CAM-B3LYP Levels Research Articles

The Effect of the π-Electron Delocalization Curvature on the Two-Photon Circular Dichroism of Molecules with Axial Chirality.

Herein we report on the theoretical-experimental study of the effect of curvature of the π-electron delocalization on the two-photon circular dichroism (TPCD) of a family of optically active biaryl derivatives (S-BINOL, S-VANOL, and S-VAPOL). The comparative analysis of the influence of the different transition moments to their corresponding TPCD rotatory strength reveals an enhanced contribution of the magnetic transition dipole moment on VAPOL. This effect is hereby attributed to the additional twist in the π-electron delocalization on this compound. TPCD measurements were done using the double L-scan technique in the picosecond regime. Theoretical calculations were completed using modern analytical response theory, within a time-dependent density functional theory (TD-DFT) approach, at both, B3LYP and CAM-B3LYP levels, with the aug-cc-pVDZ basis set for S-BINOL and S-VANOL, and 6-31G* for S-VAPOL. Solvent effects were included by means of the polarizable continuum model (PCM) in CH2Cl2.

Mechanistic DFT studies – helicate-type complexes with different alcylic spacers

Metal-controlled self-assembly of complexes is of high interest in the field of Supramolecular Chemistry [1,2]. In the current study, we synthesized binuclear complexes with different spacers and study the influence of chain length on their relative energy. The considered complexes prefer the zigzag conformation. Thus a bridge with an odd number of methylene units forms a meso-Helicate (ΔΛ or ΛΔ) and one with an even number leads to a Helicate (ΔΔ or ΛΛ) (figure ​(figure1)1) [3,4]. Figure 1 Geometrically optimized complexes with Ti(IV); left: energies of the complexes with different alcylic spacers; right: ΔΔ and ΛΔ form of the complex with a propylene spacer. Comparison of the calculated transition energies for the non-dissociative interconversions of the diastereomeres with experimental results provides inside into the isomerization process. Moreover, insertion of different cations (templates) into the cavities of the binuclear complexes and corresponding calculations allow prediction of their influence on the isomerization. Enlargement of the studied system results in binuclear complexes with imino-bridged ligands. The obtained computational results provide a possible explanation for the experimentally observed high diastereoselectivity. As the DFT functionals like B3LYP do not describe long-range interactions properly, we chose the coulomb-attenuating method CAM-B3LYP [5] which corrects the exchange interaction at long range. The complexes with Ti(IV) in their helical or meso form have been geometrically optimized at the CAM-B3LYP level of theory with the TZVP basis set and MDF10 as ECP for Ti(IV) as implemented in the program package Gaussian09 [6].

Evaluation of the Nonlinear Optical Properties for Annulenes with Hückel and Möbius Topologies.

Recently, much attention has been focused on the design and synthesis of molecules with aromatic Möbius topology. One of the most promising applications is the manufacture of Hückel-to-Möbius topological optical switches with high nonlinear optical properties. In this work, we evaluate the electronic and vibrational contributions to static and dynamic nonlinear optical properties of the CS Hückel and C2 Möbius topologies synthesized by Herges and co-workers (Ajami, D. et al. Nature2003, 426, 819). Calculations are performed at the HF, B3LYP, BHandHLYP, BMK, M052X, CAM-B3LYP, and MP2 levels with the 6-31+G(d) basis set. Our results conclude that the BHandHLYP, M052X, and CAM-B3LYP methods correctly reproduce the X-ray crystal structure and provide similar nonlinear optical properties.

Conformational study of the structure of free 12-thiacrown-4 and some of its cation metal complexes

Conformational search of 12-thiacrown-4, 12t4, was performed using the CONFLEX method and the MMFF94S force field whereby 156 conformations were predicted. Optimized geometries of the 156 predicted conformations were calculated at the HF, B3LYP, CAM-B3LYP, M06, M06L, M062x and M06HF levels using the 6-311G** basis set. The correlation energy was recovered at the MP2 level using the same 6-311G** basis set. Optimized geometries at the MP2/6-311G** level and G3MP2 energies were calculated for some of the low energy conformations. The D4 conformation was predicted to be the ground state conformation at all levels of theory considered in this work. Comparison between the dihedral angles of the predicted conformations indicated that for the stability of 12t4, a SCCS dihedral angle of 180° requirement is more important than a gauche CSCC dihedral angle requirement. Conformational search was performed also for the 12t4–Ag+, Bi3+, Cd2+, Cu+ and Sb3+ cation metal complexes using the CONFLEX method and the CAChe-augmented MM3 and MMFF94S force fields. Conformations with relative energies less than 10 kcal/mol at the MP2/6-31+G*//HF/6-31+G* level, with double zeta quality basis set on the metal cations, were considered for computations at the same levels as those used for free 12t4, using also the 6-311G** basis set. The cc-pVTZ-pp basis set was used for the metal cations. The predicted ground state conformations of the 12t4–Ag+, Bi3+, Cd2+, Cu+ and Sb3+ cation metal complexes are the C4, C4, C4, C2v and C4 conformations, respectively. This is in agreement with the experimental X-ray data for the 12t4–Ag+ and Cd2+ cation metal complexes, but experimentally by X-ray, the 12t4–Bi3+ and Cu+ cation metal complexes have Cs and C4 structures, respectively.

The excited electronic states of adenine-guanine stacked dimers in aqueous solution: a PCM/TD-DFT study

The excited-state behavior in the Franck-Condon (FC) region of the d(ApG) and d(GpA) dinucleoside monophosphate (A = adenine, G = guanine) is investigated in aqueous solution by means of time-dependent Density Functional Calculations, including solvent effects by the Polarizable Continuum Model and using three different functionals, i.e. PBE0, M052X, and CAM-B3LYP. Our analysis, focussed mainly on the two stacked dimers formed by 9-methyl-adenine and 9-methyl-guanine in the same arrangement as in the B structure of DNA (AG and GA), provides absorption and ECD spectra in very good agreement with their experimental counterparts. The sequence dependence of the dinucleoside excited-state properties is fully reproduced and it is explained on the grounds of the different interactions among the nucleobases' frontier orbitals existing in AG and GA. Our calculations predict that the 9Me-G --> 9Me-A charge transfer (CT) excited state is, at least, as stable as the lowest energy bright state of the dimers and that it is more stable than the intra-strand CT state in the (9Me-A)(2) stacked dimer. On the other hand, in AG and GA the 9Me-G --> 9Me-A CT state is significantly coupled to the dimer bright excited states and deviations from the decay rate predicted on the ground of the Marcus Theory are possible.