Chromone-Based Cd(II) Fluorescent Coordination Polymer Fabricated to Study Optoelectronic and Explosive Sensing Properties.

Here, electrical conductivity and explosive sensing properties of multifunctional chromone-Cd(II)-based coordination polymers (CPs) (1-4) have been explored. The presence of different pseudohalide linkers, thiocyanate ions, and dicyanamide ions resulted in 1D and 3D architecture in the CPs. Thin film devices developed from CPs 1-4 (complex-based Schottky devices, CSD1, CSD2, CSD3, and CSD4, respectively) showed semiconductor behavior. Their conductivity values increased under photo illumination (1.37 × 10-5, 1.85 × 10-5, 1.61 × 10-5, and 2.01 × 10-5 S m-1 under dark conditions and 5.06 × 10-5, 8.78 × 10-5, 7.26 × 10-5, and 10.21 × 10-5 S m-1 under light). The nature of the I-V plots of these thin film devices under light irradiation and dark are nonlinear rectifying, which has been observed in Schottky barrier diodes (SBDs). All four CPs (1-4) exhibited highly selective fluorescence quenching-based sensing properties toward well-known explosives, 2,4-dinitrophenol (DNP) and 2,4,6-trinitrophenol (TNP). The limit of detection (LOD) values are 55, 28, 27, and 31 µM for TNP and 78, 44, 32, and 41 µM for DNP for complexes 1-4, respectively. A structure property correlation has been established to explain optoelectronic and explosive sensing properties.

Aza-phenol Based Macrocyclic Probes Design for "CHEF-on" Multi Analytes Sensor: Crystal Structure Elucidation and Application in Biological Cell Imaging.

Metal bound macrocyclic compounds found in biological systems inspired us to design and synthesize two Robson-type macrocyclic Schiff-base chemosensors, H 2 L1 (H 2 L1=1,11-dimethyl-6,16-dithia-3,9,13,19-tetraaza-1,11(1,3)-dibenzenacycloicosaphane-2,9,12,19-tetraene-1,11-diol) and H 2 L2 (H 2 L2=1,11-dimethyl-6,16-dioxa-3,9,13,19-tetraaza-1,11(1,3)-dibenzenacycloicosaphane-2,9,12,19-tetraene-1,11-diol). Both the chemosensors have been characterized with different spectroscopic techniques. They act as multianalyte sensor and exhibit "turn-on" fluorescence toward different metal ions in 1X PBS (Phosphate Buffered Saline) solution. In presence of Zn2+, Al3+, Cr3+ and Fe3+ ions, H 2 L1 exhibits ∼6-fold enhancement of emission intensity, while H 2 L2 shows ∼6-fold enhancement of emission intensity in the presence of Zn2+, Al3+ and Cr3+ ions. The interaction between the different metal ion and chemosensor have been examined by absorption, emission, and 1H NMR spectroscopy as well as by ESI-MS+ analysis. We have successfully isolated and solved the crystal structure of the complex [Zn(H 2 L1)(NO3)]NO3 (1) by X-ray crystallography. The crystal structure of 1 shows 1:1 metal:ligand stoichiometry and helps to understand the observed PET-Off-CHEF-On sensing mechanism. LOD values of H 2 L1 and H 2 L2 toward metal ions are found to be ∼10-8 and ∼10-7 M, respectively. Large Stokes shifts of the probes against analytes (∼100 nm) make them a suitable candidate for biological cell imaging studies. Robson type phenol based macrocyclic fluorescence sensors are very scarce in the literature. Therefore, the tuning of structural parameters as the number and nature of donor atoms, their relative locations and presence of rigid aromatic groups can lead to the design of new chemosensors, which can accommodate different charged/neutral guest(s) inside its cavity. The study of the spectroscopic properties of this type of macrocyclic ligands and their complexes might open a new avenue of chemosensors.

Selective Low-Level Detection of a Perilous Nitroaromatic Compound Using Tailor-Made Cd(II)-Based Coordination Polymers: Study of Photophysical Properties and Effect of Functional Groups.

Three coordination polymers (CPs 1-3) are prepared based on diverse electron-donating properties and coordination arrangements of conjugated ligands. Interestingly, this is also reflected in their photophysical properties. The distinguishable high emissive nature of the luminescent coordination polymer shows its potentiality toward the detection of the perilous substance 2,4,6-trinitrophenol (TNP) or picric acid (PA). TNP has a higher propensity among explosive nitroaromatic compounds (epNACs) due to its significant π···π interaction with the free benzene moieties present in the CPs. Among CPs 1-3, 2 exhibits the highest sensitivity and selectivity toward TNP because of the most favorable π-π stacking with the conjugated organic linker. The calculated limit of detection (LOD) and corresponding quenching constant (KSV) from the Stern-Volmer (SV) plot for 1, 2, and 3 are found to be 0.68 µM and 7.49 × 104 M-1, 0.41 µM and 8.01 × 104 M-1, and 1.18 µM and 8.1 × 104 M-1, respectively. The fluorescence quenching mechanism is also highly influenced by their structure and coordination arrangement.

