A facile synthesis of a novel 4-hydroxyl-3-azo coumarin based colorimetric probes for detecting Hg2+ and a fluorescence turn-off response of 3CBD to Fe3+ in aqueous environment

Two azo dyes, (E)-3-(benzo[d]thiazol-2-yldiazenyl)-4-hydroxy-2H-chromen-2-one (3CBD) and (E)-4-hydroxy-3-(quinolin-2-yldiazenyl)-2H-chromen-2-one (3CQD), were designed and synthesized using facile methods. The structures were validated through FTIR and NMR spectroscopy. The photophysical property analyses were further studied using UV-Vis and fluorescence spectrophotometers. Consequently, the absorption and emission spectra of 3CBD confirmed its selectivity of Hg2+ and turn-off response to Fe3+. On the other hand, the absorption spectra analysis of 3CQD demonstrated selectivity in the presence of Hg2+. The colorimetric investigations demonstrated a significant visual response specifically for Hg2+, enabling real-time analysis in the corresponding solutions. The presence of other coexisting metal ions does not interfere with the detection of the target metal ion. The fluorescence studies of the two probes revealed that 3CBD was highly fluorescent, which was significantly quenched by Fe3+, upon excitation at 340 nm. Utilizing Job plot analyses, it was determined that the complexes 3CBD-Hg2+ and 3CQD-Hg2+ exhibit a binding stoichiometry of 1 : 1. The association constants for these complexes were measured to be 7.48 × 105 and 9.12 × 105 M-1, respectively, indicating a strong association between both probes and their respective metal ions. Both chemosensors exhibited comparable limits of detection (LOD) and limits of quantification (LOQ) of 0.03 μM and 0.10 μM, respectively. Reversible studies confirmed that only chemosensor 3CQD could serve as a secondary sensor for EDTA. The theoretical studies calculated using Density Functional Theory (DFT) program at B3LYP/6-31G** (Spartan '10 package) level.

Copper(ii) complexes supported by modified azo-based ligands: Nucleic acid binding and molecular docking studies

Two new copper(ii) complexes [CuL1] (1) and [CuL2] (2) derived from azo-based ligands 2-hydroxy-5-p-tolylazo-benzaldehyde (HL1) and 1-(2-hydroxy-5-p-tolylazo-phenyl)-ethan-one (HL2) were synthesized. These two ligands and their metal complexes were characterized by elemental analysis, nuclear magnetic resonance (1H and 13C), infrared, and UV/Vis spectroscopic techniques. Spectroscopy and other theoretical studies reveal the geometry of copper complexes, and their binding affinity towards nucleic acids are major groove binding.

Revisiting salicylidene-based anion receptors

Several salicylidene-based colorimetric and fluorimetric anion sensors are known in the literature. However, our 1H-NMR experimental results (in DMSO-d6) showed hydrolysis of imine (-N[double bond, length as m-dash]CH-) bonds in salicylidene-based receptors (SL, CL1 and CL2) in the presence of quaternary ammonium salts (n-Bu4N+) of halides (Cl- and Br-) and oxo-anions (H2PO4 -, HSO4 - and CH3COO-). The mono-salicylidene compound CL1 showed the most extensive -N[double bond, length as m-dash]CH- bond hydrolysis in the presence of anions. In contrast, the di-salicylidene compound CL2 and the tris-salicylidene compound SL showed comparatively slow hydrolysis of -N[double bond, length as m-dash]CH- bonds in the presence of anions. Anion-induced imine bond cleavage in salicylidene compounds could easily be detected in 1H-NMR due to the appearance of the salicylaldehyde -CHO peak at 10.3 ppm which eventually became more intense over time, and the -N[double bond, length as m-dash]CH- peak at 8.9-9.0 ppm became considerably weaker. Furthermore, the formation of the salicylidene O-H⋯X- (X- = Cl-/Br-) hydrogen-bonded complex, peak broadening due to proton-exchange processes and keto-enol tautomerism have also been clearly observed in the 1H-NMR experiments. Control 1H-NMR experiments revealed that the presence of moisture in the organic solvents could result in gradual hydrolysis of the salicylidene compounds, and the rate of hydrolysis has further been enhanced significantly in the presence of an anion. Based on 1H-NMR results, we have proposed a general mechanism for the anion-induced hydrolysis of imine bonds in salicylidene-based receptors.

