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No significant stereoselectivity could be identified in photoinduced electron transfer in the static regime. Sufficiently high electronic coupling can be achieved with all diastereomeric pairs for this process to occur in the adiabatic regime.

Using electron-rich or electron-poor N-substituted oxazolidines as substrates, selective formation of either ammonium or oxonium ylides is possible in the presence of α-imino carbenes. As such, treatment of 5-membered oxazolidine precursors with N-sulfonyl-1,2,3-triazoles under dirhodium catalysis (2 mol%) affords the regiodivergent synthesis of either 8-membered 1,3,6- or 1,4,6-oxadiazocines upon the initial N or O reactivity with the carbene.

A straightforward two-step synthesis protocol affords a series of chiral amide-based bis-pyridine substituted polyether macrocycles. One ligand is particularly able to complex Terbium(III) ion spontaneously. Upon complexation, interesting chiroptical properties are observed both in absorbance (ECD) and in fluorescence (CPL). In ligand-centered electronic circular dichroism, a sign inversion coupled with a signal enhancement is measured; while an easily detectable metal-centered circularly polarized luminescence with a glum of 0.05 is obtained for the main 5D4 → 7F5 terbium transition. The coordination mode and structure of the complex was studied using different analysis methods (NMR analysis, spectrophotometric titration and solid-state elucidation).

An original and straightforward entry to polysubstituted indenes from readily available ynamides is reported. Upon reaction with a NHC-gold complex under mild conditions, activated keteniminium ions are generated whose unique electrophilicity triggers a [1,5]-hydride shift and a subsequent cyclization. The presence of an endocyclic enamide in the densely functionalized resulting indenes was shown to be especially useful and versatile, offering a range of opportunities for their further post-functionalization., info:eu-repo/semantics/published

Malonate enol ethers are afforded in one step by condensation of cyclic ketones with α-diazomalonates under [CpRu(CH3CN)3][BArF] catalysis. The dual reactivity of these 2-vinyloxymalonates can be used to expand the classical range of cyclizations derived from carbonyl ylide intermediates.

A series of highly emissive inert and chiral CrIII complexes displaying dual circularly polarized luminescence (CPL) within the NIR region have been prepared and characterized. The helical [Cr(dqpR)2 ]3+ (dqp=2,6-di(quinolin-8-yl)pyridine; R=OCH3 , Br or C≡CH) complexes were synthesized as racemic mixtures and resolved into their respective PP and MM enantiomers by chiral stationary phase HPLC. The corresponding enantiomers show large glum ≈0.2 and high quantum yield of up to 17 %, which afford important CPL brightness of up to 170 m-1 cm-1 , a key point for applications as chiral luminescent probes. Moreover, the long-lived CP-NIR emission provided by these chromophores (ms range) in aqueous solution opens the way toward the quantification of chiral targets in biological systems with time-gated detection. Thus, such chiral chromophores based on earth abundant and inert 3d metals open new perspectives in the field of CPL and represent an alternative to precious 4d, 5d and to labile 4f metal-based complexes.

Double hydrothiolation of bis enol ether macrocycles was achieved under photo-mediated conditions. The thiol-ene reactions afford a fully regioselective anti-Markovnikov post-functionalization. Thanks to the use of ethanedithiol as reagent, moderate to excellent diastereoselectivity was accomplished leading to macrocycles containing four defined stereocenters in only three steps from 1,4-dioxane, tetrahydrofuran (THF) or tetrahydropyran (THP).

International audience; We demonstrate the possibility to detect selectively the two enantiomers of a model [Ru(bpy) 3 ] 2+-based dye by circularly polarized-electrochemiluminescence (CP-ECL). This new nature of the ECL emission combines the chiral information intrinsic of CPL methods with an electrogeneration of the excited state. Thus, it opens the possibility to perform ECL-based bioassays or microscopy with efficient chiral dyes.

