Small: combining donor acceptor structure and non planar conformation to realize high performance near infrared photothermal and photodynamic effects of organic small molecular materials

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Due to the high penetration non-invasive properties of near-infrared light (NIR) materials scientists have developed a variety of near-infrared one region nanomaterials for photodynamic therapy / photothermal therapy (PDT / PTT). These materials include carbon nanomaterials organic small molecule / polymer semiconductors transition metal compounds metal nanomaterials black phosphorus biomolecules Self assembly materials etc. Compared with inorganic nanomaterials organic nanomaterials have the advantages of adjustable absorption wavelength good biodegradability low cost fast metabolism of biological tissue. Although conjugated polymers play a leading role in this field their synthesis purification are relatively difficult there are also differences between batches difficulties in quality control. Compared with conjugated polymers small organic molecules have many advantages such as clear chemical structure high purity good reproducibility easy modification processing. Although many PTT organic small molecule nanomaterials for 808 nm laser have been reported only a few materials can be used for PDT. In addition the mechanism of PDT under NIR is not clear.

design 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) the energy gap between singlet trilinear states (Δ EST). Larger ξ can improve KISC. Heavy atom effect is a common way to achieve large ξ but heavy atom is harmful to human beings. At the same time small Δ EST can also improve KISC. In order to reduce Δ EST the strategy of donor (d) - receptor (a) structure distorted conformation can be adopted. However conformational twist usually leads to blue shift of absorption decrease of extinction coefficient which makes it difficult to achieve strong absorption under 808 nm laser. Therefore it is challenging to design non heavy atom PTT / PDT nanomaterials with high efficiency.

Professor Huang Hui from the school of materials science optoelectronic technology of the University of Chinese Academy of Sciences Professor Zhang Shiming of Nanjing University of technology cooperated to design synthesize small molecule nanomaterials with electron deficient large π conjugated core distorted conformation to achieve efficient near-infrared photothermal photodynamic effects. By introducing large π - conjugated electron deficient unit D-A structure into organic small molecular materials the strong absorption at 808 nm is ensured. By introducing D-A structure distorted conformation the energy gap (Δ EST) between the singlet state the triplet state is reduced the effective inter system crossing is realized the PDT effect is enhanced. At the same time the mechanism of PDT / PTT is discussed through experimental theoretical evidence which provides a new strategy for the design of efficient PDT / PTT small molecule NIR materials.

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