Construction of novel unsymmetrical rhodamine analogue and its application as nitric oxide probe

Traditional rhodamine dyes' absorption and emission wavelengths are in the visible region and Stokes shifts are less than 30 nm, which limit their biological imaging applications. To regulate the photophysical properties of xanthene chromophores, we reported a novel mitochondria-targeted unsymmetrical fluorescent thiophene-hybridized xanthene dye DTPO with deep-red emission wavelength (640 nm) and improved Stokes shift (58 nm) in water. DTPO exhibited multiple excellent properties, such as high molar extinction coefficients, large fluorescence quantum yields, tolerance to photobleaching. Meanwhile, the dye is lower toxic to living cell, and could accumulate in mitochondria. By using DTPO as a fluorophore, a highly selective fluorescent probe DTPO-OPD for the fast detection of mitochondrial NO was synthesized based on the NO-triggered the spiro-ring opening mechanism.