Controlling electrochemiluminescence (ECL) color(s) is crucial for many applications ranging from multiplexed bioassays to ECL microscopy. This can only be achieved through the fundamental understanding of high-energy electron-transfer processes in complex and competitive reaction schemes. Recently, this field has generated huge interest, but the effective implementation of multicolor ECL is constrained by the limited number of ECL-active organometallic dyes. Herein, the first self-enhanced organic ECL dye, a chiral red-emitting cationic diaza [4]helicene connected to a dimethylamino moiety by a short linker, is reported. This molecular system integrates bifunctional ECL features (i.e. luminophore and coreactant) and each function may be operated either separately or simultaneously. This unique level of control is enabled by integrating but decoupling both molecular functions in a single molecule. Through this dual molecular reactivity, concomitant multicolor ECL emission from red to blue with tunable intensity is readily obtained in aqueous media. This is done through competitive electron-transfer processes between the helicene and a ruthenium or iridium dye. The reported approach provides a general methodology to extend to other coreactant/luminophore systems, opening enticing perspectives for spectrally distinct detection of several analytes, and original analytical and imaging strategies., Controlling electrochemiluminescence (ECL) color(s) is crucial for many applications ranging from multiplexed bioassays to ECL microscopy.

Chirality is a structural property of molecules lacking mirror symmetry that has strong implications in diverse fields, ranging from life to materials sciences. Established spectroscopic methods that are sensitive to chirality, such as circular dichroism (CD), exhibit weak signal contributions on an achiral background. Helical dichroism (HD), which is based on the orbital angular momentum (OAM) of light, offers a new approach to probe molecular chirality, but it has never been demonstrated on disordered samples. Furthermore, in the optical domain the challenge lies in the need to transfer the OAM of the photon to an electron that is localized on an {\AA}-size orbital. Here, we overcome this challenge using hard X-rays with spiral Fresnel zone, which can induce an OAM. We present the first HD spectra of a disordered powder sample of enantiopure molecular complexes of [Fe(4,4'-diMebpy)3]2+ at the iron K-edge (7.1 keV) with OAM-carrying beams. The HD spectra exhibit the expected inversions of signs switching from a left to a right helical wave front or from an enantiomer to the other. The asymmetry ratios for the HD spectra are within one to five percent for OAM beams with topological charges of one and three. These results open a new window into the studies of molecular chirality and its interaction with the orbital angular momentum of light., Comment: 15 pages, 5 figures

Cationic triangulenes, and related helicenes, constitute a rich class of dyes and fluorophores, usually absorbing and emitting light at low energy, in the orange to red domains. Recently, to broaden the scope of applications, regioselective late-stage functionalizations on these core moieties have been developed. For instance, with the introduction of electron-donating groups (EDGs), important bathochromic shifts are observed pushing absorptions towards or in the near-infrared (NIR) spectral domain while emissive properties disappear essentially completely. Herein, to upset this drawback, acetylene derivatives of cationic diazaoxa triangulenes (DAOTA) and [4]helicenes are prepared (16 examples). Contrary to other EDG-functionalized derivatives, C≡C− functionalized products remain broadly fluorescent, with red-shifted absorptions (Δλabs up to 25 nm) and emissions (Δλem up to 73 nm, ΦPL up to 51 %). Quite interestingly, a general dynamic stereoisomerism phenomenon is evidenced for the compounds derived from achiral DAOTA cores. At low temperature in 1H NMR spectroscopy (218 K), N−CH2 protons become diastereotopic with chemical shifts differences (Δδ) as high as +1.64 ppm. The signal coalescence occurs around 273 K with a barrier of ∼12 kcal mol−1. This phenomenon is due to planar chiral conformations (Sp and Rp configurations), induced by the geometry of the alkyl (n-propyl) side-chains next to the acetylenic substituents. Ion pairing studies with Δ-TRISPHAT anion not only confirm the occurrence of the chiral conformations but evidence a moderate but definite asymmetric induction from the chiral anion onto the cations. Finally, DFT calculations offer a valuable insight on the geometries, the corresponding stereodynamics and also on the very large difference in NMR for some of the diastereotopic protons.

