, the Fellow has produced a review article that covers the vast scientific areas that the study of CB[n] host-guest chemistry has affected. These areas include polymer chemistry, hydrogel formation, nanoparticle and bulk surface functionalisation, gas encapsulation, catalysis and many more. In addition, comprehensive tables were produced that include guest molecules specific to CBs 5, 6, 7 and 8, along with binding constants and methods of determination. This represents the first time that such information has been available in one place. Given that the application of CB[n] host-guest chemistry is driven by the types of guest molecules that CB[n]s can accommodate, it is envisaged that these tables will encourage the discovery of new guest molecules, and thus new applications, for CB[n] macrocycles.