Search results for "Theoretical Chemistry"
showing 10 items of 8456 documents
Ligand-Centred Fluorescence and Electronic Relaxation Cascade at Vibrational Time Scales in Transition-Metal Complexes
2015
Using femtosecond-resolved photoluminescence up-conversion, we report the observation of the fluorescence of the high-lying ligand-centered (LC) electronic state upon 266 nm excitation of an iridium complex, Ir(ppy)(3), with a lifetime of 70 +/- 10 fs. It is accompanied by a simultaneous emission of all lower-lying electronic states, except the lowest triplet metal-to-ligand charge-transfer ((MLCT)-M-3) state that shows a rise on the same time scale. Thus, we observe the departure, the intermediate steps, and the arrival of the relaxation cascade spanning similar to 1.6 eV from the (LC)-L-1 state to the lowest 3MLCT state, which then yields the long-lived luminescence of the molecule. This …
Dynamics of Metal Centers Monitored by Nuclear Inelastic Scattering
2005
Nuclear inelastic scattering of synchrotron radiation has been used now since 10 years as a tool for vibrational spectroscopy. This method has turned out especially useful in case of large molecules that contain a M\"ossbauer active metal center. Recent applications to iron-sulfur proteins, to iron(II) spin crossover complexes and to tin-DNA complexes are discussed. Special emphasis is given to the combination of nuclear inelastic scattering and density functional calculations.
Dimethyl 2-(1-methyl-3-oxo-1,3-dihydroisobenzofuran-1-yl)malonate
2020
In this work we report a facile access to a 3,3-disubstituted isobenzofuranone by tandem addition/cyclization reaction to methyl 2-acetylbenzoate in the presence of dimethyl malonate, under basic conditions.
The Photocycle of Bacteriophytochrome Is Initiated by Counterclockwise Chromophore Isomerization.
2022
Photoactivation of bacteriophytochrome involves a cis–trans photoisomerization of a biliverdin chromophore, but neither the precise sequence of events nor the direction of the isomerization is known. Here, we used nonadiabatic molecular dynamics simulations on the photosensory protein dimer to resolve the isomerization mechanism in atomic detail. In our simulations the photoisomerization of the D ring occurs in the counterclockwise direction. On a subpicosecond time scale, the photoexcited chromophore adopts a short-lived intermediate with a highly twisted configuration stabilized by an extended hydrogen-bonding network. Within tens of picoseconds, these hydrogen bonds break, allowing the c…
On the local mode behaviour of the XH2/XD2 and XD/XH fragments with respect to the deuterated species of the near local mode XH3(C3v ) molecule
2009
International audience; Effect of isotopic substitution in the near local mode, XH3(C3v), molecules is considered. On that basis it is shown that the spectroscopic properties of deuterated and/or di-deuterated isotopic species of the XH3(C3v) molecule with the value of interbond angle close to π/2 are analogous to the spectroscopic properties of its separate fragments: of a three-atomic local mode 'molecule' XH2/XD2 and of a diatomic XD/XH 'molecule'. The phosphine molecule is considered as an illustration.
Conformations and Energetics of Sulfur and Selenium Diimides
2003
The geometries and energetics of different conformations of sulfur and selenium diimides E(NR) 2 (E = S, Se; R = H, Me, 'Bu, C 6 H 3 Me 2 -2,6, SiMe 3 ) have been studied by using various ab initio and DFT molecular orbital techniques. The syn,syn conformation is found to be most stable for parent E(NH) 2 , but in general, the preferred molecular conformation for substituted chalcogen diimides is syn,anti. In the case of E(NH) 2 the present calculations further confirm that syn,syn and syn,anti conformations lie energetically close to each other. From the three different theoretical methods used, B3PW91/6.31G * proved to be the most suitable method for predicting the geometries of chalcogen…
The S … Hal and Se … Hal chalcogen bonding in a series of thiourea, selenourea and their derivatives
2021
The chalcogen bonding (ChB) in a series of thiourea, selenourea and their derivatives has been investigated in the present paper. Thus, selenourea and dimethylselenourea undergo dimerization and trimerization processes in the presence of various halogen species (1–5). Selenourea and dimethylselenourea form trimers 3–4 in the presence of lighter halogens (chlorine and bromine) through Se⋯Se chalcogen bonding. When moving to heavier halogen (iodine), the dimers 1–2 are formed. Thiourea and its derivatives also tend to make very strong S⋯S bonds and form dimers in the case of lighter halogens chlorine and bromine (compounds 6–7). However, the monomers separated by the iodine species are formed…
Pt(II) and Pd(II)-assisted coupling of nitriles and 1,3-diiminoisoindoline : Synthesis and luminescence properties of (1,3,5,7,9-pentaazanona-1,3,6,8…
2017
Treatment of trans-[PtCl2(NCR)2] 1 (R = Me (1a), Et (1b), o-ClC6H4 (1c), p-ClC6H4 (1d), p-(HCdouble bond; length as m-dashO)C6H4 (1e), p-O2NC6H4CH2 (1f)) with 1,3-diiminoisoindoline HNdouble bond; length as m-dashCC6H4C(NH)double bond; length as m-dashNH 2 gives access to the corresponding (1,3,5,7,9-pentaazanona-1,3,6,8-tetraenato)Pt(II) complexes [PtCl{NHdouble bond; length as m-dashC(R)Ndouble bond; length as m-dashC(C6H4)NCdouble bond; length as m-dashNC(R)double bond; length as m-dashNH}] 3a–f, in good yields (65–70%). The reaction of trans-[PdCl2(NCMe)2] 4a with 2 furnishes (1,3,5,7,9-pentaazanona-1,3,6,8-tetraenato)Pd(II) complex [PdCl{NHdouble bond; length as m-dashC(Me)Ndouble bond…
Dioxidomolybdenum(VI) and –tungsten(VI) complexes with tetradentate amino bisphenolates as catalysts for epoxidation
2017
Sixteen molybdenum and tungsten complexes with tripodal or linear tetradentate amino bisphenol ligands were studied as catalysts for the epoxidation of cis-cyclooctene, 1-octene, styrene, limonene and α-terpineol. These complexes can be divided into different categories upon key features, i.e. central metal (Mo versus W), side-arm donor (O versus N), hybridization of the N-donor (pyridine versus amine), ligand geometry (tripodal versus linear diamine) and sterical hindrance (Me versus tert-Bu substituents in the phenol part). All complexes can catalyse selectively the epoxidation of cis-cyclooctene by tert-butylhydroperoxide whereas the activities and selectivities towards other olefins (1-…
Addressing Dynamics at Catalytic Heterogeneous Interfaces with DFT-MD: Anomalous Temperature Distributions from Commonly Used Thermostats.
2022
Density functional theory-based molecular dynamics (DFT-MD) has been widely used for studying the chemistry of heterogeneous interfacial systems under operational conditions. We report frequently overlooked errors in thermostated or constant-temperature DFT-MD simulations applied to study (electro)catalytic chemistry. Our results demonstrate that commonly used thermostats such as Nose−Hoover, Berendsen, and simple velocity rescaling methods fail to provide are liable temperature description for systems considered. Instead, nonconstant temperatures and large temperature gradients within the different parts of the system are observed. The errors are not a “feature” of any particular code but …