Search results for "Theoretical"
showing 10 items of 11439 documents
Electronic structure of phthalocyanines : Theoretical investigation of the optical properties of phthalocyanine monomers, dimers, and crystals
1990
We present valence effective Hamiltonian (VEH) calculations on the optical absorptions of a series of phthalocyanine compounds: the metal‐free phthalocyanine molecule, a model system for the lithium phthalocyanine molecule, the metal‐free phthalocyanine dimer, and model systems for the lutetium diphthalocyanine and the lithium phthalocyanine crystal. For these compounds, it is found that the major factor influencing the evolution of the optical transitions is not the electronic structure of the metal but rather the geometric structure: phthalocyanine intraring geometry and, in the dimers and crystals, interring separation and staggering angle. The origin of the so‐called Soret or B absorpti…
Synthesis, structural diversity, inter-conversion and reactivity of Cu(II) complexes of hydroxy-rich molecules
2002
Tetranuclear Cu(II) complexes having linear, cubane and pseudodouble-cubane cores were synthesized using hydroxy-rich molecules possessing amine and imine groups. The products were structurally characterized and were studied for their ability to oxidize catechol as well as for their inter-conversion between mono- and tetra-nuclear complexes.
Recognition of oxovanadium(V) species and its separation from other metal species through selective complexation by some acyclic ligands
1998
Acyclic molecules possessing –OH (phenoxo and alkoxo type) groups and imine or amine moieties have been developed to sense the specific preference for VO3+ species. These molecules also showed a capability to quantitatively separate oxovanadium(V) species from a reaction mixture containing metal species of V, Mo, U, Fe, and Mn ions in solution. A cascade quantitative separation of VO3+ followed by cis–MoO2+2 followed by trans –UO2+2 species is demonstrated from their mixture. Synthesis and structural details of oxo-species of vanadium molybdenum and uranium are also discussed. Factors influencing the complexation of these molecules towards oxo metal species of V, Mo and U are also addressed.
Mechanochemical Synthesis, Photophysical Properties, and X-ray Structures of N-Heteroacenes
2016
The described mechanochemical methodology is an example of a proof-of-concept in which solution-based tedious, poor yielding, and difficult syntheses of pyrazaacenes are achieved under solvent-free ball-milling conditions; the method is easy, high yielding, time-efficient, and environmentally benign. The synthesized compounds also include pyrazaacenes (N-heteroacenes) that are octacene analogues containing pyrene building blocks. The compounds were sparingly soluble in common solvents, and column chromatographic purifications could be avoided after the solvent-free syntheses. The UV/Vis absorption spectra of the pyrazaacenes show intense absorption bands in the near-IR region. The single-cr…
Electronic Absorption Spectra of HXeCl, HXeBr, HXeI, and HXeCN in Xe Matrix
2000
The electronic UV absorption spectra of thermal reaction products H−Xe−Y (Y= Cl, Br, I, or CN) have been measured in solid Xe at 12 K. The spectra are obtained after the annealing of an extensively...
Rotational spectra and hyperfine structure of isotopic species of deuterated cyanoacetylene, DC3N
2008
Abstract Cyanoacetylene enriched in deuterium was used to record pure rotational transitions of DC 3 N and its rare 13 C and 15 N isotopic species by employing Fourier transform microwave (FTMW) spectroscopy on a supersonic-jet expansion at centimeter wavelengths (8.2–25.4 GHz) and by using long-path absorption spectroscopy at millimeter and submillimeter wavelengths (82–900 GHz). In addition, submillimeter wave measurements (304–897 GHz) have been performed for DC 3 N in its v 7 = 1 lowest excited vibrational state. Hyperfine structure caused by the 14 N and D nuclei has been resolved in the FTMW spectra. Quantum-chemical calculations have been performed on the hyperfine structure paramete…
Study of water adsorption and capillary bridge formation for SiO(2) nanoparticle layers by means of a combined in situ FT-IR reflection spectroscopy …
2014
Water adsorption and capillary bridge formation within a layer of SiO2-nanoparticles were studied in situ by means of a combination of quartz crystal microbalance (QCM-D) with dissipation analysis and Fourier transformation infrared reflection absorption spectroscopy (FT-IRRAS). FT-IR data were employed to distinguish the “ice-like” and “liquid-like” contributions and to support the analysis of the QCM-D data concerning mass change and dissipation. Combined measurements show that for SiO2-nanoparticles with a diameter of about 250 nm, the formation of two adsorbed monolayers of water as well as bulk water leads to a rather linear increase in the dissipation for relative humidity values of u…
Spectroscopic and quantum chemical study of pressure effects on solvated chlorophyll
2004
Abstract Hydrostatic pressure effects up to 907 MPa on absorption spectra of chlorophyll a molecules dissolved in diethyl ether have been studied at ambient temperature both experimentally and theoretically using quantum chemistry methods. The fluorescence spectra are studied only experimentally. The data suggest that coordination interactions between the central Mg atom of the chlorophyll and solvent molecules along with interactions that modify the porphyrin skeleton of the solute are responsible for the observed differences of pressure dependence of the Q y , Q x , and Soret spectral bands. The coordination number of the Mg atom changes from five to six between 400 and 600 MPa.
Ab Initio Studies of Triplet-State Properties for Organic Semiconductor Molecules
2012
Triplet–triplet annihilation (TTA) leads to a reduced efficiency of organic light-emitting diodes (OLEDs) at high current densities. Spacial confinement of the triplet excitons, which is mainly dependent on triplet energy differences, can reduce the TTA rate. Therefore, a deliberate choice of the organic semiconductor materials with particular attention to their triplet energies can help to considerably increase the device efficiency. Organic solid-state lasers are, on the other hand, efficiently quenched by singlet–triplet annihilation (STA), which is closely related to the triplet–triplet absorption of the organic semiconductors. To establish a useful set of parameters related to the proc…
A butterfly like motion as a clue to the photophysics of thioxanthone
2006
Abstract A theoretical, quantum-chemical study of the thioxanthone (TX) molecule has been performed at the MP2 and CASPT2 levels of theory. Geometries, absorption energies, and transition and state properties have been investigated. Two conformers have been found very close in energy with planar (P) and non-planar (NP) structures, the latter characterized by a dihedral angle θ = 173.3° representing the bend of the side benzene rings and an out-of-plane angle ϕ = 4° of the C O bond. Large changes in the relative positions and properties of the two low-lying electronic absorption bands, ππ * and nπ * , are computed when changing the conformation. As a consequence of the analysis of the TX a…