π‐π‐Coupled J‐Aggregates Synergized With Hydrogen Bonding via Molecular Planarity Engineering for Second Near‐Infrared Imaging and Phototherapy

A novel J-aggregates configuration, termed π-π-coupled J-aggregates, was successfully constructed based on low-molecular-weight hemicyanine dyes (HCY-3). Unlike classical J-aggregates, the π-π-coupled J-aggregates are formed through synergistic π-π stacking and hydrogen bonding interactions between monomeric molecules, The rigidified- molecular planar architecture not only avoids fluorescence quenching of the photosensitizer but also significantly broadens the bathochromic absorption band owing to enhanced conjugation effects while preserving photodynamic activity. As a result, a broad bathochromic absorption from 600 nm to an absorption tail over 1100 nm was achieved, allowing the photosensitizer to be compatible with a variety of laser sources. The enhanced-receptor conjugation significantly boosts singlet oxygen generation efficiency while reinforcing π-π interactions, endowing the J-aggregates with exceptional thermal stability, chemical stability, and photothermal generation capability. Under 980 nm laser excitation, the π-π-coupled J-aggregations based on HCY-3 J-NPs exhibited excellent ROS generation capacity and NIR-II fluorescence emission, successfully achieving multimodal photothermal/photodynamic antitumor therapy guided by NIR-II FL imaging. Such π-π-coupled J-aggregates may represent a new route for the design of NIR-II photosensitizers.