From X‐ To J‐Aggregation: Subtly Managing Intermolecular Interactions for Superior Phototheranostics with Precise 1064 nm Excitation

Abstract The stacking mode in aggregate state results from a delicate balance of supramolecular interactions, which closely affects the optoelectronic properties of organic π‐conjugated systems. Then, managing these interactions is crucial for advancing phototheranostics, yet remains challenging. A subtle strategy involving peripheral phenyl groups is debuted herein to transform X‐aggregated SQ‐H into J‐aggregated SQ‐Ph, reorienting intermolecular dipole interactions while rationally modulating π–π interactions. Co‐assembled with liposomes (DSPE‐PEG2000), SQ‐Ph nanoparticles (NPs) exhibit low toxicity, superior biocompatibility, and a bathochromic shift to the 1064 nm match‐excited NIR‐II region, with a fluorescence brightness (ε 1064 nm Φ NIR‐II ) of 4129 M −1 cm −1 and a photothermal conversion efficiency (PCE) of 48.3%. Preliminary in vivo experiments demonstrate that SQ‐Ph NPs achieve a signal‐to‐background ratio (SBR) of up to 14.29 in NIR‐II fluorescence imaging (FLI), enabling highly efficient photothermal therapy (PTT) of tumors guided by combined photoacoustic imaging (PAI). This study not only enriches the J‐aggregation library but also provides a paradigm for optimizing photosensitizers at the supramolecular level.