donor-π-acceptor structure

Dansyl-morpholine (DNS-M) is a Fluorescent probe for lipid droplet imaging, cancer cell discrimination, and real-time tracking of lipid droplet dynamics. As a solvatochromic probe with a donor-π-acceptor structure, it relies on hydrophobic interaction for its mechanism of action: its good lipophilicity, confirmed by an oil-water partition coefficient LogP = 2.35, allows it to rapidly penetrate cell membranes, and it specifically localizes to the hydrophobic core of lipid droplets; its fluorescence is strongly enhanced in the nonpolar environment of lipid droplets, while it emits very weak fluorescence in polar environments like PBS buffer, and it exhibits a bathochromic shift in emission wavelength with increasing solvent polarity. It has negligible cytotoxicity, with cell viability remaining over 95% after 24-hour incubation with 100 μM of the probe, and it possesses excellent photostability, retaining over 97% of initial fluorescence intensity after 60 continuous laser scans. For cell imaging applications, its excitation/emission wavelengths for lipid droplet labeling are Ex/Em = 405/480−540 nm, and in a simulative lipid environment O/W emulsion, it has an excitation wavelength of ~346 nm and emission wavelength of ~500 nm, giving a Stokes shift of 154 nm[1].

DCA is a Fluorescent probe for visualization of phase behavior in ER membranes. DCA is an ER-targeting, polarity-responsive NIR ratiometric probe, with its p-toluenesulfonamide group responsible for ER localization; its sensitivity to polarity relies on its donor-π-acceptor (D-π-A) structure, where aniline acts as the donor and dicyanomethylene acts as the acceptor, driving an intramolecular charge transfer (ICT) process upon excitation. In environments with low polarity, such as the closely packed, low water content ERₒ phase of ER membranes, DCA emits at a shorter wavelength, while in high polarity environments like the loosely packed, higher water content ERd phase, ICT leads to a red-shifted emission, allowing discrimination of the two phases via dual NIR emission colors and ratiometric imaging. Ex/Em = 488/570–620 nm and 488/665–735 nm; additional excitation/emission pairs include Ex/Em = 488/631 nm in low polarity 1,4-dioxane and Ex/Em = 488/677 nm in 1,4-dioxane with 30% water, the higher polarity condition. It shows a large Stokes shift of ~170 nm, and pH, viscosity, and biologically relevant species including Cys, GSH, H₂O₂, and metal ions do not exert marked interference on its fluorescence spectra[1].