320 research outputs found
5,11,17,23-Tetra-tert-butyl-25,26,27,28-tetraÂkis[2-(2-chloroÂethoxy)ethÂoxy]-2,8,14,20-tetraÂsulfonylÂcalix[4]arene
MolÂecules of the title compound, C56H76Cl4O16S4, have crystallographic C
2 symmetry and adopt a 1,3-alternate conformation where the four –OCH2CH2OCH2CH2Cl groups are located alternately above and below the virtual plane (R) defined by the four bridging S atoms. The dihedral angles between the plane (R) and the phenolic rings are 72.85 (7) and 74.57 (7)°. An unusual 24-membered macrocyclic ring is formed in the crystal structure with an array of eight intraÂmolecular C—H⋯O hydrogen bonds between the ether arm H atoms and the sulfonyl O atoms. In the supraÂmolecular structure, the molÂecular components are linked into infinite zigzag one-dimensional chains by a combination of four interÂmolecular C—H⋯O hydrogen bonds, forming R
2
2(13), R
2
2(16), R
2
2(21) and R
2
2(26) ring motifs. These chains are augmented into a wave-like two-dimensional network by weak C⋯O interÂactions. One tert-butyl group shows rotational disorder, and one CH2CH2Cl group is disordered over two orientations; the site-occupation factors are 0.756 (6) and 0.244 (6) for the two tert-butyl groups, and 0.808 (3) and 0.192 (3) for the two CH2CH2Cl units
Cyclometalated platinum(II) with ethynyl-linked azobenzene ligands: an original switching mode.
International audienceThe photophysical properties of 6-phenyl-2,2'-bipyridyl platinum(ii) complexes bearing different σ-alkynyl-linked azobenzene ancillary ligands were investigated. These complexes exhibited strong, broad, structureless charge-transfer bands in the visible region, which were red-shifted when the electron-donating ability of the para substituent on the azo-acetylide ligand increased. When excited at the charge-transfer absorption band, the complexes exhibited weak green emission, which was assigned to a triplet metal-to-ligand charge transfer/interligand charge transfer emission ((3)MLCT/(3)L'LCT). The presence of an amino substituent in the azobenzene moiety opened the possibility of protonation, which led to the formation of an azonium based derivative and resulted in drastic perturbations of the molecular orbitals and photophysical properties of the Pt-acetylide complex. These studies are fully supported by DFT and TD-DFT calculations
Conformational studies of bipyrimidine-based mesogens by combination of DFT calculations and temperature-dependent infrared studies
International audienceCombination of DFT calculations and solid-state temperature-dependent infrared spectroscopy has confirmed that the central core of recently developed bipyrimidine-based mesogens is not flat, i.e. do not adopt a disc shape, inside the columnar liquid-crystalline phase. For this purpose, the intensities and the frequency shifts of the most sensitive C–N and C–C bands of the central bipyrimidine core have been studied as a function of the temperature and of the dihedral angle. The results support the reported packing model in which the molecules are interdigitated alternatively along their long axis and their short axis to form columns inside the mesophase
Heteroleptic diimine copper(i) complexes with large extinction coefficients: synthesis, quantum chemistry calculations and physico-chemical properties.
International audience: Using the HETPHEN approach, five new heteroleptic copper(i) complexes composed of a push-pull 4,4'-styryl-6,6'-dimethyl-2,2'-bipyridine ligand and a bulky bis[(2-diphenylphosphino)phenyl]-ether (DPEphos) or a bis2,9-mesityl phenanthroline (Mes2Phen) were prepared and characterized by electronic absorption spectroscopy, electrochemistry, and TD-DFT calculations. These complexes exhibit very intense absorption bands in the visible region with extinction coefficient in the range of 5-7 × 10(4) M(-1) cm(-1). The analysis of the position, intensity and band shape indicates a strong contribution from an intra-ligand charge-transfer transition centered on the styrylbipyridine ligand along with MLCT transitions. These new complexes experimentally demonstrate that good light harvesting properties with bis-diimine copper(i) complexes are a reality if one chooses suitable ligands in the coordination sphere. This constitutes a milestone towards using bis-diimine copper(i) complexes for solar energy conversion (artificial photosynthesis and solar cells)
Any -state solutions of the Hulth\'en potential by the asymptotic iteration method
In this article, we present the analytical solution of the radial
Schr\"{o}dinger equation for the Hulth\'{e}n potential within the framework of
the asymptotic iteration method by using an approximation to the centrifugal
potential for any states. We obtain the energy eigenvalues and the
corresponding eigenfunctions for different screening parameters. The wave
functions are physical and energy eigenvalues are in good agreement with the
results obtained by other methods for different values. In order to
demonstrate this, the results of the asymptotic iteration method are compared
with the results of the supersymmetry, the numerical integration, the
variational and the shifted 1/N expansion methods.Comment: 14 pages and 1 figur
Photoisomerisation in Aminoazobenzene-Substituted Ruthenium(II) Tris(bipyridine) Complexes: Influence of the Conjugation Pathway.
International audienceTransition-metal complexes containing stimuli-responsive systems are attractive for applications in optical devices, photonic memory, photosensing, as well as luminescence imaging. Amongst them, photochromic metal complexes offer the possibility of combining the specific properties of the metal centre and the optical response of the photochromic group. The synthesis, the electrochemical properties and the photophysical characterisation of a series of donor-acceptor azobenzene derivatives that possess bipyridine groups connected to a 4-dialkylaminoazobenzene moiety through various linkers are presented. DFT and TD-DFT calculations were performed to complement the experimental findings and contribute to their interpretation. The position and nature of the linker (ethynyl, triazolyl, none) were engineered and shown to induce different electronic coupling between donor and acceptor in ligands and complexes. This in turn led to strong modulations in terms of photoisomerisation of the ligands and complexes
Synthesis, photophysics and nonlinear optical properties of stilbenoid pyrimidine-based dyes bearing methylenepyran donor groups.
International audienceThe nonlinear properties and the photophysical behavior of two π-conjugated chromophores that incorporate an electron-deficient pyrimidine core (A) and γ-methylenepyrans as terminal donor (D) groups have been thoroughly investigated. Both dipolar and quadrupolar branching strategies are explored and rationalized on the basis of the Frenkel exciton model. Even though a cooperative effect is clearly observed if the dimensionality is increased, the nonlinear optical (NLO) response of this series is moderate if one considers the nature of the D/A couple and the size of the chromophores (as measured by the number of π electrons). This effect was attributed to a disruption in the electronic conjugation within the dyes' scaffold for which the geometry deviates from planarity owing to a noticeable twisting of the pyranylidene end-groups. This latter structural parameter also has a strong influence on the excited-state dynamics, which leads to a very efficient fluorescence quenching
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