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    Home > Tang benzhong, academician of Hong Kong University of science and technology, develops a new strategy for building deep red / near infrared AIE materials: smaller conjugated systems with longer absorption and emission wavelengths

    Tang benzhong, academician of Hong Kong University of science and technology, develops a new strategy for building deep red / near infrared AIE materials: smaller conjugated systems with longer absorption and emission wavelengths

    • Last Update: 2018-07-14
    • Source: Internet
    • Author: User
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    The author: Zhao Zheng's organic dark red / near-infrared luminescent materials are in great demand in biological imaging and optoelectronics In biological imaging, low-energy, long wavelength dark red / near-infrared light can reduce cell damage, improve penetration depth and avoid interference caused by spontaneous fluorescence of biological tissue In the field of organic optoelectronics, OLEDs made of dark red / near-infrared organic light-emitting materials are also used in optical communication, night vision equipment and information encryption display However, compared with blue light, green light, yellow light and other visible light materials, the development of efficient dark red / near-infrared organic light-emitting materials is still very challenging The main reason is that the narrow energy gap usually leads to the electronic coupling (energy band gap rule) between the ground state and the excited state, which makes the quantum yield of luminescence decrease sharply Up to now, the molecular design of organic dark red / near-infrared luminescent materials mainly depends on the expansion of conjugation system of organic molecules and the increase of donor receptor interaction in the molecules to achieve longer emission wavelength, which also makes the organic dark red / near-infrared luminescent materials easy to achieve strong π - π stacking or twisted intramolecular charge transfer The non radiative transition of the band gap is further reduced, which leads to fluorescence quenching In addition, a larger conjugated system often means a longer synthesis route, which also limits the development of such compounds to a certain extent Fig 1 The synthesis route of the target compound (source: chem SCI.) on the other hand, the research and application of the concept of aggregation induced luminescence (CLIL) have been booming in recent years This concept was first proposed by academician Tang benzhong of Hong Kong University of science and technology in 2001, which provides a mature and reliable design idea for the design and synthesis of solid-state luminescent materials Recently, on the basis of previous work (adv.funct Mater., 2014, 24, 635; J mater Chem B, 2017, 5, 1650), the research team of academician Tang benzhong of Hong Kong University of science and technology has successfully developed a class of dark red / near-infrared luminescent molecules with smaller conjugate system but longer absorption and emission wavelength The monomers are commercial 4,7-dibromobenzo [C] - 1,2,5-thiadiazole (bt-2br) and easily obtained diarylamine derivatives Through Buchwald Hartwig coupling reaction, the aromatic secondary amines and bt-2br were directly coupled, and bt-2atpe and bt-2natpe were obtained In this work, a catalytic system consisting of PD 2 (DBA) 3 and ruphos was used to overcome the problem of large steric hindrance of secondary amines, with a yield of 79% At the same time, the strategy can change the proportion of reactants to obtain the asymmetric structure that can be modified, which is helpful to modify the molecules according to the needs of different applications (Figure 1) Fig 2 Photophysical properties of target compounds bt-2atpe and bt-2natpe (source: chem SCI) After the synthesis of target compounds, the photophysical properties of target compounds were studied first (Fig 2) These molecules show twisted intramolecular charge transfer (TICT) and aggregation induced fluorescence enhancement (AEE) phenomena The emission wavelength is in the dark red / near infrared band of 670-680 nm, and the quantum efficiency of fluorescence in solid is as high as 30% - 40% Interestingly, although the molecular structure and conjugation degree of these molecules are smaller than those of TTB developed by our research group, their absorption and emission wavelengths are obviously red shifted Taking bt-2atpe as an example, its maximum absorption wavelength is 522 nm, and its maximum emission wavelength is 674 nm, which is significantly longer than that of TTB (maximum absorption wavelength: 471 nm, maximum emission wavelength: 616 nm) Through a series of analysis, the author attributed this phenomenon to the enhancement of intramolecular charge transfer (ICT) caused by the shortening of the distance between electron donor and acceptor The ICT in this kind of molecule mainly comes from the transfer of lone pair electrons on the donor nitrogen atom to the receptor unit BT The lone pair electrons on the nitrogen atom in TTB are delocalized by more benzene rings, and their electron delivery ability is weakened The target molecule bt-2atpe directly bridges the nitrogen atom of secondary amine with the BT unit Compared with TTB, it can not only enhance the ICT effect, but also increase the potential resistance of other benzene rings and BT units on the nitrogen atom, restrict the intramolecular rotation and weaken the TICT effect, so as to avoid the fluorescence quenching This hypothesis is further verified by Lippert mataga equation, et (30) equation and calculation of dipole moment of excited state Figure 3 Design idea, optical properties and device performance diagram of the subject (source: chem SCI.) based on the good optical properties of the series of molecules, the team members and Professor Ma Dongge of South China University of technology have worked together to test the application of the target product in undoped near-infrared OLED, and achieved better device properties (irradiance: 5772 MW · SR-1 · m-2, external quantum efficiency: 1.73%) This strategy breaks the traditional design which needs to expand the molecular conjugation structure to increase the absorption and emission wavelength, and helps to design and develop more efficient dark red / near-infrared organic luminescent materials This achievement was recently published in Chem SCI (DOI: 10.1039 / c8sc01377b) The author of this paper is will W H Lee Chen, Zheng Zhao Chen, Yuan Jing Cai Chen (joint work), Zeng Xu, Ying Yu, Yuxiong, Ryan T K Kwok, Yue Chen, Nelson L C Leung, Dongge ma * Jacky w y.lam, Anjun Qin, Tang benzhong, academician team of Hong Kong University of science and technology, AIE) academician Tang benzhong of Hong Kong University of science and technology research group: simple multi-component polymerization method to prepare non-traditional light-emitting small heterocyclic polymer academician Tang benzhong of Hong Kong University of science and technology team: starting from aggregation induced light-emitting silver ion probe, Fluorescence silver staining and dynamic monitoring of silver ion release
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