All reagents and starting materials were purchased from Acros and used without further purification. Thin layer chromatography (TLC) was performed on silica gel 60 F254 (E. Merck). Column chromatography was performed on silica gel (Silicycle, 230-400 mesh). The melting point was recorded on an Electrothermal 9100 instrument in open capillary tubes and is uncorrected. Deuterated solvents (Cambridge Isotope Laboratories and Acros) for NMR spectroscopic analyses were used as received. NMR spectra were recorded on a Varian Unity Plus 500 MHz spectrometer, with working frequency of 499.87 MHz for 1 H nuclei, and 125.7 MHz for 13 C nuclei, respectively. Chemical shifts are quoted in ppm relative to tetramethylsilane, using the residual solvent peak as a reference standard. High-resolution mass spectra were measured on a Micromass Q-Tof Ultima capable of running HR-ESI MS. UV-Vis spectra was recorded on a Shimadzu UV spectrophotometer (UV-1800). Infrared spectra were obtained using a Shimadzu IRAffinity-1 spectrometer equipped with a ZnSe Single reflection ATR. UV/Vis Titrations: Trifluoroacetic acid (CF 3 CO 2 H or TFA, Merck Uvasol, 99.5%, for spectroscopy) and triethylamine (NEt 3 , SDS, 99.3%, synthesis grade) were purchased from commercial sources and used without further purification. All analyses were carried out with spectroscopic grade acetonitrile CH 3 CN (Acros Organics, 99+% for spectroscopy), which was used as received. All solutions were protected from daylight to avoid any potential photochemical degradation. All stock solutions were prepared using an AG 245 Mettler Toledo analytical balance (precision 0.01 mg). The concentrations of the stock solutions of the targeted compounds were calculated by quantitative dissolution

The replacement of one of the carbonyl groups in a 1,2,3-triketone-2-naphthylhydrazone with a pyridine ring yields an original molecular switch that can be switched fully, effectively, and reversibly between the E and Z configurations. This hydrazone-based, pH-controlled, molecular switch is the first example of a chemically controlled configurational rotary switch. The bistable switch exists primarily (97%) as the E configuration in solution and can be converted quantitatively to the Z-H(+) configuration upon treatment with trifluoroacetic acid. When Z-H(+) is passed over a plug of K(2)CO(3), the "metastable" Z configuration is observed using (1)H NMR spectroscopy, which thermally equilibrates to give back the E configuration. The rate of this process is dependent on the polarity of the solvent, indicating that the E/Z isomerization takes place via a rotation around the hydrazone C=N bond.

1,2,3-Triazole based chemosensor is synthesized using “Click chemistry” approach. Addition of fluoride ion “turn-on” the fluorescence response of probe.