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

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.