Science

The absorption of light by molecules leads to the formation of molecular excited states, consisting of electron-hole pairs, called excitons. Control of excitons is essential for many new and emerging technologies identified in the Government’s Industrial Strategy as being vital to the economic success of the UK, including solar energy capture, photocatalysis, quantum technologies, and the design of diagnostic devices for personalised medicine.

An unsolved grand challenge has been to develop design rules for the long-range transport of excitons. Our goal is to solve this grand challenge.

The problem is that exciton diffusion lengths are small in most molecular materials: excitons move typically only about 10 nm, perhaps exceptionally a few 10s of nm, before they recombine, cancelling themselves out. This places severe constraints on the development of new technologies.

The goal of our five year, £7.25M programme is to explore an entirely new approach to the design of molecular photonic materials that could extend excitation transfer distances from nm to cm. At the core of our proposal is the construction of programmable molecular photonic breadboards, a modular approach to the design of photonic materials that is inspired by natural photosynthetic membranes. In optics, breadboards are used to organise optical components precisely in space. In molecular photonic breadboards, minimal units – synthetic antenna complexes – are designed from scratch to organise molecular components precisely in space. These building blocks are assembled to form nanostructured films in which energy transfer pathways are controlled from the nm to the cm scale.

At the heart of our strategy is the combination of biologically-inspired design principles with the exciting new physics of strong light-matter coupling, in which, under certain conditions, the properties of excitons are mixed with those of localised surface plasmon resonances to yield new hybrid states that combine the properties of light and matter. There is now a large body of theory literature that suggests that these strongly coupled materials may have extraordinary properties. For example, theory suggests that the excited states in strongly-coupled systems are delocalised across many molecules, enabling coherent, long-range transport of energy and information, and allowing us to create new optical states to order by mixing the properties of multiple excitons Thus, the physics of strong light-matter coupling enable us to reimagine the design of photonic materials in entirely new ways.

At the moment, there are no established methods to build materials to take advantage of these effects. Molecular photonic breadboards will provide this for the first time. We will develop design principles for the programmable fabrication of materials in which transport of energy and information is controlled from the nm to the cm scale, materials that are capable of being tailored to meet the needs of many different kinds of applications, including (as illustrated in our proposal) optoelectronics, medical diagnostics and photocatalysis. Our goal is to lay the foundations for a revolution in the design of molecular photonic materials.