Boron dipyrromethene (BODIPY) based fluorescent probes have been widely used for many applications such as fluorescent labeling of biomolecules, ion sensing and energy transfer cassettes. These fluorescence probes are also essential tools for biological imaging for monitoring biomolecules in living cells. Derivatives of 3,5-dichloro-BODIPY 1 are becoming important due to their high photostability, large absorption coefficients and fluorescence quantum yields. Introducing appropriate nucleophiles at 3,5-positions on compound 1 can alter the photophysical and spectral properties, such as absorption and emission spectra. Hydrazine-containing fluorophores can be used for bioorthogonal labeling; however, few examples of these molecules exist. It was shown recently that compound 1 reacts readily with nucleophiles to form monosubstituted and disubstituted products. Reaction of 1 with hydrazine under mild conditions cleanly affords the monohydrazinyl product, which can subsequently react with other nucleophiles to form asymmetric 3,5-disubstituted products 2. The emission energy of the BODIPY-hydrazine can be adjusted by altering the nature of the second nucleophile. The synthesis, reactivity and photochemical properties of these new fluorophores will be presented.
