Preparing Multimetallic Architectures for the Control of Multiple Excited States

This project will investigate multimetallic complexes of trivalent lanthanide ions. A trivalent lanthanide ion is a 3+ ion of any of the lanthanide elements (from cerium to lutetium). A multimetallic complex is a molecular entity which contains two or more different metal atoms and a ligand framework holding the complex in place. To make well-defined multimetallic lanthanide complexes, where the molecular distribution of the different ions is known and consistent this project will use kinetically inert complexes. Kinetically inert complexes do not 'scramble' in solution i.e. once the metal is in one binding site it remains in that binding site.
The photophysical properties of the complexes will be studied; to examine how they behave when they have light shone on them. The photophysical properties of the lanthanide ions are generally dominated by their f-electrons, and f-f transitions. An f-f transition is where the ion goes from one energy state to another, which occurs solely within the f-orbitals of an ion. When the lanthanide ions have light shone on them (are illuminated) they can absorb light, undergoing a transition and moving to an excited state (a state higher in energy than the ground state, the lowest energy state, it is in this state that the complex usually exists). According to the selection rules which govern how molecules absorb and emit light these f-f transitions have a very low probability of occurring, thus, the ions do not absorb well. It is common to sensitise a complex, by appending a group which does absorb light well. Sensitisation is the name given to building in another part of the molecule which can absorb light well. Once this part has absorbed the light it goes from its ground state (where it exists normally) to an electronically excited state. An excited state is a name given to any state of a molecule which is higher in energy than the ground state. The excited state can transfer its energy to the lanthanide ion, which is then moved to its excited state, whilst the other part is returned to its ground state.
Whilst energy transfer from a sensitising molecule is fairly well understood, what is not well understood is energy transfer between lanthanide ions in a molecular system. This project wants to look at how the lanthanide ions transfer energy between each other in multimetallic complexes.
This project will also look at what happens when a complex contains two lanthanides in their excited state. The lifetime of a molecule that emits light is the average amount of time the molecule exists in the excited state. For organic species, such as the ligands used to sensitise lanthanide emission, this is commonly on the order of 10s of nanoseconds (ns), one nanosecond is one billionth of a second. For the lanthanide ions this can be thousands to millions of times longer. The lifetimes are, comparatively, long for the same reason that the ions do not absorb light well, the f-f transitions have a very low probability of occurring.
By exploiting the longer lifetimes of lanthanide ions, and that the sensitising ligand returns to the ground state after it has transferred its energy, we envision that we can go through the process a second time, exciting a second lanthanide ion, before the first has emitted light (decayed). The processes required for sensitisation are typically faster than the average lifetimes of several lanthanide ions, thus, this is feasible. To the best of our knowledge this has not been attempted before.
This project falls within the EPSRC synthetic coordination chemistry research area.

The primary impact of the OxICFM CDT will be the highly-trained world-class scientists that it delivers. This impact will encompass both the short term (during their doctoral studies), the medium term (subsequent employment) and ultimately the longer timescale defined by their future careers and consequent impact on science, engineering and policy in the UK.

The impact of OxICFM students during their doctoral studies will be measured by the culture change in graduate training that the Centre brings about - in working at the interface between inorganic synthesis and manufacturing, and fostering cross-sector industry/academia working practices. By embedding not only from larger companies, but also SMEs, we have developed a training regime that has broader relevance across the sector, and the potential for building bridges by fostering new collaborations spanning enormous diversity in scientific focus and scale. Moreover, at a broader level, OxICFM offers to play a unique role as a major focus (and advocate) for manufacturing engagement with academic inorganic synthetic science in the UK.

From a scientific perspective, OxICFM will be uniquely able to offer a broad training programme incorporating innovative and challenging collaborative projects spanning all aspects of fundamental and applied inorganic synthesis, both molecular and materials based (40+ faculty). These will address key challenges in areas such as energy provision/storage, catalysis, and resource provision/renewal necessary to enhance the capability and durability of UK plc in the medium term. To give some idea of perspective, the output from previous CDTs in Oxford's MPLS Division include two start-up companies and in excess of 30 patents.

It is not only in the industrial and scientific realms that students will have impact during their timeframe of their doctorate. Part of the training programme will be in public engagement: team-based challenges in resource development/training and outreach exercises/implementation will form part of the annual summer school. These in turn will constitute a key part of the impact derived from the CDT by its engagement with the public - both face-to-face and through electronic/web-based media. As the centre matures, our aspiration is that our students - from diverse backgrounds - will act as ambassadors for the programme and promote even higher levels of inclusion from all parts of society.

For our partners, and businesses both large and small in the manufacturing sector, it will be our students who are considered the ultimate output of the OxICFM CDT. Our programme has been shaped by the need of such companies (frequently expressed in preliminary discussions) to recruit doctoral graduates who can apply themselves to a broad spectrum of multi-disciplinary challenges in manufacturing-related synthesis. OxICFM's cohort-based training programme integrates significant industry-led training components and has been designed to deliver a much broader skill set than standard PhD schemes. The current lack of CDT training at the interface of inorganic chemistry and manufacturing (and the relevance of inorganic molecules/materials to numerous industrial sectors) heightens the need for - and the potential impact of - the OxICFM CDT. Our students will represent a tangible and valuable asset to meet the long-term skills demand for scientists to develop new materials and nanotechnology identified in the UK Government's 2013 Foresight report.

In the longer term, the broad and relevant training delivered by OxICFM, and the uniquely wide perspective of the manufacturing sector it will deliver, will allow our graduates to obtain (and thrive in) positions of significant responsibility in industry and in research facilities/institutes. Ultimately we believe that many will go on to be future research leaders, driving innovation and changing research culture, and thereby making a lasting contribution to the UK economy.