Group 14 Metallafluorenes for Lipid Structure Detection and Cellular Imaging

Lipid droplets (LD) are lipid-rich cellular organelles that play a critical role in energy metabolism and some disease pathology. Due to the highly diverse nature of lipid composition, it is difficult to address fundamental questions regarding their mechanism of action. Environmentally sensitive dyes have been shown to be useful in probing lipid dynamics, and there is ongoing interest in developing dyes that are nontoxic, photostable, and sensitive. Recently we evaluated a small library (4) of 2,7-disubstituted-alkynyl(aryl)-3,6-dimethoxy-9,9-diphenylsilafluorenes/germafluorenes with different -alkynyl(aryl) substituents for their potential as cellular fluorescent probes. These compounds are soluble in water and luminesce in aqueous solution. In this library, emission maxima differ by as much as 67 nm, providing wavelength tunability. Moreoever, these compounds exhibit remarkable quantum yields in hydrophobic environments (approaching 1.00) and dramatic increases in emission intensity in the presence of surfactants (up to 25x). Here we show that they are nontoxic to E. coli, S. aureus, and S. cerevisiae. Further, they exhibit significant emission enhancements in the presence of small unilamellar vesicles (SUVs) (2-6x). We also note that they luminesce in S. cerevisiae cells with strong photostability in vivo. These sila- and germafluorenes colocalize with the LD stain Nile Red in S.