Aza-Crown-Based Macrocyclic Probe Design for "PET-off" Multi-Cu2+ Responsive and "CHEF-on" Multi-Zn2+ Sensor: Application in Biological Cell Imaging and Theoretical Studies.

The work represents a rare example of an aza-crown-based macrocyclic chemosensor, H2DTC (H2DTC = 1,16-dihydroxy-tetraaza-30-crown-8) for the selective detection of both Zn2+ and Cu2+ in HEPES buffer medium (pH 7.4). H2DTC exhibits a fluorescence response for both Zn2+ and Cu2+ ions. The reversibility of the chemosensor in its binding with Zn2+ and Cu2+ ions is also examined using a Na2EDTA solution. H2DTC exhibits a chelation-enhanced fluorescence (CHEF) effect in the presence of Zn2+ ions and a quenching effect (CHEQ) in the presence of paramagnetic Cu2+ ions. Furthermore, the geometry and spectral properties of H2DTC and the chemosensor bound to Zn2+ have been studied by DFT and TDDFT calculations. The limit of detection (LOD) values are 0.11 × 10-9 and 0.27 × 10-9 M for Cu2+ and Zn2+, respectively. The formation constants for the Zn2+ and Cu2+ complexes have been measured by pH-potentiometry in 0.15 M NaCl in 70:30 (v:v) water:ethanol at 298.1 K. UV-vis absorption and fluorometric spectral data and pH-potentiometric titrations indicate 1:1 and 2:1 metal:chemosensor species. In the solid state H2DTC is able to accommodate up to four metal ions, as proved by the crystal structures of the complexes [Zn4(DTC)(OH)2(NO3)4] (1) and {[Cu4(DTC)(OCH3)2(NO3)4]·H2O}n (2). H2DTC can be used as a potential chemosensor for monitoring Zn2+ and Cu2+ ions in biological and environmental media with outstanding accuracy and precision. The propensity of H2DTC to detect intracellular Cu2+ and Zn2+ ions in the triple negative human breast cancer cell line MDA-MB-468 and in HeLa cells has been determined by fluorescence cell imaging.

Proton controlled synthesis of two dicopper(II) complexes and their magnetic and biomimetic catalytic studies together with probing the binding mode of the substrate to the metal center.

This paper describes the synthesis, and structural and spectroscopic characterizations of two doubly bridged dicopper(II) complexes, [Cu2(µ-H2L)(µ-OMe)](ClO4)4·2H2O (1) and [Cu2(µ-L)(µ-OH)](ClO4)2 (2), with a binucleating ligand (HL) derived from the Schiff base condensation of DFMP and N,N-dimethyldipropylenetriamine, and their biomimetic catalytic activities were related to CAO and phenoxazinone synthase using 3,5-di-tert-butylcatechol and o-aminophenol (OAPH), respectively, as model substrates. Structural studies reveal that the major differences in these structures appear to be from the distinct roles of the tertiary amine groups of the ligands, which are protonated in 1, whereas it coordinates the metal centers in 2. Magnetic studies disclose that two copper(II) centers are strongly antiferromagnetically coupled with slightly different J values, which is further interpreted and discussed. They exhibited very different biomimetic catalytic activities; whereas 2 is an efficient catalyst, complex 1 showed somewhat lower substrate oxidation. The higher reactivity in 2 is rationalized by the strong involvement of the tertiary amine group of the Schiff base ligand, where the substrate oxidation is favored because of the transfer of protons from the substrate to the tertiary amine group, showing the importance of the functional groups in proximity to the bimetallic active site. Emphasis was also given to probing the binding mode of the substrate using an electronically deficient tetrabromomocatechol (Br4CatH2) and the isolated compound [Cu6(µ-HL)2(µ-OH)2(Br4Cat)4](NO3)2·4H2O (3) which suggests that monodentate asymmetric binding of 3,5-di-tert-butylcatechol and OAPH occurs during the course of the catalytic reaction.

Multifunctional Ni(II)-Based Metamagnetic Coordination Polymers for Electronic Device Fabrication.

