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Evolution of lattice, spin, and charge properties across the phase diagram of FeSe1-x Sx
2022, Lazarević, N., Baum, A., Milosavljević, A., Peis, L., Stumberger, R., Bekaert, J., Šolajić, A., Pešić, J., Wang, Aifeng, Šćepanović, M., Abeykoon, A. M. Milinda, Milošević, M.V., Petrovic, C., Popović, Z.V., Hackl, R.
A Raman scattering study covering the entire substitution range of the FeSe1-xSx solid solution is presented. Data were taken as a function of sulfur concentration x for 0≤x≤1, of temperature and of scattering symmetry. All types of excitations including phonons, spins, and charges are analyzed in detail. It is observed that the energy and width of the iron-related B1g phonon mode vary continuously across the entire range of sulfur substitution. The A1g chalcogenide mode disappears above x=0.23 and reappears at a much higher energy for x=0.69. In a similar way the spectral features appearing at finite doping in A1g symmetry vary discontinuously. The magnetic excitation centered at approximately 500 cm-1 disappears above x=0.23 where the A1g lattice excitations exhibit a discontinuous change in energy. The low-energy mode associated with fluctuations displays maximal intensity at the nematostructural transition and thus tracks the phase boundary.
Mixed-halide triphenyl methyl radicals for site-selective functionalization and polymerization
2021, Chen, Lisa, Arnold, Mona, Blinder, Rémi, Jelezko, Fedor, Kuehne, Alexander J. C.
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.