Optical signatures of borico dyes: a TD-DFT analysis

International audienceUsing time-dependent density functional theory, we investigate the excited-state properties of a series of emissive dyes combining the properties of coumarins and fluoroborate compounds. These boron-iminocoumarins (borico) compounds have been synthesized very recently by Frath et al. (Chem Commun 49:4908, 2013) . We determine both their vertical and 0-0 energies, reproduce and analyze their characteristic experimental band shape, investigate the nature of the excited-states in large dyads containing two different fluoroborate complexes and design red-shifted compounds. We also consider an additional panel of fused coumarin-BODIPY emitters

Étude théorique de la stabilité et de la mobilité des atomes de gaz nobles dans le silicium et le carbure de silicium

Les propriétés d'un atome de gaz noble (He, Ne, Ar, Kr, Xe) en interaction avec une matrice de silicium ou de carbure de silicium cubique ont été déterminées à l'aide de simulations numériques ab initio et d'une technique de recherche des points cols, afin de mieux comprendre les premiers stades de la formation de défauts étendus de type bulle dans ces matériaux. Nous avons ainsi obtenu les configurations les plus stables et leurs énergies de formation, de type interstitiel dans un cristal parfait et de type complexe en présence de monolacunes et de bilacunes. Dans un second temps, nos simulations ont permis la détermination des mécanismes de migration des interstitiels de gaz nobles et des complexes, ainsi que les énergies d'activation associées, dans le cas du silicium. En particulier, nous proposons un nouveau mécanisme d'échange pour la migration d'un complexe gaz noble-bilacune. Dans tous les cas, la plupart des résultats s'explique par un effet stérique découlant du caractère inerte des gaz nobles, avec quelques exceptions concernant l'hélium. Enfin, les mécanismes permettant à un atome d'hélium ou de néon de sortir ou d'entrer dans une bulle déjà formée dans le silicium, ont été déterminés en prenant en compte l'influence de la pression et de la température au sein de la bulle. Ces travaux ont permis de montrer la perméabilité de la surface de Si, ainsi que d'estimer une pression interne comprise entre 3 et 6 GPa pour une bulle remplie d'hélium, en accord avec les expériences.The properties of a noble gas atom (He, Ne, Ar, Kr, Xe) interacting with a silicon or a cubic silicon carbide matrix have been determined using first-principles numerical simulations and a saddle points searching technique, in order to better understand the first steps of the formation of extended defects such as bubbles in these materials. Hence, we have obtained the most stable configurations, interstitials in a perfect crystal and complexes in presence of mono and divacancies, as well as their formation energies. In a second step, our simulations have allowed us to determine the migration mechanisms of noble gas interstitials and of complexes, and the associated activation energies, in the case of silicon. In particular, we propose a new exchange mechanism for the migration of a noble gasdivacancy complex. In all cases, most of our results can be explained by a sterical effect ensueing from the inert character of noble gas, with few exceptions for He. Finally, the mechanisms allowing for a He and Ne atom to enter or escape an already formed bubble in silicon, have been computed taking into account the influence of pressure and temperature into the bubble. These works revealed the permeability of the silicon surface, and indicate that the internal pressure for a He-filled bubble ranges from 3 to 6 GPa, in agreement with experiments.POITIERS-BU Sciences (861942102) / SudocSudocFranceF

Excited-states of BODIPY–cyanines: ultimate TD-DFT challenges?

International audienceWe have investigated with first principle approaches the optical signatures of derivs. combining a BODIPY core and cyanine-​like side chains. More precisely, we computed the 0-​0 energies with a Time-​Dependent D. Functional Theory (TD-​DFT) procedure systematically including both vibrational and continuum solvent effects. However, despite its refinement, this protocol yields large deviations compared to exptl. refs. For this reason, we turned towards a mixed protocol where the potential energy surfaces of both the ground and the first electronically excited states are evaluated with TD-​DFT whereas the vertical transition energies (both absorption and emission) are detd. with the CIS(D)​/SOS-​CIS(D) approaches, that include a perturbative correction for the double excitations. The pros and cons of such a mixed method are discussed in the framework of these challenging dyes