The combination of two 8-aminoquinoline-based Schiff base ligands (L1 and L2) with SCN- and Ni(II) has led to the synthesis of two new one-dimensional thiocyanato-bridged coordination polymers: [Ni(L1)(NCS)2]n (1) and [Ni(L2)(NCS)2]n (2). Both compounds are isostructural and consists of regular zigzag thiocyanato-bridged chains with very weak S···S interchain interactions. The measured room-temperature conductivities of compounds 1 and 2 (7.0 × 10-5 and 2.0 × 10-5 S m-1, respectively) are indicative of semiconductor behavior which increases in the presence of photoillumination (3.5 × 10-4 and 4.9 × 10-4 S m-1, respectively). The measured I-V characteristics of compound 1 and 2 based thin film metal-semiconductor (MS) junction devices under irradiation and nonirradiation conditions show a nonlinear rectifying behavior, typical of a Schottky diode (SD). The rectification ratios (Ion/Ioff) of the SDs in the dark at ±2 V (26.96 and 31.96 for 1- and 2-based devices, respectively) increase to 44.19 and 79.42, respectively, upon light irradiation. The photoinduced behavior has been analyzed by thermionic emission theory, and to determine the diode parameters, the Cheung's method has been employed. These diode parameters indicate that compound 2 has a better performance in comparison to compound 1 and that these materials are good candidates for applications in electrochemical devices. Magnetic measurements show that both compounds present ferromagnetic Ni-Ni intrachain and weak antiferromagnetic interchain interactions. The isothermal magnetizations at 2 K show that both compounds are metamagnets with critical fields of ca. 130 mT in 1 and 90 mT in 2 at 2 K. In the ferromagnetic phase (above the critical field), both compounds exhibit a long-range ferromagnetic order with critical temperatures of around 3.5 K in 1 and 3.0 K in 2. DC and AC measurements with different applied DC fields confirm the metamagnetic behaviors and have allowed the determination of the magnetic phase diagram in both compounds.

The development of two fluorescent chemosensors for the selective detection of Zn2+ and Al3+ ions in a quinoline platform by tuning the substituents in the receptor part: elucidation of the structures of the metal-bound chemosensors and biological studies.

Here, two 8-aminoquinoline-based chemosensors, namely, HL1 and HL2 (HL1 = 2,4-dibromo-6-((quinolin-8-ylimino)methyl)phenol and HL2 = 4-nitro-2-((quinolin-8-ylimino)methyl)phenol) were synthesized by simply changing the substituents in the ligand framework under ambient conditions. They were thoroughly characterized using different spectroscopic techniques, including ESI-mass spectrometry and elemental analysis. HL1 selectively sensed Zn2+ ions, whereas HL2 detected Al3+ ions. The metal-bound chemosensors (complexes 1 and 2) were also investigated using different techniques including X-ray crystallography. The binding stoichiometry of the probes with the respective ions was confirmed to be 2 : 1 by Job's plot analysis and X-ray crystallography. The limit of detection (LOD) values for both chemosensors towards the respective metal ions were in the order of ∼10-7 M, which clearly indicates that these probes have significant potential for biological applications. The capability of our synthesized chemosensors to detect intracellular Zn2+ and Al3+ ions in the triple negative human breast cancer cell line MDA-MB-468 was evaluated with the aid of fluorescence imaging. Mechanistic insights into the anticancer activity of complexes 1 and 2 were also demonstrated in this study. To the best of our knowledge, this is the first time that this type of biological and sensing activity for 8-aminoquinoline-based complexes has been demonstrated in a single platform.

Development of Rhodamine 6G-Based Fluorescent Chemosensors for Al3+-Ion Detection: Effect of Ring Strain and Substituent in Enhancing Its Sensing Performance.

Four rhodamine 6G-based chemosensors (H 3 L1-H 3 L4) are designed for selective detection of Al3+ ion. They are characterized using various spectroscopic techniques and X-ray crystallography. All absorption and emission spectral studies have been performed in 10 mM N-(2-hydroxyethyl)piperazine-N'-ethanesulfonic acid (HEPES) buffer solution at pH 7.4 in H2O/MeOH (9:1, v/v) at 25 °C. In absorption spectra, chemosensors exhibit an intense band around 530 nm in the presence of Al3+ ion. Chemosensors (H 3 L1-H 3 L4) are nonfluorescent when excited around 490 nm. The presence of Al3+ ion enhances the emission intensity (555 nm) many times. The formation of complexes 1-4 is established with the aid of different spectroscopic techniques. The limit of detection value obtained in the nanomolar range confirms the high sensitivity of the probes toward Al3+ ion. It has been observed that the presence of aliphatic spacers in the diamine part and different halogen substituents in the salicylaldehyde part strongly influences the selectivity of the chemosensors toward Al3+ ion. The propensity of the chemosensors to identify intracellular Al3+ ions in triple-negative human breast cancer cell line MDA-MB-468 by fluorescence imaging is also examined in this study.

The development of a promising photosensitive Schottky barrier diode using a novel Cd(ii) based coordination polymer.

A novel 1D Cd(ii) based coordination polymer (complex 1) has been synthesized involving an 8-aminoquinoline based Schiff base ligand and cyanate ion. It has been characterized by elemental analysis, different spectroscopy methods and X-ray single crystal diffraction technique. Most interestingly it exhibits unique properties like electrical conductivity and photosensitivity which shows its potential in optoelectronic device application. We prove both experimentally and theoretically that electrical conduction under irradiation of visible light increases many fold in comparison with that under dark condition. Our synthesized material based device shows some paramount behaviour under irradiance of light which is obvious in light sensing Schottky devices. The rectification ratio of our complex based device was found to be 12.44 and 27.74 under dark and photoirradiation conditions respectively. The discovery of such type of coordination polymer advances the area of optoelectronic devices.