Photostability of Phenoxazine Derivatives.

Phenoxazine is a commonly used molecular building block, for example in optoelectronic applications and pharmaceuticals. However, it is highly susceptible to rapid photodegradation, especially in halogenated solvents. In the present study, we identify the degradation products in both halogenated and non-halogenated solvents by UV/Vis absorption, NMR spectroscopy and mass spectrometry. We also propose a substitution strategy aimed at effectively suppressing the high photoreactivity. Kinetic studies show that the quantum yield of photodegradation Ï• differs by a factor of more than 1000 between trisubstituted derivatives and N-substituted phenoxazine.

A Stable Chichibabin Diradicaloid with Near-Infrared Emission.

Conjugated molecules with multiple radical centers such as the iconic Chichibabin diradicaloid hold promise as building blocks in materials for quantum sensing and quantum information processing. However, it is a considerable challenge to design simple analogues of the Chichibabin hydrocarbon that are chemically inert, exhibit high diradical character and emit light at a distinct wavelength that may offer an optical readout of the spin state in functional ensembles. Here we describe the serendipitous discovery of the stable TTM-TTM diradicaloid, which exhibits high diradical character, a striking sky-blue color and near-infrared (NIR) emission (in solution). This combination of properties is unique among related diradicaloids and is due to the presence of hydrogen and chlorine atoms in "just the right positions", allowing a perfectly planar, yet predominantly benzenoid bridge to connect the two sterically stabilized radical centers. In-depth studies of the optical and magnetic properties suggest that this structural motif could become a mainstay building block of organic spin materials.

Giant Quantum Electrodynamic Effects on Single SiV Color Centers in Nanosized Diamonds.

Understanding and mastering quantum electrodynamics phenomena is essential to the development of quantum nanophotonics applications. While tailoring of the local vacuum field has been widely used to tune the luminescence rate and directionality of a quantum emitter, its impact on their transition energies is barely investigated and exploited. Fluorescent defects in nanosized diamonds constitute an attractive nanophotonic platform to investigate the Lamb shift of an emitter embedded in a dielectric nanostructure with high refractive index. Using spectral and time-resolved optical spectroscopy of single SiV defects, we unveil blue shifts (up to 80 meV) of their emission lines, which are interpreted from model calculations as giant Lamb shifts. Moreover, evidence for a positive correlation between their fluorescence decay rates and emission line widths is observed, as a signature of modifications not only of the photonic local density of states but also of the phononic one, as the nanodiamond size is decreased. Correlative light-electron microscopy of single SiVs and their host nanodiamonds further supports these findings. These results make nanodiamond-SiVs promising as optically driven spin qubits and quantum light sources tunable through nanoscale tailoring of vacuum-field fluctuations.

Mixed-halide triphenyl methyl radicals for site-selective functionalization and polymerization.

Derivatives of the stable, luminescent tris-2,4,6-trichlorophenylmethyl (TTM) radical exhibit unique doublet spin properties that are of interest for applications in optoelectronics, spintronics, and energy storage. However, poor reactivity of the chloride-moieties limits the yield of functionalization and thus the accessible variety of high performance luminescent radicals. Here, we present a pathway to obtain mixed-bromide and chloride derivatives of TTM by simple Friedel-Crafts alkylation. The resulting radical compounds show higher stability and site-specific reactivity in cross-coupling reactions, due to the better leaving group character of the para-bromide. The mixed halide radicals give access to complex, and so far inaccessible luminescent open-shell small molecules, as well as polymers carrying the radical centers in their backbone. The new mixed-halide triphenyl methyl radicals represent a powerful building block for customized design and synthesis of stable luminescent radicals.

Input of solid-state 13 C NMR to study permeation of wet archaeological bones by dicarboxylic fatty diacid-based chemicals.

Conservation treatment of degraded archaeological osseous materials is still an open challenge, since no specific conservation protocol is currently available for restorers or museum curators. This work aims to test the efficiency of two original consolidant solutions in consolidating archaeological material. Archaeological osseous materials remain rare and sparsely available, it is a real drawback for optimization of conservation treatments, therefore in the present work a set of representative samples was chosen. The consolidants tested were a solution of disodium sebacate and a novel polyalcohol (SG1.2) obtained by esterification of 5 succinic diacids with 6 molecules of glycerol at 150°C. Characterization studies of archaeological bones, combining SEM microscopy, IR spectroscopy and high-resolution solid-state 13 C NMR investigations, have been carried out to assess the effective permeation of bone by the consolidant solutions and to determine their chemical interactions with the residual components of archaeological bones. Although both water solutions significantly impregnate bone, we show that, the solution with disodium sebacate leads to chemical attack on the mineral component due to preferential precipitation of endogenous calcium by the sebacate ions. Such deleterious behaviour is not observed at all with the SG1,2 chemicals. The added value of the polyalcohol treatment as strengthening agent suitable for archaeological bony materials should be further demonstrated by mechanical and ageing tests.

Nuclear Magnetic Resonance Reveals Disordered Level-Crossing Physics in the Bose-Glass Regime of the Br-Doped Ni(Cl_{1-x}Br_{x})_{2}-4SC(NH_{2})_{2} Compound at a High Magnetic Field.

By measuring the nuclear magnetic resonance (NMR) T_{1}^{-1} relaxation rate in the Br (bond) doped DTN compound, Ni(Cl_{1-x}Br_{x})_{2}-4SC(NH_{2})_{2}(DTNX), we show that the low-energy spin dynamics of its high magnetic field "Bose-glass" regime is dominated by a strong peak of spin fluctuations found at the nearly doping-independent position H^{*}≅13.6 T. From its temperature and field dependence, we conclude that this corresponds to a level crossing of the energy levels related to the doping-induced impurity states. Observation of the local NMR signal from the spin adjacent to the doped Br allowed us to fully characterize this impurity state. We have thus quantified a microscopic theoretical model that paves the way to better understanding of the Bose-glass physics in DTNX, as revealed in the related theoretical study [M. Dupont, S. Capponi, and N. Laflorencie, Phys. Rev. Lett. 118, 067204 (2017).PRLTAO0031-900710.1103/PhysRevLett.118.067204].

Efficient radio frequency filters for space constrained cryogenic setups.

Noise filtering is an essential part for measurement of quantum phenomena at extremely low temperatures. Here, we present the design of a filter which can be installed in space constrained cryogenic environment containing a large number of signal carrying lines. Our filters have a -3 db point of 65 kHz and their performance at GHz frequencies is comparable to the best available RF filters.