Molecular Photonic Breadboards

New manufacturing methods are required if we are to live sustainably on the earth. In the electronics industry there is enormous interest in the possibility of manufacturing devices using organic materials: they can be manufactured sustainably from earth-abundant resources at energy costs that are typically significantly less than those associated with the production of equivalent inorganic materials. Electronic devices based on organic components are now readily available in the high street. For example, organic light-emitting diodes are used to produce the displays used in some high-end TV sets and in smartphones (e.g. iPhone X). However, a fundamental problem prevents the realisation of the full potential of organic materials in electronic devices. When light is absorbed by molecular semiconductors, it causes the creation of excitons - pairs of opposite charges - that carry excitation through the device. However, the excitons in organic materials recombine and cancel themselves out extremely rapidly - they can only move short distances through the material. This fundamental obstacle limits the application of organic materials in consumer electronics and also in many other areas of technology - in quantum communications, photocatalysis and sensor technologies. We propose an entirely new approach to solving this problem that is based on combining molecular designs inspired by photosynthetic mechanisms with nanostructured materials to produce surprising and intriguing quantum optical effects that mix the properties of light and matter. On breadboards, threaded mounts hold optical components relative to one another so that rays of light can be directed through an optical system. This proposal also aims to design breadboards, but of a very different kind. The smallest components will be single chromophores (light absorbing molecules), held at fixed arrangements in space by minimal building blocks called antenna complexes, whose structures are inspired by those of proteins involved in photosynthesis. Antenna complexes are designed and made from scratch using synthetic biology and chemistry so that transfer of energy can be controlled by programming the antenna structure. Instead of using threaded mounts, we will organise these components by attachment to reactive chemical groups formed on solid surfaces by nanolithography. In these excitonic films, we will develop design rules for efficient long-range transport. In conventional breadboards, light travels in straight lines between components. However, we will use the phenomenon of strong light-matter coupling to achieve entirely different types of energy transfer. In strong coupling, a localised plasmon resonance (an light mode confined to the surface of a nanoparticle) is hybridised with molecular excitons to create new states called plexcitons that combine the properties of light and matter. We will create plexcitonic complexes, in each of which an array of as many as a thousand chromophores is strongly coupled to a plasmon mode. In these plexcitonic complexes, the coupling is collective - all the chromophores couple to the plasmon simultaneously, and so the rules of energy transfer are completely re-written. Energy is no longer transferred via a series of linear hopping steps (as it is in organic semiconductors), but is delocalised instantaneously across the entire structure - many orders of magnitude further than is possible in conventional organic semiconductors. By designing these plexcitonic complexes from scratch we aim to create entirely new properties. The resulting materials are fully programmable from the scale of single chromophores to macroscopic structures. By combining biologically-inspired design with strong light-matter coupling we will create many new kinds of functional structures, including new medical sensors, 'plexcitonic circuits', and quantum optical films suitable for many applications, using low-cost, environmentally benign methods.