BODIPY

BODIPY, an abbreviation for boron-dipyrromethene, is a family Organoboron compounds of interest as fluorescent dyes. BODIPY is composed of dipyrromethene complexed with a disubstituted boron center, typically BF2. The IUPAC name for the BODIPY core is 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene. Reflecting its instability, the unsubstituted BODIPY dye had not been prepared until 2009. BODIPY, an abbreviation for boron-dipyrromethene, is a family Organoboron compounds of interest as fluorescent dyes. BODIPY is composed of dipyrromethene complexed with a disubstituted boron center, typically BF2. The IUPAC name for the BODIPY core is 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene. Reflecting its instability, the unsubstituted BODIPY dye had not been prepared until 2009. BODIPY dyes have been well investigated. Most BODIPY dyes have small Stokes shift and are relatively chemically inert. Fluorescence is quenched in a solution, which limits application. This problem has been handled by synthesizing asymmetric boron complexes and replacing the fluorine groups with phenyl groups. BODIPY dyes are notable for their uniquely small Stokes shift, high, environment-independent fluorescence quantum yields, often approaching 100% even in water, sharp excitation and emission peaks contributing to overall brightness, and high solubility in many organic solvents. The combination of these qualities makes BODIPY fluorophores promising for imaging applications. The position of the absorption and emission bands remain almost unchanged in solvents of different polarity as the dipole moment and transition dipole are mutually orthogonal. BODIPY are prepared by treating a dipyrromethene precursor with boron trifluoride etherate in the presence of a tertiary amine. Dipyrromethenes are accessed from a suitable pyrrole by several methods. Normally, one alpha-position in employed pyrroles is substituted and the other is free. Condensation of such pyrrole, often available from Knorr pyrrole synthesis, with an aromatic aldehyde in the presence of TFA gives dipyrromethane, which is oxidized to dipyrromethene using a quinone oxidant such as DDQ or p-chloranil.