Amar Hens

Photophysical property vs. medium: mononuclear, dinuclear and trinuclear Zn(II) complexes

Three complexes [Zn2(L)2(μ1,2-OAc)(μ1,1-OAc)]·C9H8N2 1·C9H8N2, [Zn3(L)4]·(ClO4)2 2 and [Zn(L)2]·CH3OH 3 were synthesized using a common Schiff base 2,4-dimethyl-6-((quinolin-8-ylimino)methyl)phenol (HL) and characterized by various methods such as elemental analysis, 1H NMR, FT-IR, UV-Vis and mass spectroscopy. The single crystal XRD analysis revealed that complex 1 is dinuclear, complex 2 trinuclear and complex 3 mononuclear in nature. The photophysical properties of the ligand and complexes were also investigated by different techniques such as UV-Vis spectroscopy, fluorescence spectroscopy, fluorescence lifetime measurement, DFT, and TDDFT calculations in solvents of different polarity. The complexes exhibited higher quantum yields than the ligand in solution. The trinuclear complex had higher emission intensity than the mono and dinuclear complexes in solution as well as in the solid state. In addition, complex 1 exhibited a unique dissymmetric coordination mode of the oxygen atom in the acetate bridging moiety.

Mononuclear rhenium(I) complexes incorporating 2-(arylazo)phenyl benzyl thioethers: synthesis, structure, spectral, DFT and TDDFT studies

The stoichiometric reaction of [Re(CO)5Cl] with 2-(arylazo)phenyl benzyl thioethers [ArNNC6H4SCH2Ph: Ar = Ph, 4-chlorophenyl, 4-nitrophenyl] (L1–L3) in a ratio of 1:1 in dry toluene under refluxing condition afforded the Re(I) complexes of general formula fac-[Re(L)(CO)3Cl] in excellent yields. The ligands used in this present work are 2-(phenylazo)phenyl benzyl thioether (L1), 2-(4-chlorophenylazo)phenyl benzyl thioether (L2) and 2-(4-nitrophenylazo)phenyl benzyl thioether (L3). The elemental analysis and ESI mass spectroscopic measurements ensure the formation of desired complexes. The crystal structure of the complexes [Re(L1)(CO)3Cl], 1 and [Re(L2)(CO)3Cl], 2 were determined by X-ray diffractometry study. The molecular structures observed in the solid state were retained in the solution (1H and 13C NMR spectra). The ground and excited-state geometries, NMR, absorption, and luminescent properties of three Re(I) complexes were examined by DFT and TDDFT methods. The introduction of an electron withdrawing group at the para position of the phenyl ring attached to the NN bond varies the frontier molecular orbital energies, compositions and optical properties of these molecules significantly. The lowest lying triplet excited is associated with an admixture of the 3MLCT and 3ILCT excited state having a cis conformation of the azoaryl moiety. The emission like transition having mixed 3MLCT and 3ILCT nature was characterized by natural transition orbital (NTO) and spin density difference map analysis. The presence of the electron withdrawing NO2 group leads to the low quantum yield through enhanced non-radiative deactivation. The cis orientation at the lowest lying triplet excited state (T1) may imply some kind of photoinduced isomerization in the ligand frame and as a result there may be more than one emitting species in the solution and hence bi-exponential decay nature was observed for all the complexes.

Synthesis, characterization and DFT study of oxorhenium(V) complexes incorporating quinoline based tridentate ligands

Two tridentate quinoline based Schiff base ligands HL1 and HL2 were prepared by condensation of salicylaldehyde and 2-hydroxy naphthaldehyde with 8-aminoquinoline, respectively in excellent yield. These ligands react with [ReOCl3(OPPh3)(SMe2)] in a ratio of 1 : 1 in acetone to form mononuclear trans-dichloro oxo complexes of general formula [ReVO(L)Cl2]. Here L− is the deprotonated form of 2-((quinolin-8-ylimino) methyl)phenol (HL1) or 1-[(quinolin-8-ylimino)methyl]naphthalene-2-ol (HL2). The elemental analysis and ESI mass spectroscopic measurements ensure the formation of the desired complexes. The molecular structure of mer-[ReVO(L1)Cl2] was confirmed by single-crystal X-ray diffraction. The complexes were also characterized by different spectroscopic techniques and electrochemical methods. The ground state geometry, NMR and absorption of Re(V) complexes were examined by DFT and TDDFT methods. The natural transition orbital (NTO) and spin density difference map analysis reveal the nature of the excitations. It was also found that the complexes act as a catalyst for oxidation of cis-cyclooctene to the corresponding epoxide by tert-butyl hydroperoxide (TBHP). The NMR and ESI mass spectroscopic analysis ensure the formation of the desired product which was obtained from catalysis.

Selective fluorometric detection of F− and Zn(II) ions by a N, O coordinating sensor and naked eye detection of Cu(II) ions in mixed-aqueous solution

Through click chemistry, salicylaldehyde and fluorene groups have been explored to recognize anions through O–H⋯A– hydrogen-bonding complexation followed by an ESIPT mechanism and cation sensing via CHEF and CHEQ mechanisms for Zn2+ and Cu2+ metal ions respectively. Herein, we demonstrate evidence of the interactions between the O–H bond and F− which were studied by fluorescence spectroscopic, UV-Vis spectroscopic, lifetime spectroscopic, 1H NMR spectroscopic titrations and theoretical treatment. This sensor could simultaneously detect two biologically important metal ions (Cu2+ and Zn2+) through colorimetric methods in mixed aqueous solution. The 2:1 binding stoichiometry ratio of the ligand and metal in the complexes was established by UV-Vis, fluorescence, 1H NMR and ESI-MS spectroscopy, and their corresponding association constants, Kassoc observed at 8.13 × 104 and 5.12 × 106 M−1 corresponds to Zn2+ and Cu2+ metal ions in aqueous buffer–CH3OH (2:1, v/v) at pH 7.2. In addition, the electronic structures and photo physical properties of the ligand and complexes were calculated by DFT and time-dependent DFT (TDDFT) methods.

A reversible turn-off fluorescence probe (HNAPP) for Zn(II) ion and inorganic phosphate ions (H2P and HP) at physiological pH

A simple and low-cost new Schiff base compound (HNAPP) of 2-hydroxynaphthaldehyde and 2-amino-3-phenyl-1-propanol was synthesized and characterized by 1H NMR and mass spectroscopic technique. The optimized structure of the probe in different polarity solvents and the potential energy scan reveal that the probe is stable as an enol tautomer in polar solvent, while in less polar solvent the keto tautomer is more prominent. In dichloromethane, the keto tautomeric form of the probe undergoes an excited state intramolecular proton transfer, ESIPT, into a stable enol structure that reveals unusual relaxation routes after electronic excitation. The results, accompanied by TDDFT calculations, are used to diagram the relaxation routes of an excited HNAPP molecule. The probe exhibited highly selective and sensitive turn-on fluorescence emission towards Zn2+ over other common metal ions in a physiological pH window with a 2:1 binding mode. The association constant, Kassoc, was observed at 5.2 × 104 M−1. The fluorescence decay constant (s) values were determined from time-resolved fluorescence study. The addition of inorganic phosphate ions quenched the fluorescence intensity of the complex at different pH values, enabling the receptor HNAPP to act as a reversible chemosensor and a pH modulator. On the basis of these observations, I developed a unique molecular system capable of performing logic functions such as INHIBIT by simply varying the level of various ionic inputs in a systematic manner.