Aza-boron-dipyrromethene dyes: TD-DFT benchmarks, spectral analysis and design of original near-IR structures

International audienceThe excited-state energies of aza-boron-dipyrromethene (Aza-BODIPY) derivatives are investigated with Time-Dependent Density Functional Theory (TD-DFT), with twin goals. On the one hand, a pragmatic, yet efficient, computational protocol is defined in order to reach rapidly semi-quantitative estimates of the λmax of these challenging dyes. It turned out that a PCM-TD-BMK/6-311+G(2d,p)//PCM-PBE0/6-311G(2d,p) approach delivers appropriate lower bounds of the experimental results, despite the inherent limits of the vertical approximation. On the other hand, the method is applied to design new dyes absorbing in the near-IR. The spectral features of ca. 30 new compounds have been simulated in a systematic way, trying to efficiently combine several available synthetic strategies leading to significant bathochromic displacements. A series of dyes absorbing above 850 nm are proposed, illustrating that (relatively) fast theoretical calculations might be a useful pre-screening step preceding synthesis

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

The resolution of the weak-exchange limit made rigorous, simple and general in binuclear complexes

The correct interpretation of magnetic properties in the weak-exchange regime has remained a challenging task for several decades. In this regime, the effective exchange interaction between local spins is quite weak, of the same order of magnitude or smaller than the various anisotropic terms, which \textit{in fine} generates a complex set of levels characterized by spin intercalation if not significant spin mixing. Although the model multispin Hamiltonian, \hms{} = \js{} + \da{} +\db{} + \dab{}, is considered good enough to map the experimental energies at zero field and in the strong-exchange limit, theoretical works pointed out limitations of this simple model. This work revives the use of \hms{} from a new theoretical perspective, detailing point-by-point a strategy to correctly map the computational energies and wave functions onto \hms{}, thus validating it regardless of the exchange regime. We will distinguish two cases, based on experimentally characterized dicobalt(II) complexes from the literature. If centrosymmetry imposes alignment of the various rank-2 tensors constitutive of \hms{} in the first case, the absence of any symmetry element prevents such alignment in the second case. In such a context, the strategy provided herein becomes a powerful tool to rationalize the experimental magnetic data, since it is capable of fully and rigorously extracting the multispin model without any assumption on the orientation of its constitutive tensors. Finally, previous theoretical data related to a known dinickel(II) complex is reinterpreted, clarifying initial wanderings regarding the weak-exchange limit

A 1D coordination polymer built on asymmetric µ1,1,3-azide bridge: from unusual topology to magnetic properties and Cu(II)/Cu(I) redox reversibility

International audienceAn azide-bridged Cu(II) one dimensional polymer was synthesized in a one pot reaction in the presence of ammonia. The refined crystal structure evidenced the unusual asymmetric μ1,1,3 coordination mode of the azide ion leading to a {Cu(μ1,1,3-N3)(μ1-N3)(NH3)0.8(H2O)1.2}n chain. The redox process of this complex was studied by cyclic voltammetry evidencing the Cu(II)/Cu(I) reversibility. Magnetic measurements were interpreted as a uniform antiferromagnetic chain (J = −15.2 cm−1) holding rather strong inter-chain exchange (zJ′ = −2.8 cm−1). Multireference difference dedicated configuration interaction (DDCI) calculations confirmed the non-negligible intensity of inter-chain interactions and evidenced a strong influence of the type of coordinated solvent, NH3 or H2O, on the nature and magnitude of the magnetic exchange

Continuous Symmetry Breaking Induced by Ion Pairing Effect in Heptamethine Cyanine Dyes: Beyond the Cyanine Limit

WOS:000276009500058International audienceThe association of heptamethine cyanine cation 1(+) with various counterions A (A = Br(-), I(-), PF(6)(-), SbF(6)(-), B(C(6)F(5))(4)(-), TRISPHAT) was realized. The six different ion pairs have been characterized by X-ray diffraction, and their absorption properties were studied in polar (DCM) and apolar (toluene) solvents. A small, hard anion (Br(-)) is able to strongly polarize the polymethine chain, resulting in the stabilization of an asymmetric dipolar-like structure in the crystal and in nondissociating solvents. On the contrary, in more polar solvents or when it is associated with a bulky soft anion (TRISPHAT or B(C(6)F(5))(4)(-)), the same cyanine dye adopts preferentially the ideal polymethine state. The solid-state and solution absorption properties of heptamethine dyes are therefore strongly correlated to the nature of the counterion

Covalency and magnetic anisotropy in lanthanide single molecule magnets: the DyDOTA archetype

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Editorial note to present the new model of open-access journal of the Association Science

Redox-Active Dysprosium Single-Molecule Magnet: Spectro-Electrochemistry and Theoretical Investigations

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Stable Near-Infrared Anionic Polymethine Dyes: Structure, Photophysical, and Redox Properties

International audienceThe concept of cyanine has been successfully extended to anionic heptamethine dye featuring tricyanofuran (TCF) moieties in terms of structure, reactivity and photophysical properties. Importantly, absorption and emission are red-shifted compared to its classical cationic analog without any cost in term of thermal stability. In addition to its "cyanine" behavior, this molecule exhibits further redox properties: oxidation and reduction led to the reversible formation of radical species whose absorption is in marked contrast with that of cyanines