Perylene Diimide Appended with 8-Hydroxyquinoline for Ratiometric Detection of Cu2+ Ions and Metal Displacement Driven “Turn on” Cyanide Sensing

Perylene diimide (PDI) 3 and 4 appended with 8-hydroxyquinoline derivatives have been synthesized and their photophysical and spectroscopic properties have been experimentally determined. Moreover, PDIs 3 and 4 show ratiometric behavior to detect Cu²⁺ colorimetrically with visible color change from coral red to light pink, whereas 3 and 4 show “turn-off” behavior in fluorescence with lowest limit of detection 5?×?10^?7 M. The PDI 3 could be further utilized for ratiometric CN^? detection colorimetrically and as “turn-on” sensor for CN^? detection fluorometrically with lowest limit of detection 8?×?10^?6 M. The comparison of spectroscopic properties of PDI 1-4 highlights the importance of linking 8-hydroxyquinoline units on the PDI core at bay position for achieving Cu²⁺ recognition event into ratiometric signal.

Fluorescent Styryl Dyes Based on Novel 4-Methoxy-9-Methyi-9H-Carbazole-3-Carbaldehyde—Synthesis,Photophysical Properties and DFT Computations

Novel carbazole based styryl derivatives (6a–6c) having styryl group at third position and a methoxy substitution were synthesized by condensing 4-methoxy-9-methyl-9H-carbazole-3-carbaldehyde 3 and different active methylene derivatives (5a–5c). Evaluated photophysical properties of these synthesized novel chromophores, studied the effect of solvent polarity on absorption, emission and quantum yield of these styryl derivatives. DFT and TD-DFT computations are carried out to study structural, molecular, electronic and photophysical parameters of dyes. The ratio of ground state to excited state dipole moment was calculated using Bakhshiev and Kawski-Chamma-Viallet correlations.     

Indole-based Fluorescent Sensors for Selective Detection of Hg2+

A series of indole-based fluorescent chemosensors 1–4 were prepared and investigated characteristick features with transition metal ions. Sensors 1 and 2 were selective for Hg²⁺ ion among a series of metal ions in H₂O–DMSO with association constants of 4.60×10⁴ and 5.90×10⁴?M^?1 and detection limits of 140 and 101.6 μM, respectively.

The Smart 2-(2-Fluorobenzoyl)-N-(2-Methoxyphenyl)Hydrazinecarbothioamide Functionalized as Ni(II) Sensor in Micromolar Concentration Level and its Application in Live Cell Imaging

In recent years, fluorescent probes for the detection of environmentally and biologically important metal cations have received extensive attention for designing and development of fluorescent chemosensors. Herein, we report the photophysical results of 2-(2-fluorobenzoyl)-N-(2-methoxyphenyl) hydrazinecarbothioamide (4) functionalized as Ni (II) sensor in micromolar concentration level. Through fluorescence titration at 488 nm, we were confirmed that ligand 4 showed the remarkable emission by complexation between 4 and Ni (II) while it appeared no emission in case of the competitive ions (Cr³⁺, Fe²⁺, Co²⁺, Ba²⁺, Cu²⁺, Ca²⁺, Na⁺, K⁺, Cu⁺, Cs⁺). Furthermore, ligand 4 exhibited no toxicity with precise cell permeability toward normal living cells using L929 cell lines in bio imaging experiment investigated through confocal fluorescence microscope. The non-toxic behavior of ligand 4 (assessed by MTT assay) and its ability to track the Ni²⁺ in living cells suggest its possibility to use in biological system as nickel sensor.

Morphological Effect on Fluorescence Behavior of Silver Nanoparticles

Effect of Silver nanoparticles (AgNPs) morphology on their fluorescence behavior is reported. AgNPs sol stabilized by Ethylene Diamine Tetra Acetic-Acid (EDTA) was prepared by chemical reduction method. Morphology of the AgNPs was tuned through changing the Ag⁺ ion concentration and P^H of reaction mixture. Additional peaks observed in surface Plasmon resonance spectra suggest the an-isotropic nature of AgNPs. Actual morphology was judged by Transmission Electron Microscopy. Emission spectra recorded using Spectrofluoremeter suggest the fluorescent nature of AgNPs, which also influenced by morphology of AgNPs and attributed to the variation in surface structure of an-isotropic AgNPs.

