Construction and Properties of Strong Near-IR Absorption Photosensitizers

The design of near-infrared photosensitizers with high photodynamic and photothermal synergistic therapeutic properties is of great significance for tumor therapy. In this study, An-cyclic-BDP with excellent near-infrared absorption (ε = 1.94 × 10⁵ m⁻¹cm⁻¹ at 804 nm) is prepared using a dual strategy of twisted π-conjugated system induction (T-π-CSI) and spin-orbit charge transfer (SOCT). Theoretical calculations, steady-state and transient absorption spectra are used to investigate the intrinsic regulatory mechanisms between molecular structure and intersystem crossing (ISC) capacity. The results indicate that the application of the T-π-CSI and SOCT approach can be superimposed to increase ISC capacity and the triplet lifetime of An-cyclic-BDP (τ = 2961 ps). Electron paramagnetic resonance (EPR) results confirm that An-cyclic-BDP has the ability to generate hydroxyl radical (·OH) and singlet oxygen (¹O₂). Furthermore, the calculated ¹O₂ yield of An-cyclic-BDP is found to be 13%. The experimental results of the photothermal conversion indicates that An-cyclic-BDP exhibits a photothermal conversion efficiency of up to 48%. In vitro cell experiments demonstrate that An-cyclic-BDP-NPs, constructed by encapsulating An-cyclic-BDP with DSPE-mPEG₂₀₀₀, exhibit excellent biocompatibility and tumor cell-killing ability. Therefore, the strong near-IR absorption photosensitizer prepared in this study exhibits significant potential for application in the area of photodynamic and photothermal synergistic therapy.