The intramolecular condensation of ortho substituents of triaryl carbenium ions can lead to the formation of cationic helicenes. These chiral and configurationally stable molecules exhibit extended optical properties reminiscent of their parent methylium ions. Among them, cationic [6]helicenes are particularly interesting as orthogonal late-stage functionalization strategies allow the introduction of a variety of auxochromes with different regiochemistry. Intense chiroptical properties can thus be tailored in the far red and up to the near infra-red (NIR) spectral windows. A wealth of applications can be foreseen, in particular in material sciences., University of Geneva; Swiss National Science Foundation; European Union (EU); Horizon 2020; Scientific and Technological Research Council of Turkey (TÜBİTAK); Co-Funded Brain Circulation2 Scheme; CoCirculation2 Programme

Iron-based spin-crossover (SCO) complexes hold tremendous promise as multifunctional switches in molecular devices. However, real-world technological applications require the excited high-spin (HS) state to be kinetically stable – a feature that has only been achieved at cryogenic temperatures in the light-induced excited spin-state trapping effect. Here we demonstrate HS state trapping by controlling the chiral configuration of FeII(4,4’-dimethyl-2,2’-bipyridine)3 in solution, associated for stereocontrol with enantiopure ∆- or Λ-TRISPHAT anions. We characterize the HS state relaxation using a newly developed ultrafast circular dichroism technique in combination with transient absorption and anisotropy measurements. We find that the decay of the HS state is accompanied by ultrafast changes of its optical activity, reflecting the coupling to a symmetry-breaking torsional twisting mode, contrary to the commonly assumed picture. Furthermore, we show that the diastereoselective ion-pairing with the enantiopure anions suppresses the vibrational population of the identified twisting mode, thereby achieving a four-fold extension of the HS lifetime. Transferred to the solid state, this novel strategy may thus significantly improve the kinetic stability of iron(II)-based magnetic switches at room temperature.

A series of highly emissive inert and chiral Cr(III) complexes displaying dual Circularly Polarized Luminescence (CPL) within the NIR region have been prepared and characterized. The helical [Cr(dqpR)2]3+ (dqp = 2,6-di(quinolin-8-yl)pyridine; R = OCH3, Br or C≡CH) complexes were synthesized as racemic mixtures and resolved into their respective PP and MM enantiomers by chiral stationary phase HPLC. The corresponding enantiomers show large glum ~ 0.2 and high quantum yield of up to 17%, which afford important CPL brightness of up to 170 m−1×cm−1, a key point for applications as chiral luminescent probes. Moreover, the long-lived CP-NIR emission provided by these chromophores (ms range) in aqueous solution opens the way toward the quantification of chiral targets in biological systems with time-gated detection. Thus, such chiral chromophores based on earth abundant and inert 3d metals open new perspectives in the field of CPL and represent an alternative to precious 4d, 5d and to labile 4f metal-based complexes.

International audience; Synthesis, electronic and structural properties of a chiral NHC bearing a N-bonded cationic [4]helicene moiety are reported. This ligand is used to construct Au(I), Au(III) and Rh(I) complexes exhibiting far-red (chir)optical properties regardless of the metal.

International audience; In one pot, tertiary alkyl amines are oxidized to enamines by cationic dioxa[6]helicene, which further reacts as electrophile and oxidant to form mono or bis donor-π-acceptor coupling products. This original and convergent synthetic approach provides a strong extension of conjugation yielding chromophores that absorb intensively in far-red or NIR domains (λmax up to 791 nm) and fluoresce in the NIR as well (λmax up to 887 nm). Intense ECD properties around 790 nm with a |Δϵ| value up to 60 M-1 cm-1 are observed.

Singlet fission (SF), i.e., the splitting of a high-energy exciton into two lower-energy triplet excitons, has the potential to increase the efficiency for harvesting spectrally broad light. The path from the photopopulated singlet state to free triplets is complicated by competing processes that decrease the overall SF efficiency. A detailed understanding of the whole cascade and the nature of the photoexcited singlet state is still a major challenge. Here, we introduce a pentacene dimer with a flexible crown ether spacer enabling a control of the interchromophore coupling upon solvent-induced self-aggregation as well as cation binding. The systematic change of solvent polarity and viscosity and excitation wavelength, as well as the available conformational phase space, allows us to draw a coherent picture of the whole SF cascade from the femtosecond to microsecond time scales. High coupling leads to ultrafast SF (

