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Almost no research topic will develop exactly as expected; if there were, there would be no breakthrough or surprise.
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As we all know, there are already many papers published by Chinese scientists. As I have said many times, it ranks first in the world in terms of total and second in terms of high quality papers (such as the Nature Index or highly cited papers). However, most of them are still of a follow-up nature, and there are still relatively few scientific discoveries that are entirely original to China.
Recently, I saw an interesting example of a Chinese original: aggregation induced luminescence. This phenomenon, known in English as aggregation-induced emission, or AIE for short, was discovered in 2001 by the team of Professor Tang Benzhong of the Department of Chemistry at the Hong Kong University of Science and Technology, who was elected an academician of the Chinese Academy of Sciences in 2009.
Aggregation induces luminescence
In 2016, Nature listed AIE dots, that is, aggregation of induced luminescent nanoparticles, as one of the four major nanomaterials that support and drive the "future nanolight revolution", which is also the only new material original by Chinese scientists. This year marks the 20th anniversary of the concept of AIE, and China's top comprehensive scientific journal, the National Science Review, interviewed Academician Tang Benzhong (Academician of the Chinese Academy of Sciences: Almost no research topic will develop exactly as expected; if there is, there will be no breakthrough in such research and will not bring any surprises).
Academician Tang Benzhong
The discovery came from an accident. At the time, new luminescent materials and organic light-emitting diodes were hot topics, and they were also trying to synthesize organic light-emitting materials. There is a molecule called thack, which has a beautiful molecular structure and looks like it has the potential to emit light, so Tang Benzhong asked the students to synthesize a variety of thackor derivatives.
One day, a student said that the solution he had prepared did not glow under ultraviolet light. This surprised Teacher Tang very much, because he clearly remembered that the hexaphenyl thioxaline crystals he prepared during his doctoral studies were luminous. He immediately went to the laboratory to discuss with the students, and after careful verification and repeated discussion, he finally confirmed that both were right: the solution of thack did not emit light, but the solid of thacked glowed. Individual molecules that did not emit light in dilute solutions emit light after agglomerating into a solid, so they named this phenomenon Aggregation Induced Luminescence (AIE).
Aggregation induces luminescence is counterintuitive because the opposite phenomenon has often been observed before, that is, molecules that would otherwise emit light do not emit light after gathering, which is called aggregation-caused quenching (ACQ). For example, it used to be common for three monks to have no water to eat, but now I suddenly find that there is a temple where a monk has no water to eat, and three monks have water to eat.
After a lot of theoretical and experimental research, they found the basic principles of AIE. The molecular structure of the thiogle is highly distorted, and there are many rotatable substituent groups on its central ring. In the excited state, the intramolecular movements of these structural units convert light energy into thermal energy and therefore do not emit light. When the aggregate is formed, the structure of the thiogle is just hardened, and the intramolecular movement of these molecules is inhibited, resulting in the excitation of energy that can only be released through the way of radiation transitions, that is, luminescence. They named this mechanism restriction of intramolecular motion (RIM).
And where did the opposite ACQ phenomenon come about? That's because the planar conjugate structure of a single molecule can emit light, but when it gathers, other molecules interfere with the structure of the single molecule through hydrogen bonding, hydrophobic effect, electrostatic attraction, etc., making the luminescence weaken or even disappear.
They initially thought that AIE was just a unique phenomenon of the Tack system, but later learned that this was not the case, and that it was a universal phenomenon that existed in many luminous systems. With the joint efforts of scientists around the world, thousands of fluorescence and phosphorescent AIE systems have been developed, some of which have a fluorescence quantum yield of up to 100%. Their luminous color covers the entire visible range and extends to the near-infrared band. AIE systems are diverse: from organics to inorganics, from small molecules to macromolecules, from conjugate nanoparticles to non-conjugate supramolecular clusters, from organometallic complexes to metal-organic frameworks, from single crystals to mixed crystals to amorphous multi-component mixtures... Either type has a common structural feature: they are flexible and easy to move in the single-molecule state, and difficult to move in the aggregate state.
AIE has broad application prospects in many high-tech fields, such as biological imaging, medical diagnosis and treatment, chemical sensing, environmental monitoring, optoelectronic devices, intelligent stimulus response and so on. Because you think, is it more useful for single molecules to emit light, or is it more useful for aggregates to emit light? Of course it is the latter, because the practical materials are all aggregates. In Google Scholar's search for aggregation-induced emission keyword, you can see as many as 6170 related papers published in 2020. This is a thriving field, and one of the few fields that has flourished entirely pioneered by Chinese scholars.
There is a famous saying: There is nothing new under the sun. Tang And others initially thought that AIE was a new phenomenon with no precedent, but after in-depth literature research, they found that other scientists had reported similar phenomena. For example, George Stokes wrote in an article in 1853 that some inorganic platinum cyanide salts are "sensitive" when solid (translated into modern term "luminescence"), but their solutions look no different from water (i.e., do not emit light). Unfortunately, he did not conduct in-depth research on this phenomenon. Other scientists should have found similar phenomena in different dye systems, but they did not attract attention.
George Stokes
It was not easy to find the literature, in fact, they did not have a hard time digging out Stokes's 1853 article from the literature pile until 2018. However, they are not surprised by these early works, because they understand that scientific progress is a continuous process, not a one-step achievement of unprecedented progress. Discoveries are often accidental, and the AIE is an ancient but unappreciated natural phenomenon they "rediscovered." Fortunately, they seized the opportunity to stand on the shoulders of giants and see higher and farther.
A philosophical concept advocated by Teacher Tang is very comedic: "Unity is strength, and gathering can shine!" "He strives to achieve a win-win situation with his collaborators, helping others develop while developing his own career, especially supporting the growth of young people."
Finally, Mr. Tang has a feeling that deserves everyone's deep consideration, especially for scientific research administrators: almost no research topic will develop exactly as expected; if there is, this kind of research will not have any breakthroughs and will not bring any surprises, because you can think about what will happen and what results your students will get when you sit in your office. The real joy of scientific research lies in its unpredictability: a small, unexpected detail has the potential to completely change the trajectory of your research.