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Herein, we have reported a novel quinazolin-based Schiff base chemosensor ( E )-2-benzamido- N '-(1-(pyridin-2-yl)ethylidene)benzohydrazide (L). L has been designed, synthesised and characterised by 1 H-NMR, IR spectroscopy, ESI-MS spectrometry and theoretical studies. The receptor showed appreciable colorimetric λ max shift for both Ni 2+ and Zn 2+ ions and fluorometric " turn on " response in presence of only Zn 2+ ion. The Jobs plot analysis revealed that receptor forms 2 : 1 complex with both the ions Ni 2+ and Zn 2+ , further confirmed by ESI-MS analysis. The single crystal structure of L-Ni 2+ complex (1) has also been determined. The colorimetric detection limits were calculated to 7.9 nM and 7.5 nM respectively for Ni 2+ and Zn 2+ in methanol-Tris-HCl buffer medium (10 mM, pH 7.2, 1 : 1 v/v). The chemosensor L can be applied for the recovery of contaminated water samples., Competing Interests: Authors declare no conflicts of interest., (This journal is © The Royal Society of Chemistry.)

A triazole-based novel bis Schiff base colorimetric and fluorescent chemosensor (L) has been designed, synthesized and characterized by elemental analysis, 1 H-NMR, ESI-MS, FTIR spectra and DFT studies. The receptor L showed selective and sensitive colorimetric sensing ability for Cu 2+ and Pb 2+ ions by changing color from colorless to yellow and light yellow respectively in CH 3 OH-tris-buffer (1 : 1, v/v). However, it displayed strong fluorescence enhancement upon the addition of both Cu 2+ and Pb 2+ ions, attributed to the blocking of PET. The fluorometric detection limits for Cu 2+ and Pb 2+ were found to be 12 × 10 -7 M and 9 × 10 -7 M and the colorimetric detection limits were 3.7 × 10 -6 M and 1.2 × 10 -6 M respectively; which are far below the permissible concentration in drinking water determined by WHO. Moreover, it was found that chemosensor L worked as a reversible fluorescence probe towards Cu 2+ and Pb 2+ ions by the accumulation of S 2- and EDTA respectively. Based on the physicochemical and analytical methods like ESI-mass spectrometry, Job plot, FT-IR, 1 H-NMR spectra and DFT studies the detection mechanism may be explained as metal coordination, photoinduced electron transfer (PET) as well as an internal charge transfer (ICT) process. The sensor could work in a pH span of 4.0-12.0. The chemosensor L shows its application potential in the detection of Cu 2+ and Pb 2+ in real samples, living cells and building of molecular logic gate., Competing Interests: The authors declare no conflicts of interest., (This journal is © The Royal Society of Chemistry.)