Ultra-fast, ultra-small and ultra-dilute: an integrated understanding of conjugated polymers in solution across spatial and temporal scales

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Conjugated polymers are an important class of organic (carbon-based) semiconductor. They combine novel semiconducting electronic properties with simple fabrication of devices from solution. They enable the field of plastic electronics including flexible lighting, displays, solar cells and electronics. Their combination of flexibility, ability to interconvert electricity and light, and simple fabrication is very unusual and enables many applications. One of the most interesting features of these materials is that they are both semiconductors and soluble. This means they can be dissolved to make a solution and deposited by simple processes such as ink jet printing to make working electronic and optoelectronic devices (such as light sources and solar cells). The behaviour of conjugated polymers in solution is very complicated because each polymer consists of a chain of atoms that is ultra-small and flexible, and so can fold in a different way. A particular shape of the polymer is known as its conformation. The conformation of the polymer is not static and can change at ultra-fast timescales in solution. The properties of the material then depend on the conformations of the constituent polymer chains, and the structure of films of the material are strongly influenced by the conformation of the polymers in the solution used to make the film.The aim of this proposal is to achieve a breakthrough in our understanding of conjugated polymers in solution by developing and applying new measurement techniques. Remarkably it is now possible to study individual molecules, one at a time to see how they are different from each other. In contrast to these ultra-dilute conditions, most experiments just measure average properties. The difference between these approaches is huge - like the difference between knowing the average height of people is 165 cm and the actual height of every person. We have made the first measurements in the world of single conjugated polymers in solution, demonstrating the feasibility of the approach. We now aim to transform our understanding of conjugated polymers in solution by studying individual molecules over a very wide range of timescales and length scales. In addition, we will study the interactions between polymers and how they form aggregates in solution, which are also known to impact the conformation of the polymer and the properties of the material.This work will involve developing measurements of exceptional spatial and temporal resolution. By bridging the gap between ultra-dilute single-molecule methods in solution, ultra-fast pump-probe and ultra-small super-resolution imaging, the proposal will deliver a set of 'first of its kind techniques' that will give unprecedented insights into CP function. The proposal will provide, for the first time, a measurement of the structural heterogeneity and dynamics of CP chains in solution and a direct correlation between each conformation and its photophysical properties. This basic knowledge will lay the foundations for improved conjugated polymers and devices and empower a broad range of applications across material sciences.