Intramolecular twisting of cyanine dyes into compact J-aggregated nanorings for gentle light-irradiated photothermal and photodynamic synergistic therapy with antibacterial protection

Photodynamic therapy (PDT) and photothermal therapy (PTT) synergistic treatment for hypoxic tumors, always requires high-intensity light irradiation. This study introduces an intramolecular modulation approach for achieving PDT and PTT synergy under gentle light irradiation via the formation of tightly packed J-aggregated nanorings. Specifically, cyanine dyes, designated as TYA and TYB, were synthesized and compared to investigate the influence of intramolecular and intermolecular forces on the formation of compact J-aggregates. Compared to TYA (14.22°, 8.58 Å), the planar quinoline moieties in TYB exhibit a more pronounced rotation around the methylene linker (50.21°), which facilitates intermolecular slippage and reduces the stacking distance to 4.91 Å in J-aggregated nanorings (TYB J-NPs). The smaller monomer separations facilitate the generation of photothermal effects under mild light irradiation. These TYB J-NPs generate reactive oxygen species (ROS) levels comparable to those produced by TYA J-aggregates, while simultaneously producing a thermal effect under near-infrared (NIR) light irradiation (35 mW/cm², 10 min, ΔT > 20 °C). This dual functionality synergistically enables in vivo fluorescence and photothermal imaging, and effectively inhibits the growth and invasion of 4T1 tumors in mice. Moreover, TYB J-NPs demonstrate substantial antibacterial efficacy against both Gram-positive and Gram-negative bacteria, thereby offering effective antibacterial protection during tumor phototherapy. In summary, the intramolecular twisting of TYB effectively resolves the bottleneck associated with intermolecular repulsions at large molecular separations, thereby facilitating the formation of densely packed J-aggregates. This represents the first instance where J-aggregated nanorings enable concurrent PDT and PTT with antibacterial effectiveness under low-density NIR light irradiation. This work may significantly enhance the therapeutic potential of cyanine dyes in cancer treatment, pathogenic bacterial infections, and other diseases.