Charge Transfer-Mediated J-Aggregates of Azaindole Cyanine with 160 nm Absorption Redshift for Efficient NIR-II Photothermal Tumor Therapy

The J-aggregation of organic chromophores with ultralarge redshifts (>150 nm) represents a promising strategy for advancing photothermal therapy in the second near-infrared (NIR-II, 1000-1700 nm) window for tumor treatment. In this study, we designed and synthesized a heptamethine cyanine dye, CyN-OMe, by incorporating azaindole moieties. These moieties allowed the precise modulation of the intramolecular electronic distribution and intermolecular interactions, facilitating the rapid formation of the charge transfer-mediated J-aggregates of CyN-OMe in saline solutions. The maximum absorption wavelength of this aggregate red-shifted to 1035 nm in the NIR-II window, representing a substantial redshift of 160 nm relative to that of the monomer. We systematically explored the mechanism underlying the J-aggregate formation of CyN-OMe and evaluated its stability under varied conditions. Furthermore, the CyN-OMe J-aggregates demonstrated a high photothermal conversion efficiency of 63.7% under 1064 nm laser irradiation and successfully achieved complete tumor ablation in a mouse model. This work provides a general molecular design strategy for developing J-aggregates with ultralarge redshifts.