<scp>BODIPY</scp> ‐based J‐aggregates: From supramolecular chemistry to <scp>NIR</scp> bioimaging and phototherapies

Abstract Boron‐dipyrromethene (BODIPY) dyes have attracted sustained interest owing to their exceptional photophysical properties, including high fluorescence quantum yields, tunable absorption and emission wavelengths, and excellent photostability. Beyond their molecular‐level attributes, the supramolecular organization of BODIPY derivatives provides a powerful means of modulating their optical and electronic properties. In particular, J‐aggregation has emerged as a key self‐assembly mode that gives rise to narrow, red‐shifted spectral bands, small Stokes shift, and enhanced radiative constants. The formation of BODIPY J‐aggregates is governed by a delicate balance of non‐covalent interactions, including π–π stacking, hydrogen bonding, van der Waals interactions, hydrophobic effects, and, in selected systems, halogen bonding. These interactions can be systematically regulated through molecular geometry, substitution pattern, amphiphilicity, solvent environment, and external stimuli, thereby enabling access to diverse supramolecular architectures with tailored functions. This review provides a comprehensive overview of the fundamental principles underlying J‐aggregate formation in BODIPY‐based systems, with particular emphasis on molecular design strategies, aggregation mechanisms, solvent and environmental effects, and structure–property relationships. Recent advances in the application of self‐assembled BODIPY J‐aggregates are surveyed across diverse fields, including fluorescence sensing, bioimaging, and photodynamic and photothermal therapy.