Search results for "Witch"
showing 10 items of 542 documents
A Dendrimer Chiroptical Switch Based on the Reversible Intramolecular Photoreaction of Anthracene and Benzene Rings
2010
A series of Fréchet-type dendrimers with 9-benzyloxymethylanthracene cores were synthesized and characterized. The chiral source for the dendrimers was an (S)-2-methyl-1-butoxy group in the 3-position of the benzene ring. Irradiation at 366 nm of a dilute benzene solution led to the formation of two diastereomers (1:1) through a quantitative intramolecular [4pi+4pi] cycloaddition between the central anthracene ring and the neighboring benzene ring. The process can be reversed with 254 nm UV light or heat. The benzene rings in the dendrons work as a light-harvesting system. The optical rotation values measured for the reversible process showed fatigue resistance. Thus, a promising new type o…
A pH-triggered bistable copper(II) metallacycle as a reversible emulsion switch for biphasic processes.
2013
A unique bistable copper-metallacyclic complex is used as an elegant molecular switch for the reversible formation of emulsions by simple pH variation. This switch may have several exciting applications in biphasic processes such as catalysis and separation science technologies.
Helicates with Ether-Substituted Catechol Esters as Ligands
2020
European journal of organic chemistry 2020(32), 5161-5172 (2020). doi:10.1002/ejoc.202000843
Synthesis and immobilization of molecular switches onto titaniumdioxide nanowires
2009
Abstract The precursor [Fe III (L)Cl (L = N , N ′-bis(2′-hydroxy-3′-methyl-benzyliden)-1,7-diamino-4-azaheptane) is combined with [Mo(CN) 8 ] 4− yields a star shaped nona-nuclear cluster, [Mo IV {(CN)Fe III (L)} 8 ]Cl 4 . This Fe 8 Mo molecule is a high-spin system at room temperature. On cooling to 20 K some of the iron(III) centres in the molybdenum(IV)-star switch to the low-spin state as proven by Mossbauer spectroscopy. This molecule was deposited on TiO 2 nanowires by electrostatic interactions between the cluster cations and the surface functionalized titanium oxide nanowire. The synthesis and surface binding of the multistable molecular switch was demonstrated using IR and UV–Vis s…
Dinuclear Iron(II) Spin Crossover Compounds: Singular Molecular Materials for Electronics
2006
Dinuclear spin crossover molecules can adopt three different spin-pair states: a fully diamagnetic low spin state, [LS–LS], with both iron(II) atoms in the LS state; a paramagnetic mixed spin-pair state [LS–HS]; and an antiferromagnetically coupled [HS–HS] state. Stabilisation of the [LS–HS] state depends on a subtle balance between intra- and inter-molecular interactions in the solid state, consequently, the thermal dependence of the physical and structural properties can present one-step or two-step spin transitions. The former case involves the [LS–LS] ↔ [HS–HS] transformation while in the latter case the intermediate stage responsible for the plateau, at 50% conversion between the two s…
Spin crossover in a catenane supramolecular system.
1995
The compound [Fe(tvp)(2)(NCS)(2)] . CH(3)OH, where tvp is 1,2-di-(4-pyridyl)-ethylene, has been synthesized and characterized by x-ray single-crystal diffraction. It consists of two perpendicular, two-dimensional networks organized in parallel stacks of sheets made up of edge-shared [Fe(II)](4) rhombuses. The fully interlocked networks define large square channels in the [001] direction. Variable-temperature magnetic susceptibility measurements and Mossbauer studies reveal that this compound shows low-spin to high-spin crossover behavior in the temperature range from 100 to 250 kelvin. The combined structural and magnetic characterization of this kind of compound is fundamental for the inte…
Phycocyanobilin in solution – a solvent triggered molecular switch
2014
We present a computational investigation of the conformational response of phycocyanobilin (PCB) to the ability of solvents to form hydrogen bonds. PCB is the chromophore of several proteins in light harvesting complexes. We determine the conformational distributions in different solvents (methanol and hexamethylphosphoramide HMPT) by means of ab initio molecular dynamics simulations and characterize them via ab initio calculations of NMR chemical shift patterns. The computed trajectories and spectroscopic fingerprints illustrate that the energy landscape is very complex and exhibits various conformations of similar energy. We elucidate the strong influence of the solvent characteristics on…
Reversible and Efficient Light-Induced Molecular Switching on an Insulator Surface
2018
Prototypical molecular switches such as azobenzenes exhibit two states, i.e., trans and cis, with different characteristic physical properties. In recent years various derivatives were investigated on metallic surfaces. However, bulk insulators as supporting substrate reveal important advantages since they allow electronic decoupling from the environment, which is key to control the switching properties. Here, we report on the light-induced isomerization of an azobenzene derivative on a bulk insulator surface, in this case calcite (101̅4), studied by atomic force microscopy with submolecular resolution. Surprisingly, cis isomers appear on the surface already directly after preparation, indi…
Molecular Switching, Logics, and Memories
2013
The concepts of molecular switch, molecular logics and memories are intimately related. In this work a review of these three topics is given. While the main examples concern the field of inorganic chemistry, in a few cases organic systems are presented to better illustrate the concepts. The basic notions of the logics gates usually used by the nowadays computers is presented and the modus operandi to transpose these concepts to the molecular level is discussed. Examples of switches driven by external stimuli such as light-induced, metal-ion, redox, photobistable, and complexation–decomplexation are described in this chapter. The extension of switches working in solution to solid devices are…
On the FCNS⇆FC(NS) reaction: A matrix isolation and theoretical study
2015
Abstract The FCNS ⇆ FC(NS) photoisomerization process is a simple model system for molecular switches. Here, we examined the switching processes by experimental and theoretical methods. Prior matrix-isolation IR spectroscopic studies were complemented by matrix-isolation UV spectroscopic measurements to assist the interpretation of the mechanism of the ring closure and opening processes and to verify the accuracy of the computations on the vertical excitation energies. Vertical excitation energies were computed by the EOMEE-CCSD, MCSCF, and MR-CISD methods. Conical intersections were also searched for and three conical intersections along the reaction path FCNS → FC(NS) were located, one co…