Readily constructed squaraine J-aggregates with an 86.0 % photothermal conversion efficiency for photothermal therapy

The development of photothermal agents with high photothermal conversion efficiency (PCE) and long absorption wavelengths is crucial for safe and effective anti-cancer treatment. However, achieving these advantages often requires precise molecular design and complex synthetic procedures. In this study, we present a simple, precise, and effective method for fabricating photothermal agents with high PCE using long wavelength excitation. This approach involves linking two electron-donating components, diphenylamine (DPA), and an electron-withdrawing squaraine (SQ), via a π-bridge thiophene (T). The resulting D-π-A-π-D structure leads to a red-shifted absorption band. Within the DTS structure, DPA functions as a molecular rotor, T serves as a coplanar backbone, and SQ promotes J aggregation. When DTS nanoparticles (NPs) are fabricated using an amphiphilic nano-carrier, the maximum absorption wavelength shifts from 701 to 803 nm. This shift is accompanied by reduced fluorescence and an exceptionally high PCE of 86.0 %. Both in vitro and in vivo assessments confirm that DTS NPs exhibit strong potential for photothermal antitumor therapy. Overall, this strategy offers a valuable framework for designing photothermal agents with clinical applications in mind, offering a simpler and more efficient approach to achieving high PCE and long absorption wavelengths.