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1.
Normal modes and their dispersion are obtained for syndiotactic polystyrene (sPS) in the planar zigzag and s(2/1)2 helical conformations. Comparison is made with the spectra of isotactic polystyrene (ips) to identify the conformation-sensitive modes; for example, the 1221 cm?1 mode is identified as a skeletal mode sensitive to chain structure and it also shows maximum dispersion. Bunching of dispersion curves and their intersection are among the characteristic features which are discussed. A check on the dispersion curves below 400 cm?1 is made from the spectra of polystyrene oligomers. 相似文献
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Jos I. Urgel Marco Di Giovannantonio Kristjan Eimre Thorsten G. Lohr Junzhi Liu Shantanu Mishra Qiang Sun Amogh Kinikar Roland Widmer Samuel Stolz Max Bommert Reinhard Berger Pascal Ruffieux Carlo A. Pignedoli Klaus Müllen Xinliang Feng Roman Fasel 《Angewandte Chemie (International ed. in English)》2020,59(32):13281-13287
Cumulene compounds are notoriously difficult to prepare and study because their reactivity increases dramatically with the increasing number of consecutive double bonds. In this respect, the emerging field of on‐surface synthesis provides exceptional opportunities because it relies on reactions on clean metal substrates under well‐controlled ultrahigh‐vacuum conditions. Here we report the on‐surface synthesis of a polymer linked by cumulene‐like bonds on a Au(111) surface via sequential thermally activated dehalogenative C?C coupling of a tribenzoazulene precursor equipped with two dibromomethylene groups. The structure and electronic properties of the resulting polymer with cumulene‐like pentagon–pentagon and heptagon–heptagon connections have been investigated by means of scanning probe microscopy and spectroscopy methods and X‐ray photoelectron spectroscopy, complemented by density functional theory calculations. Our results provide perspectives for the on‐surface synthesis of cumulene‐containing compounds, as well as protocols relevant to the stepwise fabrication of carbon–carbon bonds on surfaces. 相似文献
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Shantanu Mishra Doreen Beyer Kristjan Eimre Ricardo Ortiz Joaquín Fernndez‐Rossier Reinhard Berger Oliver Grning Carlo A. Pignedoli Roman Fasel Xinliang Feng Pascal Ruffieux 《Angewandte Chemie (International ed. in English)》2020,59(29):12041-12047
Triangular zigzag nanographenes, such as triangulene and its π‐extended homologues, have received widespread attention as organic nanomagnets for molecular spintronics, and may serve as building blocks for high‐spin networks with long‐range magnetic order, which are of immense fundamental and technological relevance. As a first step towards these lines, we present the on‐surface synthesis and a proof‐of‐principle experimental study of magnetism in covalently bonded triangulene dimers. On‐surface reactions of rationally designed precursor molecules on Au(111) lead to the selective formation of triangulene dimers in which the triangulene units are either directly connected through their minority sublattice atoms, or are separated via a 1,4‐phenylene spacer. The chemical structures of the dimers have been characterized by bond‐resolved scanning tunneling microscopy. Scanning tunneling spectroscopy and inelastic electron tunneling spectroscopy measurements reveal collective singlet–triplet spin excitations in the dimers, demonstrating efficient intertriangulene magnetic coupling. 相似文献
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Dr. Shantanu Ganesh Kulkarni Kristýna Jelínková Dr. Marek Nečas Dr. Zdeňka Prucková Dr. Michal Rouchal Dr. Lenka Dastychová Dr. Petr Kulhánek Dr. Robert Vícha 《Chemphyschem》2020,21(18):2084-2095
Stilbene derivatives are well-recognised substructures of molecular switches based on photochemically and/or thermally induced (E)/(Z) isomerisation. We combined a stilbene motif with two benzimidazolium arms to prepare new sorts of supramolecular building blocks and examined their binding properties towards cucurbit[n]urils (n=7, 8) and cyclodextrins (β-CD, γ-CD) in water. Based on the 1H NMR data and molecular dynamics simulations, we found that two distinct complexes with different stoichiometry, i. e., guest@β-CD and guest@β-CD2, coexist in equilibrium in a water solution of the (Z)-stilbene-based guests. We also demonstrated that the bis(benzimidazolio)stilbene guests can be transformed from the (E) into the (Z) form via UV irradiation and back via thermal treatment in DMSO. 相似文献
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Dr. José I. Urgel Dr. Marco Di Giovannantonio Kristjan Eimre Thorsten G. Lohr Dr. Junzhi Liu Shantanu Mishra Dr. Qiang Sun Amogh Kinikar Dr. Roland Widmer Samuel Stolz Max Bommert Dr. Reinhard Berger Dr. Pascal Ruffieux Dr. Carlo A. Pignedoli Prof. Dr. Klaus Müllen Prof. Dr. Xinliang Feng Prof. Dr. Roman Fasel 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(32):13383-13389
Cumulene compounds are notoriously difficult to prepare and study because their reactivity increases dramatically with the increasing number of consecutive double bonds. In this respect, the emerging field of on-surface synthesis provides exceptional opportunities because it relies on reactions on clean metal substrates under well-controlled ultrahigh-vacuum conditions. Here we report the on-surface synthesis of a polymer linked by cumulene-like bonds on a Au(111) surface via sequential thermally activated dehalogenative C−C coupling of a tribenzoazulene precursor equipped with two dibromomethylene groups. The structure and electronic properties of the resulting polymer with cumulene-like pentagon–pentagon and heptagon–heptagon connections have been investigated by means of scanning probe microscopy and spectroscopy methods and X-ray photoelectron spectroscopy, complemented by density functional theory calculations. Our results provide perspectives for the on-surface synthesis of cumulene-containing compounds, as well as protocols relevant to the stepwise fabrication of carbon–carbon bonds on surfaces. 相似文献
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Chaos synchronization in a master-slave configuration has been studied in this paper with a fractional order (FO) Proportional-Integral-Derivative (PID) controller using an intelligent Bacterial Foraging Optimization (BFO) algorithm. A?comparative study has been made to highlight the advantage of using a fractional order PI ?? D ?? controller over the conventional PID controller for chaos synchronization using two Lu systems as a representative example. