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International audience; The development of fluorescence materials with switched on/off emission has attracted great attention owing to the potential application of these materials in chemical sensing. In this work, the photophysical properties of a series of original 2-(2′hydroxyphenyl)pyrimidines were thoroughly studied. The compounds were prepared by following well-established and straightforward methodologies and showed very little or null photoluminescence both in solution and in the solid state. This absence of emission can be explained by a fast proton transfer from the OH group to the nitrogen atoms of the pyrimidine ring to yield an excited tautomer that deactivates through a nonradiative pathway. The key role of the OH group in the emission quenching was demonstrated by the preparation of 2′-unsubstituted derivatives, all of which exhibited violet or blue luminescence. Single crystals of some compounds suitable for an X-ray diffraction analysis could be obtained, which permitted us to investigate inter-and intramolecular interactions and molecular packing structures. The protonation of the pyrimidine ring by an addition of trifluoroacetic acid inhibited the excited-state intramolecular proton transfer (ESIPT) process, causing a reversible switch on fluorescence response detectable by the naked eye. This acidochromic behavior allows 2-(2′-hydroxyphenyl)pyrimidines to be used as solid-state acid−base vapor sensors and anticounterfeiting agents. Extensive density functional theory and its time-dependent counterpart calculations at the M06-2X/6-31+G** level of theory were performed to rationalize all the experimental results and understand the impact of protonation on the different optical transitions.

Silver is considered to be the king among plasmonic materials because it features low inelastic absorption in the visible and infrared (vis-IR) spectral regions compared to other metals. In contrast, copper is commonly regarded as being too lossy for plasmonic applications. Here, we experimentally demonstrate vis-IR plasmons in long copper nanowires (NWs) with quality factors that exceed a value of 60, as determined by spatially resolved, high-resolution electron energy-loss spectroscopy (EELS) measurements. We explain this counterintuitive result by the fact that plasmons in these metal wires have most of their electromagnetic energy outside the metal, and thus, they are less sensitive to inelastic losses in the material. We present an extensive set of data acquired on long silver and copper NWs of varying diameters supporting this conclusion and further allowing us to understand the relative roles played by radiative and nonradiative losses in plasmons that span a wide range of energies down to $, 13 pages, 9 figures, 56 references

International audience; Plasmonic materials are intensively used to extend the photoactivity of large bandgap semiconductors into the visible light region. In this framework, the present study examines the joint role played by the morphology and composition of plasmonic nano-particles in their photosensitizing capabilities. The critical influence of these parameters is evidenced by the effect of Au and core−shell Au@Ag nanorods on a TiO 2-driven photochemical probe reaction. In this case, the use of the bimetallic composites leads to a remarkable increase in the photocatalytic activity of the semiconductor compared to that found for the monometallic Au sensitizers. The mechanism behind this observation has then been computed theoretically concluding that, in terms of hot electron injection, the contribution of the transversal modes of the Au@Ag NRs and the low damping of these nanostructures are responsible for the photocatalytic properties reported herein. The great potential of these architectures is confirmed by their notable performance toward photocatalytic hydrogen generation, rendering this approach an appealing strategy in the search for efficient solar-driven energy systems. N oble metal nanoparticles (NPs) present outstanding optical properties given their strong interaction with light in the visible and near-infrared (NIR) ranges of the electromagnetic spectrum. 1 This coupling arises because of the coherent oscillation of conduction electrons of the metallic objects in resonance with the incoming electromagnetic field, an effect known as localized surface plasmon resonance (LSPR). 2 As a result, a short-lived population of charge carriers ("hot" electrons) is created, being thermalized within the crystalline lattice of the metal on the femtosecond time scale. 3,4 Recent reports have shown that the combination of plasmonic objects with acceptor species such as organic molecules or semiconductors can lead to the exchange of charge carriers and hence to the possibility of using such species to drive chemical processes of interest. 5 Along these lines, plasmonic photosensitization has been identified as a promising interaction between a noble metal and a large bandgap semiconductor toward the formation of hybrid photocatalysts with improved efficiencies and broadband activity. 6,7 In this manner, the Schottky barrier created between both materials extends the lifetime of the hot carriers, thus leading to an accumulation of electrons at the conduction band

International audience; A magnetically induced catalysis can be promoted taking advantage of optimal heating properties from the magnetic nanoparticles to be employed. However, if unprotected, these heating agents that are usually air-sensitive, get sintered under the harsh catalytic conditions. In this context, we present, to the best of our knowledge, the first example of air-stable magnetic nanoparticles that: a) show an excellent performance as heating agents in the CO 2 methanation catalyzed by Ni/SiRAlOx, with CH 4 yields above 95%, and b) do not sinter under reaction conditions. To attain both characteristics we demonstrate, first the exchange-coupled magnetic approach as an alternative and effective way to tune the magnetic response and heating efficiency, and second, the chemical stability of cuboctahedron-shaped core-shell hard CoFe 2 O 4-soft Fe 3 O 4 nanoparticles.