A Schiff-Based Colorimetric Fluorescent Sensor with the Potential for Detection of Fluoride Ions

A simple Schiff-based colorimetric fluorescent receptor 1 was prepared. It exhibits a “turn-on-type” mode with high sensitivity in the presence of F^?. The change in color is very easily observed by the naked eye in the presence of F^?, whereas other anions do not induce such a change. Job plot indicated a 1:2 complexation stoichiometry between receptor 1 and F^?. The association constant for 1-F^? in CH₃CN was determined as 1.32*10⁵ M^?2 by a Hill plot.

Synthesis, Photo-physical and DFT Studies of ESIPT Inspired Novel 2-(2′,4′-Dihydroxyphenyl) Benzimidazole, Benzoxazole and Benzothiazole

Novel ESIPT inspired benzimidazole, benzoxazole and benzothiazole were synthesized from 2,4-dihydroxy benzoic acid and 1,2-phenelenediamine, 2-aminophenol, and 2-aminothiophenol respectively. The synthesized 2-(2′,4′-dihydroxyphenyl) benzimidazole, benzoxazole and benzothiazole are fluorescent and the emission characteristic are very sensitive to the micro-environment. They show a single absorption and dual emission with large Stokes shift originating from excited state intramolecular proton transfer. The absorption-emission characteristics of all these compounds are studied as a function of pH. The change in the electronic transition, energy levels, and orbital diagrams of synthesized compounds were investigated by the molecular orbital calculation and were correlated with the experimental spectral emission. Experimental absorption and emission wavelengths are in good agreement with those predicted using the Density Functional Theory (DFT) and Time-Dependent Density Functional Theory (TD-DFT) [B3LYP/6-31G(d)].

Photoinduced Electron Transfer Reactions of Ruthenium(II)-Complexes Containing Amino Acid with Quinones

With the aim of mimicking, at basic level the photoinduced electron transfer process in the reaction center of photosystem II, ruthenium(II)-polypyridyl complexes, carrying amino acids were synthesized and studied their photoinduced electron transfer reactions with quinones by steady state and time resolved measurements. The reaction of quinones with excited state of ruthenium(II)-complexes, I–V in acetonitrile has been studied by luminescence quenching technique and the rate constant, k_q, values are close to the diffusion controlled rate. The detection of the semiquinone anion radical in this system using time-resolved transient absorption spectroscopy confirms the electron transfer nature of the reaction. The semiclassical theory of electron transfer has been successfully applied to the photoluminescence quenching of Ru(II)-complexes with quinones.

New Application of a Known Molecule: Rhodamine B 8-hydroxy-2-quinolinecarboxaldehyde Schiff Base as a Colorimetric and Fluorescent “Off-On” Probe for Copper (II)

Rhodamine B 8-hydroxy-2-quinolinecarboxaldehyde Schiff base (1) has been investigated as a colorimetric and fluorescent “off-on” probe for the recognition of Cu²⁺ in aqueous solution. Probe 1 was synthesized by condensation of rhodamine B hydrazide and 8-hydroxy-2-quinolinecarboxaldehyde, which exhibited good selectivity for Cu²⁺ among a range of biologically and environmentally important metal ions. The Cu²⁺ recognition event undergoes a Cu²⁺ promoted hydrolysis of probe 1 to release rhodamine B and the recognition process is barely interfered by other coexisting metal ions.

Confinement of 4,4-Diaminodiphenyl Sulfone by γ –CD in Micellar Environment: A Spectroscopic Investigation

This paper reports the double confinement of 4,4-diaminodiphenyl sulfone (Dapsone) inside γ–cyclodextrin (CD) in presence of surfactants (cationic, anionic and nonionic) using steady-state and time-resolved fluorescence spectroscopy. Interpretation of fluorescence spectra, fluorescence anisotropy and time resolved fluorescence decay of the γ-CD?Dapsone?micellar system hints at lesser microviscosity and the partial release of the probe molecule from the supramolecular host–guest complex in ionic micelles, of which greater in cationic micelles, but due to greater restriction and rigidity in presence of non-ionic micelle makes the probe more rigidly inside CD. Changes in computed rotational decay also corroborate the above findings.

Selective Fluorescent Detection of Aspartic Acid and Glutamic Acid Employing Dansyl Hydrazine Dextran Conjugate

Highly water soluble polymer (DD) was prepared and evaluated for its fluorescence response towards various amino acids. The polymer consists of dansyl hydrazine unit conjugated into dextran template. The conjugation enhances higher water solubility of dansyl hydrazine moiety. Of screened amino acids, DD exhibited selective fluorescence quenching in the presence of aspartic acid (Asp) and glutamic acid (Glu). A plot of fluorescence intensity change of DD against the concentration of corresponding amino acids gave a good linear relationship in the range of 1?×?10^?4 M to 25?×?10^?3 M. This establishes DD as a potential polymeric sensor for selective sensing of Asp and Glu.

