Synthesis And Applications Of Boron-dipyrromethene Based Fluorescent Dyes

Near infrared fluorescence dyes have received considerable attentions in the recent years due to its advances in optical imaging, microarrays, tumour detection and electrophoresis.It is very meaningful to develop labels and optical sensors for biological and medical applications. The key advantage of NIR dyes in biology imaging is that the scattering of light, auto fluorescence, and absorption by tissues is minimized.Boron-dipyrromethene(BODIPY) derivatives are fascinating dyes with large extinction coefficients, high fluorescence quantum yields, and photostability. Due to these favourable properties, BDPs have attracted special interest in drug discovery, biomedical imaging, and optical sensing. Therefore the success of these applications relys on the long-wavelength absorbing and emitting BDPs(ca. 650-900nm) to produce an enhanced biological effect in deeper tissues. This goal has been achieved by several strategies of chemical modifications such as fusing an aromatic ring at pyrrolic-position(s) of the BODIPY core, installing aryl, vinyl, styryl and arylethynyl substituents at 3,5-positions of the chromophore and replacing the meso-carbon atom with aza-nitrogen atom to form aza-BODIPYBased on the above strategies, we designed and synthesized a series of novel visible/NIR fluorescent probes based on BODIPY dyes, the results are summarized as follows:1. Designed ansynthesized α-substituted BODIPY 1a-1d with strong electron withdrawing ester and cyano- group. As π-conjugation increases, its absorption and emission spectra red-shifted to above 630 nm in chloroform. In polar solvent such as methanol, the π-conjugation of the BODIPY core was destroyed and the solution become colourless. The emission and absorption spectra recover after addition of H+. The destroy of π-conjugation has been confirmed in 1H NMR spectra. Compoud la is an excellent fluorescent probe for detecting lysosomers in cell.2. Designed and synthesized a pyrazine fused aza-BODIPY 6. The replacement of the meso-carbon atom with nitrogen atom leads to a red shift of the absorption spectrum to 680 nm. The addition of ammonium ion produces significant quenching of the fluorescence intensity and a visible colorimetric change from green to pink. Theoretic calculation indicates that the neighboring BODIPY molecules form H-aggregation through intermolecular hydrogen bonding between the pyrazine moiety with ammonium ions. Compound 6 can be used as a NIR ratio metric probe for ammonium ion.