Identification of static JT in copper(II) doped hexaimidazole M(II) lattices: M=Co and Ni: an EPR study

Single crystal EPR studies on Cu(II) doped paramagnetic host lattices, hexaimidazole M(II) dichloride tetrahydrate (M=Co and Ni), isomorphous with M=Zn, have been carried out from room temperature to 77K to understand the nature of Jahn-Teller (JT) distortion in these paramagnetic host systems. The paramagnetic impurity, doped in the present two paramagnetic host lattices, shows anisotropic EPR spectra with superhyperfine from ligands, even at room temperature. An interesting observation noticed in the EPR spectra at room temperature is that there are more resonances corresponding to the second site in the paramagnetic hosts than in the diamagnetic host at 4.2K. This difference in behavior between the diamagnetic and paramagnetic host lattices indicates a change in the depth of the JT valleys. The spin Hamiltonian parameters are evaluated for Cu(II) ion in both the host lattices and the relaxation times have been calculated for the ion in cobalt host lattice only.     

Stereochemical effect on biological activities of new series of piperidin-4-one derivatives

New series of (2S,3R,4S,6R)-3-methyl-4-alkyl-2,6-diarylpiperidin-4-ol were synthesised by the reduction of cis-3-alkyl-2,6-diarylpiperidin-4-one using Grignard reagent. The structural assignments and conformational studies of the synthesised compounds were established based on the IR, ¹H NMR, ¹³C NMR, NOESY and mass spectral studies. Their stereochemical effect on antibacterial, antifungal and anthelmintic activities was studied.     

4H‐cyclopenta[2,1‐b:3,4‐b′]dithiophen‐4‐one (CPDTO) homopolymer with side chains on every other CPDTO

A soluble 4H‐cyclopenta[2,1‐b ;3,4‐b ′]dithiophene‐4‐one (CPDTO)‐based polymer (C₆‐PCPDTO) has been synthesized from two monomers derived from nonalkylated CPDTO and didodecyl CPDTO (C₁₂‐CPDTO). Proton NMR, thermal analysis, UV–vis absorption, cyclic voltammetry, and XRD are used to characterize the polymer in solution and film. The new polymer has an optical bandgap of 1.28 eV in film, and has strong interchain interaction in chloroform solutions. The polymer contains a significant amount of homocoupled segments. The regular segments and homocoupled CPDTO segments render the polymer highly aggregating in solution. The non‐planar homocoupled C₁₂‐CPDTO segments prevent the polymer from forming regular π‐stacks, resulting in a low SCLC hole mobility (3.88 × 10^?7 cm²V^?1s^?1). CV experiments show that C₆‐PCPDTO is stable in its oxidized and reduced states. Solar cell devices were fabricated from C₆‐PCPDTO2 :PC₆₀BM blends of different weight ratios. High PC₆₀BM loading (80% or greater) was required for the devices to show measurable efficiency, indicating that the limited π‐stacking of the polymer is not sufficient to cause effective phase separation. Further development of synthetic method is still needed to eliminate structural defects so that long‐range ordered pi‐stacking can be realized in the polymer for these applications. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55 , 1077–1085     

Development of Optical Biosensor for the Detection of Glutamine in Human Biofluids Using Merocyanine Dye

Merocyanine dye based fluorescent organic compound has been synthesized for the detection of glutamine. The probe showed remarkable fluorescent intensity with glutamine through ICT (Intermolecular Charge Transfer Mechanism). Hence, it is tested for the detection of glutamine using colorimetric and fluorimetric techniques in physiological and neutral pH (7.2). Under optimized experimental conditions, the probe detects glutamine selectively among other interfering biomolecules. The probe has showed a LOD (lower limit of detection) of 9.6?×?10^–8 mol/L at the linear range 0–180 µM towards glutamine. The practical application of the probe is successfully tested in human biofluids.

