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Berlin Brandenburg

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  • 1
    Language: English
    In: The journal of physical chemistry. A, 24 January 2013, Vol.117(3), pp.670-8
    Description: The magnetic properties of a series of manganese(II) diacetylacetonate and dihexafluoroacetylacetonate hybrid-spin complexes with neutral pyridine-based organic radicals were characterized theoretically by DFT calculations. Three stable radicals, in which a radical group is bound in either para or meta position with respect to the pyridine nitrogen atom, were considered. The correct stable structures and multiplets of the complexes were obtained by full geometry optimization starting from an ideal structure. A total of three important geometry descriptors of the complexes were monitored and related to their magnetic characteristics. These structural parameters are (i) the torsion angle governing the conjugation of the organic radical m-PyNO (anti versus gauche), (ii) the coordination geometry of the acetyl acetonate ligands around the metal ion (square versus rhombic), and (iii) the relative orientation of the organic radical with respect to the acetyl acetonate plane (parallel versus perpendicular). It was found that the magnetic properties are not sensitive to the orientation of the radicals with respect to the equatorial plane but do depend on the conformation of the organic radicals. Even a spin switch between the ferromagnetic (S = (7)/(2)) and antiferromagnetic (S = (3)/(2)) ground state was found to be feasible for one of the complexes upon variation of the organic radical geometry, namely, the dihedral angle between the organic radical moiety and the pyridine ring. The pattern of molecular orbital overlap was determined to be the key factor governing the exchange coupling in the modeled systems. Bonding π-type overlap provides antiferromagnetic coupling in all complexes of the para radicals. In the meta analogues, the spins are coupled through the σ orbitals. A low-spin ground state occurs whenever a continuous σ-overlap pathway is present in the complex. Ferromagnetic interaction requires σ-π orthogonality of the pyridine atomic orbitals and/or π-antibonding Mn-pyridine natural orbital overlap. Using an estimate of the donor-acceptor energy stabilization, the affinity of a given Mn(II) d-orbital to mix with the sp(2) orbital from pyridine can be predicted.
    Keywords: Quantum Theory ; Manganese -- Chemistry ; Organometallic Compounds -- Chemistry
    ISSN: 10895639
    E-ISSN: 1520-5215
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  • 2
    In: Physical Chemistry Chemical Physics, 2014, Vol.16(39), pp.21721-21731
    Description: The resonant Raman and UV/vis absorption spectra of two diradicalod compounds, methyl viologen and phenylene-extended viologen in their neutral state, have been simulated using multiconfigurational wavefunction methods. For methyl viologen, a good agreement with experiment is evidenced for the UV/vis absorption vibronic structure, provided dynamic correlation is accounted for to get the vibrational frequencies and normal modes. To some extent, the agreement with experiment is also good for the RR spectrum and the differences have been attributed to the presence in the experimental spectrum of surface-enhanced effects due to adsorption on the electrodes. As a result of inserting a phenylene group between the pyridinium units, the simulations have demonstrated that (i) in the UV/vis absorption spectrum, the relative intensity of the second band with respect to the 00 band increases, (ii) additional strong bands are observed in the RR spectrum, and (iii) the RR excitation profiles of the phenylene-extended viologen present less structure than in the case of methyl viologen where the relative mode intensities can strongly depend on the incident light wavelength. These differences are signatures of the extension of the effective conjugation length as well as of the increase in diradical character.
