Progress in the Research on the Ultrafast Dynamics of the “Optical Dark State” of the Molecular System of China University of Science and Technology

Recently, Prof. Zhang Qun’s professor Luo Yi’s research team at the University of Science and Technology of China has made important progress in the study of the ultrafast kinetics of the “optical dark state” (spin forbidden triplet state) of the condensed phase molecular system.

How to effectively detect the kinetic evolution of the spin banned triplet state ("optical dark state") has always been a difficult problem in the fields of photophysics, photochemistry and photobiology research. Due to the existence of fast relaxation processes such as internal transition and intramolecular vibrational energy redistribution, it is very difficult to extract and characterize the dynamical evolution that occurs in the "optically dark" space.

To this end, team researchers have taken a different approach, using high-inspired “optical bright states” (spin allowed singlet states) to “optical dark states” (spin forbidden triplets) for rapid energy transfer (intersystem enthusiasm). An anti-conventional "time-reversal femtosecond pump-probe" technique that achieves a "pure" ultrafast kinetic evolution in the "optical dark" space in the model molecular system (malachite green) Real-time tracking and characterization. The development of this non-linear spectroscopy technology has opened up a new window for related studies such as molecular luminescence, photonics, and quantum control. The research results were published in Phys. Chem. Chem. Chem. Phys. 17, 13129-13136 (2015). The first author of the thesis was Ph.D. student Ge Jing, who was researched and researched by Professor Jiang Jun. The research team strongly supports spectral and dynamic simulations.

Based on this research idea, the researchers collaborated with Wang Chunru, a researcher at the Institute of Chemistry at the Chinese Academy of Sciences, to develop an ultra-fast kinetics mechanism for metal-bound fullerenes. By selecting a typical metal-embedded fullerene Sc2C2@C82, femtosecond time-resolved ultrafast spectrometry techniques were used to systematically examine three different carbon cage symmetry (Cs, C2v, C3v) and the same carbon cage. Symmetry and visible light excitation of electron dynamic behavior in the case of different modifications of the molecular group outside the cage (electronic donor/acceptor).

Based on the first-principles calculations, we first discovered the high correlation between the opening of the triplet channel in the molecular system and the fullerene carbon cage symmetry and the electronic properties of the polymer group outside the cage, thus revealing the “optical dark state”. "The decisive role in manipulating the evolution of its light-excited electrokinetics." These studies have found that it provides new ideas for a mechanism that is universally applicable for the research and development of photoelectric conversion based on the metal embedded fullerenes molecular system and the application of solar visible light. The results of this study are published in the American Chemical Society [J. Am. Chem. Soc. 137, 8769–8774 (2015)]. The first authors of the dissertation were Ph.D. students Wu Bo, Hu Jiahua, and postdoctoral Cui Peng.

The above work was funded by the Ministry of Science and Technology, the National Natural Science Foundation of China and the Chinese Academy of Sciences.

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