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Owing to their easy accessibility and high degree of structural and functional diversity, many multicomponent reactions (MCRs) have been a rich source of conjugate π-systems, functionalised chromophores (or fluorophore) and redox active molecules. Despite their high explorative potential and practical benefits, only a few MCR products have been so far investigated for their metal sensing abilities. In the present report, two furopyrimidinones (FPys) based molecular systems have been synthesized by [4 + 1] cycloaddition based MCR sequence. Designed chemosensors displayed optic (absorption spectra) as well as electroanalytical (ion selective electrode) response toward Cu2 + ion in solution and membrane phase respectively (dual channel sensing). Different aspects of both the sensing phenomena such as selectivity, association constants, detection limit, membrane composition etc. were studied in detail using UV–Vis spectroscopy, NMR titration and cell assembly. Both the compounds showed excellent performance characteristics such as high selectivity, acceptable affinity and low detection limits (10− 7 M) in both sensing assays with potential utility in the area of sample monitoring.

A new sensing functionalized chemosensor 3-hydroxy-2-(1H-indol-3-yl)-4H-chromen-4-one ( M1) was readily prepared in facile reaction conditions and explored its sensing nature response towards metal ions in semi-aqueous medium. The chemosensor M1 exhibited high selective and sensitive fluorescence turn “off-on” response for Al 3+ and Zn 2+ ions in the existence of several metal ions and the changes are enabled for naked-eye detection. These high selectivity expressed by high binding constants 2.62 × 10 4 (Al 3+ ) and 1.92 × 10 4 M −1 (Zn 2+ ) calculated by the Benesi-Hildebrand equation based on the emission studies. The binding strategy was also supported by 1 H NMR titration.

Despite the fact that a large number of chemical sensors for Cu 2+ have been proposed by different groups in recent past, most of them fall into very few classes of molecular framework with similar utilities and limitations. In order to broaden the scope and to overcome the limitation of present day chemical sensors, design, synthesis and testing of molecular systems based on novel fluoro/chromophore is a research goal of significant interest. In the present report, two novel furan-2-yl substituted imidazoazine based optic chemosensors ( IA-1 and IA-2 ) for Cu 2+ have been disclosed for the first time. Proposed sensors were found to have high association constants (10 4 M −1 ), acceptable detection limits (10 −7 M), high selectivity and reversibility/reusability. Different aspects of this sensing phenomenon were studied using fluorescence spectroscopy and NMR based titrations. Designed probe have shown potential applications in the area of sample monitoring, photo-printing and membrane sensing.

New antipyrine Schiff bases 2,3-dimethyl-4-(3-oxo-1,3-diphenylpropylideneamino)-1-phenyl-1,2-dihydropyrazol-5-one ( AP1 ) and 2,3-dimethyl-4-(2-oxo-1,2-diphenylethylideneamino)-1-phenyl-1,2-dihydropyrazol-5-one ( AP2 ) have been synthesized by simple condensation method and investigated their metal recognition abilities. Different aspects of metal sensing phenomena were extensively studied and results indicated that Schiff base AP1 and AP2 exhibited selective colorimetric and fluorescent sensing behavior towards Al 3+ and Cr 3+ in methanol with high binding nature, which could be directly detected by the naked-eye. Stoichiometry of metal-ligand complexes were determined by job's plots titrations and further verified with HRMS data. Both sensors exhibited excellent fluorescent sensing behavior in acidic and neutral pH with low detection limits 0.49, 0.96 μM for AP1 + Al 3+ , AP1 + Cr 3+ and 0.73, 1.21 μM for AP2 + Al 3+ and AP2 + Cr 3+ , respectively.

A new rhodamine-derived Schiff base RH was synthesized and its sensing behavior toward various metal ions was investigated by UV–vis and fluorescence spectroscopic techniques. The sensor exhibited highly selective and sensitive colorimetric response to Cu2+ and Al3+, and “off–on” fluorescence response toward Fe3+ in semi-aqueous media. The spectral changes obtained are large enough in the visible region of the spectrum and thus enable naked-eye detection. Experimentally proved that the formation of RH–Al3+ complex is fully reversible and can sense to AcO−/F− via break the complex. The results revealed that the sensor offers the sequential detection of Al3+ and AcO−/F−.

