Molecular Engineering of a Tumor-Targeting Thione-Derived Diketopyrrolopyrrole Photosensitizer to Attain NIR Excitation Over 850 nm for Efficient Dual Phototherapy

Photosensitizers with near-infrared (NIR) excitation, especially above 800 nm which is highly desired for phototherapy, remain rare due to the fast nonradiative relaxation process induced by exciton-vibration coupling. Here, a diketopyrrolopyrrole-derived photosensitizer (DTPA-S) is developed via thionation of carbonyl groups within the diketopyrrolopyrrole skeleton, which results in a large bathochromic shift of 81 nm, endowing the photosensitizer with strong NIR absorption at 712 nm. DTPA-S is then introduced with a functional biomolecule (N3-PEG2000-RGD) via click reaction for the construction of integrin αvβ3 receptor-targeted nano-micelles (NanoDTPA-S/RGD), which endows the photosensitizer with a further superlarge absorption redshift of 138 nm, thus extending the absorption maxima to ≈850 nm. Remarkably, thiocarbonyl substitution increases the nonbonding characters in frontier molecular orbitals, which can effectively suppress the nonradiative vibrational relaxation process via reducing the reorganization energy, enabling efficient reactive oxygen species (ROS) generation under 880 nm excitation. Screened by in vitro and in vivo assays, NanoDTPA-S/RGD with high water solubility, excellent tumor-targeting ability, and photodynamic/photothermal therapy synergistic effect exhibits satisfactory phototherapeutic performance. Overall, this study demonstrates a new design of efficient NIR-triggered diketopyrrolopyrrole photosensitizer with facile installation of functional biomolecules for potential clinical applications.