The fluorescent biomarkers for lipid droplets with quinolone-coumarin unit

Two quinolone–coumarin skeleton derivatives (1a, 1b) have been prepared by Friedländer synthesis with 2-aminoaryl ketone and 3-acetyl-7-diethylaminocoumarin. The dyes showed excellent photo stability. Their optical properties in five organic solvents have been measured, and the wavelength range of the maximum fluorescence emission peaks was from 469 nm to 509 nm. Besides, both of them exhibited high fluorescence quantum yields (0.79–0.96) in these organic solvents. The pH influenced optical properties tests indicated dyes 1a–b have strong fluorescence in sub acid (pH = 6.0) to alkaline environment (pH = 9.0). Their fluorescence quantum yields in neutral aqueous solution (pH = 7.0) were 0.82 (1a) and 0.78 (1b) respectively. In addition, dyes 1a–b exhibited stable fluorescence intensity in the presence of some metal cations and biomolecules in neutral solution (pH = 7.0). Subsequently, confocal microscopy imaging indicated that dyes 1a–b could be used as biomarkers for lipid droplets in living and fixed cells (I929 and HeLa cells).