Measuring Nanoscale Exciton Motion & Annihilation in Single Molecules with Photon Statistics

Organic semiconductors are an important optoelectronic technology that have achieved widespread adoption in displays with organic light emitting diodes (OLEDs). Upon electrical or photo excitation, excited state quasiparticles called excitons are created. Excitons can move in the material before decaying and emitting light. If two excitons meet, one can often eliminate the other (a process called annihilation), a loss mechanism that reduces light emission. For high brightness application of OLEDs such as lighting, high exciton densities are required, thus the movement of excitons and their annihilation can curb light emission. Exciton motion and annihilation are typically challenging to measure, therefore there is a knowledge gap in understanding these processes that limits the rational design of new materials.

In this proposal unique new background-free single molecule spectroscopic measurements of the absolute number of, motion and annihilation between excitons on single molecules will be made. By measuring molecules with known geometries and different chemical moieties, the relationship between the structure of a molecule and how excitons move and annihilate will be established. The realisation of organic semiconductor materials that can sustain high exciton densities, suitable for use in lighting or organic lasers depends upon fundamental understanding. Thus, the vision in this work is to close the knowledge gap in understanding, lighting a path towards the design of advanced next generation organic semiconductor materials that will have enhanced device performance.

Impact from this proposal will be delivered in the following areas:

Knowledge: The science in this proposal lends itself well to publication in internationally leading research journals and dissemination at international conferences. Publications will conform to UKRI open access guidelines, and underpinning data will be lodged with the University of Glasgow data repository. Knowledge impacts from these dissemination routes are fundamental knowledge on important fundamental processes in organic semiconductors, and knowledge of advantageous chemical structures/geometries that have minimised exciton annihilation that will lead to improved device performance.

Society: Novel online streaming of the science in this proposal will be established to reach new demographics with cutting-edge science. The underpinning concept behind this is to put into practice the idea that we as scientists are inspired by the process of discovery, not just having a completed story told to us in summary form. Consequently, live streaming of microscopy images/data will be made, with support from the university of Glasgow's chemistry outreach team and Dr Zara Gladman, the University's public engagement officer.

Economy: This proposal will determine the design rules for materials that have advantageously low annihilation. The knowledge base that will be established at the School of Chemistry, University of Glasgow, will offer significant long-term economic impact in devising new materials that have beneficial device relevant properties. It is anticipated that longer-term impact will occur in future follow-on proposals that seek to build devices. The time-resolved antibunching methodology has potential commercial impact, so any possible intellectual property will be examined. Companies such as Horiba, who's division that build photon counting & correlation products is based in Glasgow, will be approached to explore possible commercialisation.

People: Impact will occur in the transfer of skills and knowledge to the appointed PDRA and PhD students. Specifically, the new time-resolved photon antibunching technique is a powerful new methodology, and knowledge of it and wider single molecule spectroscopy techniques will be valuable for future career development within research. Additionally, new knowledge obtained on exciton motion and annihilation with this proposal would be beneficial for researchers continuing in organic semiconductor or spectroscopic fields of research. Furthermore, the University of Glasgow provides the Researcher Development Framework, giving appropriate training on advanced professional skills and career development opportunities and the PI would offer his expertise in helping PDRA and PhD students reach career maturity.