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Posts

Beyond optical spectroscopies: using electron spin resonance to understand organic LED efficiency

less than 1 minute read

Published: July 31, 2021

To accompany my publication Electron spin resonance resolves intermediate triplet states in delayed fluorescence, I wrote a ‘Behind The Paper’ blog post for the Nature Portfolio Chemistry Community that gives a more general overview of the research motivation and journey. Read the blog post here.

Flipping spins to boost the efficiency of LEDs

less than 1 minute read

Published: May 09, 2021

I wrote a short article for my Doctoral Training Centre that explains the physics behind one area of my research: flipping spins to boost the efficiency of LEDs. The target audience is the general public and those interested in joining the NanoDTC programme. Read the article here.

Japan 2019: Culture & Collaboration

1 minute read

Published: October 14, 2019

In September and October 2019 I visited Japan for the NanoDTC JapaNano symposium. The 1-week symposium was based in Tokyo and aimed to develop NanoDTC PhD students’ understanding of research and, more broadly, life in Japan through visits to Tokyo Tech, Toshiba, InspireLab, RIKEN and a number of start-up companies. However, already being half-way around the world, and in what you could say is the heart of TADF research, I decided to extend my stay by a couple of weeks in order to visit some more laboratories!

portfolio

Delayed fluorescence from organometallic emitters for OLEDs

I completed my three-month Master of Research project in the Credgington group (Optoelectronics group) investigating how molecular modifications changed the photophysics of a class of organometallic emitters known as carbene-metal-amides.

Porosifying gallium nitride for sensors in outer space

I investigated the properties and uses of porous GaN for space applications during my two-month research project at the Cambridge Centre for Gallium Nitride in 2018.

Synthesising and characterising colloidal perovskite nanocrystals

I worked with the Catalysis & Process Integration Group and Stranks Lab at the University of Cambridge in 2017 to synthesise perovskite nanocrystals using a 3D flow reactor, which I designed and built.

Probing defects in commercial silicon solar cells using electron microscopy

During my MPhys project in 2017 at the Photon Science Institute, University of Manchester I used electron microscopy to investigate the role of different types of defects present in multicrystalline silicon solar cells.

publications

Dendritic Carbene Metal Carbazole Complexes as Photoemitters for Fully Solution-Processed OLEDs

Published in Chemistry of Materials, 2019

A Simple Molecular Design Strategy for Delayed Fluorescence toward 1000 nm

Published in Journal of the American Chemical Society, 2019

Harnessing the near-infrared (NIR) region of the electromagnetic spectrum is exceedingly important for photovoltaics, telecommunications, and the biomedical sciences. While thermally activated delayed fluorescent (TADF) materials have attracted much interest due to their intense luminescence and narrow exchange energies, they are still greatly inferior to conventional fluorescent dyes in the NIR, which precludes their application. This is because securing a sufficiently strong donor−acceptor interaction for NIR emission alongside the narrow exchange energy required for TADF is highly challenging. Here, we demonstrate that by abandoning the common polydonor model in favor of a donor−acceptor dyad structure, a sufficiently strong donor−acceptor interaction can be obtained to realize a TADF emitter capable of photoluminescence close to 1000 nm. Electroluminescence at a peak wavelength of 904 nm is also reported. This strategy is both conceptually and synthetically simple and offers a new approach to the development of future NIR TADF materials.

Carbene metal amide photoemitters: tailoring conformationally flexible amides for full color range emissions including white-emitting OLED

Published in Chemical Science, 2020

Selenium Substitution Enhances Reverse Intersystem Crossing in a Delayed Fluorescence Emitter

Published in Journal of Physical Chemistry C, 2020

Organic emitters exhibiting delayed fluorescence (DF) are promising luminescent materials for next-generation organic light-emitting diodes (OLEDs). Faster intersystem crossing rates and shorter emission lifetimes can be achieved in luminescent molecules through the incorporation of heavy atoms, which enhance spin–orbit coupling and promote intersystem crossing between singlet and triplet states. DF molecules often contain a sulfur atom, and reports of selenium-containing DF OLEDs also exist. However, the literature lacks a direct exploration of the effect of spin–orbit coupling on reverse intersystem crossing in a delayed fluorescence emitter by the substitution of selenium for sulfur. Here we show that substitution of selenium for sulfur in a modified thioxanthenone-triphenylamine analogue increases the rate of forward intersystem crossing by a factor of over 250 and the rate of reverse intersystem by a factor of 22. We attribute the increased rates to enhanced spin–orbit coupling from heavy atom substitution, and computational and electron spin resonance studies support this. This work provides an insight into future molecular design strategies for heavy-atom-containing, DF emitters.

Efficient and Stable Deep‐Blue Fluorescent Organic Light‐Emitting Diodes Employing a Sensitizer with Fast Triplet Upconversion

Published in Advanced Materials, 2020

Suppressing aggregation induced quenching in anthracene based conjugated polymers

Published in Polymer Chemistry, 2021

Electron spin resonance resolves intermediate triplet states in delayed fluorescence

Published in Nature Communications, 2021

Molecular organic fluorophores are currently used in organic light-emitting diodes, though non-emissive triplet excitons generated in devices incorporating conventional fluorophores limit the efficiency. This limit can be overcome in materials that have intramolecular charge-transfer excitonic states and associated small singlet-triplet energy separations; triplets can then be converted to emissive singlet excitons resulting in efficient delayed fluorescence. However, the mechanistic details of the spin interconversion have not yet been fully resolved. We report transient electron spin resonance studies that allow direct probing of the spin conversion in a series of delayed fluorescence fluorophores with varying energy gaps between local excitation and charge-transfer triplet states. The observation of distinct triplet signals, unusual in transient electron spin resonance, suggests that multiple triplet states mediate the photophysics for efficient light emission in delayed fluorescence emitters. We reveal that as the energy separation between local excitation and charge-transfer triplet states decreases, spin interconversion changes from a direct, singlet-triplet mechanism to an indirect mechanism involving intermediate states.