Synthesis and photophysical characterization of highly water-soluble PEGylated BODIPY derivatives for cellular imaging

A series of poly(ethylene glycol) (PEG)-modified water-soluble boron dipyrromethene (BODIPY) dyes (EtBOD-PEG and BOD-PEG) were synthesized and their photophysical properties in various solutions were investigated. The presence of ethyl groups at the 2,6-positions of the BODIPY core in EtBOD-PEG resulted in bathochromic shifts in both the absorption and emission spectra relative to those of the unsubstituted BOD-PEG. Importantly, bulky di-branched PEG chains were introduced at the meso position of the BODIPY core, leading to enhanced solubilities and high fluorescence quantum yields in aqueous solutions. The water-soluble BODIPY dyes were explored for their applicability in fluorescent bio-imaging using MCF-7 human breast cancer cells. The dyes were cell-permeable and were concentrated in cellular cytoplasm area, suggesting that they have potential applications as bio-imaging agents.