"Seldom heard the sound of shuttle weaving, mistakenly entered into chemistry. Spent more than ten years in the wilderness, fortunately got an inch of farmland. Spring sows new seeds, summer draws irrigation systems. Autumn gets micro devices, winter promotes their integration. Once recited the praises of Taibai, now only Mojie's achievements. If you talk about the affairs of Fenyang, you can talk and laugh in the empty alleys."

On the personal homepage of Wang Yu, a deputy researcher at the Dalian Institute of Chemical Physics, Chinese Academy of Sciences, he uses such a doggerel poem as "a brief introduction".

Indeed, before joining the Dalian Institute of Chemical Physics, he spent more than ten years studying at Qingdao University and Kyungpook National University in South Korea. Now, he has spent another ten years at the Dalian Institute of Chemical Physics.

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In the past ten years, he has been deeply involved in the two major fields of self-assembled carbon dots and nanomaterials. In the summer of 2024, he and his team published two back-to-back papers in succession.

Regarding these two papers, he said: "We hope that the physical model of carbon dots we have established can help the basic research and applied research of carbon dot materials, so that this magical emerging nanomaterial can one day, like its predecessor quantum dots, step onto the Nobel stage."In the carbon dots prepared by Wang Yu this time, thanks to the relatively fewer derivatization structures and by-products within the skeleton, after the introduction of metal ions through self-assembly, the catalytic oxidation capability of the carbon dots is far higher than that of carbon dots prepared by conventional methods.

Furthermore, after the introduction of metal ions, the number of active sites can be effectively increased, thus achieving reversible adsorption of different gases.

Moreover, the types and weights of gases that different doped metals can adsorb are also different, so this material is expected to be used for solid gas storage materials.

However, Wang Yu also frankly said: "Although we have verified the peculiar properties of the vast majority of carbon dots through experiments, and we still have some unpublished papers, our understanding of carbon dots based on this model is far from enough, so we dare not make hasty conclusions about the application prospects."

(Note: The original text contained HTML entities, which have been replaced with the corresponding characters in the translation.)Carbon Quantum Dots: The "Offspring" of Quantum Dots

So, what are carbon quantum dots and why study them?

Many people are aware that scholars studying semiconductor quantum dots in nanomaterials were awarded the 2023 Nobel Prize in Chemistry, which also sparked interest in the term "quantum."

Among various new types of nanomaterials, there is a material known as "carbon quantum dots."

Due to their low cost, easy preparation, resistance to photobleaching, and good biocompatibility, carbon quantum dots have attracted significant attention in the fields of luminescent materials, bioimaging, photocatalysis, and other areas over the past decade.However, due to the reasons of the preparation methods, the chemical structure of these nanomaterials is complex, and the photoluminescence mechanism is unclear. And whether the so-called quantum effects really exist is also quite controversial.

For example, people have only observed the size effect in a few carbon quantum dots, that is, the fluorescence emission band will undergo a red shift as the size increases.

Therefore, neither the "Carbon Quantum Dots" in Baidu Baike nor the "carbon quantum dots" in Wikipedia have explicitly introduced its luminescence mechanism or quantum characteristics.

In addition, carbon dots also show many peculiar phenomena, such as anti-Kasha fluorescence, multiple fluorescence emission, solid-state fluorescence, etc., which further increase the difficulty of people's understanding of the essence of carbon dot materials.

In fact, at the beginning of the discovery of carbon dots, people called them "carbon nanodots". With the deepening of research, in order to explain the various unique optical properties of carbon dots, four physical models have been proposed for explanation.These four types of physical models are graphene quantum dots, carbon quantum dots, carbon nanodots, and carbonized polymer dots.

The vast majority of the preparation methods for carbon dots with peculiar fluorescent properties come from the bottom-up approach. That is, they are prepared from small molecules as precursors through hydrothermal, solvothermal, or solvent-free thermal methods.

As for Wang Yu personally, he believes that more organic reactions occur in the preparation of carbon dots, rather than simple high-temperature carbonization reactions.

Then, there should be a simpler and more universal theory to reasonably explain the various unique optical properties of carbon dots.

Like the quantum confinement effect of quantum dots, it also follows the simple, universal, and straightforward objective laws.In 2020, Wang Yu's team published the first paper on the preparation of carbon dots by the dissolution heat method, revealing the impact of solvent-dominated reactions on the skeletal structure of carbon dots.

For example, ethanol can be directly embedded into the carbon dot skeleton through esterification reactions, or it can induce self-polymerization reactions of precursor molecules.

It was the publication of this paper that strengthened their confidence in the following theory: that the formation process of carbon dots is dominated by various organic reactions.

