Abstract
The search for non-invasive methods for the deep diagnosis and therapy of malignant tumors remains one of the priority tasks of modern medicinal chemistry. Conventional approaches are associated with a high risk of side effects and insufficient selectivity. Optical methods, such as phototherapy and tumor bioimaging, are regarded as a promising alternative, but their efficiency is largely determined by the penetration depth of radiation into tissue. At present, most photoactive agents operate within the first near-infrared window (NIR-I, 650–950 nm), where the penetration depth is limited by tissue light scattering and by light absorption from blood components, hemoglobin, melanin, and water. Shifting the absorption of an organic chromophore into the second near-infrared window (NIR-II, 1000–1700 nm) without loss of biocompatibility can be achieved through donor–acceptor (D–A) design of conjugated polymers. The combination of donor and acceptor units induces charge transfer, narrows the energy gap, and shifts absorption toward longer wavelengths [1]. In this work, this strategy is implemented for a series of conjugated D–A polymers based on a common thiadiazoloquinoxaline acceptor core combined with different donor units. The physicochemical properties of the polymers and of the nanoparticles prepared from them were investigated, and all of the polymers were shown to absorb within the second near-infrared window. The average hydrodynamic diameters of the resulting nanoparticles reached up to 150 nm. The cytotoxicity of the series toward tumor cells was also evaluated in vitro, which together allows the potential of the series as phototherapy and bioimaging agents to be assessed.