Two new highly selective colorimetric and fluoregenic aminopyridine Schiff bases (L1 and L2) were synthesized by simple refluxing method and characterised via standard NMR and HRMS techniques. Its excellent metal sensing abilities explored on absorbance and fluorescence spectroscopy. The recognition colorimertric sensing behavior of probes L1 and L2 towards Ni(II), Zn(II), Fe(III) and UO2(II) ions were carefully investigated with different aspects of sensing behavior such as sensitivity, binding constant, stoichiometry, pH range and interference effect. Moreover, L1 and L2 also displayed excellent “off-on” fluoregenic selectivity with Zn(II). The results revealed that the sensors provided colorimetric and fluoregenic sensing excellent response with low limit of detection, under neutral conditions.

Phthalocyanine tetrasulfonic acid (PCTS) performed as a optical probe for selective detection of Cu2+ in DMSO solution over other metal ions used. The complexation behavior of chemodosimeter toward various metal ions has been studied via UV–vis absorption and fluorescence emission spectra. Induced changes were found to be observable from naked eye. The association constant (Ka) and low limit of detection were found to be 8.80 × 105 M−1 and 5.53 × 10−7 M, respectively. The optode showed excellent selectivity behavior in the environmental pH range.

A new azo compound, 1-(2-pyridylazo)-2-naphthol, has been prepared and characterized. The synthesized compound shows a very high affinity for aluminium. The complexation reaction of aluminium has been explored by Colorimetry, FT-IR, 1 H NMR, HRMS and fluorescence spectroscopy. The detection limit has been found to be 1.81 × 10 −8 M estimated by the titration method. The turn-on fluorescence behaviour of aluminium interaction with ligand has been found to be so fast (

A simple 4-Methyl-7-hydroxy-8-formyl Coumarin (CS) serves as a selective chemosensor for Mg 2+ in the presence of alkali and alkaline earth metal ions. It showed a significant fluorescence enhancement towards Mg 2+ . The receptor CS exhibited a good binding constant and lowest detection limit for Mg 2+ . The variation of emission signal exists via of reversible chelation enhanced fluorescence (CHEF) with this inherent quenching metal ion.

Antipyrine schiff bases 4-(4-hydroxy-3-methoxybenzylideneamino)-2,3-dimethyl-1-phenyl-1,2-dihydropyrazol-5-one (L1) was successfully synthesized and characterized. The complexation behavior of chemosensor with different metal ions including Zn2+ ions in methanolic solution was studied on UV–vis absorption spectra and Photofluorescent spectra. Results showed that the chemosensor (L1) exhibited 55 fold enhancements in fluorescence at 533 nm after adding Zn2+ ions. Such fluorescent responses could be detected by naked eye under UV-lamp. The limit of detection was calculated to be 10−7 M by titration method. The chemosensor (L1) showed excellent selectivity fluorescent behavior in acidic pH range. The complex solution (L1-Zn2+) exhibited reversibility with EDTA.

Thiazole Schiff bases 2-(4-phenyl-1,3-thiazol-2-yliminomethyl)phenol (L 1 ) and 1-(4-phenyl-1,3-thiazol-2-yliminomethyl)naphthalen-2-ol (L 2 ) have synthesized and characterized. The interaction of Schiff bases with different metal ions has been studied over UV–vis absorption spectra and photofluorescent spectra. The results are indicated that Schiff base L 1 and L 2 exhibited turn-on fluorescent behavior with Al 3+ ions in methanol, which could be directly detected by the naked-eye under the UV-lamp. The limits of detection were calculated for L 1 and L 2 since 1.0 × 10 −6 and 7.5 × 10 −7 by the titration method. Both sensors exhibited excellent fluorescent behavior in 5.0–13.5 pH range. The fluorescent behavior of legends-aluminum complex solution goes to turn-off in the presence of Ni 2+ and EDTA.