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    Home > The latest JACS appreciation by academician Tang benzhong and Professor Ding Dan team: "unconventional" strategy: enhancing photothermal properties by enhancing molecular aggregation

    The latest JACS appreciation by academician Tang benzhong and Professor Ding Dan team: "unconventional" strategy: enhancing photothermal properties by enhancing molecular aggregation

    • Last Update: 2019-03-26
    • Source: Internet
    • Author: User
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    Author: in the field of tumor photothermal therapy, the conventional design principle of organic dyes is to design strong electron donor and strong electron acceptor into planar conjugate structure The principle is: when dye molecules are in the aggregation state (i.e nanoparticles), strong intermolecular interaction restricts the movement of molecules, thus enhancing the non radiative transition and improving the photothermal conversion efficiency However, this strategy may prevent other non radiative transitions, so the photothermal conversion efficiency of organic materials is usually low Recently, academician Tang benzhong of Hong Kong University of science and technology, in cooperation with Professor Ding Dan of Nankai University, proposed an "unconventional" strategy: to enhance the movement of molecular aggregation and enhance the photothermal performance The idea of this design is to enhance the non radiative transition by adjusting the properties of the excited intramolecular twisted charge transfer (TICT), and then improve the photothermal conversion Relevant achievements were published in J am Chem SOC (DOI: 10.1021 / JACS 8b13889) under the title of "molecular motion in aggregates: adjusting TICT for boosting photothermal thermodynamics" Figure 1 Schematic diagram of molecular design and regulation of TICT to enhance photothermal conversion (source: J am Chem SOC.) intramolecular twisted charge transfer (TICT) is a common photophysical phenomenon in donor and acceptor conjugated molecules When the molecule is excited by light, the excited state molecules enter the TICT state under the condition of polarity, and the TICT state returns to the ground state mainly in the form of non radiative transition Therefore, the research group uses the method of enhancing TICT properties to improve the photothermal properties However, the molecular motion of organic molecules is limited in the aggregation state, which greatly hinders the formation of TICT state (the prerequisite for the formation of TICT state is molecular motion) On the other hand, the group first proposed the concept of aggregation induced luminescence (AIE) in 2001: fluorescent molecules do not emit light in the dissolved state, but strongly emit light due to the restriction of molecular movement in the aggregated state There seems to be a contradiction between TICT and AIE: in the aggregation state, TICT state cannot be formed due to the restriction of molecular movement, while AIE benefits from it and emits light strongly However, the team noticed that the fluorescence would be quenched gradually due to the activation of molecular motion (the inverse process of AIE) when a good solvent was added to the aggregated AIE molecule Therefore, if the dye molecules move in the aggregation state, on the one hand, it can improve the TICT properties and enhance the non radiative transition; on the other hand, it can quench the fluorescence, so that more energy can be used for heat generation Therefore, the research group proposed a new strategy: aggregate molecular motion, which combines the TICT properties with the AIE inverse process When the molecular rotor and branched long alkyl chain are introduced into the dye molecular backbone, the photothermal conversion efficiency of the obtained molecules is significantly improved (Fig 1) Fig 2 Molecular photophysical and photothermal properties (source: J am Chem SOC.) the author selected benzobisthiadiazole (BBT) as strong electron acceptor, thiophene (T) as electron donor, triphenylamine (TPA) as both electron donor and molecular rotor, branched long alkyl chain located on thiophene unit The existence of branched long alkyl chains plays an important role in the regulation of TICT properties In the solution state, the long alkyl chain is conducive to the molecular distortion, which is more conducive to the formation of TICT state In the aggregation state, the branching of alkyl chain can effectively weaken the strong intermolecular interaction and provide space for intramolecular rotation, which is conducive to the formation of TICT state, thus enhancing the non radiative transition and photothermal conversion efficiency It is worth noting that the branching point of branched alkyl chain is preferably located at the second carbon If it is located in the first carbon, it is easy to emit fluorescence if the steric hindrance is too large; if it is not branched, it can not effectively prevent the interaction between molecules, and can not achieve the purpose of enhancing the photothermal efficiency In conclusion, through a series of characterization (absorption / emission spectrum, solvation effect, aggregation emission, relative quantum efficiency, X-ray diffraction, photothermal conversion efficiency, etc.), the author found that the dye molecule nirb14 (containing 2-decyltetradecane group) has the best photothermal effect (Fig 2) Fig 3 Photothermal conversion performance of nirb14 (source: J am Chem SOC.) it can be seen from Fig 3 that compared with the straight chain molecule nir6 and gold nanorods (GNR), nirb14 has better photothermal conversion performance, its photothermal conversion efficiency (31.2%) is significantly higher than that of nir6 (22.6%) and GNR (20.7%), and has good thermal stability Figure 4 PH responsive nirb14-pae / PEG nanoparticles (source: J am Chem SOC.) although there are excellent photothermal converters (nirb14), if they can not be effectively transported to the tumor site, they still can not achieve the purpose of treatment In order to solve this problem, a pH responsive polymer (pae-b-peg) was used The polymer has no charge in the blood environment (pH = 7.4), and the blood circulation time can be increased due to the surface phase separation When pH responsive nanoparticles (nirb14-pae / PEG) are passively transported to the tumor site (pH = 6.5), the polymer is protonated and positively charged, thus enhancing the enrichment of the tumor site and improving the treatment effect (Fig 4) Fig 5 Comparison of photoacoustic experiments in vitro and in vivo (source: J am Chem SOC.), the author conducted photoacoustic imaging of nirb14-pae / PEG in vitro and in vivo (Fig 5) The results showed that the aggregation of nirb14-pae / PEG in the tumor site of mice was significantly enhanced, and the circulation time in vivo increased Fig 6 Photothermal effect of tumor in mice (source: J am Chem SOC.) finally, the author conducted photoacoustic guided photothermal treatment in mice (Fig 6) Compared with the control group (saline and PEG coated nanoparticles), nirb14-pae / PEG nanoparticles produced higher temperature at the tumor site, and significantly inhibited tumor growth In this paper, a new method of photothermal enhancement by molecular excited state control is proposed This method is helpful for the design of novel conjugated small molecules and polymers with high photothermal properties The first author of this work is Dr Liu Shunjie from Hong Kong University of science and technology, and Dr Zhou Xin from Nankai University is the co first author of this paper The corresponding authors are academician Tang benzhong of Hong Kong University of science and technology, Professor Ding Dan and Professor Shi Linqi of Nankai University This work also received the help of Dr Zhang Haoke from Hong Kong University of science and technology in theoretical calculation PH responsive polymers were supported by Dr o'hanlin and Dr Liu Yang of Nankai University The research was supported by NSFC, ITC, RGC of Hong Kong and open fund of National Key Laboratory of light emitting devices of South China University of technology.
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