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With this research we set out to develop a number of coumarin-based ‘AND’ logic fluorescence probes that were capable of detecting a chosen analyte in the presence of HCys. Probe JEG-CAB was constructed by attaching the ONOO� reactive unit, benzyl boronate ester, to a HCys/Cys reactive fluorescent probe, CAH. Similarly, the core unit CAH was functionalised with the nitroreductase (NTR) reactive p-nitrobenzyl unit to produce probe JEG-CAN. Both, JEG-CAB and JEG-CAN exhibited a significant fluorescence increase when exposed to either HCys and ONOO� (JEG-CAB) or HCys and NTR (JEG-CAN) thus demonstrating their effectiveness to function as AND logic gates for HCys and a chosen analyte.

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.

With this research we set out to develop a coumarin-based novel fluorescent probe NTR-AHC for the detection of biological thiols and nitroreductase (NTR). Probe NTR-AHC was constructed by attaching the NTR trigger moiety (p-nitrobenzyl) and biothiol acceptor (maleic acid monoamide), to the core fluorophore AHC. In the presence of both glutathione (GSH) and NTR, probe NTR-AHC produced a >8-fold increase in fluorescence intensity at 463 nm.

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 furochromenone based molecular systems (FC1 and FC2) were synthesized by a microwave assisted three component reaction and investigated for their metal sensing abilities. Reported chemosensors displayed a selective turn off fluorescence response in the presence of Cu2+ in solution phase with high association constants [1.27×104 M–1 (FC1) and 1.05×104 M–1 (FC2)] and low detection limits [2.88 × 10−7 M (FC1) and 2.87 × 10−7 M (FC2)]. Both the molecular systems were also selective for cupric ion in voltammetric and membrane base studies.

The present report highlights the role of comprehensive structure property relationships (SPRs) in the discovery of a new and more effective molecular system for sensing purposes. From an extensive survey of different classes of amino substituted annulated furanones, it was realized that with some exceptions, these functionalized furanones could sense Cu2+ ions in the semi-aqueous phase irrespective of the nature of substituents; furthermore the same scaffolds could also detect Al3+, if the aldehydic position is specifically filled by a 3-indoyl group. As a result, amino substituted annulated furanones with 3-indoyl groups could detect both metal ions, response time of which mainly depends on the overall molecular framework. After replacing different furanone frameworks, a dual metal ion sensor (for Cu2+ and Al3+) with short response time and high selectivity and association constant was identified. The proposed bifunctional sensor displayed a distinct but observable response (turn off colorimetric for Cu2+ and turn on fluorescence for Al3+) to both metal ions with potential applications in the area of real sample analysis and membrane sensing.

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.

Two molecular probes based on the furoquinolinol (FQ) framework have been rationally designed for the rapid detection and trace level quantification of Cu2+ in organic and semi-aqueous mediums. Synthesized FQs were extensively examined for their Cu2+ sensing abilities by UV-vis/fluorescence experiments, NMR titrations and DFT based calculations. Higher binding constant [2.11 × 104 M−1 (FQ1) and 1.87 × 104 M−1 (FQ2)], low detection limit [1.52 × 10−7 M (FQ1) and 2.13 × 10−7 M (FQ2)], high selectivity, fast response, wide operational pH range, and repeated usability are some of the salient features of the reported sensors. Furthermore, these compounds (FQs) retained their metal detection abilities in thin PVC membranes.

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.

A new rhodamine functionalized fluorogenic Schiff base CS was synthesized and its colorimetric and fluorescence responses toward various metal ions were explored. The sensor exhibited highly selective and sensitive colorimetric and "off-on" fluorescence response towards Al(3+) in the presence of other competing metal ions. These spectral changes are large enough in the visible region of the spectrum and thus enable naked-eye detection. Studies proved that the formation of CS-Al(3+) complex is fully reversible and can sense to AcO(-)/F(-) via dissociation. The results revealed that the sensor provides fluorescence "off-on-off" strategy for the sequential detection of Al(3+) and AcO(-)/F(-).