Bright red-emitting highly reliable styryl probe with large stokes shift for visualizing mitochondria in live cells under wash-free conditions

Bright red-emitting pyridinium cyanine based styryl probe 2 is synthesized in good yields. Probe 2 demonstrated a large Stokes' shift (Lambda lambda approximate to 128 nm, 4227 cm(-1) in DCM) and excellent fluorescent quantum yield (Phi(f1) approximate to 0.2 - 0.7) due to strong Intra-molecular charge transfer (ICT). Probe 2 was found to exhibit exceptional selectivity for cellular mitochondria in both normal (COS-7) and cancer (A549) cell lines. Probe 2 is readily applicable as a wash-free dye to visualize mitochondria as it does not require post-staining washing prior to imaging. Styryl probe 2 also showed an excellent biocompatibility as the calculated LC50 (lethal concentration, 50%) value was > 20 mu M. Probe 2 emission did not show any interferences from anionic species or other biological molecules. Probe 2 is readily excitable (lambda(ex)similar to 460 and lambda(em)similar to 618 nm) with the available laser (454 nm) in commercial microscopes and thus it can be a useful probe for mitochondrial tracking in live cells.