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The synthesis of the tetradentate dianionic ligand, H2 L (2,2'-(1E,1'E)-(2,2-dimethylpropane-1,3-dyl)bis(azanylylidene) bis(methanylylidene)diphenol), from 2,2-dimethyl-1,3-diaminopropane and its reaction with UO2(CH3COO)2-2H2O in a 1:1 molar ratio in methanol to produce the complex [UO2(L)(CH3OH)] are reported. The isolated compounds have been characterized by elemental analysis, ionization mass spectrometry (ESI-MS), UV/Vis, FT-IR, 1H- and 13C-NMR, DEPT-135 spectroscopy, TGA and single-crystal X-ray diffraction. As shown by X-ray crystallography, the coordination geometry around the uranium centre is distorted pentagonal bipyramidal with two imine nitrogen atoms, two phenolic oxygen atoms and one methanol O atom occupying equatorial sites, together with two axial oxo groups. To obtain insights into the structure and spectral properties of the studied complex, density functional theory (DFT) and time dependent density functional theory (TD-DFT) calculations have been carried out. The computed results show that LUMO of the complex is featured with uranium f orbital character. TD-DFT results indicate that the complex displays two intense bands and one weak charge transfer band. The charge transfer band is primarily due to HOMO LUMO (53%). Two intense bands have main contributions from HOMO-2 LUMO (81%) and HOMO-3 LUMO (77%) transitions, respectively. TD-DFT results indicate that the complex displays the charge transfer band primarily due to HOMO LUMO (53%) and other two charge transfer bands have main contributions from HOMO-2 LUMO (81%), HOMO-3 LUMO (77%) transitions, respectively. NBO analysis reveals that the ground state of the complex is mainly stabilized by n-n* interaction. EDA analysis reveals that the interaction existing between the ligand and other parts of the complex is mainly electrostatic in nature. [ABSTRACT FROM AUTHOR]

The possibility of simultaneous addition of η2-H2 to both the metals (Ni and Fe) in the active site of the as isolated state of the enzyme (Ni-SI) is examined here by an atom-by-atom electronic energy partitioning based on the QTAIM method. Results show that the 4LS state prefers H2 removal than addition. Destabilization of the atomic basins of the thiolate bridges and decrease of the electrophilicity of the Fe and Ni, resulting in poor back donation to the CO ligand, are the bottlenecks that hamper dihydrogen activation simultaneously. The study helps to understand why such states are seldom accessed in the activation of dihydrogen. Moreover, Ni has been found to be the natural choice for the dihydrogen binding. [ABSTRACT FROM AUTHOR]

A series of 2-quinolinone-based molecular systems with three different acceptor groups and N/ O-alkylated quinolinone compounds have been synthesised in an attempt to understand their optical properties. All the compounds were characterised by 1H NMR, 13C NMR and mass analysis. Absorption measurements revealed that charge-transfer transition was observed by introducing electron-withdrawing acceptor groups. Alkylation of 2-quinolinone at the O-position thwarts the charge-transfer transitions, whereas N-alkylation retains the charge-transfer property. The presence of resonance zwitterionic forms in the unalkylated and N-alkylated quinolinone compounds play an important role in charge-transfer transition. The effects of solvents on the absorption and emission properties of these compounds were probed through Lippert Mataga and ET(30) correlation. The Stokes shifts of O-alkylated compounds were larger than those of the unalkylated and N-alkylated quinolinone compounds. The observed higher quantum yield and Stokes shift for these compounds will make them ideal fluorescent probes. Incorporation of acceptor groups and alkylation in the quinolinone moiety alters their energy levels. Good thermal stability was observed for both unalkylated and alkylated quinolinone compounds. The trends observed in the photophysical and electrochemical properties were supported by theoretical studies. The observed tunable optical properties, which were achieved through simple N- vs. O-alkylation, results in large Stokes shifts and thermal stability, which means that the 2-quinolinone-based molecular systems are expected to emerge as potential candidates for photovoltaic and biological applications. [ABSTRACT FROM AUTHOR]

