Selective recognition of fluoride ions through fluorimetric and colorimetric response of a first mesitylene based dipodal sensor 15employing thiosemicarbazones

A new dipodal chromo-fluorogenic anion sensor (2Z,2′Z)-2,2′-(((((2,4,6-trimethyl-1,3-phenylene)bis-(methyl-ene))bis-(oxy))bis(2,1-phenylene))bis(methanylylidene))bis(N-methylhydrazinecarbothio-amide) has been synthesized and characterized for the detection of F− ion in DMSO. The sensor has proven to be highly selective and sensitive to F− ion, moreover it can act as naked eye chromogenic sensor. The mechanism involved in the detection of fluoride ion is the deprotonation of the –NH groups, which was confirmed by using TBAOH. The pre-organization of the dipodal receptor provides chelating H-bonds with the spherical F− ion. These strong H-bonding interactions result in fast deprotonation of the sensor, producing an optical response. Employing only a weak fluorescence capability of the imine groups, 1 behaves as a fluorogenic sensor by exhibiting fluorescence enhancement at λex 438 nm upon addition of F− ions.