Boranil and related NBO Dyes: Insights From Theory

International audienceThe simulations of excited-state properties, that is, the 0-0 energies and vibronic shapes, of a large panel of fluorophores presenting a NBO atomic sequence have been achieved with a Time-Dependent Density Functional Theory (TD-DFT) approach. We have combined eight hybrid exchange-correlation functionals (B3LYP, PBE0, M06, BMK, M06-2X, CAM-B3LYP, ωB97X-D, and ωB97) to the linear-response (LR) and the state specific (SS) Polarizable Continuum Model (PCM) methods in both their equilibrium (eq) and nonequilibrium (neq) limits. We show that the combination of the SS-PCM scheme to a functional incorporating a low amount of exact exchange can yield unphysical values for molecules presenting large increase of their dipole moments upon excitation. We therefore apply a functional possessing a large exact exchange ratio to simulate the properties of NBO dyes, including large dyads

Understanding the mechanism of carbon dioxide uptake by a photoresponsive MOF

255th National Meeting and Exposition of the American-Chemical-Society (ACS) - Nexus of Food, Energy, and Water, New Orleans, LA, MAR 18-22, 201

Interplay between solvent models and predicted optical spectra: A TD-DFT study of 7-OH-coumarin

Using time-dependent density functional theory, we investigate the solvatochromic effects on the optical spectra of a typical hydroxy coumarin, considering its enol, keto, anionic and cationic forms. The absorption and fluorescence transitions energies have been computed within both the linear-response (LR) and the more refined state specific (SS) approaches, with explicit solvent molecules. These energies have also been used to compute 0-0 transitions and vibrationally resolved spectra. We show that the SS approach is mandatory to describe the solvent response due to the large increase of dipole moment upon the excitation while hydrogen bonds tune both absorption and emission energies. (C) 2012 Elsevier B. V. All rights reserved

Tight-binding modeling of interstitial ordering processes in metals: Application to zirconium hydrides

International audienceWe present here a theoretical study of ordering processes in metal-hydrogen compounds based on a generalized perturbation method and on tight-binding coherent potential approximation. This approach is illustrated for zirconium hydrides, in which case we demonstrate that a cluster expansion of the ordering energy can be limited to effective pair interactions, the leading one being between hydrogen atoms in third-neighbor positions. These results are quantitatively confirmed by comparison to density functional theory calculations and qualitatively interpreted through orbital symmetry analysis. The method is then applied first to draw a preliminary Zr-H phase diagram and then to characterize the effect of lattice deformation on the ordering processes in zirconium hydrides

Understanding the mechanism of carbon dioxide uptake by a photoresponsive MOF

255th National Meeting and Exposition of the American-Chemical-Society (ACS) - Nexus of Food, Energy, and Water, New Orleans, LA, MAR 18-22, 201

Choosing a Functional for Computing Absorption and Fluorescence Band Shapes with TD-DFT

The band shapes corresponding to both the absorption and emission spectra of a set of 20 representative conjugated molecules, including recently synthesized structures, have been simulated with a Time-Dependent Density Functional Theory model including diffuse atomic orbitals and accounting for bulk solvent effects. Six hybrid functionals, including two range separated hybrids (B3LYP, PBE0, M06, M06-2X, CAM-B3LYP, and LC-PBE) have been assessed in light of the experimental band shapes obtained for these conjugated compounds. Basis set and integration grid effects have also been evaluated It turned out that all tested functionals but LC-PBE reproduce the main experimental features for both absorption and fluorescence, though the average errors are significantly larger for the latter phenomena. No single functional stands out as the most accurate for all aspects, but B3LYP yields the smallest mean absolute deviation. On the other hand, M06-2X could be a valuable compromise for excited states as it reproduces the 0-0 energies and also gives reasonable band shapes: The typical mean absolute deviations between the relative positions of the experimental and theoretical peaks in the vibrationally resolved spectra are ca. 100 cm(-1) for absorption and 250 cm-1 for emission. In the same time, the relative intensities of the different maxima are reproduced by TD-DFT with a ca. 10-15% accuracy

Optical signatures of OBO fluorophores: a theoretical analysis

International audienceDioxaborines dyes, based on the OBO atomic sequence, constitute one promising series of molecules for both organic electronics and bioimaging applications. Using Time-Dependent Density Functional Theory, we have simulated the optical signatures of these fluoroborates. In particular, we have computed the 0−0 energies and shapes of both the absorption and the emission bands. To assess the importance of solvent effects three polarization schemes have been applied within the Polarizable Continuum Model: the linearresponse (LR), the corrected linear-response (cLR), and the state-specific (SS). We show that the SS approach is unable to yield consistent chemical trends for these challenging compounds that combine charge-transfer and cyanine characters. On the contrary, LR and cLR are more effective in reproducing chemical trends in OBO dyes. We have applied our computational protocol not only to analyze the signatures of existing dyes but also to design structures with red-shifted absorption and emission bands