PhD Project : Single-molecule spectroscopy and super-resolution imaging of organic semiconductor materials  

Organic semiconductors based on light-emitting conjugated polymers are attracting considerable interest in semiconductor physics and are emerging as exceptional 'plastic-like' materials for optoelectronic applications including displays, lasers and solar cells. 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 strongly on the range of conformations adopted by the constituent polymer chains forming the film. Remarkably it is now possible to study individual molecules, one at a time to see how they are different from each other and we have recently reported the first single-molecule studies regarding the optical properties of individual semiconducting materials in organic solvents commonly used for device fabrication [1-3]. In this project, we aim to combine single-molecule super-resolution spectroscopy with magnetic tweezers to apply force to individual molecules. By merging these techniques, we will be able to stretch the polymer chain at will and understand in more detail how the conformation of the polymer chain impacts its light-emission properties. Importantly, we will apply for the first-time super-resolution imaging methods to resolve, beyond the diffraction limit, the structure of the polymer chain as a function of applied force. The results will help to understand, with an unprecedented level of detail, how the shape of the polymer impacts light absorption and emission processes. Gaining this fundamental knowledge is crucial to rationalize the development of new solution-processing methods that improve device performance. The project is a collaboration between the groups of Prof Ifor Samuel and Dr Carlos Penedo. Applicants should have a degree in Physics or Chemistry, particularly Physical Chemistry, and be motivated to explore new research questions and directions. Some previous experience in photo-physics, optical instrumentation or fluorescence spectroscopy is desirable but not required. The project will combine experimental measurements, instrument development and advanced data analysis. The student will join the Centre of Biophotonics (https://synergy.st-andrews.ac.uk/cob/) and the Organic Semiconductor Centre (https://www.st-andrews.ac.uk/~osc/home.shtml). Informal enquiries regarding this project may be addressed to Dr Carlos Penedo – email jcp10@st-andrews.ac.uk and to Prof Ifor Samuel (idws@st-andrews.ac.uk). 

References:

 [1] Dalgarno, Paul A., Christopher A. Traina, J. Carlos Penedo, Guillermo C. Bazan, and Ifor D. W. Samuel. (2013) Solution-Based Single Molecule Imaging of Surface-Immobilized Conjugated Polymers. J. Am. Chem. Soc. 135 (19): 7187–93. 

[2] Tenopala-Carmona, F., Fronk, S., Bazan, G., Samuel, I. D. W., Penedo, J.C. (2018) Real-time observation of conformational switching in single conjugated polymer chains. Sci. Advances, 4: eaao5786. 

[3] Brenlla, A., Tenopala-Carmona, F., Kanibolotsky, A. L., Skabara, P., Samuel, I. D. W., Penedo, J.C. (2019) Single-Molecule Spectroscopy of Polyfluorene Chains Reveals β-Phase Content and Phase Reversibility in Organic Solvents. Matter, 1, 1399–1410.

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