Highly effective thieno[2,3-b]indole-diketopyrrolopyrrole near-infrared photosensitizer for photodynamic/photothermal dual mode therapy

Synthesis of photodynamic and photothermal agents with absorption in the near-infrared (NIR) region and featuring excellent photostability, high singlet oxygen generation efficiency, good photothermal conversion efficiency, and good biocompatibility is necessary for the application of photodynamic therapy (PDT) and phtothermal therapy (PTT). Three NIR absorption compounds based on thieno[2,3-b]indole (TI) and diketopyrrolopyrrole (DPP) were designed and synthesized. Their UV-vis-NIR absorption, photoluminescence, electronic distribution, energy levels and thermally induced phase transitions have been carefully determined. As structural analogues, only DPP-TI possesses excellent singlet oxygen quantum yield (¹O₂, Φ_Δ = 48.5%), which displays effective photothermal conversion efficiency (η = 15.8%) as nanoparticles in water. The potential of DPP-TI nanoparticles as fluorescence imaging therapeutic agent for synergetic PDT and PTT in vitro using only one wavelength light were explored preliminarily.