Hexahydropyrazinoindoles were prepared in a single step from N-sulfonyl triazoles and imidazolidines. Under dirhodium catalysis, α-imino carbenes were generated and formed nitrogen ylide intermediates that, after subsequent aminal opening, afforded the pyrazinoindoles predominantly via formal [1,2]-Stevens and tandem Friedel–Crafts cyclizations. Of mechanistic importance, a regiodivergent reactivity was engineered through the use of a specific unsymmetrically substituted imidazolidine that promoted the exclusive formation of 8-membered ring 1,3,6-triazocines. Based on DFT calculations, an original Curtin–Hammett-like situation was demonstrated for the mechanism. Further derivatizations led to functionalized tetrahydropyrazinoindoles in high yields., Hexahydropyrazinoindoles are prepared in a single step from N-sulfonyl triazoles and imidazolidines. Of mechanistic importance, a regiodivergent reactivity can be engineered towards the exclusive formation of 8-membered ring 1,3,6-triazocines.

The synthesis of spirocyclic amide acetals (33–93 %) has been achieved through Ru(II)-catalyzed condensations of N-carbamate protected pyrrolidinones with metal carbenes derived from α-diazo-β-ketoesters. Thanks to the mildness of the diazo decomposition conditions induced by a 1 : 1 combination of [CpRu(MeCN)3][BArF] and 1,10-phenanthroline, the formation of the sensitive products is possible. Full characterization of this carbonyl-ylide mediated process is provided by DFT calculations.

International audience; Chiral hemicyanine fluorophores are afforded in three steps only from Tröger bases via α-imino carbene additions, an original aminal deprotection and Cu(II)-mediated oxidation. The stable benzodiazepinoindolium salts are readily isolated and present (chir)optical properties that can be fine-tuned by late-stage cross-coupling functionalization. The hemicyanine character of dyes was rationalized using first principles.

International audience; A straightforward approach to the synthesis of two different series of cationic [5]helicenes has been achieved including, in dioxa series, the possibility to introduce aromatic functional groups at the periphery of the helical structure. While photophysical study highlights that the introduction of aryl substituents at position 23 of the helical moieties has a negligible impact on the optical properties, styryl substituents allow a welcoming extension of the conjugation pathways. Finally, a red shift of the optical properties was evidenced upon introduction of nitrogen atoms in the helicene scaffold, leading to particularly good fluorescence efficiencies in the red domain for a helicenic dye. Detailed information on racemization kinetics was collected for the most stable species upon direct high-performance liquid chromatography (HPLC) resolution or, when configurational lability was too high, through VT-HPLC analysis on the chiral stationary phase (ΔG‡ values ranging from 85.0 to 137.1 kJ·mol–1 and above).

In this chapter, examples of circularly polarized luminescence (CPL) stemming from intramolecularly formed excimers will be reviewed. Emission from excimers has peculiar photophysical properties with respect to fluorescence of regular monomers. In addition, if the fluorophoric couple forming the excimer in the excited state is mounted on a chiral scaffold, a strong CPL can be usually observed. Examples of chiral scaffolds include oligopeptides, macrocycles, binaphthyl, and diaminocyclohexane derivatives. CPL from excimers has mainly been observed from pyrenes but other molecules are also able to give rise to such phenomenon, e.g., perylenes and 1,8-naphthalene monoimide. Excimer CPL can provide important information about the conformation of a molecule in the excited state and how it evolves depending on the environment (e.g., solvent and temperature) or external stimuli (e.g., light irradiation and cation addition). Moreover, thanks to the peculiar photophysical nature of excimers, the degree of circular polarization associated with excimer emission is usually much larger than the one associated with the absorption (electronic circular dichroism, ECD) for the same molecule. This allows to study chiroptical emission properties of molecules which are ECD-silent (ground state cryptochirality). As a whole, excimer CPL is an interesting and useful strategy to develop organic molecular systems endowed with bright and highly polarized luminescence.

A series of chiral fluorescent helicene-BODIPY conjugates was prepared by the regioselective formylation of aza[4]helicene precursors and then an efficient one-pot two-step BODIPY synthesis (13 examples, 28-82%). Fused conjugates exhibit absorption and fluorescence properties (ΦF 30-45%) in the red visible domain, and a CPL signature could be measured at 605 nm (glum ±5 × 10-4). Photophysical and electronic properties were investigated and rationalized through first principles.

