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21 Aug 2024
Prof. Bin Liu of the National University of Singapore describes “impurity conundrum” of ultralong organic phosphorescence.
By Karen Thomas
The impurity conundrum of ultralong organic phosphorescence: Commercial carbazole (Cz, which is an aromatic heterocyclic organic compound) has been widely used to synthesize organic functional materials, which are entwined with recent breakthroughs in ultralong organic phosphorescence, thermally-activated delayed fluorescence, organic luminescent radicals, and organic semiconductor lasers.
Recently, Prof. Bin Liu’s group at the National University of Singapore (NUS) discovered that – in contrast to commercial Cz – the fluorescence of lab-synthesized-Cz (“Lab-Cz”) is blue-shifted by 54 nm and the compound’s well-known room-temperature ultralong phosphorescence almost disappears. Prof. Liu is the Tan Chin Tuan Centennial Professor at NUS.
Detailed studies have revealed the presence of a Cz isomer as the impurity, which is widespread in commercial Cz sources, at a level of <0.5 mol%. Ten representative Cz derivatives were resynthesized from the Lab-Cz and all failed to show the reported ultralong phosphorescence in the same crystal states.
However, even 0.1 mol% isomer doping can recover the reported ultralong phosphorescence. Prof. Liu commented that the presence of the isomer in commercial carbazole “triggers us to re-examine the structure-property of many optically active materials with important discoveries”.
Interview with SPIEBefore this week’s SPIE Optics + Photonics conference, Prof. Liu was interviewed by SPIE about her work – and the contents of her plenary presentation, that she delivered on Tuesday in San Diego.
“I have some very important and unexpected results to share at the meeting,” she said. “Detailed studies have revealed the presence of a carbazole isomer as the impurity, which is widespread in commercial carbazole sources.”
Liu, who is also the deputy president for research and technology at NUS, noted that the presence of the isomer in commercial carbazole has prompted her research team to re-examine the structure property of many optically active materials, some of which are key building blocks for organic electronic materials.
“Interesting results have been obtained for how the isomer-doping process has influenced room-temperature phosphorescence, thermally activated delayed fluorescence, mechano-luminescence, and organic photosensitizers,” she said.
You are also the founding director of the Flagship Green Energy Programme and Centre for Hydrogen Innovations at NUS. What are some of the current projects there that you’re most excited about?
Our Green Energy Programme is dedicated to advancing scalable catalytic technologies that convert CO2 into green liquid fuels, offering affordable and ecologically balanced energy solutions. The Centre for Hydrogen Innovations is focused on overcoming technological challenges in scaling hydrogen conversion technologies, with particular emphasis on hydrogen carriers. Exciting projects include direct CO2 capture from ambient air, and ammonium cracking to produce hydrogen.
In Feb 2019, you shared your insights on tackling climate change through technological innovation at the World Economic Forum Annual Meeting in Davos (2019). What were some of the ideas you shared? What advances have you seen since then?
Five years ago, in Davos, I presented the NUS’s vision for storing solar energy in liquid chemical form through the capture of atmospheric carbon, and its direct conversion to alternative green fuels. Since then, my colleagues have focused on direct CO2 capture, green hydrogen production, and catalysis for green fuel development. Through dedicated teamwork, we have made significant progress, successfully scaling up several technologies for demonstration. The key to facilitating the widespread adoption of green fuels lies in reducing costs, which will require continued effort in the coming years.
What originally captured your interest in chemistry and organic nanomaterials?My parents encouraged me to study natural sciences when I was very young. I ended up with doing a PhD in chemistry at NUS and met many great people who nurtured me and guided me to pursue this path.
What do you see as the most important aspect of your work at this time?
Many researchers are working on organic functional materials, but we made a difference by focusing on introducing organic functional materials into aqueous media and exploring their applications in energy and biomedical fields.
Recently, we collaborated with our colleagues on using machine learning for materials design. Within less than a year, we screened more than seven million compounds and came out with numerous recommended structures for laboratory synthesis and property tests. It worked very well, and we are quite fascinated with the impact of machine learning in accelerating materials innovation. As we always create new research directions that are relatively under-explored, we are able to progress well so far.
What is most exciting or surprising about your work? What are some of the challenges?
I believe that the most compelling aspect of our work lies in our commitment to research with both high intellectual rigor and significant translational value. We continually seek innovative solutions to address pressing challenges, which motivates us to make daily progress. My philosophy is that while basic research is essential, it should ultimately aim to tackle important societal issues, such as disease treatment or energy solutions. Translating fundamental science into commercial products is a highly rewarding endeavor, though it often demands substantial effort and time to realize.
What do you see as the future of organic functional materials? What would you like to see?
The future of organic functional materials is very promising, driven by advancements in various fields such as electronics, energy storage, and biomedical applications. I hope that more researchers will come together to share ideas, discuss challenges, and find solutions. We need more collaboration and good leadership.
Karen Thomas is a Staff Writer at SPIE.
This article was first published on spie.org.
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