Search results for "Basis-Sets"
showing 10 items of 16 documents
The first example of cofacial bis(dipyrrins)
2016
International audience; Two series of cofacial bis(dipyrrins) were prepared and their photophysical properties as well as their bimolecular fluorescence quenching with C-60 were investigated. DFT and TDDFT computations were also performed as a modeling tool to address the nature of the fluorescence state and the possible inter-chromophore interactions. Clearly, there is no evidence for such interactions and the bimolecular quenching of fluorescence, in comparison with mono-dipyrrins, indicates that C-60-bis(dipyrrin) contacts occur from the outside of the "mouth" of the cofacial structure.
Intermolecular oxidative dehydrogenative 3,3′-coupling of benzo[b]furans and benzo[b]thiophenes promoted by DDQ/H+: total synthesis of shandougenine B
2016
With an excess of a strong acid, 2,3-dichloro-5,6-dicyano-1,4-quinone (DDQ) is shown to promote metal-free intermolecular oxidative dehydrogenative (ODH) 3,3'-coupling of 2-aryl-benzo[b]furans and 2-aryl-benzo[b]thiophenes up to 92% yield as demonstrated with 9 substrates. Based on the analysis of oxidation potentials and molecular orbitals combined with EPR, NMR and UV-Vis observations, the studied reaction is initiated by a DDQ-substrate charge transfer complex and presumably proceeds via oxidation of the substrate into an electrophilic radical cation that further reacts with another molecule of a neutral substrate. The coupling reactivity can easily be predicted from the oxidation potent…
Experimental and DFT studies on competitive heterocyclic rearrangements. part 2: A one-atom side-chain versus the classic three-atom side-chain (Boul…
2007
The experimental investigation of the base-catalyzed rearrangements of 3-acylamino-1,2,4-oxadiazoles evidenced a new reaction pathway which competes with the well-known ring-degenerate Boulton- Katritzky rearrangement (BKR). The new reaction consists of a one-atom side-chain rearrangement that is base-activated, occurs at a higher temperature than the BKR, and irreversibly leads to the corresponding 2-acylamino-1,3,4-oxadiazoles. An extensive DFT study is reported to elucidate the proposed reaction mechanism and to compare the three possible inherent routes: (i) the reversible three-atom side-chain ring-degenerate BKR, (ii) the ring contraction-ring expansion route (RCRE), and (iii) the one…
Assessment of the Potential Energy Hypersurfaces in Thymine within Multiconfigurational Theory: CASSCF vs. CASPT2
2016
The present study provides new insights into the topography of the potential energy hypersurfaces (PEHs) of the thymine nucleobase in order to rationalize its main ultrafast photochemical decay paths by employing two methodologies based on the complete active space self-consistent field (CASSCF) and the complete active space second-order perturbation theory (CASPT2) methods: (i) CASSCF optimized structures and energies corrected with the CASPT2 method at the CASSCF geometries and (ii) CASPT2 optimized geometries and energies. A direct comparison between these strategies is drawn, yielding qualitatively similar results within a static framework. A number of analyses are performed to assess t…
A Comparative Analysis of the Electrophilicity of Organic Molecules between the Computed IPs and EAs and the HOMO and LUMO energies
2007
[EN] The electrophilicity index, omega, of a series of substituted ethylenes used in some relevant organic reactions has been evaluated from the ionization potential JP) and the electron affinity (EA) computed by vertical ionization at the B3LYP/aug-cc-PVTZ level. The corresponding electrophilicity values are well correlated with those obtained from the HOMO and LUMO energies of the neutral molecules. The good linear correlation found between omega(I,A) and omega(H,L)(LBS), and between omega(H,L)(LBS) and omega(H,L)(SBS) allows to confirm the use of the easily available B3LYP/6-31G(*) HOMO and LUMO energies to obtain reasonable values of the global electrophilicity index of organic molecule…
Molecular structures of Se(SCH3)2 and Te(SCH3)2 using gas-phase electron diffraction and ab initio and DFT geometry optimisations
2005
The molecular structures of Se(SCH3)2 and Te(SCH3)2 were investigated using gas-phase electron diffraction (GED) and ab initio and DFT geometry optimisations. While parameters involving H atoms were refined using flexible restraints according to the SARACEN method, parameters that depended only on heavy atoms could be refined without restraints. The GED-determined geometric parameters (rh1) are: rSe-S 219.1(1), rS-C 183.2(1), rC-H 109.6(4) pm; S-Se-S 102.9(3), Se-S-C 100.6(2), S-C-H (mean) 107.4(5), S-Se-S-C 87.9(20), Se-S-C-H 178.8(19)° for Se(SCH3)2, and rTe-S 238.1(2), rS-C 184.1(3), rC-H 110.0(6) pm; S-Te-S 98.9(6), Te-S-C 99.7(4), S-C-H (mean) 109.2(9), S-Te-S-C 73.0(48), Te-S-C-H 180.…
Excited-state non-radiative decay in stilbenoid compounds: An: Ab initio quantum-chemistry study on size and substituent effects
2019
In the framework of optoelectronic luminescent materials, non-radiative decay mechanisms are relevant to interpret efficiency losses. These radiationless processes are herein studied theoretically for a series of stilbenoid derivatives, including distyrylbenzene (DSB) and cyano-substituted distyrylbenzene (DCS) molecules in vacuo. Given the difficulties of excited-state reaction path determinations, a simplified computational strategy is defined based on the exploration of the potential energy surfaces (PES) along the elongation, twisting, and pyramidalization of the vinyl bonds. For such exploration, density functional theory (DFT), time-dependent (TD)DFT, and complete-active-space self-co…
Calculation of vibrationally resolved absorption and fluorescence spectra of the rylenes
2020
A generating function method was used to simulate the vibrationally resolved absorption and emission spectra of perylene, terrylene and quaterrylene. This method operates on the basis of adiabatic excitation energies and electronic ground and excited state vibrational frequencies. These parameters were calculated using density functional theory with the PBE0 functional for perylene and terrylene and with the BH-LYP functional for quaterrylene. The vertical excitation energies of the lower excited states were calculated using functionals with differing amounts of Hartree-Fock exchange. The optimal functional for each molecule was chosen by comparing these energies to literature excitation en…
Random Structural Modification of a Low-Band-Gap BODIPY-Based Polymer
2017
International audience; A BODIPY thiophene polymer modified by extending conjugation of the BODIPY chromophore is reported. This modification induces tunability of energy levels and therefore absorption wavelengths in order to target lower energies.
Modelling Photoionisation in Isocytosine: Potential Formation of Longer‐Lived Excited State Cations in its Keto Form
2021
Abstract Studying the effects of UV and VUV radiation on non‐canonical DNA/RNA nucleobases allows us to compare how they release excess energy following absorption with respect to their canonical counterparts. This has attracted much research attention in recent years because of its likely influence on the origin of our genetic lexicon in prebiotic times. Here we present a CASSCF and XMS‐CASPT2 theoretical study of the photoionisation of non‐canonical pyrimidine nucleobase isocytosine in both its keto and enol tautomeric forms. We analyse their lowest energy cationic excited states including 2π+ , 2nO+ and 2nN+ and compare these to the corresponding electronic states in cytosine. Investigat…