As a pioneer in the field of organic electronics and flexible electronics in China, for many years, Huang Wei, a member of the Chinese Academy of Sciences, led a team across multiple disciplines such as physics, chemistry, materials, electronics, information and life, and has achieved a number of systematic and innovative The international cutting-edge research achievements were praised by the Nobel Prize winner Allen Hager as "the international leader in the field of organic optoelectronics."

In 1963, Huang Wei was born into a traditional medical worker‘s family. The special atmosphere made Huang Weier‘s eyes irritated, accustomed to constant knowledge and rigorous reason. In 1979, Huang Wei entered Peking University to study. Yan Yuan ’s “always new” environment made him like a fish. He explored the unknown in enough space and finally was able to let him “seems to have no endless curiosity”.

In the early 1990s, Huang Wei went to the Department of Chemistry of the National University of Singapore to do research work. He admitted that there were many problems in the domestic scientific research environment at that time: such as the lack of systematic and efficient innovation management capabilities of research institutions; the lack of high-level and international academic exchange opportunities for scientific researchers; the lack of publicity and transparency in the resource allocation mechanism; overall social innovation The cultural atmosphere is not ideal.

Now, Huang Wei firmly stated that China is reshaping the world‘s technological landscape. Whether it is the speed, quantity and quality of important articles published by Chinese scientists in top journals, or the presence of Chinese experts in the jury of major science and technology awards, all prove that China‘s scientific and technological level has been upgraded from "tracking" to "parallel" in many fields, and even To achieve "leading" in individual fields.

"For many years, I have hoped to use my meager efforts to build a research institution that represents the highest level in China and can participate in substantive international competition in the high-tech frontier field."

In order to realize this dream, Huang Wei gave up the excellent treatment and platform abroad and chose to return to China at the turn of the century. He successively established the “Advanced Materials Research Institute” at Fudan University and the “National Key Experiment of Organic Electronics and Information Display” at Nanjing University of Posts and Telecommunications. "Cultivation Base", established "Overseas Talent Buffer Base" at Nanjing University of Technology.

Among them, the "IAM team" of Nanjing University of Technology has attracted 100 overseas high-end talents and outstanding young scholars, has produced a series of high-level original achievements, and has become a number of national, provincial and ministerial scientific research platforms and intelligence bases. Looking at the team from scratch, to becoming one of the international academic brands, Huang Wei said frankly, "Nothing makes me more proud than this."

"A team of life, one life, only new but real but hoof". Huang Wei said that bravely climbing the peak of scientific research is the duty and responsibility of every scientific researcher. Only by doing research and doing scientific research unswervingly can we uphold the truth and practice the scientific nature of "regardless of benefits, only asking right and wrong".

In April 2017, Academician Huang Wei became the executive vice president of Northwestern Polytechnical University, in charge of personnel and personnel work. In his view, the most objective and feasible way to attract high-end talents is to give full play to the role of existing talents and let them "appear."

Huang Wei emphasized that the key to "introducing talents" is "inviting hearts". Only by setting up a career platform for returning overseas talents, creating a warm and positive growth environment, and at the same time supplemented by policy support, can it be effective.

【Introduction】

As a new type of long-lasting luminescence phenomenon, ultra-long organic phosphorescence (UOP) has been particularly attractive in recent years because materials with such characteristics show great potential in sensing, display, bio-imaging and anti-counterfeiting. In order to obtain UOP materials, there are mainly two prerequisites: one is the introduction of heavy halogen atoms, aromatic carbonyl groups or other substituents to accelerate the intersystem crossing (ISC) between singlet and triplet excited states; the other is Provide a rigid molecular environment to suppress non-radiative transitions to promote UOP emission. Among the reported strategies, such as polymerization, host-guest doping methods, etc., crystal engineering is an important method to obtain UOP because molecular motion can be effectively restricted in a rigid crystal environment. In this case, the analysis of molecular packing in the crystal and understanding the generation of UOP are crucial.

So far, a large number of studies on the relationship between UOP behavior and molecular accumulation have been reported. The results show that the solid-state molecular stacking method usually plays a vital role in adjusting UOP lifetime, luminous efficiency, luminous color, and even achieving unique dynamic UOP and mechanically induced sustained phosphorescence emission. Despite the great success of studying the relationship between phosphorescence properties and molecular packing types, the underlying mechanism of UOP properties is unclear due to the complexity of the factors affecting phosphorescence. Therefore, it is very important to gain a deeper understanding of effective molecular packing. Generally, each organic phosphor is composed of several functional molecules. In fact, not all organic group couplings are effective for the generation of UOP. Broadly defined molecular stacking involves stacking between components. Some groups that favor triplet excited states, such as carbazole, phenothiazine, etc., can be considered as triplet chromophores to control the generation of phosphorescence, while others can be considered as likely to be adjusted by intermolecular interactions Functional group that controls molecular packing.

