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Tuning the fluorescence of π-conjugated small organic molecules through the structural modifications and in the presence of external stimuli have found immense applications ranging from sensing, switching, optoelectronics to bioimaging. Herein, we demonstrated a simple design strategy for the synthesis of a pyrene-cyanostyrene-pyridine molecular triad (PYBNP) using a cost-effective, one-step Knoevenagel condensation between 1-pyrenecarboxaldehyde and 2-(4-(pyridin-4-yl)phenyl)acetonitrile. PYBNP exhibited strong solid-state emission having a quantum yield of ∼ 36 ± 3% due to the deactivation of nonradiative decay channels through the restriction of intramolecular rotations and reduced π-π stacking interactions as revealed from the crystal structure analysis. Similarly, PYBNP was found to be highly emissive in the constrained environments like viscous medium and aggregated state. The optical properties of PYBNP could be tuned by the UV light-mediated dynamic Z/E-isomerization as elucidated through fluorescence spectroscopy and NMR analysis. Additionally, the pyridinic nitrogen centre allowed the fabrication of methylated analog (PYBNPM; a new cationic photoresponsive species). The cationic PYBNPM showed a better solvatochromic behavior contrary to PYBNP due to the efficient intramolecular charge transfer (ICT). The different crystal packing of PYBNP and that of hexafluorophosphate salts of PYBNPM led to distinct fluorescent properties in the solid-state. As a preliminary exploration, the cationic PYBNPM(PF6) was employed for the specific imaging of the mitochondria through multiple fluorescence channels in an aqueous medium. The cost-effective and viable design strategy demonstrated for the fabrication of a simple molecular triad holds the promise for the emergence of new functional fluorescent molecules to molecular materials for task-specific applications.

The thiophene appended Schiff's base ligand, 1-(2-(thiophen-2-yl)ethylimino)methyl)naphthalene-2-ol (HL) with N,O donor sites has been synthesized by the condensation between 2-hydroxy-1-naphthaldehyde and thiophene-2-ethylamine. The square planar 1:2 complexes of HL having general formula [M(L)2] (M = Ni(1) and Pd(2)) with nickel(II) and palladium(II) have been synthesized and characterized by several spectroscopic techniques. The geometry has been confirmed by single crystal X-ray study for complex 1. The electronic structure and spectral properties of the complexes are interpreted by DFT and TDDFT studies.

The square planar nickel(II) complexes have been synthesized by the reaction of nickel(II) chloride hexahydrate and the in situ condensed thiophene appended Schiff base ligands of thiophene-2-ethylamine with 3,5-dimethyl-2-hydroxybenzaldehyde or 3,5-dichloro-2-hydroxybenzaldehyde for [Ni(L1)2] (1) and [Ni(L2)2] (2) respectively. The complexes have been characterized by several spectroscopic techniques, viz. FT-IR, 1H NMR, absorption and emission spectroscopy. The complexes crystallize in monoclinic crystal system with C2/c space group for 1 and triclinic crystal system with P−1 space group for 2. In complex 1 the nickel sits on an inversion centre with symmetry –x, 2–y, –z. Cyclic voltammgrams of the complexes show quasi-reversible NiII/NiIII oxidation couple along with irreversible NiII/NiI reduction. Electronic structure and spectral properties are well interpreted by DFT and TDDFT calculations.

New rhodium(III)-triphenylphosphine complex, [Rh(PPh3)(L)Cl2](PF6) (1) with thioether containing NNS donor ligand (L) (L = 2-(methylthio)-N-((pyridine-2-yl)methylene)benzenamine) has been synthesized and characterized. The pseudo octahedral geometry of the complex has been confirmed by single crystal X-ray analysis. The electronic structure, redox properties, absorption and emission properties of the complexes have been interpreted by DFT and TDDFT calculations. The complex effectively catalyzed the transfer hydrogenation reaction of ketones in 2-propanol and oxidation of alcohols in presence of NMO.

The paper presents a combined experimental and computational study of tricarbonyl complexes fac -[Re(CO) 3 (L 1 /L 2 )Cl] ( 1a/1b ) (L 1 = 2-(methylthio)-N-((pyridine-2-yl)methylene)benzenamine and L 2 = 2-(ethylthio)-N-((pyridine-2-yl)methylene)benzenamine). The Schiff base ligands L 1 and L 2 have been synthesized and characterized by elemental and spectroscopic analysis. Along with spectral characterizations, the structural confirmation by single crystal X-ray study has been done for complex 1a . The rhenium atom adopts a distorted octahedral geometry and is coordinated by three carbonyl ligands in a fac arrangement. The electronic structure, redox properties, absorption and emission properties of ligands and complexes have been explained based on DFT and TDDFT calculations. The complexes show MLCT bands at 443–448 nm and emitted at 405–410 nm upon excitation at 320–326 nm, characterized as ILCT transitions.

