Aggregation-induced Emission Active Naphthalimide Derived Schiff Base for Detecting Cu2+ and Its Applications.

Herein, an aggregation-induced emission (AIE) active Schiff base (NHS) was synthesized by condensing naphthalimide hydrazide with salicylaldehyde. The non-fluorescent solution of NHS in DMSO turned to emissive NHS upon increasing the HEPES fraction in DMSO from 70 to 95%. The UV-Vis absorption and DLS studies supported the self-aggregation of NHS that restricted the intramolecular rotation and activated the ESIPT process. The blue fluorescence of AIE luminogen NHS in DMSO:HEPES (5:95, v/v, pH = 7.4) was examined by adding different metal ions (Al3+, Ca2+, Cd2+, Co2+, Cu2+, Cr2+, Fe2+, Fe3+, Hg2+, Mg2+, Mn2+, Ni2+, Pb2+ and Zn2+). NHS showed a selective fluorescence switch-off response for Cu2+ due to the chelation enhancement quenching effect (CHEQ). The quenching of NHS by Cu2+ was explored by using density functional theory (DFT) and Stern-Volmer plot. The practical utility of NHS was examined by quantitative and qualitative analysis of Cu2+ in real water samples.

Improving Copper(II) Sensitivity by Combined use of AIEE Active and Inactive Schiff Bases.

An aggregation-induced emission enhancement (AIEE) active Schiff base PNN was synthesized by condensing benzidine with 2-hydroxynaphthaldehyde. The green-fluorescent PNN (λem = 510 nm) in DMF turned to yellow-fluorescent PNN (λem = 557 nm) upon increasing the fractions of HEPES buffer (10 mM, pH 7.4) above 40%. The DLS study supports the self-aggregation of PNN that restricts the intramolecular rotation and activates the excited-state intramolecular proton transfer (ESIPT) process. The fluorescence emission of AIEE active PNN was quenched by Cu2+ with an estimated detection limit of 2.1 µM. Interestingly, the detection limit of PNN towards Cu2+ was improved in the presence of an AIEE inactive Schiff base PBPM obtained by reacting 1,4-diaminobenzene with pyridine-4-carbaldehyde. The mixed PNN-PBPM showed a detection limit of 0.49 µM. The practical utility of PNN-PBPM was validated by quantifying Cu2+ ions in real environmental water samples and green tea.

Aggregation-Induced Emission Active Benzidine-Pyridoxal Derived Scaffold for Detecting Fe3+ and pH.

Present work introduces an aggregation-induced emission (AIE) active Schiff base 4,4'-((1E,1'E)-([1,1'-biphenyl]-4,4'-diylbis(azaneylylidene))bis(methaneylylidene))bis(5-(hydroxymethyl)-2-methylpyridin-3-ol) (BNPY). Schiff base BNPY was synthesized by reacting benzidine with pyridoxal. The non-fluorescent BNPY in freely soluble DMSO medium showed a significant fluorescence enhancement at 563 nm (λex = 400 nm) upon increasing the water fraction (fw) in DMSO above 60% due to the restriction of intramolecular rotation upon the aggregation of BNPY. The AIE active BNPY was employed for the detection of metal ions in DMSO:H2O (fw = 70%). Upon the addition of Fe3+, the fluorescence emission of BNPY at 563 nm was quenched due to the chelation-enhanced fluorescence quenching (CHEQ). The Job's plot experiment supported the formation of a complex between BNPY and Fe3+ in 1:2 binding ratio. With an estimated detection limit of 5.6 × 10-7 M, BNPY was employed to detect and quantify Fe3+ ion in real water samples with satisfactory recovery percentages. Moreover, the pH studies of BNPY aggregates revealed three different fluorescence windows: non-fluorescent in acidic pH 2.02 to 3.16, yellow fluorescent between pH 3.60 to 9.33, and green fluorescent in basic pH 9.96 to 12.86.

Fluorescence Sensing of pH and p-Nitrophenol Using an AIEE Active Pyridoxal Derived Schiff Base.

