Home About us Contact
|
Home About us Contact | ||
|
|
||
Time-dependent DFT (time-dependent + dft)
Selected AbstractsMetal-Induced Tautomerization of p - to o -Quinone Compounds: Experimental Evidence from CuI and ReI Complexes of Azophenine and DFT StudiesCHEMISTRY - A EUROPEAN JOURNAL, Issue 1 2004Stéphanie Frantz Abstract Azophenine (7,8-diphenyl-2,5-bis(phenylamino)- p -quinonediimine, Lp) reacts with [Cu(PPh3)4](BF4) or [Re(CO)5Cl] to yield the (Ph3P)2Cu+ or [(OC)3ClRe] complex of the tautomeric form 7,8-diphenyl-4,5-bis(phenylamino)- o -quinonediimine, Lo, as evident from structure determinations and from very intense metal-to-ligand charge transfer (MLCT) transitions in the visible region. Time-dependent DFT (TD-DFT) calculations on model complexes [(N,N)Re(CO)3Cl] confirm the spectroscopic results, showing considerably higher oscillator strengths of the MLCT transition for the o -quinonediimine complexes in comparison to compounds with N,N=1,4-dialkyl-1,4-diazabutadiene. The complexes are additionally stabilized through hydrogen bonding between two now ortho -positioned NHPh substituents and one fluoride of the BF4, anion (Cu complex) or the chloride ligand (Re complex). DFT Calculations on the model ligands p -quinonediimine or 2,5-diamino- p -quinonediimine and their ortho -quinonoid forms with and without Li+ or Cu+ are presented to discuss the relevance for metal-dependent quinoproteins. [source] Calculated spectral properties of perylene orange, perylene red, and their complex with sodium azideINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 13 2007Anuar Aldongarov Abstract Using the method of density functional theory in approximating B3LYP with the basis set 6-31G(d) the computations of structures of the following dyes 2,2,- N - N,-di(1,3-diisopropylbenzene)-diimide 3,4,9,10-perylenetethracarbon acid (Perylene Orange-PO) and 1,6,7,12-tethraphenyl ether 2,2,- N,N,-di(1,3-diisopropylbenzene)-diimide 3,4,9,10-perylenetethracarbon acid (Perylene Red-PR) were performed. It was revealed that PO and PR have nonplanar structures. On the basis of the predicted geometrical structures and molecular orbitals of S0 ground state their theoretical UV-vis spectra, which are in good agreement with experiment, were obtained by applying time-dependent DFT (TDDFT) method. In addition, the calculations of complex [PR , NaN3] and its UV-vis spectrum, which was compared with the observed electron spectrum of PR ethanol solution in the presence of NaN3 under the laser irradiation at 532 nm, were carried out. By using DFT method at B3LYP level the calculations of the assumed complex were made where the reaction coordinate was the distance between Na+ and carbonyl group O atom. It was suggested that [PR , NaN3] complex formation involves transition of PR to the triplet state which brings about formation of PR anion. New peak at 793 nm in UV-vis spectrum of this solution under the laser irradiation at 532 nm is supposed to be a PR anion band. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 [source] Computational study of titanium (IV) complexes with organic chromophoresINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 6 2006Ivan Kondov Abstract A computational study of small titanium complexes with the chromophores catechol, alizarin, and coumarin 343 is presented. Employing density functional theory (DFT), the ground-state geometries, energies, and harmonic frequencies of the different compounds are calculated. Furthermore, time-dependent DFT and the configuration interaction singles (CIS) method are used to determine excitation energies and excited-state gradients. Based on these results, the character of the excited states as well as electronic-vibrational coupling strengths are analyzed, and the implications for electron-transfer reactions at dye,semiconductor interfaces are discussed. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2006 [source] Structural, electronic, bonding, magnetic, and optical properties of bimetallic [RunAum]0/+ (n + m , 3) clustersJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 16 2010Dimitrios N. Garbounis Abstract The structural, electronic, bonding, magnetic, and optical properties of bimetallic [RunAum]0/+ (n + m , 3; n, m = 0,3) clusters were computed in the framework of the density functional theory (DFT) and time-dependent DFT (TD-DFT) using the full-range PBE0 non local hybrid GGA functional combined with the Def2-QZVPP basis sets. Several low-lying states have been investigated and the stability of the ground state spinomers was estimated with respect to all possible fragmentation schemes. Molecular orbital and population analysis schemes along with computed electronic parameters illustrated the details of the bonding mechanisms in the [RunAum]0/+ clusters. The TD-DFT computed UV-visible absorption spectra of the bimetallic clusters have been fully analyzed and compared to those of pure gold and ruthenium clusters. Assignments of all principal electronic transitions are given and interpreted in terms of contribution from specific molecular orbital excitations. © 2010 Wiley Periodicals, Inc. J Comput Chem 2010 [source] Conformations and properties of the L -tryptophyl-containing peptides in solution, depending on the pH,Theoretical study vs. experimentsBIOPOLYMERS, Issue 