High pH Sensing Properties of a New Schiff-base Compound

Abstract A new Schiff‐base molecule, 4‐chloro‐2‐((2‐(pyridin‐4‐yl)hydrazono)methyl)phenol (LH 2 ) has been found as a fluorescent chemosensor for high pH. It has been synthesized by condensation of 4‐hydrazinylpyridine and 5‐chlorosalicylaldehyde (1:1) in methanol. It has been characterized by elemental analysis and different spectroscopic methods. LH 2 shows emission peak at 571 nm (λ ex =390 nm) upto pH 10.5 and a new peak at 504 nm emerges with increasing intensity with higher pH value of the media. Several cations and anions do not have any significant effect on the emission intensity of LH 2 . Color of LH 2 changes distinctly when pH of aqueous medium is changed from 10.5 to 11 when observed under both visible and UV light. Some theoretical calculations have been performed to look into the spectral transitions. This probe has been used for the detection of pH regions using sea water.