International audience; A series of w ater-soluble helicene dyes generating intense electrochemiluminescence (ECL) signal in physiological conditions is reported. Those species were prepared using diaza [4] and [6]helicenes as structural cores modified with sulfonate groups in various positions. Such groups improve their water solubility and induce a red-shifted emission. Efficient ECL up to the near-infrared is achieved in water, demonstrating a viable strategy for the design of new near-infrared ECL dyes for bioassays and microscopy.

Chiral polyether macrocycles are versatile molecules. For their preparation, original two-step procedures were recently developed and present the advantages of high concentration conditions and simple starting reagents (stable diazo reagents, small cyclic ethers, aliphatic or aromatic amines). Enantiopure materials are readily afforded by CSP-HPLC on a semi-preparative scale. Flexibility and adaptability in the macrocyclic design are provided by a large selection of amines to choose from while the ring size and chemical nature are controlled by the choice of 5 to 7-membered cyclic ether precursors. Such macrocycles have already been used as asymmetric catalysts, mono and ditopic receptors, fluorescent sensors and probes, and chiroptical reversible switches., Chiral polyether macrocycles are versatile molecules.

International audience; Verkade's superbases, entrapped in the cavity of enantiopure hemicryptophane cages, have been synthesized with enantiomeric excess (ee) superior to 98%. Their absolute configuration has been determined by using electronic circular dichroism (ECD) spectroscopy. These enantiopure encaged superbases turned out to be efficient chiral derivatizing agents for chiral azides, underlining that the chirality of the cycloveratrylene (CTV) macrocycle induces different magnetic and chemical environments around the phosphazide functions.

International audience; Cationic [Ru(η 5-C5H5)(CH3CN)3] + complex, tris(acetonitrile)(cyclopentadienyl)ruthenium(II), gives rise to a very rich organometallic chemistry. Combined with diimine ligands, and 1,10-phenanthroline in particular, this system efficiently catalyzes diazo decomposition processes to generate metal-carbenes which undergo a series of original transformations in the presence of Lewis basic substrates. Herein, syntheses and characterizations of [CpRu(Phen)(L)] complexes with (large) lipophilic non-coordinating (PF6 − and BArF −) and coordinating N-TRISPHAT − anions are reported. Complex [CpRu(η 6-naphthalene)][BArF] [1][BArF] is readily accessible, in high yield, by direct counterion exchange between [1][PF6] and sodium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (NaBArF) salts. Ligand exchange of [1][BArF] in acetonitrile generated stable [Ru(η 5-C5H5)(CH3CN)3][BArF] [2][BArF] complex in high yield. Then, the desired [CpRu(Phen)(CH3CN)] [3] complexes were obtained from either the [1] or [2] complex in the presence of the 1,10-phenanthroline as ligand. For characterization and comparison purposes, the anionic hemilabile ligand TRISPHAT-N (TTN) was introduced on the ruthenium center, from the complex [3][PF6], to quantitatively generate the desired complex [CpRu(Phen)(TTN)] [4] by displacement of the remaining acetonitrile ligand and of the PF6 − anion. Solid state structures of complexes [1][BArF], [2][BArF], [3][BArF], [3][PF6] and [4] were determined by X-ray diffraction studies and are discussed herein.

Following a late-stage functionalization strategy, a series of heteroditopic cryptand receptors were prepared in three steps only from 1,4-dioxane. As evidenced by 1 H NMR spectroscopic and solid state analyses, these polyamide-crown ether conjugates present general ion pair binding capacity towards salts of monovalent cations and linear triatomic anions.

Interaction of electrons with chiral matter gives rise to interesting phenomena such as the chirality-induced spin selectivity. The interdependence of reflectivity of spin-polarized low energy electrons and the absolute handedness of chiral molecules is investigated. First, the growth of homochiral films of helical aromatic hydrocarbons, so-called helicenes, on a Cu(100) surface is studied by means of low energy electron microscopy and scanning tunneling microscopy in ultrahigh vacuum. As soon as the coverage exceeds one monolayer, double-layer nucleation and growth is favored such that depletion in the first layer occurs. Spatially resolved work function measurements show that second-layer patches have a lower work function than first-layer areas. Reflectivity spectra of spin-polarized electrons do not show any asymmetry between homochiral films of the enantiomers. Laterally resolved work function measurements do not confirm work function differences such as those reported earlier for photoelectron studies of chiral peptide films on ferromagnetic substrates.