An easy-to-prepare aggregation-induced emission enhancement (AIEE) active Schiff base NPY was synthesized by condensing vitamin B6 cofactor pyridoxal with 3-hydroxy-2-naphthoic hydrazide, and employed for the fluorescent sensing of pH and p-nitrophenol (p-NP). The AIEE phenomenon of NPY was investigated in mixed DMSO/H2O medium. The weakly yellow-fluorescent NPY (λem = 535 nm) in pure DMSO turned to a bright cyan-fluorescent NPY (λem = 490 nm) upon addition of poor solvent water. The DLS and SEM analyses supported the self-aggregation of NPY that restricted the intramolecular rotation and activated the excited state intramolecular proton transfer (ESIPT) process. The AIEE luminogen (AIEEgen) NPY containing 90% of water fraction (fwater) was employed for the fluorescent sensing of pH. AIEEgen NPY displays three distinct fluorescent pH windows: non-fluorescent below pH 3.0 and above pH 10.0, cyan fluorescent between pH 3.0 to 8.0, and yellow fluorescent between pH 8.0 to 10.0. AIEEgen NPY was also applied for the detection of nitroaromatics in HEPES buffer (10% DMSO, 10 mM, pH 7.0). The addition of p-NP selectively quenched the fluorescent intensity of AIEEgen NPY with an estimated detection limit of 1.73 µM. The analytical utility of AIEEgen NPY was examined by quantifying p-NP in different real water samples.

Cost-effective approach to detect Cu(ii) and Hg(ii) by integrating a smartphone with the colorimetric response from a NBD-benzimidazole based dyad.

A new optical chemosensor N1 was designed and synthesized by condensing 4-chloro-7-nitrobenzofurazan with 2-aminophenylbenzimidazole. In CH3OH : H2O (1 : 1, v/v) medium, sensor N1 exhibited high selectivity and sensitivity towards Cu2+ and Hg2+ ions by showing a distinct colour change from pale yellow to pink due to the internal charge transfer occurring between the sensor N1 and the Cu2+/Hg2+ ions upon complexation in 1 : 1 stoichiometry. Also, the binding of Cu2+ and Hg2+ ions with N1 resulted in new absorption bands at 540 nm and 375 nm with the concurrent disappearance of the sensor absorption bands at 485 nm and 321 nm. Using the spectral changes of N1, the concentrations of Cu2+ and Hg2+ ions can be detected down to 1.23 × 10-7 M and 4.70 × 10-7 M, respectively. Further, the colour change of N1 in the presence of Cu2+/Hg2+ ions was integrated with a smartphone colour-scanning app to measure the red-green-blue (RGB) colour intensity, and a cost-effective method was developed for the on-site detection of Cu2+/Hg2+ ions. Finally, the practicability of sensor N1 to quantify Cu2+ and Hg2+ ions in real water samples was successfully validated by using both the UV-vis spectrophotometer and the smartphone.

A novel Schiff base derivative of pyridoxal for the optical sensing of Zn2+ and cysteine.

An easy to prepare novel vitamin B6 cofactor derivative 3-hydroxy-N'-((3 hydroxy-5-(hydroxymethyl)-2-methylpyridin-4-yl)methylene)-2-naphthohydrazide (NPY) was synthesized by a one pot condensation reaction of pyridoxal with 3-hydroxy-2-naphthoic hydrazide and applied for the optical detection of Zn2+ and cysteine in the aqueous DMSO medium. The addition of Zn2+ ions leads to a selective blue-shift in the fluorescence emission spectrum of NPY from 530 nm to 475 nm, which allowed ratiometric detection of Zn2+ ions down to 8.73 × 10-7 M without any interference from other tested metal ions. This system was also successfully applied to detect intracellular Zn2+ ions in live HeLa cells. Further, when the in situ generated NPY·Zn2+ complex was interacted with various amino acids, the addition of cysteine resulted in an instantaneous colour change from light yellow to colourless and the absorbance at 435 nm of the complex was quenched selectively. Also, the fluorescence of the NPY·Zn2+ complex was quenched, which allowed the detection of cysteine down to 6.63 × 10-7 M.

A novel terephthalaldehyde based turn-on fluorescent chemosensor for Cu2+ and its application in imaging of living cells.

A new terephthaldehyde-based chemosensor 1 bearing an aminophenol recognition unit has been synthesized and applied to the fluorescent sensing of metal ions. Molecular system 1 acts as a highly selective and sensitive fluorescence turn-on sensor for Cu2+. The sensing mechanism has been explored. It is proposed that Cu2+ binds with the imine and hydroxyl moiety of 1 in 1 : 2 binding stoichiometry, thereby enhancing the fluorescence at 386 nm. The detection limit and association constant (Ka) of 1 with Cu2+ were found to be 0.62 µM and 6.67 × 104 M-1, respectively. Chemosensor 1 has shown excellent specificity towards Cu2+ and has been successfully applied to the determination of Cu2+ in live L929 cells.

