Synthesis and Characterization of Far-Red/NIR-Fluorescent BODIPY Dyes, Solid-State Fluorescence, and Application as Fluorescent Tags Attached to Carbon Nano-onions

A series of pi-extended distyryl-substituted boron dipyrromethene (BODIPY) derivatives with intense far-red/near-infrared (NIR) fluorescence was synthesized and characterized, with a view to enhance the dye's performance for fluorescence labeling. An enhanced brightness was achieved by the introduction of two methyl substituents in the meso positions on the phenyl group of the BODIPY molecule; these substituents resulted in increased structural rigidity. Solid-state fluorescence was observed for one of the distyryl-substituted BODIPY derivatives. The introduction of a terminal bromo substituent allows for the subsequent immobilization of the BODIPY fluorophore on the surface of carbon nano-onions (CNOs), which leads to potential imaging agents for biological and biomedical applications. The farred/NIR-fluorescent CNO nanoparticles were characterized by absorption, fluorescence, and Raman spectroscopies, as well as by thermogravimetric analysis, dynamic light scattering, high-resolution transmission electron microscopy, and confocal microscopy.