8 2010Bojidarka B. Ivanova Abstract The conformational preference and electronic properties of three L -tryptophyl-containing dipeptides, i.e., glycyl- L -tryptophane (H-Gly-Trp-OH), L -alanyl- L -tryptophane (H-Ala-Trp-OH), and L -methionyl- L -tryptophane (L -Met-Trp-OH) in solution depending on the pH of the media are studied both theoretically and experimentally. The effect of the protonation of the COO, and deprotonation of the NH as well as the alkaline hydrolysis of the amide fragment in a strong basic media on the electronic spectra are discussed. Ab initio and density functional theory (DFT) methods as well as the time-dependent DFT (TD-DFT) method as a function of the basis set are performed with a view to obtain the geometry and electronic properties of all of the species as well as the intermediate, obtained in the alkaline hydrolysis mechanism. © 2010 Wiley Periodicals, Inc. Biopolymers 93: 727,734, 2010. This article was originally published online as an accepted preprint. The "Published Online" date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com [source] Photoinduced Excited State Intramolecular Proton Transfer of New Schiff Base Derivatives with Extended Conjugated Chromophores: A Comprehensive Theoretical SurveyCHINESE JOURNAL OF CHEMISTRY, Issue 6 2010Qi Wang Abstract This paper presented comprehensive theoretical investigation of excited state intramolecular proton transfer (ESIPT) of four new large Schiff base derivatives with extended conjugated chromophores. The properties of the ground state and the excited state of phototautomers of C1 to C4 [C1: 2-(4,-nitro-stilbene-4-ylimino)methylphenol; C2: 2-(4,-cyano-stilbene-4-ylimino)methylphenol; C3: 2-(4,-methoxyl-stilbene-4-ylimino)methylphenol; C4: 2-(4,- N,N -diethylamino-stilbene-4-ylimino)methylphenol], which included geometrical parameter, energy, rate constant, frontier orbit, Mulliken charge, dipole moment change, were studied by DFT (density functional theory), CIS (configuration interaction singles-excitation), TDDFT (time-dependent DFT) methods to analyze the effects of chromophore part on the occurrence of ESIPT and the role of substituent groups. The structural parameter calculation showed that the shorter RHN and larger ROH from enol to enol* form, and less twisted configuration in the excited state implied that these molecules could undergo ESIPT as excitation. Stable transition states and a low energy barrier were observed for C1 to C4. This suggested that chromophore part increased some difficulty to undergo ESIPT for these molecules, while the possibility of occurrence of ESIPT was quite high. The negative ,E* (,9.808 and ,9.163 kJ/mol) of C1 and C2 and positive ,E* (0.599 and 1.029 kJ/mol) of C3 and C4 indicated that withdrawing substituent groups were favorable for the occurrence of ESIPT. The reaction rate constants of proton transfer of these compounds were calculated in the S0 and S1 states respectively, and the high rate constants of these compounds were observed at S1 state. C1 even reached at 1.45×1015 s,1 in the excited state, which is much closed to 2.05×1015 s,1 of the parent moiety (salicylidene methylamine). Electron-donating and electron-withdrawing substituent groups had different effects on the electron density distribution of frontier orbits and Mulliken charges of the atoms, resulting in different dipole moment changes in enol*,keto* process. These differences in turn suggested that C1 and C2 had more ability to undergo ESIPT than C3 and C4. The ultraviolet/visible absorption spectra, normal fluorescence emission spectra and ESIPT fluorescence emission spectra of these compounds were predicted in theory. [source] Chirality of camphor derivatives by density functional theory,CHIRALITY, Issue 10 2006Hayato E. Morita Abstract Infrared (IR) and vibrational circular dichroism (VCD) spectra of chiral camphor, camphorquinone and camphor-10-sulfonic acid (CSA), known as standard compounds for electronic circular dichroism (ECD) spectroscopy, are measured and their vibrational frequencies, infrared intensities, and rotational strengths are calculated using density functional theory (DFT). The observed IR and VCD spectra of chiral camphor and camphorquinone in carbon tetrachloride solution are reproduced by the DFT calculations, but those of CSA are not. DFT calculations of hydration models, where an anionic CSA specifically binds a few water molecules, are carried out. The average of the simulated VCD spectra in the hydration models is more consistent with the observed spectra. In addition, the wavelengths and dipole and rotational strengths for chiral camphor, camphorquinone, anionic CSA, and the hydration models were calculated by time-dependent DFT. In the region of 280,300 nm, the calculated wavelengths of the ECD bands for chiral camphor and camphorquinone coincide with the observed wavelengths that have been reported, and the calculated wavelengths for the hydration models are closer to the observed wavelengths reported than are those calculated for chiral anionic CSA. Consequently, the analysis combined with VCD and ECD spectroscopy using DFT calculations can elucidate the chirality of optically active molecules, even in an aqueous solution. Chirality, 2006. © 2006 Wiley-Liss, Inc. [source] | ||||||||||