4,4'-Sulfonyldianiline Derived AIE Luminogen for the Detection of Ofloxacin.

The excessive use of antibiotic ofloxacin (Oflx) can cause serious detrimental effects to human health. Therefore, the utmost research priority is required to develop facile methods to detect Oflx. Herein, a V-shaped aggregation-induced emission (AIE) active Schiff base SDANA was introduced for the fluorescent turn-on detection of Oflx. The Schiff base SDANA was synthesized by condensing 4,4'-sulfonyldianiline with two equivalents of 2-hydroxy-1-naphthaldehyde. The nearly non-fluorescent SDANA in DMSO showed strong orange emission with the increase in HEPES buffer (H2O, 10 mM, pH 7.4) fractions in DMSO from 70% to 95% due to the combined effects of AIE and ESIPT. The DLS and SEM analyses were performed to complement the formation of self-aggregates of SDANA. With the addition of Oflx, the fluorescence emission of AIE luminogen (AIEgen) SDANA (lem = 575 nm, lex = 400 nm) was blue-shifted and enhanced at 530 nm. The interactions of Oflx over the surface of SDANA aggregates disrupted the intramolecular charge transfer and aggregation morphology of SDANA, which gave a distinct fluorescence response to detect Oflx. The detection limit for Oflx was estimated as 0.81 µM, and the developed probe AIEgen SDANA was applied for the quantification of Oflx in human blood serum.

Turn-on fluorescent chemosensor for Zn(II) via ring opening of rhodamine spirolactam and their live cell imaging.

A new rhodamine based selective and sensitive turn-on fluorescent Zn(2+)chemosensor has been developed. A prominent fluorescence enhancement was found in the presence of Zn(2+), which was accompanied by changes in the absorption spectrum. The new sensor showed 'naked-eye' detection of Zn(2+) ions: a color change of the solution from colorless to pink. Furthermore, by means of confocal laser scanning microscopy experiments, it has been demonstrated that it can be used as a fluorescent probe for monitoring Zn(2+) in living cells.

A dual colorimetric chemosensor for Hg(ii) and cyanide ions in aqueous media based on a nitrobenzoxadiazole (NBD)-antipyrine conjugate with INHIBIT logic gate behaviour.

In this work, we have synthesized nitrobenzoxadiazole-antipyrine conjugate 1 from chloro substituted nitrobenzoxadiazole (NBD) with 4-aminoantipyrine by an elegant method which provides good yield and it is characterized by various spectroscopic techniques. The sensing ability of compound 1 is analyzed with the addition of different metal ions and anions in an aqueous methanol medium. It shows rapid colorimetric response for Hg2+ and CN- ions over a wide range of competitive metal ions and anions. On addition of Hg2+/CN- ions, 1 shows a distinct color change from pale yellow to pink and orange red, respectively, thus permitting chemosensor 1 to be used for 'naked eye' detection of Hg2+ and CN- ions. The change in spectral features and color of 1 with the addition of Hg2+ and CN- ions is mainly due to the formation of a charge-transfer complex (12-Hg2+) and cyanide ion induced deprotonation of 1. The interaction between the Hg2+/CN- ion and 1 is characterized by mass spectrometry and 1H-NMR spectral titrations. In addition, sensor 1 is reversible and reusable and it can be developed as an INHIBIT type logic gate. Compound 1 detects Hg2+ and CN- ions upto 2.57 × 10-8 M and 1.67 × 10-7 M, respectively. Further, compound 1 pre-coated test strips detect Hg2+ and CN- ions and they provide a simple and convenient method for determination of Hg2+/CN- ions.

A new Al3+ selective fluorescent turn-on sensor based on hydrazide-naphthalic anhydride conjugate and its application in live cells imaging.