Fluorescence Turn on Sensor for Sulfate Ion in Aqueous Medium Using Tripodal-Cu2+ Ensemble

We report the selective recognition of sulfate anion in aqueous medium at biological pH 7.2 over the other interfering anions based on naphthoic acid bearing tripodal ligand by applying fluorescence turn off-on mechanism. The carboxylic acid groups in the ligand enhance the solubility in water and enable it to form complex with copper salt. Thus formed L-Cu²⁺ ensemble quench the fluorescence of the parent ligand and in turn recognize sulfate anion via revival of fluorescence intensity. The 1:2 stoichiometry was confirmed by ESI mass spectral data and Job’s plot. The average binding constant was found to be 6.2?×?10⁸ M^?2.

The Effects of Different Solvents and Excitation Wavelength on the Photophysical Properties of Two Novel Ir(III) Complexes Based on Phenylcinnoline Ligand

Two novel cyclometalated iridium(III) complexes, Ir(pcl)₂(pic) and Ir(pcl)₂(fpic) (pcl: 3-phenylcinnoline, pic: picolinic acid, fpic: 5-fluoro-2-picolinic acid) were synthesized and characterized by FTIR, ¹H NMR spectroscopy, UV-vis, PL, and MALDI-TOF. These two Ir-complexes geometry were predicted using the Sparkle/PM6 model and suggested to a chemical environment of very low symmetry around the Ir ions (C ₁). The PL spectrum of Ir(pcl)₂(pic) and Ir(pcl)₂(fpic) indicated that these complex belonged to red light emission, and maximum emission wavelength located at 647 and 641 nm, respectively. Most importantly, the effects of different solvents on their photoluminescent properties were detailed investigated. The results indicated that the polarity of solvent played an important role for their emission spectra. With introducing fluoro group to the pyridyl ring, the maximum emission wavelength of Ir(pcl)₂(fpic) was blue shifted about 6 nm, and the quantum yield was slightly higher than that of Ir(pcl)₂(pic). In addition, the thermal properties of these two Ir-complexes were measured by TGA, and results indicated that they had relative good thermal properties.

Urea Based Dipodal Fluorescence Receptor for Sensing of Fe3+ Ion in Semi-Aqueous Medium

Urea based fluorescent chemosensor 1 was synthesized. Receptor 1 shows unique selectivity for the Fe³⁺ion and no such significant response was noticed with other metal ions (Cr³⁺, Mn²⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Cd²⁺, Hg²⁺, Pb²⁺ and Bi³⁺) in DMSO/H₂O (50:50,v/v) semi-aqueous solution. The binding features have been established by absorption and fluorescence spectroscopic methods. The binding constant (K) values obtained from Benesi-Hildebrand, Scatchard and Connor plot for receptor 1 is (8.3?±?0.3) × 10³ M^?1 and has good detection limit 0.7?μM. The stoichiometry of 1.Fe³⁺ complex was confirmed by mass spectroscopy and Job’s plot.

A New Thiophenyl Pyrazoline Fluorescent Probe for Cu2+ in Aqueous Solution and Imaging in Live Cell

A new thiophenyl pyrazoline probe for Cu²⁺ in aqueous solution was synthesized and characterized by IR, NMR, HRMS and X-ray analysis. The probe displays remarkably high selectivity and sensitivity for Cu²⁺ with a detection limit of 1.919?×?10^?7 M in aqueous solution (EtOH:HEPES = 1:1, v/v, 0.02 M, pH?=?7.2). In addition, the probe is further successfully used to image Cu²⁺ in living cells and the probe possesses good reversibility.

Interaction Mechanism of Trp-Arg Dipeptide with Calf Thymus DNA

The interaction between Trp-Arg dipetide (WR) and calf thymus DNA (ctDNA) in pH 7.4 Tris-HCl buffer was investigated by multi-spectroscopic techniques and molecular modeling. The fluorescence spectroscopy and UV absorption spectroscopy indicated that WR interacted with ctDNA in a minor groove binding mode and the binding constant was 4.1?×?10³. The ionic strength effect and single-stranded DNA (ssDNA) quenching effect further verified the minor groove binding mode. Circular dichroism spectroscopy (CD) was employed to measure the conformation change of ctDNA in the presence of WR. The molecular modeling results illustrated that electrostatic interaction and groove binding coexisted between them and the hydrogen bond and Van der Waals were main acting forces. All the above methods can be widely used to investigate the interaction of peptide with nucleic acids, which contributes to design the structure of new and efficient drugs.

