Search results for "Intermolecular"

Tuning of the electronic and photophysical properties of ladder-type quaterphenyl by selective methylene-bridge fluorination

2016

The photophysics (spectral positions, band shapes, fluorescence quantum yields and lifetimes) of a series of fluorinated ladder type quaterphenyls L4P and L4P-Fn (n = 2, 4, 6) depend strongly on the degree and position of fluorine, despite the fact that substitution is not performed in the rings but only in methylene-bridges. This is driven by subtle differences in the molecular orbitals (MOs) participating in the electronic transitions, and in the vibronic pattern of the S0 and S1 electronic states as revealed by (TD)DFT calculations. Solid state spectra for n = 0, 2, 4 are similar to those of solution due to small intermolecular interactions as revealed by combined X-ray and (TD)DFT analy…

Electrochemically Induced Reversible and Irreversible Coupling of Triarylamines

2011

The electrochemical coupling and dimerization behavior of the low molecular compounds triphenylamine (TPA) and 9-phenylcarbazole (PHC) in comparison to tri-p-tolylamine (p-TTA) with para-blocked methyl groups has been investigated in detail. In contrast to the unsubstituted radical cations of TPA and PHC, the radical cations of p-TTA are stable in the radical cation state and do not undergo any further coupling reactions. However, we found that the dicationic state of p-TTA does undergo two different competitive reaction pathways: (1) an irreversible intramolecular coupling reaction which leads to phenylcarbazole moieties and (2) a reversible intermolecular dimerization leading to charged σ…

Intermolecular interactions in metastable protein solutions.

2011

A Synthetic Model for the [4+2] Cycloaddition in the Biosynthesis of the Brevianamides, Paraherquamides, and Related Compounds

2000

Abstract The reactivity of model systems for the proposed [4+2] cycloaddition in the biosynthesis of the brevianamides, paraherquamides, and marcfortines is explored. The model for the intermolecular reaction reveals that the cycloaddition takes place under mild conditions only if activated, very reactive dienophiles are used. When relatively unreactive dienophiles such as cyclopentene and cyclohexene are used, harsh reaction conditions and/or a Lewis acid catalyst are necessary for the reaction. In contrast, the model for the intramolecular reaction demonstrates that the cycloaddition takes place within a few hours at room temperature, even in the absence of a Lewis acid catalyst. Conclusi…

Associative behaviour of κ-carrageenan in aqueous solutions and its modification by different monovalent salts as reflected by viscometric parameters

2019

Abstract The viscometric behaviour of κ-carrageenan in aqueous solutions and in the presence of monovalent salts was investigated at 25 °C. Coil, helix or double helix conformations were induced by cooling hot κ-carrageenan solutions under appropriate ionic conditions. A new viscometric approach was used for modeling the behaviour of κ-carrageenan solutions. The intrinsic viscosity, [η], is markedly changed by the presence of different monovalent salts (NaCl, NaI and CsI). In pure water, the intrinsic viscosity amounts to 48 dL·g−1. In 0.1 M NaCl solutions (single helix state) [η] is 6.2 dL·g−1, whereas in 0.1 M NaI (double helix conformation) it is approximately twice as large. In 0.1 M Cs…

Investigating Intermolecular Interactions in a DME-Based Hybrid Ionic Liquid Electrolyte by HOESY NMR

2019

The intermolecular interactions in a hybrid electrolyte based on various compositions of the ionic liquid N-methyl-N-propyl pyrrolidinium bis-fluorosulfonylimide (C3mpyrFSI), LiFSI salt and an ether-based additive, 1,2-dimethoxy ethane (DME), have been investigated using the HOESY (Heteronuclear Overhauser Effect SpectroscopY) NMR experiment. This NMR technique allows a quantification of the intermolecular interactions in ionic liquids (ILs) by measuring the cross-relaxation rate (σ) between different pairs of nuclei. Thereby, we compare the cross-relaxation rates between the cations, anions and DME in these hybrid electrolyte systems using 1H-7Li and 1H-19F HOESY experiments, and interpret…

Switching of easy-axis to easy-plane anisotropy in cobalt(ii) complexes

2021

A tetranuclear cubane-type complex [Co4(ntfa)4(CH3O)4(CH3OH)4] (1) with a {Co4O4} core, and a mononuclear complex [Co(ntfa)2(CH3OH)2] (2) have been rationally obtained by adjusting the ratio of the β-diketonate and Co(II) ions, with the synthetic processes being monitored by in situ microcalorimetry. Then, following synthetic conditions to obtain 2, but using three distinct N-donor coligands - 2,2'-bipyridyl (bpy), 6,6'-dimethyl-2,2'-bipyridyl (6,6-(CH3)2-bpy) and 5,5'-dimethyl-2,2'-bipyridyl (5,5-(CH3)2-bpy) - three novel mononuclear complexes have been obtained, [Co(ntfa)2(bpy)2] (3), [Co(ntfa)2(6,6-(CH3)2- bpy)2] (4) and [Co(ntfa)2(5,5-(CH3)2-bpy)2] (5). The introduction of different cap…

Self-assembly of Organic Molecules on Insulating Surfaces

2015

Molecular self-assembly is known to provide a powerful tool for creating functional structures, with the ultimate structure and functionality encoded in the molecular building blocks. Upon molecule deposition onto surfaces, functional structures have been created ranging from defect-free, highly symmetric two-dimensional layers to complex assemblies with dedicated functionality. Especially organic molecules play a key role for molecular self-assembly due to their impressive structural flexibility and the high degree of control by chemical synthesis. Furthermore, the surface itself provides another exciting dimension: adjusting the subtle balance between intermolecular and molecule-surface i…

Capping N‐Donor Ligands Modulate the Magnetic Dynamics of Dy III β‐Diketonate Single‐Ion Magnets with D 4 d Symmetry

2019

A family of four mononuclear DyIII β-diketonate complexes with formulas [Dy(tmhd)3 (Br2 -bpy) (1), [Dy(tmhd)3 (Br-bpy)] (2), [Dy(tmhd)3 (dppz)] (3), and [Dy(tmhd)3 (mcdpq)] (4) (tmhd=2,2,6,6-tetramethyl-3,5-heptanedione, Br2 -bpy=5,5'-dibromo-2,2'-bipyridine, Br-bpy=5-bromo-2,2'-bipyridine, dppz=dipyrido [3,2-a:2',3'-c]phenazine, mcdpq=2-methoxyl-3-cyanodipyrido[3,2-f:2,3'-h]quinoxaline) were prepared by modifying the capping N-donor coligands. DyIII centers in these complexes feature an N2 O6 octacoordinate environment with distorted square-antiprismatic D4d symmetry. Magnetic investigations evidenced single-ion magnet behavior in all complexes with energy barriers Ueff of 42.10 (1), 61.47…

Coordination isomerism in spin crossover (SCO) materials

2021

International audience; A new series of three spin crossover (SCO) Fe(II) complexes based on a cyanocarbanion and on the neutral quinolin-8-amine (aqin) ligands, [Fe(aqin)2(tcnsme)2] (1), [Fe(aqin)2(tcnset)2] (2), and [Fe(aqin)2(tcnspr)2] (3), has been studied. The three complexes display similar molecular structures consisting of discrete [Fe(aqin)2(tcnsR)2] complexes [R = Me (1), Et (2), and Pr (3)]. Infrared spectroscopy and magnetic studies, performed on the three complexes, revealed the presence of similar SCO behaviors which strongly differ by their transition temperatures [234 K (1) < 266 K (2) < 360 K (3)]. The increase of the transition temperatures when passing from 1 to 3 may be …