Aluminium(iii) and zinc(ii) complexes of azobenzene-containing ligands for ring-opening polymerisation of ε-caprolactone and rac-lactide

The ability to control the outcome of polymerisations using an external stimulus remains a formidable challenge.

An efficient ICT-based ratio/colorimetric tripodal azobenzene probe for the recognition/discrimination of F-, AcO- and H2PO4- anions

The tripodal probe L was readily prepared via introducing rhodamine and azobenzene groups in a two-step procedure. Studies of the recognition properties indicated that probe L exhibited high sensitivity and selectivity towards F^-, AcO^- and H₂PO₄^- through a ratiometric colorimetric response with low detection limits of the order of 10^-7 M. The complexation behaviour was fully investigated by spectral titration, ¹H NMR spectroscopic titration and mass spectrometry. Probe L not only recognizes F^-, AcO^- and H₂PO₄^-, but can also distinguish between these three anions via the different ratiometric behaviour in their UV-vis spectra (387/505 nm for L-H₂PO₄^-, 387/530 nm for L-AcO^- and 387/575 nm for L-F^- complex) or via different colour changes (light coral for L-H₂PO₄^-, light pink for L-AcO^- and violet for the L-F^- complex). Additionally, given the presence of NH and OH groups in probe L, which can be protonated and deprotonated, probe L further exhibited an excellent pH response over a wide pH range (pH 3 to pH 12).

Photoswitchable transition metal complexes with azobenzene-functionalized imine-based ligands: structural and kinetic analysis

We report on the characterization of two imine type ligands containing photoresponsive azobenzene units as side groups and their transition metal ions complexes.

Synthesis of Novel phenylazo-Substituted Salicylaldimine-Based Boron Difluoride Complexes

Salicylaldimines with a phenylazo-group substituent have been prepared and reacted with BF3·Et2O in the presence of N,N-diisopropylethylamine to give novel N,O-bidentate boron difluoride complexes. Spectroscopic properties and thermal stability of the complexes are also reported.

Isatinphenylsemicarbazones as efficient colorimetric sensors for fluoride and acetate anions - anions induce tautomerism

The anion induced tautomerism of isatin-3-4-phenyl(semicarbazone) derivatives is studied herein. The interaction of F(-), AcO(-), H2PO4(-), Br(-) or HSO4(-) anions with E and Z isomers of isatin-3-4-phenyl(semicarbazone) and N-methylisatin-3-4-phenyl(semicarbazone) as sensors influences the tautomeric equilibrium of these sensors in the liquid phase. This tautomeric equilibrium is affected by (1) the inter- and intra-molecular interactions' modulation of isatinphenylsemicarbazone molecules due to the anion induced change in the solvation shell of receptor molecules and (2) the sensor-anion interaction with the urea hydrogens. The acid-base properties of anions and the difference in sensor structure influence the equilibrium ratio of the individual tautomeric forms. Here, the tautomeric equilibrium changes were indicated by "naked-eye" experiment, UV-VIS spectral and (1)H NMR titration, resulting in confirmation that appropriate selection of experimental conditions leads to a high degree of sensor selectivity for some investigated anions. Sensors' E and Z isomers differ in sensitivity, selectivity and sensing mechanism. Detection of F(-) or CH3COO(-) anions at high weakly basic anions' excess is possible.

A catalyst-free approach to a novel imidazo [4,5-f][1,10] phenanthroline ligand and its corresponding ruthenium(ii) complex: insights into their applications in colorimetric anion sensing

Novel imidazo[4,5-f][1,10]phenanthroline ligand and its corresponding Ru(ii) complex are synthesized from green protocol for colorimetric detection of anions in water.