Spectroscopic response of pH sensitive 5-hydroxy-5-methyl-3-[(4-phenlazo-phenylimino)-methyl]-benzaldehyde probe: a selective sensor towards acetate anion

Sensing specific biological agents is important in terms of medicinal and pharmaceutical sectors. In this connection, development of point of care (POC) devices as per requirement with significant limit of detection (LOD) is of utmost importance. The present study reports the synthesis of a new class of sensing probe viz. 5-Hydroxy-5-methyl-3-[(4-phenlazo-phenylimino)-methyl]-benzaldehyde which bears a phenolic O–H group as the binding site and diazinyl functional group (Ph-N==N-Ph) as optical signalling moiety. Preliminary colorimetric studies establish that the presence of acetate anion (AcO⁻) in the solution causes a colour change from light yellow to red. NMR studies suggest probable binding mode of the reported probe is through the deprotonation of labile hydrogen of the phenolic OH-group, which in turn subsequently altered the optical properties of the probe. The sensing specificity of the reported probe is established through its photophysical characteristics. The binding constant magnitude of the probe using AcO⁻ is calculated from fluorescence titration and determined to be 5.43× 106 M⁻¹. This ascertains the strong binding ability of the probe with AcO⁻ with an experimentally calculated limit of detection (LOD) to be ∼0.256 μM (15.11 ppb), as also substantiated through theoretical study. Such lower sensing level poses the present probe to be an effective anion sensor for acetate ion. The potential novelty lies in the detection of inorganic AcO⁻ in aqueous analytical medium.