    Keywords: Absorptionsspektrum ; Resonanzspektrum ; Einfallendes Licht ; Elektrode ; Pyridinium ; Wellenfunktion ; Oberflächeneinfluss ; Phenylgruppe ; Wellenlänge ; Signatur ; Schwingungsfrequenz ; Chemistry;
    ISSN: 1463-9076
    E-ISSN: 1463-9084
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  • 3
    Language: English
    In: The journal of physical chemistry. B, 07 June 2012, Vol.116(22), pp.6543-52
    Description: The theoretical study addresses the type and nature of the transitions in the absorption spectra of octamers, dodecamers, and hexadecamers of the emeraldine salt-the conducting form of polyaniline. Each of the fully protonated oligomers is modeled in its lowest singlet (bipolaronic form) and highest possible multiplicity (polaronic form). Two configurations of the chloride counterions with respect to the oligomer chains are considered. All structures are optimized with BLYP/6-31G*/PCM, while the spectra are evaluated with CIS/6-31G*/PCM. The optical behavior of the bipolaronic and polaronic forms of the investigated systems is discussed and compared to relevant experimental data. The optical transitions at about 400 and 800 nm characteristic for the emeraldine salt are registered for all model structures. Weighed against experimental and earlier theoretical findings the results prove that CIS gives qualitatively correct electronic spectra of these conjugated species. While the two configurations have almost identical spectra in the highest multiplicity, the singlets' absorption conduct turns out to be sensitive to the counterions position. In all cases the most intensive absorption is the longest wavelength one in the near-IR region, but the number and oscillator strengths of the polaronic and bipolaronic bands are noticeably dissimilar. The bands of the low-spin oligomers are grouped, while those of the high-spin species cover the entire visible region. Each extension of the chain with one elementary unit contributes systematically a set of new bands to the spectrum. The possibility for a solvatochromic effect is estimated.
    Keywords: Aniline Compounds -- Chemistry
    ISSN: 15206106
    E-ISSN: 1520-5207
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  • 4
    Language: English
    In: The Journal of Physical Chemistry C, 06/12/2014, Vol.118(23), pp.12469-12484
    ISSN: 1932-7447
    E-ISSN: 1932-7455
    Source: American Chemical Society (via CrossRef)
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  • 5
    Language: English
    In: The journal of physical chemistry. B, 14 April 2011, Vol.115(14), pp.3765-76
    Description: Calculations for model oligomers of the emeraldine salt with UBLYP/6-31G*/PCM are performed. The models differ in number of monomers, in the position of the counterions (Cl(-)), and in multiplicity. The molecular features affected most prominently by the protonation, namely, structure, energetics, and electron and spin density partitioning are analyzed. The results show unequivocally that the studied molecular characteristics are essentially size independent. The octamer profiles of all parameters are repeated in the dodecamer and the hexadecamer. The bipolaronic forms are energetically more favorable than the polaronic ones within the chosen protocol. The electronic structure in the intermediate multiplicities differs from the bipolaronic and polaronic periodicity. The geometrical changes and electron density redistribution upon increase of multiplicity illustrate the pathway of intramolecular bipolaron-polaron conversion. The orbital analysis rationalizes the observed behavior of the oligomers.
    Keywords: Electron Spin -- Analysis ; Molecular Structure -- Analysis ; Oligomers -- Structure ; Polarons -- Analysis;
    ISSN: 15206106
    E-ISSN: 1520-5207
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  • 6
    Language: English
    In: The Journal of Physical Chemistry C, 01/28/2016, Vol.120(3), pp.2002-2012
    Description: DFT/TD-DFT investigation has been performed on pyridyl triazolatoplatinum(II) complexes with a systematic variation of the donor/acceptor properties of the ligand in order to illuminate its effect on the metallophilic intermolecular interaction in ground and excited states. The π-electronic properties of the pyridyl triazolate ligand were modified by the pyridine substituent: -N(CH3)2, -H, -CHO, or -CHC(CN)2. The simulations reveal that the donor/ acceptor strength of the substituent has a strong impact on the metallophilic interaction in the excited state and affects the emission properties at the supramolecular level. The theoretically derived structure-property relationships are corroborated by experimental data. Finally, it is proposed that the modification of the π-electronic character of the substituent (ligand field) can be applied in the molecular design of smart luminescent materials with light-driven metallophilic interactions.
    Keywords: Ligands ; Molecular-Modeling ; Excited-State ; Pyridine ; Luminescent-Materials ; Structure-Property-Relationship ; Substituent ; Experimental-Data ; Luminescence ; Ligand ; Molekulardesign ; Angeregter Zustand ; Pyridin ; Leuchtstoff ; Struktur-Eigenschaft-Beziehung ; Substituent ; Experimentelle Daten ; Lumineszenz ; Chemistry;
    ISSN: 1932-7447
    E-ISSN: 1932-7455
    Source: American Chemical Society (via CrossRef)
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  • 7
    Language: English
    In: The Journal of Physical Chemistry C, 02/02/2017, Vol.121(4), pp.2333-2343
    Description: Excited state design is an efficient approach toward new applications in molecular electronics spanning solar cells, artificial photosynthesis and biomedical diagnostics. Ruthenium(II)–polypiridyl based complexes are an example of molecular building blocks with tunable single and dual wavelength emission that can be controlled by excited state engineering via selective ligand modification. Here we investigate three new heteroleptic [Ru(bpy)2X]+ complex ions, where X represents pyridinyl or pyrazinyl derivatives of diazolates, providing tunable emission in the visible and infrared region. The dual emission is shown to arise from the presence of two excited states consisting of a triplet metal-to-ligand charge transfer state localized on a bipyridine ligand, 3MLCT (bpy), and a state that either is entirely localized on the X ligand or is partially delocalized also spanning part of the bipyridine ligands, 3MLCT(X). By a suitable choice of the X ligand, emission from 3MLCT(bpy) and 3MLCT (X) states can be rat...
