Photo‐Induced Electron Transfer‐Triggered Structure Deformation Promoting Near‐Infrared Photothermal Conversion for Tumor Therapy

Abstract

AbstractPhotothermal therapy (PTT) is a promising approach to cancer treatment. Heptamethine cyanine (Cy7) is an attractive photothermal reagent because of its large molar absorption coefficient, good biocompatibility, and absorption of near‐infrared irradiation. However, the photothermal conversion efficiency (PCE) of Cy7 is limited without ingenious excitation‐state regulation. In this study, the photothermal conversion ability of Cy7 is efficiently enhanced based on photo‐induced electron transfer (PET)‐triggered structural deformation. Three Cy7 derivatives, whose Cl is replaced by carbazole, phenoxazine, and phenothiazine at the meso‐position (CZ‐Cy7, PXZ‐Cy7, and PTZ‐Cy7), are presented as examples to demonstrate the regulation of the energy release of the excited states. Because the phenothiazine moiety exhibits an obvious PET‐induced structural deformation in the excited state, which quenches the fluorescence and inhibits intersystem crossing of S1→T1, PTZ‐Cy7 exhibits a PCE as high as 77.5%. As a control, only PET occurs in PXZ‐Cy7, with a PCE of 43.5%. Furthermore, the PCE of CZ‐Cy7 is only 13.0% because there is no PET process. Interestingly, PTZ‐Cy7 self‐assembles into homogeneous nanoparticles exhibiting passive tumor‐targeting properties. This study provides a new strategy for excited‐state regulation for photoacoustic imaging‐guided PTT with high efficiency.