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A multi-environment computational approach is proposed to study the modulation of the emission behavior of the triphenylamine (Z)-4-benzylidene-2-methyloxazol-5(4H)-one (TPA-BMO) molecule [Tang et al., J. Phys. Chem. C 119, 21875 (2015)]. We aim at (1) proposing a realistic description of the molecule in several environments (solution, aggregate, polymer matrix), (2) modelling its absorption and emission properties, and (3) providing a qualitative understanding of the experimental observations by highlighting the photophysical phenomena leading to the emission modulation. To this purpose, we rely on (TD-)DFT calculations and classical Molecular Dynamics simulations, but also on the hybrid ONIOM QM/QM' approach and the in situ chemical polymerization methodology. In low-polar solvents, the investigation of the potential energy surfaces and the modulation of the emission quantum yield can be attributed to possible photophysical energy dissipation caused by low-frequency vibrational modes. In the aggregate and in the polymer matrix, the emission modulation can be qualitatively interpreted in terms of the possible restriction of the intramolecular vibrations. For these two systems, our study highlights that a careful modelling of the environment is far from trivial but is fundamental to model the optical properties of the fluorophore.

Taking advantage of the compensation between Basis Set Superposition Error and Basis Set Incompleteness Error, a new basis is developed to improve the performances of Double Hybrid (DH) functionals in reproducing interaction energies in weak noncovalent systems. Using a self-consistent formula, containing only energy terms computed for dimers and the corresponding monomers at the same level of theory, the exponents of the more external functions of the Def2-SVPD basis were optimized on three systems extracted from the S22 set. The transferability of the obtained basis set, called DH-SVPD, was then tested on five benchmark sets, and it is assessed by considering six DH functionals, eventually corrected with empirical dispersion corrections (for a total of 16 methods). Our results show that this simple approach is able to provide accurate results for noncovalent interaction energies of all the considered systems, and, in particular, to recover the performances obtained by coupling the DH functionals with empirical dispersion corrections.

International audience; Aryl- and hetaryl-substituted acetylenes undergo regio- and stereoselective silylzincation by reaction with [(Me3Si)3Si]2Zn in the presence of Et2Zn (10–110 mol%) as additive. The distinctive feature of this addition across the C−C triple bond is its trans stereoselectivity. The radical nature of the silylzincation process is supported by diagnostic experiments and DFT calculations, which also corroborate the role played by steric effects to obtain that stereoselectivity. The procedure can be combined in one-pot with the copper(I)-mediated electrophilic substitution of the C(sp2)−Zn bond, with retention of the double bond geometry. This makes it valuable for the synthesis of stereodefined di- and trisubstituted vinylsilanes.

Luminescence of furimamide is 150 times brighter than oxidized luciferins in firefly and renilla luciferase. However, we do not have a clear understanding of the structure, function, and dynamic behavior of the nanoluciferase-furimamide complex. Here, for the first time, the absorption and emission properties of eight different possible light emitter forms of furimamide were investigated using the time-dependent density functional theory (TD-DFT) method in the gas phase and aqueous solution. The emission oscillator strengths in the gas phase showed that emission transition may be forbidden for some forms, and fluorescence would not occur. Besides, the charge transfer (CT) as well as the orbitals involved in the transitions were analyzed. Furthermore, molecular docking results showed that furimamide is situated inside the central cavity (β-barrel) of nanoluciferase. Analysis of the trajectory of molecular dynamics (MD) simulations suggested a less compact structure of protein in the presence of furimamide in comparison to its apo form. The quantum mechanical/molecular mechanical (QM/MM) spectroscopic properties of one form in the binding site of nanoluciferase were investigated. The evolution of the excited states (ESs) of furimamide in the binding pocket of the protein confirmed that after photoexcitation and during the relaxation of the system, a crossing point between the first two singlet ESs exists. Thus, the initially populated S2 (a π→π* transition) becomes the first singlet excited state.

International audience; Ferrociphenols, especially those possessing a heterocycle at the terminus of an aliphatic chain, display strong anticancer activity via a novel redox mechanism that generates active metabolites such as quinone methides (QMs). X-ray crystallography and UV-Vis spectroscopy reveal that the specific lone pair (lp)-π interaction between a carbonyl group of the imide and the quinone motif of the QM plays an important role in the exceptional cytotoxic behaviour of their imido-ferrociphenol precursors. This intramolecular lp-π interaction markedly enhanced the stability of the QMs and lowered the pKa values of the corresponding phenolates. As the first example of such a non-covalent interaction that stabilizes QMs remotely, it not only expands the scope of the lp-π interaction in supramolecular chemistry, but also represents a new mode of stabilization of a QM. This unprecedented application of lp-π interactions in imido-ferrociphenol anticancer drug candidates may also have great potential in drug discovery and organocatalyst design.

International audience; Transition Metal Complexes (TMCs) are known for the rich variety of their excited states showing different nature and degrees of locality. Describing the energies of these excited states with the same degree of accuracy is still problematic when using time-dependent density functional theory in conjunction with the most current density functional approximations. In particular, the presence of unphysically low lying excited states possessing a relevant Charge Transfer (CT) character may significantly affect the spectra computed at such a level of theory and, more relevantly, the interpretation of their photophysical behavior. In this work, we propose an improved version of the MAC index, recently proposed by the authors and collaborators, as a simple and computationally inexpensive diagnostic tool that can be used for the detection and correction of the unphysically predicted low lying excited states. The analysis, performed on five prototype TMCs, shows that spurious and ghost states can appear in a wide spectral range and that it is difficult to detect them only on the basis of their CT extent. Indeed, both delocalization of the excited state and CT extent are criteria that must be combined, as in the MAC index, to detect unphysical states.ACKNOWLEDGMEN

To provide tools to interpret photochemical reactions, in this paper we demonstrate how a recently developed density-based index (DCT), up to now used in conjunction with time dependent density functional theory methods, can be extended to multiconfigurational methods. This index can guide chemists in the interpretation of photochemical reactions providing a measure of the spatial extent of a photoinduced charge transfer and, more generally, of charge transfer phenomena. This qualitative and quantitative description can be particularly relevant in the case of multiconfigurational calculations providing a simple tool for the interpretation of their complex outputs. To prove the potentiality of this approach we have considered a simple intramolecular excited state proton transfer reaction as study case and applied both wave function (CASSCF-CASPT2) and density-based methods in conjunction with a DCT analysis. Our results confirm that, also in the case of multiconfigurational methods, the DCT provides very u...