To reveal the essence of carbon dots, a carbon dot model with a simplified structure is needed.

To this end, with the help of the air-assisted melt polymerization method, they achieved controllable preparation of carbon dots by avoiding various organic side reactions induced by solvents or intermediate state molecules.The resulting carbon dots have a relatively uniform chemical structure, and because they are formed from low molecular weight polyimides through a simple condensation reaction, their molecular weight ranges from 200 to 3000.

In this way, by simply adjusting the ratio of precursors, the physical and chemical properties of the product carbon dots can be controlled.

Interestingly, these carbon dots exhibit a clear self-assembly fluorescence enhancement property in solution. Even at low concentrations, the fluorescence is almost invisible. However, when the concentration is increased, a bright blue fluorescence can be obtained, and it has strong blue solid-state fluorescence.

Compared with carbon dots obtained by traditional preparation methods, Wang Yu and others found that supramolecular self-assembly may be an essential property of carbon dots.

By utilizing this self-assembly property, they introduced different fluorescent molecules into these carbon dots.After purification by inverse precipitation, it is possible to achieve controllable regulation of solution fluorescence and solid fluorescence within the visible spectrum range.

This phenomenon leads them to believe that for fluorescent carbon dots prepared by traditional methods, it is not the so-called quantum size effect that causes different colors of solution fluorescence and solid fluorescence.

Instead, it is because of the fluorescent derivatives generated by side reactions during the preparation, which are self-assembled and embedded into the polymer skeleton of the carbon dots, resulting in the aforementioned phenomenon.

Therefore, they named the prepared fluorescent molecule-embedded carbon dots as DICP-dots (Dye-Incorporated Carbonized Polymer Dots).

In this case, the English abbreviation DICP happens to coincide with the English abbreviation of the Dalian Institute of Chemical Physics.The translation of the provided text into English is as follows:

"We chose this name so that everyone can better remember this carbon dot physical model proposed by the Dalian Institute of Physical Chemistry," said Wang Yu.

"Convincing others is the real challenge."

During the research period, Wang Yu also encountered negative opinions from top to bottom. He said: "In 2021, on the one hand, I was facing the huge difficulty of nuclear magnetic structure analysis, on the other hand, the self-denial thought of 'why can I explain the problem that others can't?' did indeed have a great impact on my confidence."

After all, at that time, the big names in the small field had already used various models to explain the unique optical properties of various carbon dots, and the related papers were also cited by the vast majority of peers."So this stage was indeed very difficult, and I am grateful for the tolerance and support of the project leader, Researcher Feng Liang, and my family, as well as the help of my student Qin Yingxi in the experiment, and the assistance of Researcher Hou Guangjin, the late Associate Researcher Ai Xuanjun, and Teacher Xu Xiaoyan in the field of nuclear magnetic resonance, which helped me through the most difficult year," he said.

Later, through continuous exploration and learning, he established a complete new characterization method for carbon dots, providing a large amount of compelling evidence for the establishment of the above-mentioned new model, and ultimately completed the supramolecular self-assembly theory interpretation of carbon dots.

"However, compared to experiments, persuading others is the real problem. The first version of the paper was completed in July 2022, and it took a full two years to be finally published," Wang Yu continued to express.

During this period, he and his colleagues faced many doubts and negations from peers. Fortunately, they persisted, not only answering the reviewers' questions one by one, but also ultimately gaining their recognition.

At the same time, he also expressed his gratitude to the editors of the two journals for their recognition of this series of work, which gave Wang Yu and others the opportunity to respond to the reviewers' questions multiple times.Recently, the first related paper titled "Dye-Incorporated Carbonized Polymer Dots with Tunable Solid-State Emission Based on Intraparticle Förster Resonance Energy Transfer" was published in Advanced Functional Materials (IF 18.5).

Wang Yu is the first author and co-corresponding author, and Researcher Feng Liang from the Dalian Institute of Chemical Physics serves as the co-corresponding author [1].

The second related paper, titled "The Synthesis of Functionalized Carbonized Polymer Dots via Reversible Assembly of Oligomers for Anti-Counterfeiting, Catalysis, and Gas Storage," was published in Advanced Science (IF 14.3).

Wang Yu is the first author, and Researcher Feng Liang from the Dalian Institute of Chemical Physics is the corresponding author.

Based on the existing physical models, through the method of self-assembly, Wang Yu has discovered many interesting phenomena, including the selective and reversible adsorption of gases."This will also be a direction for our future work. In fact, there are some other unusual findings, but since the paper has not been published yet, I'll keep you in suspense for now, and welcome everyone to continue to pay attention to our work." Wang Yu concluded.