【Achievement Introduction】

Recently, the research group of Academician Huang Wei of Nanjing University of Technology put forward a specific explanation that the stacking between triplet chromophores does play a key role in the generation of UOP in crystals. The author designed three isomers and controlled the accumulation of triplet chromophores by fine-tuning the functional groups. With the isomerization of chlorine atoms in phenyl units, the authors found that there are interesting UOP switching behaviors in these isomers. It is worth noting that 24CPhCz exhibits an extremely long phosphorescence lifetime, up to 1.06 seconds, and 34CPhCz exhibits dual emission of UOP (770 ms) and thermally activated delayed fluorescence (TADF, 1.9 microseconds). However, for 35CPhCz, only TADF is shown, and its lifetime is short, 2.7 μs. Combining X-ray single crystal analysis and theoretical calculations, the authors propose that intermolecular coupling between carbazole chromophores plays a key role in the two competitive processes of UOP and TADF emission in crystals at custom room temperature. The result was published on Angew. Chem. Int. Ed. As "Manipulating the Triplet Chromophore Stacking for Ultralong Organic Phosphorescence in Crystal". Associate Professor Shi Huifang and Professor An Zhongfu are the corresponding authors of the article.

【Graphic introduction】

Figure 1. Schematic diagram of molecular structure and mechanism

(A) Schematic diagram of the molecular mechanism to achieve UOP switching behavior

(B) The chemical structures and luminescent properties of the three compounds

Figure 2. Photophysical properties of solid aromatic amide derivatives

(A) Steady-state photoluminescence (blue line) and phosphorescence (red line) spectra of 24CPhCz, 34CPhCz and 35CPhCz. The inset shows photographs of 24CPhCz, 34CPhCz, and 35CPhCz crystals opened and closed under 365nm UV light.

(B) Excitation-phosphorescence mapping of 24CPhCz crystal under ambient conditions

(C) The lifetime attenuation curves of the ultra-long phosphorescence bands of 24CPhCz and 34CPhCz at 532 and 537nm, respectively

(D) Lifetime decay curve of the fluorescence band of 35HChCz at 488nm

(E) Steady-state fluorescence spectra of 35CPhCz at different temperatures. The illustration shows the change in luminous intensity.

Figure 3. Possible explanation for ultra-long organic phosphorescence in crystal state

(A) 24CPhCz, (B) 34CPhCz and (C) 35CPhCz single molecule intermolecular interactions; (D) 24CPhCz, (E) 34CPhCz and (F) 35CPhCz filling patterns in crystals.

Figure 4. Molecular simulation

(A) Natural transition orbit of the lowest triplet state of 24CPhCz

(B) The mechanism of different luminescent behaviors of the three compounds

(C) Intermolecular weak interactions calculated in the dimers of 24CPhCz, 34CPhCz and 35CPhCz

【summary】

In this work, the author proposed a new understanding of the ultra-long organic phosphorescence in crystals by studying several aromatic amide derivatives. By adjusting the position of chlorine substitution, there are interesting UOP switching behaviors in these isomers. The experimental and calculation results show that the 24CPhCz with the strongest intermolecular coupling between the carbazole chromophores exhibits the most impressive UOP emission, with a long lifetime of 1.06s and a phosphorescence yield of 2.5%. 34CPhCz is a dual emission of UOP and TADF, the phosphorescence lifetime is moderately reduced by 770 ms, and the phosphorescence yield is 3.4%. However, the coupling between triplet chromophores is too weak and the strong coupling between benzene units causes UOP to disappear and only TADF emission occurs. For 35CPhCz, the luminescence lifetime is 2.7 μs. These results indicate that triplet chromophore stacking plays a vital role in UOP generation. The results of this article can provide a deeper understanding of the inherent mechanism of ultra-long phosphorescence emission in pure organic compounds, as well as guidance for obtaining UOP materials.

Manipulating the Triplet Chromophore Stacking for Ultralong Organic Phosphorescence in Crystal

(Angew. Chem. Int. Ed., 2019, DOI: 10.1002 / ange.201907572)