    Keywords: Chemistry;
    ISSN: 1932-7447
    E-ISSN: 1932-7455
    Source: American Chemical Society (via CrossRef)
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  • 8
    Language: English
    In: Journal of Molecular Structure: THEOCHEM, 2010, Vol.954(1), pp.36-44
    Description: We report a theoretical study on the geometry characteristics and the electronic properties of bipolaron defects introduced in oligomers (tetramer to hexadecamer) of emeraldine salt. The main goal of the present investigation is to establish a quantum chemical method suitable for description of the target system and for determination of the oligomer segment perturbed by protonation. For the purpose, a series of first principles methods (HF and DFT) combined with different basis sets are tested and the influence of the medium (water) dielectric constant is estimated using PCM. It is shown that the optimized molecular geometry is critically dependent on the theoretical formalism applied. HF yields geometry of the tetramer substantially distorted from planarity and bipolaron, which is highly localized in the quinoid ring. The bipolaron produced by DFT tends to delocalize, thus enhancing the conjugation along the oligomer chain. The reliability of the separate methods is commented on the basis of a list of criteria such as reproducibility of available experimental geometry, spin contamination of wavefunctions and quantification of correlation effects. The BLYP/6-31G∗/PCM method is outlined as the most appropriate. It is found that irrespective of the oligomer chain length and the degree of protonation (partial or full) a bipolaron spreads on three phenyl rings and the nitrogen atoms bound to them.
    Keywords: Polyaniline ; Bipolaron ; Hf Vs. Dft ; Pcm ; Spin Contamination ; Size Effect ; Chemistry ; Physics
    ISSN: 0166-1280
    E-ISSN: 1872-7999
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  • 9
    Language: English
    In: The Scientific World Journal, Annual, 2012, Vol.12
    Description: Examination of the effects of mononucleotides on Sma nuc endonuclease originated from Gram negative bacterium Serratia marcescens displayed that any mononucleotide produced by Sma nuc during hydrolysis of DNA or RNA may regulate the enzyme activity affecting the RNase activity without pronounced influence on the activity towards DNA. The type of carbohydrate residue in mononucleotides does not affect the regulation. In contrast, the effects depend on the type of bases in nucleotides. AMP or dAMP was classified as a competitive inhibitor of partial type. GMP, UMP, and CMP were found to be uncompetitive inhibitors that suggest a specific site(s) for the nucleotide(s) binding in Sma nuc endonuclease.
    Keywords: Serratia -- Health Aspects ; Bacterial Proteins -- Health Aspects ; Protein-Protein Interactions -- Research ; Protein Research ; Microbiological Research
    ISSN: 1537-744X
    Source: Cengage Learning, Inc.
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  • 10
    Language: English
    In: The Scientific World Journal, 01 January 2012, Vol.2012
    Description: Examination of the effects of mononucleotides on Sma nuc endonuclease originated from Gram negative bacterium Serratia marcescens displayed that any mononucleotide produced by Sma nuc during hydrolysis of DNA or RNA may regulate the enzyme activity affecting the RNase activity without pronounced influence on the activity towards DNA. The type of carbohydrate residue in mononucleotides does not affect the regulation. In contrast, the effects depend on the type of bases in nucleotides. AMP or dAMP was classified as a competitive inhibitor of partial type. GMP, UMP, and CMP were found to be uncompetitive inhibitors that suggest a specific site(s) for the nucleotide(s) binding in Sma nuc endonuclease.
    Keywords: Sciences (General)
    E-ISSN: 1537-744X
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