1H-Indazole derivatives exhibit a remarkable property since some of them form chiral supramolecular structures starting from achiral monomers. The present work deals with the study of three perfluorinated 1H-indazoles that resolve spontaneously as conglomerates. These conglomerates can contain either a pure enantiomer (one helix) or a mixture of both enantiomers (both helices) with an enantiomeric excess (e.e.) of one of them. The difficulty of the structural analysis of these types of compounds is thus clear. We outline a complete strategy to determine the structures and configurations (M or P helices) of the enantiomers (helices) forming the conglomerates of these perfluorinated 1H-indazoles based on X-ray crystallography, solid state NMR spectroscopy and different solid state vibrational spectroscopies that are either sensitive (VCD) or not (FarIR, IR and Raman) to chirality, together with quantum chemical calculations (DFT)., This work was carried out with financial support from the Ministerio de Economía y Competitividad (Project No. CTQ2014- 56833R and CTQ2015-63997-C2-2-P), CICE/Junta de Andalucía (P08-FQM-04096) and CICE/JA-FEDER-UJA: Plan de Fortalecimiento de las Capacidades de I+D+i/2014-15 (UJA2013/08/03) and Comunidad Autónoma de Madrid (Project FOTOCARBON, ref. S2013/MIT-2841). Computer, storage and other resources from the CTI (CSIC) are gratefully acknowledged. Authors thank the University of Jaén for continuing financial support, for bridge projects (UJA2015/08/07) and (UJA2016/08/15) and for Accion 2: Financiacion de Incentivos a la Excelencia de I+D+i de la UJA 2014-15 in 2014 and 2015 calls and to its CICT for instrumental facilities. Authors also thank the FQM-323 research group, especially Rafael Lopez Blanco, David Moreno Gonzalez and Jose Robles Molina, for their help in the laboratory. M. M. Q. M. thanks the University of Jaen for a pre-doctoral fellowship. The CNRS is acknowledged for support

The use of plasmonic metal nanoparticles as photosensitizers has undergone a strong development in the past few years given their ability to increase the activity of semiconductors into the visible and near-infrared regions. The present work reports an experimental and theoretical study on the critical influence that shape anisotropy of gold nanoparticles exerts on the photocatalytic performance of Au–TiO2 nanoarchitectures. The obtained results show that for a given amount of metallic material, Au nanostars endow titania with a strongly enhanced catalytic efficiency compared to that found in the presence of Au nanospheres or nanorods. This is ascribed to the ability of nanostars to locally create extremely large electromagnetic field enhancements around their spikes, which ensures an increased population of hot electrons close to the interface between the metal and the semiconductor. Therefore, these nanostructures exhibit a novel regime of photocatalytic activity that could be described as plasmonic hot...

The presence of antiphase boundaries with local ferromagnetic coupling is herein related to the magnetic performance of truncated octahedron-shaped zinc-doped magnetite nanocrystals. Atomic resolution STEM imaging reveals the presence of these antiphase boundaries perpendicular to the [111] direction of the spinel structure of the nanocrystals. Magnetic characterization and DFT calculations indicate a local ferromagnetic order, originating from Fe–Fe enrichment at these individual lattice defects in the nanocrystals, as the underlying cause of the magnetic response measured.

International audience; Tunable two-color ultrafast pump–probe experiments are performed on colloidal metal nanospheres in water and ethanol, and the results are interpreted through a model including thermal dynamics in both the nanoparticle and its environment. Transient optical signals measured for gold nanoparticles in ethanol display a complex temporal response strongly dependent on the wavelength of the probe beam. We demonstrate that its origin is related to a large contribution of liquid environment transient heating to the optical response, in contrast to the usual assumption that optical transmission changes reflect the evolution of nanoparticle temperature only. Accounting for this contribution enables an accurate measurement of thermal conductances at gold–ethanol and gold–water interfaces. Moreover, the thermal dynamics of the solvent can be selectively probed through a specific choice of probe wavelength.

This feature article focuses on the use of colloid chemistry to engineer metallic nanostructures toward application in surface enhanced Raman scattering (SERS) sensing, in particular for ‘real-life’ applications, where the analyte may be present in complex mixtures. We present a broad summary of the field, including recent advances that have been developed during the past 10 years. Real-life applications require a rational design and we aimed at identifying the key elements involved in it. The discussion is centered around colloidal plasmonic nanoparticles and therefore we start from the library of morphologies that have been reported in the literature. To complete the picture, colloidal self-assembly, surface chemistry and the combination with materials science techniques are highlighted. Considering the progress in the field, SERS may ultimately realize its full potential as an ultrasensitive tool for routine analytical applications.

