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Aryldiazonium cation undergoes C–C coupling reactions through instant formation of PdIV aryldiazenido complex with the precursor [(Tp*)PdIIMe2]- complex (Tp* = tris(3,5-dimethyl-1-pyrazolyl)borate). This PdIV arylazenido complex is the first high-valent PdIV complex in C–C coupling reactions which can decompose further into aryldiazonium cation and PdII complex and follow a series of reactions via a two-electron or ionic path. Alternatively, it can decompose into aryl radical (AniR) and follow one-electron or radical path forming the C–C coupled product. The possibility of these two mechanisms were proposed by Fekl and co-workers [Dalton Trans. 2017, 46, 4004–4008] and in this work, DFT calculations have been performed to clarify the mechanism as well as to probe the competitive role of aryldiazonium cation and aryl radical (AniR) in this reaction. In the two-electron pathway the process follows sequentially oxidative addition, transmetallation, oxidative addition and dinitrogen extrusion, and reductive elimination to form the C–C coupled product 4,4′-dimethoxybiphenyl (P1) and 4-methoxy toluene (P3). In the one-electron or radical pathway, 4-methoxyphenyl radicals are formed directly and they recombine to give P1. There are other products including [(Tp*)PdIVMe3] (P2) and ethane (P4) formed in the reaction. QTAIM calculations reveal that methyl group migrates as a cation in the transmetallation step of the two-electron path. N2 extrusion passes through a six membered cyclic transition state involving orbital and CH--.π interactions, and reductive elimination passes through a three-membered cyclic transition state. NBO calculations explain the nature of metal-ligand bonding of the species involved in the reaction path. A close inspection of the activation barriers shows the one-electron pathway seems to be favoured over two-electron path because it is low lying and everything becomes irreversible once aryl radical is formed, which quickly undergoes completely irreversible coupling, whereas the first several steps of the two-electron pathway are all reversible. This is in agreement with the experiment and calculations further clarify that the proposed PdIV diaryldiazenido complex is not feasible. Computations thus reveal that aryldiazonium cation starts the reaction by forming [(Tp*)PdIVMe2(pmbd)](RC) complex and this complex reacts favourably through aryl radical to form the products. Aryldiazonium cation readily reacts with the precursor PdII complex to give PdIV aryldiazenido complex and this complex undergoes C–C coupling reaction via radical pathway through aryl radical and forms 4, 4′-dimethoxybiphenyl as a major product, and ethane and 4-methoxytoluene as minor products following PdII/PdIV catalytic cycle. [ABSTRACT FROM AUTHOR]

The influence of phenols upon the fluorescence quenching of 9-aminoacridine (9-AA) was examined in acetonitrile solution by employing steady state and time-resolved fluorescence measurements. On increasing the concentration of quencher molecules the absorption spectra of 9-AA change with significant bathochromic shift. The fluorescence intensity of 9-AA change in presence of quencher molecules were measured at various temperatures as a function of the quencher concentrations. The observed bimolecular quenching rate constant (kq) depends on the nature and electronic effect of substituent present in the quencher molecules. The bimolecular quenching rate constant (kq) decreases on increasing the oxidation potential of quencher molecules. To examine the quenching behavior, kq values were correlated with the free energy change (ΔG). To get forthcoming in the quenching process, fluorescence quenching experiments were carried out in different solvents of varying polarities. The observed result suggest the involvement of charge-transfer quenching mechanism. Lifetime measurements support static quenching. Further, the radical scavenging potential is calculated from density functional theory (DFT) calculations to address the quenching behavior of the quencher molecules. DFT result reveals that electronic features are important in tuning the quenching ability of the quencher molecules and found to agree with the obtained experiment result. [ABSTRACT FROM AUTHOR]

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]

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.)