In this communication, we have developed an optical chemosensor 2-amino N-(6-bromo-1,3-dioxo-1H-benzo[de]isoquinolin-2(3H)-yl)benzamide (NAPH) for selective detection of Al3+ by reacting 4-bromo-1,8-naphthalic anhydride with 2-aminobenzohydrazide. In (DMSO:H2O, 1:1, v/v) medium, the selective and specific nature of NAPH towards Al3+ was observed by the quenching along with a blue-shift in the absorption of NAPH at 465 nm that resulted in the distinct colour change from light brown to colourless. The selective complexation that occurred between NAPH and Al3+ was investigated by 1H NMR and DFT methods. Under similar conditions, the weakly fluorescent receptor NAPH showed a distinct fluorescence enhancement at 555 nm in the presence of Al3+ among the other tested metal ions and anions. The NAPH·Al3+ complex formation is reversible upon addition of strong chelating agent EDTA. The receptor NAPH can be applied to detect Al3+ down to 2.9 µM without any interference from other tested metal ions. In addition, the receptor NAPH was successfully applied to detect Al3+ in live HeLa cells.

Three-in-one type fluorescent sensor based on a pyrene pyridoxal cascade for the selective detection of Zn(ii), hydrogen phosphate and cysteine.

A novel fluorescent receptor L was synthesized by Schiff base condensation of 1-pyrenemethylamine with the vitamin B6 cofactor pyridoxal. The receptor L is highly selective and sensitive towards Zn2+ ions among other tested metal ions. Upon interaction with Zn2+, the receptor L showed a distinct fluorescence enhancement at 485 nm due to the excimer formation leading to the fluorescent colour change from blue to bluish-green. Subsequently, when the in situ generated ZnL2 complex interacted with various anions and amino acids, the addition of H2PO4- and cysteine reinstated the fluorescence of the receptor L due to the demetalation of Zn2+ from the ZnL2 complex. Accordingly, the receptor L was developed for the highly selective, specific and sensitive detection of three important bioactive analytes, i.e., Zn2+, H2PO4- and cysteine with a detection limit down to 2.3 × 10-6 M, 2.18 × 10-7 M and 1.59 × 10-7 M, respectively. Additionally, the receptor L was applied to the detection of intracellular Zn2+ ions in live HeLa cells.

Aminoquinoline based highly sensitive fluorescent sensor for lead(II) and aluminum(III) and its application in live cell imaging.

We have synthesized a new probe 5-((anthracen-9-ylmethylene) amino)quinolin-10-ol (ANQ) based on anthracene platform. The probe was tested for its sensing behavior toward heavy metal ions Hg(2+), Pb(2+), light metal Al(3+) ion, alkali, alkaline earth, and transition metal ions by UV-visible and fluorescent techniques in ACN/H2O mixture buffered with HEPES (pH 7.4). It shows high selectivity toward sensing Pb(2+)/Al(3+) metal ions. Importantly, 10-fold and 5- fold fluorescence enhancement at 429 nm was observed for probe upon complexation with Pb(2+) and Al(3+) ions, respectively. This fluorescence enhancement is attributable to the prevention of photoinduced electron transfer. The photonic studies indicate that the probe can be adopted as a sensitive fluorescent chemosensor for Pb(2+) and Al(3+) ions.

Aminobenzohydrazide based colorimetric and 'turn-on' fluorescence chemosensor for selective recognition of fluoride.

Chemosensors based on aminobenzohydrazide Schiff bases bearing pyrene/anthracene as fluorophores have been designed and synthesized for F(-) ion recognition. The addition of fluoride ions to the receptors causes a dramatically observable colour change from pale yellow to brown/red. (1)H NMR studies confirm that the F(-) ion facilitates its recognition by forming hydrogen bond with hydrogens of amide and amine groups. Moreover these sensors have also been successfully applied to detection of fluoride ion in commercial tooth paste solution.

Hg(2+) mediated quinazoline ensemble for highly selective recognition of Cysteine.

A fluorimetric sensor for Hg(2+) ion and Cysteine based on quinazoline platform was designed and synthesized by one step reaction and characterized by using common spectroscopic methods. Time Dependent Density Functional Theory calculations shows that probe behaves as "ON-OFF" fluorescent quenching sensor via electron transfer/heavy atom effect. Receptor was found to exhibit selective fluorescence quenching behavior over the other competitive metal ions, and also the receptor-Hg(2+) ensemble act as an efficient "OFF-ON" sensor for Cysteine. Moreover this sensor has also been successfully applied to detection of Hg(2+) in natural water samples with good recovery.