International audience; Connecting the accurate Quantum Mechanics to the chemical view is the first of foremost purposes of interpretative methods in general, and topological analysis in particular. In this field of methods, the Maximum Probability Domains (MPD) analysis, is conceptually appealing but has not been extensively applied yet. In this study we provide the general vision coming out from MPD on the two main family of bonds: polar-covalent and ionic bonds. An interesting picture arises concerning the MPD solution associated to covalent bonds, displaying a prolate shape that extends preferentially in the orthogonal direction to the bond axis, and not along it. The polarity of the bond only affects marginally the domain shape, though further probability analysis seems to allow quantifying it. Concerning the ionic bond, a resonating picture emerges, which is compatible, and refines, the usual electrostatic vision of two oppositely-charged atoms in interaction.

The paper collects the answers of the authors to the following questions: `` What is the significance of topological approach? Can new chemical concepts be found by a topological approach? What is the status of a chemical concept within a topological approach? Should topological approaches provide measurable quantities? Is it possible to predict the outcome of a topological approach without performing a calculation on a computer? What are new domains for which topological approaches would be useful? (C) 2014 Elsevier B.V. All rights reserved.

International audience; The one-pot formation of colloidal nanocrystal clusters has recently gained attention due to the new set of phenomena that such secondary structures are endowed with. Nevertheless, given the number of complex processes at play, the correct interpretation of the chemical mechanisms behind the formation of such structures remains a particularly difficult task. In the present work, magnetic colloidal nanocrystal clusters with a spinel structure are thoroughly characterized by means of transmission electron mi-croscopy, X-ray diffraction, magnetic measurements and Raman spectroscopy. The combination of these techniques results in a means to unravel the structure of the poorly crystalline intermediates and complex products formed throughout the process. Our results suggest that the chemical and crystallographic transformations undergone by the nanostructures at the different stages of the reaction are strongly related with the final morphology of the secondary superstructures obtained, which in parallel, help to improve the magnetic properties required in their specific final applications. INTRODUCTION The development of the colloidal synthesis of nanoparticles has led to an impressive portfolio of nanomaterials with different sizes, compositions and morphologies that are currently available. 1-3 As the synthesis of individual nanocrystals has been gradually mastered, the attention of the scientific community has recently shifted towards the use of these well-studied nano-particles as building-blocks for the formation of more complex materials. Colloidal nanocrystal clusters (CNCs) are a very interesting example of this kind of superstructures. The physical and chemical interactions established between their individual units lead to a unique set of physical phenomena that can be used for the formation of plasmonic metamaterials, 4 the creation of hot-spots for surface enhanced Raman spectroscopy (SERS), 5 novel magnetoelectric multiferroic materials 6 or diagnostic and therapeutic agents with improved magnetic performance for magnetic guidance and separation or heat delivery applications, 7 among a vast set of potential applications. CNCs are the result of the interplay between different forces such as entropy-driven, electrostatics, van der Waals interactions or hydrogen bonding. 8 The control of these interactions together with conventional reaction parameters (surfactants, temperature, reaction time or solvent used) can lead to the successful control over the morphology and composition of both the primary crystallites and the CNCs. 9 It is well established that the synthesis of these structures is accomplished following one of the following pathways: (i) direct synthesis of CNCs in solu

We report a combined theoretical and experimental investigation of the exchange interactions governing the magnetic behavior of a series of nitronyl nitroxide (NIT)-based Y(III) complexes, i.e., Y(hfac)3(NIT-R)2 with R = PhOPh (1), PhOEt (2), and PhOMe (3a, 3b). Even though some of these complexes or their Dy(III) parents were previously described in the literature [ Zhao et al. Transition Met. Chem. 2006, 31, 593; Bernot et al. J. Am. Chem. Soc. 2009, 131, 5573 ], their synthesis procedure as well as their structural and magnetic properties were completely reconsidered. Depending on the nature of R and the crystallization conditions, Y(hfac)3(NIT-R)2 units can be organized as supramolecular dimers or linear or orthogonal chains. Such structural diversity within the series induces extremely different magnetic behaviors. The observed behaviors are rationalized by state-of-the-art wave function-based quantum-chemical approaches (CASSCF/DDCI) that demonstrate the existence of not only effective intramolecular interactions between the NIT-R radical ligands of an isolated Y(hfac)3(NIT-R)2 molecule but also intermolecular interactions between NIT-R moieties belonging to different Y(hfac)3(NIT-R)2 units. These results are supported by the use of spin Hamiltonian models going beyond the basic Bleaney-Bowers formalism to properly fit the experimental magnetic data. Finally, the microscopic mechanisms behind the evidenced intramolecular exchange interactions are elucidated through the inspection of the calculated wave functions. In particular, whereas the role of Y orbitals was already proposed, we herein demonstrate the contribution of the hfac- ancillary ligands in mediating the magnetic interactions between the NIT radicals. Ministerio de Economía y Competitividad CTQ-2015-69019-P