Transition Metal Trichalcogenides as Novel Layered Nano Species

In search for new materials for nanoelectronics, many efforts have been put into development of chem-istry and physics of graphene, and, more recently, of other inorganic layered compounds having a bandgap (h-BN, MoS2 etc.). Here we introduce a new view on the family of transition metal trichalcogenides MQ3 (M=Ti, Zr, Nb, Ta; Q=S, Se), which were earlier considered as quasi-one-dimensional systems, and demon-strate that they also may be regarded as layered species suitable for exfoliation by a chemical method. Stable, concentrated colloidal dispersions of high-quality crystalline NbS3 and NbSe3 nanoribbons down to mono- and few-layer-thick are prepared by ultrasonic treatment of the bulk compound in several common organic solvents (DMF, NMP, CH3CN, iPrOH, H2O/EtOH). The dispersions and thin films prepared from them by vacuum filtration or spraying are characterized by a set of physical-chemical methods. Current-voltage characteristics of the NbS3 films show that charge carrier mobility is as high as 1200 – 2400 cm2V-1s-1, exceeding that of MoS2 and making NbQ3 promising potential candidates for field-effect transistors. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3522

Near Ambient Pressure XPS and MS Study of CO Oxidation over Model Pd Au HOPG Catalysts The Effect of the Metal Ratio

In this study, the dependence of the catalytic activity of highly oriented pyrolytic graphite HOPG supported bimetallic Pd Au catalysts towards the CO oxidation based on the Pd Au atomic ratio was investigated. The activities of two model catalysts differing from each other in the initial Pd Au atomic ratios appeared as distinctly different in terms of their ignition temperatures. More specifically, the PdAu 2 sample with a lower Pd Au surface ratio 0.75 was already active at temperatures less than 150 C, while the PdAu 1 sample with a higher Pd Au surface ratio 1.0 became active only at temperatures above 200 C. NAP XPS revealed that the exposure of the catalysts to a reaction mixture at RT induces the palladium surface segregation accompanied by an enrichment of the near surface regions of the two component Pd Au alloy nanoparticles with Pd due to adsorption of CO on palladium atoms. The segregation extent depends on the initial Pd Au surface ratio. The difference in activity between these two catalysts is determined by the presence or higher concentration of specific active Pd sites on the surface of bimetallic particles, i.e., by the ensemble effect. Upon cooling the sample down to room temperature, the reverse redistribution of the atomic composition within near surface regions occurs, which switches the catalyst back into inactive state. This observation strongly suggests that the optimum active sites emerge under reaction conditions exclusively, involving both high temperature and a reactive atmospher

Supramolecular tuning of energy transfer efficiency and direction in a bis(styryl) dye–crown ether conjugate

The control of the energy transfer (FRET) in a novel bischromophoric styryl(pyridinium) dye bearing two different crown ether residues is presented. Complexation of the dye with metal cations allows to tune the FRET efficiency without changing the transfer direction or to switch the FRET off, whereas protonation launches the FRET process in the opposite direction relative to the molecular structure. © 2018 Elsevier Lt

Supramolecular tuning of energy transfer efficiency and direction in a bis(styryl) dye–crown ether conjugate

The control of the energy transfer (FRET) in a novel bischromophoric styryl(pyridinium) dye bearing two different crown ether residues is presented. Complexation of the dye with metal cations allows to tune the FRET efficiency without changing the transfer direction or to switch the FRET off, whereas protonation launches the FRET process in the opposite direction relative to the molecular structure. © 2018 Elsevier Lt

Light-induced piston nanoengines: Ultrafast shuttling of a styryl dye inside cucurbit[7]uril

The combination of photoactive styryl(pyridinium) dyes and cucurbit[7]uril (CB[7]) in an integrated supramolecular system allowed us to design a novel high speed molecular machine based on the fully reversible shuttling motion of the dye inside the CB[7] host cavity. The driving force of this movement is the electrostatic potential change after the occurrence of intramolecular charge transfer in the excited state of the dye molecule that can be externally controlled by light. Steady-state and time-resolved optical spectroscopy as well as DFT calculations provided an unambiguous evidence for the ultrafast piston-like movement of the system between two states. The shuttling process occurs in the picosecond timescale and its bistability depends on the strength of the dye donor fragment. © the Owner Societies 2017

Isomeric naphthalimides bearing pyran units: Insight into mutual relation between structure and photochromic properties

Two novel isomeric photochromic naphthopyrans (1 and 2) containing naphthalimide moieties were prepared and studied. In the compound 1, O-atom of pyran cycle is at C-3 position of naphthalene ring, whereas, in compound 2, O-atom of pyran cycle is at C-4 position. In the compound 2 due to para-position O-atom of pyran photochrome cycle is involved into the conjugated naphthalimide system. The variety in mutual position of pyran and naphthalimide units leads to remarkable difference in photochromic characteristics. Both compounds demonstrate the switching of the fluorescence by photoinduced conversion between the closed and open forms

Regio- and stereoselective [2+2] photocycloaddition in Ba2+ templated supramolecular dimers of styryl-derivatized aza-heterocycles

The regio- and stereoselective [2+2] photocycloaddition of 15-crown-5-containing styrylheterocycles resulting in formation of only one cyclobutane isomer out of eleven possible is described. It was shown that the cycloaddition takes place solely in the case of the supramolecular preorganization of the reactive molecules provided by both π–π stacking interaction of the heterocyclic fragments and sandwich-type coordination of the crown ether residues by the barium cation. The results point out the importance of the supramolecular approach for the synthesis of cyclobutane derivatives with desired structure and conformation. © 2016 Elsevier Lt

Regio- and stereoselective [2+2] photocycloaddition in Ba2+ templated supramolecular dimers of styryl-derivatized aza-heterocycles

The regio- and stereoselective [2+2] photocycloaddition of 15-crown-5-containing styrylheterocycles resulting in formation of only one cyclobutane isomer out of eleven possible is described. It was shown that the cycloaddition takes place solely in the case of the supramolecular preorganization of the reactive molecules provided by both π–π stacking interaction of the heterocyclic fragments and sandwich-type coordination of the crown ether residues by the barium cation. The results point out the importance of the supramolecular approach for the synthesis of cyclobutane derivatives with desired structure and conformation. © 2016 Elsevier Lt