Ruthenium nitrosyl complexes are fascinating versatile photoactive molecules that can either undergo NO linkage photoisomerization or NO photorelease. The photochromic response of three ruthenium mononitrosyl complexes, trans-[RuCl(NO)(py)4]2+, trans-[RuBr(NO)(py)4]2+, and trans-(Cl,Cl)[RuCl2(NO)(tpy)]+, has been investigated using density functional theory and time-dependent density functional theory. The N to O photoisomerization pathways and absorption properties of the various stable and metastable species have been computed, providing a simple rationalization of the photoconversion trend in this series of complexes. The dramatic decrease of the N to O photoisomerization efficiency going from the first to the last complex is mainly attributed to an increase of the photoproduct absorption at the irradiation wavelength, rather than a change in the photoisomerization pathways.

A theoretical study of the enantiomerization pathway of BINAP, the paradigm of atropochiral ligands in asymmetric organometallic catalysis, is reported. Density functional theory was used with the B3PW91 functional and the 6-31G(d,p) basis set. The calculation level was validated through the study of the syn and anti enantiomerization pathways of the 1,1′-binaphthyl reference for which the enantiomerization barrier was calculated to be in good agreement with experimental data. Calculations were then performed on BINAP itself using the same level of theory, and showed that its enantiomerization mechanism follows the syn route through a concerted, yet highly asynchronous, all-chiral process. The enantiomerization barrier was computed at 213 kJ mol(−1) and proved little sensitive to the functional or to the basis set used, with values always larger than 200 kJ mol(−1). The configurational stability of BINAP was finally characterized by a computed Oki’s racemization temperature of 491 °C.

The factors that explain the competition between intramolecular NO linkage photoisomerization and NO photorelease in five ruthenium nitrosyl complexes were investigated. By applying DFT-based methods, it was possible to characterize the ground states and lowest triplet potential energy surfaces of these species, and to establish that both photoisomerization and photorelease processes can occur in the lowest triplet state of each species. This work highlights the crucial role of the sideways-bonded isomer, a metastable state also known as the MS2 isomer, in the photochemical loss of NO, while the results obtained also indicate that the population of the triplet state of this isomer is compulsory for both processes and show how photoisomerization and photorelease interfere. Graphical Abstract Illustration of the crucial role of the

An unusual aryne-mediated fluorination of aromatic ring systems during the desilylation of ortho -bromo-biphenyl-trimethylsilanes with tetrabutylammonium fluoride (TBAF) is described. In situ formation of an aryne and addition of fluoride affords fluorinated biphenyls. The structures have been undoubtfully confirmed by synthesis of authentic samples via Suzuki–Miyaura cross-coupling and X-ray analysis. In situ trapping experiments with furan proved the transient formation of aryne by fluoride-induced displacement of the TMS group and subsequent bromide elimination.

The density functional theory calculations presented in this work allow the first rationalization of the full linkage photoisomerization mechanism of trans-[RuCl(NO)(py)4](2+), in both the forward and reverse directions. These mechanisms are consistent with the experimental data establishing that blue-light irradiation triggers the forward process, while red or IR photons trigger the reverse process. Characterization of the singlet and lowest triplet potential energy surfaces shows that, despite the unfavorable thermodynamic character of the forward process, the topologies of the surfaces and particularly some crucial surface crossings enable the isomerization. In the forward Ru-NO → Ru-ON direction, a sequential two-photon absorption mechanism is unraveled that involves a sideways-bonded metastable state. In contrast, in the reverse reaction, two mechanisms are proposed involving either one or two photons.

The supramolecular bonding contacts driving the recognition of chloride ions by macrocyclic imidazolium-based receptors have been investigated by density functional theory calculations, both in vacuo and in solution (DMSO). This computational study reveals that the most stable host-guest complexes in vacuo and solution are different. While the anion interacts by means of two C-H···Cl(-) hydrogen bonds with the host molecule in vacuo (in a similar manner to that observed in the published single-crystal X-ray structure of the Cl-host complex), four C-H···Cl(-) contacts are clearly present in solution, as observed experimentally by earlier studies. In addition, the computed optimal Cl-host complex in solution confirms that the cavity of the host macrocycle, formed by four aromatic rings, does not includes the anions, which are located outside the cyclic receptor with which they interact through two CPh-H···Cl(-) hydrogen bonds and two unconventional (CIm-H)(+)···X(-) interactions.

An unusual aryne-mediated fluorination of aromatic ring systems during the desilylation of ortho -bromo-biphenyl-trimethylsilanes with tetrabutylammonium fluoride (TBAF) is described. In situ formation of an aryne and addition of fluoride affords fluorinated biphenyls. The structures have been undoubtfully confirmed by synthesis of authentic samples via Suzuki–Miyaura cross-coupling and X-ray analysis. In situ trapping experiments with furan proved the transient formation of aryne by fluoride-induced displacement of the TMS group and subsequent bromide elimination.