Tian He team of East China University of science and technology: a new design strategy of all visible light molecular switch: three line state sensitization plus "building block method"

P-hotoswitch is a kind of reversible isomerized functional molecules excited by two different wavelengths of light It has a very broad application prospect in advanced functional materials, biomedicine and other fields Recently, the team of academician Tian He from the school of chemistry and molecular engineering of East China University of science and technology reported a simple and efficient new strategy for the design of all visible light-emitting switch, which not only excites the visible light of the traditional diarylethene light switch, but also further improves the light regulation performance, and provides a new idea for the design of all visible light-emitting molecular switch The research results are as follows: "a Building block design for enhanced visible light switching of diarylethenes "was published in n feature communications (DOI: 10.1038 / s41467-019-12302-6) In the development and application of light controlled molecular switches, all visible light regulation has been the focus of attention Conventional photo controlled molecular switches usually need to operate under UV excitation UV excitation has the disadvantages of high energy consumption, large damage (light side reaction), poor penetration and relatively expensive light source Long-term use of UV excitation will lead to The damage of molecular switch stability (by-product accumulation, decrease of photoisomerization reversibility) and the damage of corresponding material matrix result in the shortening of service life and performance of advanced optical materials constructed by molecular switch Recently, the application of light controlled molecular switch in the field of high-resolution biological fluorescence imaging is rising, and the accumulation of by-products in the process of light regulation will lead to the decrease of fluorescence signal contrast and toxic side effects on life In addition, the high biological toxicity and strong background fluorescence interference caused by ultraviolet light further highlight its disadvantages in practical application Therefore, the main goal of the future development in this field is to replace the UV excited light controlled molecular switch with more moderate visible light and broaden its application field Diarylethenylethylene light controlled molecular switch has become the star molecule in the field of light controlled molecular switch because of its good thermal stability, light conversion and fast response However, there are few effective strategies for visible light isomerization At present, the design strategy of visible photochromic diarylethene is to realize the red shift of the excitation wavelength of the ring opening body by extending the conjugation system of the aryl side chain, so as to realize the visible photochromic excitation However, with the increase of conjugated system, the fatigue resistance (stability reduction) and the open / closed-loop quantum efficiency (activity reduction or even deactivation) of the PCMs are significantly reduced In addition, the growth of conjugated chain also increases the complexity of molecular design and synthesis, the unpredictability of function, and the risk of product research and development Therefore, the development of new efficient, simple and feasible visible light control strategy is the key problem to be solved in the field of visible light controlled molecular switch research Figure 1 Molecular design and working mechanism of dae-dt (source: nature Communications) in order to realize the construction of all visible light controlled molecular switch system and balance the excitation and regulation performance of visible light, academician Tian He's team proposed a new strategy of three wire state sensitization plus "building block method": 1 The three line state sensitizer has a lower single line state energy level than the diarylethene ring opening body, and has the potential to realize photochromism excited by long wavelength visible light; 2 The sensitizer matching the energy level is selected to make non conjugate connection with the switch parent body, forming "independent" d Yad The precondition and difficulty of realizing visible light regulation is the three line state energy level matching between the sensitizer with long wavelength absorption and the switch matrix The highlight of this work is that the N arrow single three line state band gap molecule (n arrow Δ EST) is used as the three line state sensitizer to solve this problem cleverly It not only realizes the feasibility and high efficiency of visible light regulation, but also further simplifies the molecular design Narrow single-trilinear band gap molecules are a kind of new functional molecules (Δ E ST 104 L · mol -1 · cm -1) with similar single-state and three linear state energy levels Compared with the three linear state sensitizers based on the forbidden n- π * transition (such as 2, 3- butanedione, ε <10 2 L · mol -1 · cm - 1), their sensitization efficiency is significantly improved, which provides necessary conditions for efficient three linear state sensitization Figure 2 Research on photochromic performance and cycle stability of the optical switch molecule dae-dt (source: nature Communications) Based on this strategy, the optical switch molecule dae-dt can be backlightable under the excitation of light with wavelengths of 420 nm and 550 nm The photoisomerization behavior of dae-dt not only shows the same efficient closed-loop quantum yield and conversion rate of Photocyclization reaction as that of conventional UV excitation, but also shows excellent fatigue resistance (i.e., reverse cycle performance) Compared with the rapid photoaging (loss of more than half of 5 cycles) under the excitation of conventional UV light, the three wire sensitized visible light switch can work stably for at least 10 cycles (damage rate < 5%), which shows the advantages of three wire sensitization in the design of photoisomerization system The process and mechanism of trilinear energy transfer in visible light induced isomerization were further verified by ultrafast spectrum capture and transient / delayed fluorescence Figure 3 Research on the mechanism of visible light driven optical switch (source: nature Communications) In addition, the optical switch can still show excellent visible light photochromic performance under solid-state conditions, successfully realizing the all visible light "write erase" application Figure 4 Visible light "write erase" Application of optical switch (source: nature Communications) The design strategy can meet the requirements for the design, regulation and further application of all visible light molecular switch First of all, n arrow single triplet band gap molecule (n arrow Δ EST) as sensitizer overcomes the disadvantage of low sensitization efficiency of traditional n π * triplet sensitizer At the same time, with the rapid development of organic light-emitting materials, this kind of molecules emerge in endlessly in recent years The abundant "molecular database" makes this strategy more simple and efficient Secondly, according to the trilinear energy level of the parent diarylethene, different sensitizers can be selected to realize the "customization" of optical switches excited by different visible light wavelengths Finally, the modular construction of molecular switches can be adjusted by different means, such as supramolecular self-assembly, polymer chemistry and so on It also provides a feasible scheme for improving the application of visible light switch in aqueous environment, and further expands its application prospect in biological field This series of research was conducted by Zhang Zhiwei, Ph.D., and Wang Wenhui, Ph.D., under the guidance of Zhang Junji, associate professor, and under the careful guidance of academician Tian He The research on the mechanism of ultrafast spectroscopy has been strongly supported by Associate Professor Xue Jiadan, master Jin Peipei, Professor Zhang Qisheng and Dr Deng Chao of Zhejiang University of technology Sun Lu, a teacher from Nankai University, strongly supported the calculation of related synchronization theory The research work was supported by NSFC basic science center, general projects, major science and technology projects of Shanghai and Star program.