A search for novel organic luminogens led us to design and synthesize some N-fused imidazole derivatives based on imidazo[1,2- a]pyridine as the core and arylamine and imidazole as the peripheral groups. The fluorophores were synthesized through a multicomponent cascade reaction (A3 coupling) of a heterocyclic azine with an aldehyde and alkyne, followed by Suzuki coupling and a multicomponent cyclization reaction. All of the compounds exhibited interesting photophysical responses, especially arylamine-containing derivatives, which displayed strong positive solvatochromism in the emission spectra that indicated a more polar excited state owing to an efficient charge migration from the donor arylamine to the imidazo[1,2- a]pyridine acceptor. The quantum yields ranged from 0.2 to 0.7 and depended on the substitution pattern, most notably that based on the donor group at the C2 position. Moreover, the influence of general and specific solvent effects on the photophysical properties of the fluorophores was discussed with four-parameter Catalán and Kamlet-Taft solvent scales. The excellent thermal, electrochemical, and morphological stability of the compounds was explored by cyclic voltammetry, thermogravimetric analysis, and AFM methods. Furthermore, to understand the structure, bonding, and band gap of the molecules, DFT calculations were performed. The performance of the electroluminescence behavior of the imidazo[1,2- a]pyridine derivative was investigated by fabricating a multilayer organic light-emitting diode with a configuration of ITO/NPB (60 nm)/EML (40 nm)/BCP (15 nm)/Alq3 (20 nm)/LiF (0.5 nm)/Al(100 nm) (ITO=indium tin oxide, EML=emissive layer, BCP=2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline, Alq3=tris(8-hydroxyquinolinato)aluminum), which exhibited white emission with a turn-on voltage of 8 V and a brightness of 22 cd m−2. [ABSTRACT FROM AUTHOR]

Diels Alder reactivity of corannulene has been probed using density functional theory (DFT) at B3LYP/6-31G* level by employing it both as a diene and a dienophile in cycloaddition with ethylene and 1,3-butadiene as typical partners. Computations reveal that corannulene acts better as a dienophile than as a diene and as a dienophile it undergoes normal electron demand type addition with 1,3-butadiene, and as a diene corannulene undergoes inverse electron demand type addition with ethylene. When employed as a dienophile the addition takes place preferentially in the rim position than in the spoke position due to strong steric and electronic reasons. Further in the rim addition rim exo approach is favored kinetically and thermodynamically. As a diene, corannulene shows regioselectivity for rim–spoke addition over spoke–spoke addition. Concerted type cycloadditions have been studied and the reactions are seen to take place preferentially on the convex face. The effect of substituents in butadiene on the reactivity and the reaction of butadiene–pentaindenocorannulene (an extended corannulene) system has been investigated for the most favorable rim exo positions. Copyright © 2007 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Herein, we have synthesized 4,5-diphenyl-1 H -imidazole and 2-(1 H -indol-3-yl)acetonitrile based donor-π-acceptor fluorophores and studied their optical, thermal, electroluminescence properties. Both the fluorophores exhibit high fluorescence quantum yield ( Φ f = <0.6) and good thermal stability ( T d10 = <300 °C), and could be excellent candidates for OLED applications. Moreover, the ground and excited state properties of the compounds were analysed in various solvents with different polarities. The geometric and electronic structures of the fluorophores in the ground and excited states have been studied using density functional theory (DFT) and time-dependent density functional theory (TDDFT) methods. The absorption of BIPIAN and BITIAN in various solvents corresponds to S 0 → S 1 transitions and the most intense bands with respect to the higher oscillator strengths are mainly contributed by HOMO → LUMO transition. Significantly, the vacuum deposited non-doped OLED device was fabricated using BITIAN as an emitter, and the device shows electroluminescence (EL) at 564 nm, maximum current efficiency (CE) 0.687 cd A -1 and a maximum external quantum efficiency (EQE) of 0.24%., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)