Synchronous colorimetric determination of CN−, F−, and H2PO4− based on structural manipulation of hydrazone sensors

To explore the effect of sensor structure on anions detection, three new hydrazones P-CN , P-CF 3 and P-NO 2 having different electron-withdraw groups are synthesized. Their anions recognition properties are investigated compared with those of P-OMe , P-H and acylhydrazone B-NO 2 . It shows all non-nitro hydrazones exhibit increasing sensitivity specifically toward CN − in the order of P-OMe  <  P-H  <  P-CN  <  P-CF 3 , indicated by color change from colorless to different shades of blue. Whereas P-NO 2 responds to CN − , F − and H 2 PO 4 − concurrently and its sensitivity to CN − is more than 4 times higher compared with that of the other hydrazones. CN − can be discriminated from F − by P-NO 2 in acetonitrile/water. On the other hand, B-NO 2 has only discernible response to CN − and F − with less sensitivity than P-NO 2 does. Detection details of P-NO 2 to CN − are investigated by titration, anti-interference tests, Job’s plot, HRMS, pH effect assays. The 1 H NMR, IR and reversibility tests demonstrate the deprotonation mechanism. The detection mechanisms of P-NO 2 and B-NO 2 to CN − are compared and demonstrate the reason of their recognition difference. The detection limits of P-NO 2 to CN − , F − and H 2 PO 4 − in acetonitrile are 0.0477 μM, 0.0876 μM and 1.46 μM, respectively. Hence, this work indicates that strong electron-withdraw group in related probes can improve their anion detection ability, meanwhile conjugation effect should be also considered in structure designing.