Four dual optical signalings of fluorescent hydrazone Schiff bases were synthesized from 1,8-naphthalimide hydrazide and substituted furan and thiophene rings, employing ethanol as green solvent. All synthesized molecules can detect F and CN with fast response with naked eye color change and quenching of fluorescence. Most common competitive anions have paltry interferences during the optical sensing of F, while only nitro and methyl furan substituted provided good selectivity to CN in THF. Substituents on heterocyclic directly affect fluoride capturing sensitivity, namely, electron donating group provides more sensitivity than with electron withdrawing groups. 1H NMR confirms the H-bonding between sensor molecule and F/CN. The detection limits of the four-sensor molecules were found below 0.3 ppm for F and CN detection. The magnitude of fluorescence quenching was estimated through Stern-Volmer plots. Test strips experimentation revealed the on-site solid-state detection efficacy of the sensors. Addition of Cu(II) ions to nitro and methyl furan substituted, resulted in selective discrimination between F and CN in THF. Computational studies prove the agreement of reactivity for four optical molecules interaction with F and show that substituent at furan/thiophene does not affect the sensitivity, this is contrary to traditional school of thoughts.


“Furan/Thiophene-Based Fluorescent Hydrazones as Fluoride and Cyanide Sensors” Saini, N.; Wannasiri, C.; Chanmungkalakul, S.; Prigyai, N.; Ervithayasuporn, V.*; Kiatkamjornwong, S.* J. Photochem. Photobiol., A. 385 (2019) 112038.