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Thermally Robust and Tuneable Phosphorescent Gold(III) Complexes Bearing (N^N)-Type Bidentate Ligands as Ancillary Chelates

Phosphorescent mono-cyclometalated gold(III) complexes and their possible applications in organic light emitting diodes (OLEDs) can be significantly enhanced with their improved thermal stability by suppressing the reductive elimination of the respective ancillary ligands. A rational tuning of the π-conjugation of the cyclometalating ligand in conjunction with the non-conjugated 5,5′-(1-methylethylidene)bis(3-trifluoromethyl)-1H-pyrazole were used as a strategy to achieve room-temperature phosphorescence emission in a new series of gold(III) complexes. Photophysical studies of the newly synthesised and characterised complexes revealed phosphorescent emission of the complexes at room temperature in solution, thin films when doped in poly(methyl methacrylate) (PMMA) as well as in 2-Me-THF at 77 K. The complexes exhibit highly tuneable emission behaviour with photoluminescent quantum efficiencies up to 22 % and excited state lifetimes in the range of 63–300 μs. Detailed photophysical investigations in combination with DFT and TD-DFT calculations support the conclusion that the emission properties are strongly dictated by both the cyclometalating ligand and the ancillary chelating ligand. Thermogravimetric studies further show that the thermal stability of the Au^III complexes has been drastically enhanced, making these complexes more attractive for OLED applications.     

Single crystal EPR and optical studies of paramagnetic ions doped zinc potassium phosphate hexahydrate—Part I: Cu(II)—a case of orthorhombic symmetry

Single crystal electron paramagnetic resonance (EPR) studies on Cu(II) doped zinc potassium phosphate hexahydrate (ZPPH) were carried out at room temperature. The angular variation spectra in the three orthogonal planes indicate that the paramagnetic impurity has entered the lattice substitutionally in place of Zn(II) and the spin Hamiltonian parameters calculated from these spectra are g(xx) = 2.188, g(yy) = 2.032, g(zz) = 2.373, Axx = 50 G, Ayy = 65.0 G and Azz = 80 G. The g and A tensors were coincident and these values matched fairly well with the values obtained from powder spectrum. The bonding parameters have also been calculated.     

Tunable Light-Emission Properties of Solution-Processable N-Heterocyclic Carbene Cyclometalated Gold(III) Complexes for Organic Light-Emitting Diodes

N-Heterocyclic carbene (NHC) cyclometalated gold(III) complexes remain very scarce and therefore their photophysical properties remain currently underexplored. Moreover, gold(III) complexes emitting in the blue region of the electromagnetic spectrum are rare. In this work, a series of four phosphorescent gold(III) complexes was investigated bearing four different NHC monocyclometalated (C^C*)-type ligands and a dianionic (N^N)-type ancillary ligand ((N^N)=5,5’-(propane-2,2-diyl)bis(3-(trifluoromethyl)-1 H-pyrazole) (mepzH₂)). The complexes exhibit strong phosphorescence when doped in poly(methyl methacrylate) (PMMA) at room temperature, which were systematically tuned from sky-blue [λ_PL=456 nm, CIE coordinates: (0.20, 034)] to green [λ_PL=516 nm, CIE coordinates: (0.31, 0.54)] by varying the monocyclometalated (C^C*) ligand framework. The complexes revealed high quantum efficiencies (ϕ_PL) of up to 43 % and excited-state lifetimes (τ₀) between 15–266 μs. The radiative rate constant values found for these complexes (k_r=10³–10⁴ s⁻¹) are the highest found in comparison to previously known best-performing monocyclometalated gold(III) complexes. Density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations of these complexes further lend support to the excited-state nature of these complexes. The calculations showed a significant contribution of the gold(III) metal center in the lowest unoccupied molecular orbitals (LUMOs) of up to 18 %, which was found to be unique for this class of cyclometalated gold(III) complexes. Additionally, organic light-emitting diodes (OLEDs) were fabricated by using a solution process to provide the first insight into the electroluminescent (EL) properties of this new class of gold(III) complexes.     

Lithium assisted electrochemical reduction of uranium oxide in room temperature ionic liquid

Lithium assisted electrochemical reduction of U₃O₈ in the room temperature ionic liquid (RTIL), N-methyl-N-propylpiperidinium bis(trifluoromethylsulfonyl)imide (MPPiNTf₂), was studied to explore the feasibility of using RTILs for direct electrochemical reduction of uranium oxide at near ambient temperature. The electrochemical behavior of Li⁺ in MPPiNTf₂ at stainless steel electrode was investigated by cyclic voltammetry and chronoamperometry. The cyclic voltammogram of LiNTf₂ in MPPiNTf₂ at 373 K consisted of a surge in cathodic current occurring at a potential of −2.8 V (vs. Fc/Fc⁺) due to the reduction of Li(I) to metallic form. The nucleation phenomenon observed in the voltammogram was investigated by chronoamperometry. Electrodeposition of metallic lithium on U₃O₈ particles contained in a stainless steel (SS) basket was carried out to examine the feasibility of reducing U₃O₈ to metallic form. The results are discussed in this paper.