Studies on ionic solvation behavior of ionic liquid (tetrabutylphosphonium tetrafluoroborate) in some liquid media by volumetric,viscometric, and acoustic measurements

Physicochemical properties such as density (ρ), viscosity (η), ultrasonic speed (u) of ionic liquid tetrabutylphosphonium tetrafluoroborate in acetonitrile, tetrahydrofuran, 1,3-dioxolane, and their binaries have been studied over the entire range of composition at 298.15°K. Apparent molar volumes (? _V ) and viscosity B-coefficients supplemented with the data of densities and viscosities, respectively, have been interpreted in terms of ion–solvent interactions. The limiting apparent molar volumes (? _V ⁰ ), experimental slopes (S _V ^? ) derived from the Masson equation, and viscosity A and B-coefficients analyzed by the Jones–Dole equation have also been interpreted. The adiabatic compressibility (β) has been evaluated using the ultrasonic speed (u) values. Thereafter, limiting apparent molar adiabatic compressibilities (? _K ⁰  ) have been evaluated and discussed for the same.

Synthesis of Novel Carbazole based Styryl: Rational Approach for Photophysical Properties and TD-DFT

The synthesis and solvatochromic behavior of four novel carbazole based fluorescent styryl dyes were explained. In chlorinated solvents such as DCM and chloroform, these dyes show bathochromic shift in their absorption as well as emission. The styryl dyes 6b and 6c show solid state yellow fluorescence. DFT and TD-DFT computations were performed to study structural, molecular, electronic and photophysical properties of these dyes. The computed absorption and emission wavelength values are found to be in good agreement with the experimental results. The photophysical properties of these 1-styryl carbazole dyes are also compared with the recently reported 3-styrl carbazole dyes. The unique behavior of dye 6d is well explained by its optimized geometry found in the excited state. Ratio of ground to excited state dipole moment of the synthesized novel styryl compounds were calculated by Bakhshiev and Bilot-Kawski correlations.     

Efficient Entrapment of Dye in Hollow Silica Nanoparticles: Direct Evidence Using Fluorescence Spectroscopy

Using hollow silica nanoparticles we demonstrate a simple and highly efficient way of removing hydrophilic dye (Rhodamine B) from water by encapsulation within these hollow spheres. The hollow silica spheres were obtained by using a surfactant templated procedure. Using fluorescence spectroscopy, we also show the evidence of the dye being absorbed within the hollow core of the silica shell (which is crucial for many applications) and differentiate from the adsorption of dye on the surface of the silica shell. It was found that that up to 94 % of the hydrophilic dye could be entrapped using these hollow shells within 72 h of exposure. Fluorescence spectroscopy shows a red shift in the dye encapsulated in the hollow silica which is due to aggregation of the dye and enables us to follow quantitatively the uptake of the dye molecules by the silica shells with time. The evidence for the encapsulation of the dye in these hollow spheres was reinforced by carrying out a comparative study, using solid silica particles.

9, 10-Bis(8-Quinolinoxymethyl)Anthracene—A Fluorescent Sensor for Nanomolar Detection of Cu2+ with Unusual Acid Stability of Cu2+-Complex

In this work, the dipod 9,10-bis(8-quinolinoxymethyl)anthracene (1) and for comparison, monopod 9-(8-quinolinoxymethyl)anthracene (2) have been synthesized. The fluoroionophore 1 in pH 7.1 HEPES buffered CH₃CN:H₂O (4:1 v/v) solution shows quenching only with Cu²⁺ with lowest limit of detection 150 nM, amongst various metal ions. Fluoroionophore 1 could also be applied to sense Co²⁺ with lowest limit of detection 600 nM. By modulating the pH of the solution and concentration of Cu²⁺, 1 shows respective “On-Off-On” and “On-Off” fluorescent switching. The self-assembly of two Cu²⁺ ions and two molecules of fluoroionophore 1 to form closed structure [Cu₂(L)₂]⁴⁺ seems to be responsible for nanomolar sensitivity towards Cu²⁺. The combination of delayed second protonation of 1 (pK_a2?=?2.6) and stepwise protonation of [Cu₂ L ₂]⁴⁺ causes unusual stability of [Cu(LH)₂]⁴⁺ even at pH?<?2.