Recent advances in the construction, imaging and phototherapy applications of NIR-II J-aggregates based on different fluorophores

With the development of various near-infrared imaging technologies, near-infrared-II (NIR-II) (1000–1700 nm) dyes have attracted extensive attention from scientific researchers. NIR-II radiation exhibits superior tissue penetration capability, reduced tissue scattering effects, lower tissue autofluorescence, and minimized photodamage. These advantages provide possibilities for deeper in vivo imaging and promote advancements in biomedicine. Among them, J-aggregates are fluorescent materials composed of highly ordered organic dye molecules. In J-aggregates, the arrangement of monomer molecules' transition dipole moments in "head-to-tail" or "slip-stacked" configurations, almost parallel to the connecting central line, reduces excitonic state energy and induces strong interactions between intermolecular transition dipole moments, forming exciton coupling. Consequently, compared with monomers, J-aggregates exhibit longer absorption and emission wavelengths. Currently reported J-aggregate fluorescent dyes are mainly constructed from small organic fluorescent monomers such as cyanine and BODIPY. This review discusses strategies for constructing J-aggregates by different monomer molecules and their biological applications, and provides perspectives on future development strategies and potential application directions.