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Twisted heteroaromatic diimides: thermally-activated delayed fluorescence (TADF) emitters for next-generation organic light-emitting technologies


Department of Chemistry

About the Project

The design of thermally activated delayed fluorescence (TADF) materials has emerged as a key priority in the pursuit of sustainable organic light-emitting technologies of the future. This past decade has experienced rapid advances in molecular design criteria, our mechanistic understanding of TADF photopysics and critical proof-of-concept performance within organic light-emitting diodes (OLEDs) that suggest these next-generation electroluminsecent materials will soon overtake and replace relatively more expensive phosphorescent metal complexes in EL devices. Compared with exisiting liquid-crystal and older-generation displays, advanced OLEDs comprising TADF emitters offer improved image quality and contrast (i.e., better blacks), a fuller colour range, lower cost and enhanced energy efficiency from thinner, lighter, more flexible devices.

In order to access desireable TADF properties, organic small molecules must typically display enhanced charge transfer (CT) contributions to the singlet (S1) excited state through (i) good HOMO/LUMO separation and (ii) thermally promoted reverse intersystem crossing (RISC) from the triplet (T1) excited state back to the emissive S1 state via a small ∆EST value, leading to high photoluminescence quantum yields (PLQYs) and excited state lifetimes. Synthetically, these criteria can be achieved by incorporating twisted conformations along with steric hindrance to moderate the conjugation of intramolecular donor (D) and acceptor (A) systems within a rigid molecular structure. Moreover, the realisation of full-spectrum TADF emitters (i.e., from blue to red) relies on the systematic modulation of HOMO–LUMO gaps and emission colours using suitable D–A combinations. Therefore, the development of efficient synthetic methods to discover and widely access inherently novel D–A systems for the TADF toolbox remains at the forefront of research in the field.

At the University of York, the Avestro Group has established efficient synthetic methods to generate highly luminescent (PLQYs >85%), redox-active heteroannulated aromatic diimide acceptors that can undergo versatile substitutions, e.g., to afford new D–A systems with TADF potential. Steric effects impose twisting and/or helical chirality within structurally rigid molecules to maximise RISC for TADF. Notably, helical chiroptically-active TADF emitters that are simultaneously capable of circularly polarised (CP) luminescence may circumvent the need for expensive anti-glare CP filters that raise the cost and lower the energy efficiency of current OLED technologies. We therefore seek the next excellent member of our team to champion our organic synthetic methodology and discover desirable TADF-active systems suitable for the above goals.

Training
In addition to receiving a world-class training in organic synthesis and supramolecular chemistry of electroactive molecular materials, the successful candidate will train in advanced steady-state and time-resolved spectroscopies, electrochemistry, chiroptical analysis, and DFT/TD-DFT computational modelling in order to elucidate the structural and mechanistic origins of TADF from their compounds. The most promising TADF emitters will be assessed in prototypical OLED devices prepared by expert collaborators at Durham and Northumbria Universities via the Northeast Centre for Energy Materials (NECEM). We anticipate the student will participate in externally-funded visits to our collaborators in order to gain hands-on experience in cutting-edge OLED fabrication and evaluation techniques. Moreover, in line with our broader impact goals, the student will be encouraged and financially supported to engage with the Avestro Group in Royal Society-funded outreach to disseminate their PhD research to a wider public audience. All Chemistry research students have access to our innovative Doctoral Training in Chemistry (iDTC): cohort-based training to support the development of scientific, transferable and employability skills: https://www.york.ac.uk/chemistry/postgraduate/idtc/

The Candidate
The Avestro Group invites applications from all excellent candidates with a Chemistry or Chemistry-related background with experience in organic synthesis and enthusiasm to approach real-world problems from a fundamental and interdisciplinary perspective. You should hold or expect to achieve the equivalent of at least a UK upper second class degree in Chemistry or a related subject. Please check the entry requirements for your country: https://www.york.ac.uk/study/international/your-country/. We are a diverse, international team inclusive to all ages, identities, backgrounds and career paths. Successful candidates will not only have the appropriate scientific background, but will share—and actively promote—our inclusive team ethos of ‘winning together.’ Good humour is always a plus!

The Department of Chemistry holds an Athena SWAN Gold Award and is committed to supporting equality and diversity for all staff and students. The Department strives to provide a working environment which allows all staff and students to contribute fully, to flourish, and to excel: https://www.york.ac.uk/chemistry/ed/.

For more information about the project, click on the supervisor’s name above to email the supervisor. For more information about the application process or funding, please click on email institution


Funding Notes

This project is available to students from any country who can fund their own studies.

The Department of Chemistry at the University of York is pleased to offer Wild Fund Scholarships. Applications are welcomed from those who meet the PhD entry criteria from any country outside the UK. Scholarships will be awarded on supervisor support, academic merit, country of origin, expressed financial need and departmental strategy. For further details and deadlines, please see our website: View Website

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