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Small: combining donor receptor structure and nonplanar conformation to achieve high performance near infrared photothermal and photodynamic effects of organic small molecular materials

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Due to the advantages of near-infrared light (NIR) with high penetrability and non-invasive, material scientists have developed a variety of near-infrared nanomaterials for photodynamic therapy / photothermal therapy (PDT / PTT), including carbon nanomaterials, organic small molecule / polymer semiconductors, transition metal compounds, metal nanomaterials, black phosphorus and biomolecular self-assembly Loading materials, etc. Compared with inorganic nanomaterials, organic nanomaterials have the advantages of adjustable absorption wavelength, good biodegradability, low cost and fast metabolism of biological tissue. Although conjugated polymers play a leading role in this field, their synthesis and purification are relatively difficult, there are also differences between batches and difficulties in quality control. Compared with conjugated polymers, organic small molecules have the advantages of clear chemical structure, high purity, good reproducibility, easy modification and processing. Although many PTT organic small molecule nano materials used in 808 nano laser have been reported, only a few materials can be used in PDT. In addition, the mechanism of PDT under NIR is not clear. Design and synthesis of triplet materials with effective inter system crossing (ISC) is the key to achieve high efficiency PDT. According to the perturbation theory, the rate constant (KISC) of ISC depends on two important parameters, the spin orbit coupling (SOC) constant (ξ) and the energy gap (Δ EST) between singlet and triplet states. Large ξ can improve KISC. Heavy atom effect is a common way to realize large ξ, but heavy atom is harmful to human beings. At the same time, small Δ EST is also helpful to improve KISC. In order to reduce Δ EST, the strategies of donor (d) - receptor (a) structure and distorted conformation can be adopted. However, conformational torsion usually leads to blue shift of absorption and decrease of extinction coefficient, which makes it difficult to achieve strong absorption under 808 nm laser. Therefore, it is a challenge to design high efficient near infrared PTT / PDT nano materials with non heavy atoms.
Huang Hui, Professor of School of materials science and Optoelectronics Technology, Chinese Academy of Sciences, and Zhang Shiming, Professor of Nanjing University of technology, cooperated to design and synthesize small molecular nano materials with electron deficient large π conjugated core and distorted conformation, so as to achieve efficient near-infrared photothermal and photodynamic effects. By introducing large π - conjugated electron deficient unit and D-A structure into organic small molecular materials, the strong absorption at 808 nm can be ensured. By introducing the D-A structure and twisted conformation, the energy gap (Δ EST) between the single line state and the three line state can be reduced, and the effective inter system crossover can be realized and the PDT effect can be improved. At the same time, the mechanism of PDT / PTT is discussed through experiments and theoretical evidence, which provides a new strategy for the design of PDT / PTT small molecular near-infrared materials with high efficiency.
The results were published in small (DOI: 10.1002 / small. 202000909). Chen Jingya, a master student (co training) from Nanjing University of technology, was the first author of the paper, and Wen Kaikai, a doctoral student from the University of Chinese Academy of Sciences, was the co first author of the paper. The research project is supported by the key R & D plan of the Ministry of science and technology, the National Natural Science Foundation of China and the relevant funds of the Academy of Sciences. Guess you like it
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