A few dioxomolybdenum complexes of the type MoO2L and MoO2L·B of a new diprotic tridentate ONS chelating ligand, H2L, have been synthesized with the aim to examine their potential to behave as models for the active site of an oxidoreductase molybdoenzyme like xanthineoxidase. The MoO2L complex produces MoO2L·B on treatment with neutral monodentate Lewis bases such as γ-picoline, 2-methylimidazole or 1-allylimidazole, utilizing the vacant sixth coordination site. They have been characterized by spectroscopic and electrochemical techniques. The complexes MoO2L (1), MoO2L(γ-pic) (2) and MoO2L(1-allyl imz) (4) were structurally characterized by single crystal X-ray diffraction. The complex MoVIO2L exhibits oxotransfer to PPh3 in acetonitrile medium leading to the formation of MoIVOL, which is reoxidized to MoVIO2L on treatment with DMSO or pyridine N-oxide. DFT calculations on the ligand and complexes 1, 2 and 4 were also carried out.

The complex cis-[Ru(PPh3)(L)Cl2] (1) has been synthesized by the reaction between Ru(PPh3)3Cl2 and thioether containing azo ligand (L) (L = 1-methyl-2-{(o-thiomethyl)phenylazo}imidazole). The Cl atoms have been exchanged with Br−, I− and NCS− leading to the formation of cis-[Ru(PPh3)(L)Br2] (2), cis-[Ru(PPh3)(L)I2] (3) and cis-[Ru(PPh3)(L)(NCS)2] (4), respectively. The complexes have been characterized by spectroscopic techniques (IR, NMR and UV–Vis) and geometries have been confirmed by X-ray crystal structures of 1 and 3. The electronic spectra of the complexes show moderately intense MLCT band along with intense ILCT transitions. Cyclic voltammetric studies show one quasi reversible Ru(III)/Ru(II) oxidation couple and two successive one electron reductions leading to the formation of L − and L2−, respectively. The electronic structure, redox and absorption properties of the complexes have been explained based on DFT and TDDFT results.

The article deals with a combined experimental and computational study of rhenium tricarbonyl Schiff base complexes having general formula fac-[ReCl(CO)3(L1/L2)] (1/2) (L1 = N-[(2-pyridyl)methyliden]-α-aminonaphthalene and L2 = N-[(2-pyridyl)methyliden]-β-aminonaphthalene). The complexes fac-[ReCl(CO)3(L1/L2)] (1/2) have been synthesized and characterized by elemental analysis, spectroscopic studies, electrochemistry and X-ray crystal analysis for complex 2. Crystal structure of 2 reveals the facial geometry of the carbonyl ligand and Re is in distorted octahedral environment in the complex. The electronic structure, redox properties, absorption and emission properties have been explained based on DFT and TDDFT calculations. The complexes show MLCT bands at 395–405 nm and emitted at 425–435 nm upon excitation at 310 nm, characterized as ILCT transitions. The complexes exhibit two irreversible ReII/ReI and ReIII/ReII oxidative responses when scanned in the potential range 0.0–2.0 V in cyclic voltammetric studies.

The new rhenium(I) carbonyl complexes containing {Re(CO) 3 } + fragment with redox non-innocent ligands L 1 /L 2 (L 1 , 1-methyl-2-{( o -thiomethyl)phenylazo}imidazole and L 2 , 1-ethyl-2-{( o -thioethyl)phenylazo}imidazole) having general formula fac -[ReX(CO) 3 (L 1 /L 2 )] ( 1 / 2 ) (X = Cl ( 1 ) and Br ( 2 )) have been synthesized and characterized by both experimental and theoretical studies. The structural confirmation has been carried out for 1a . The complexes show one irreversible Re I /Re II oxidation and one reversible along with an irreversible ligand reduction in the cyclic voltammetric studies. The electronic structure and the nature of Re–CO bonding has been explained by means of DFT and NBO calculations. The spin allowed singlet–singlet electronic transitions of 1a and 2a have been calculated with TDDFT method, and the experimental spectra of the complexes have been discussed on this basis.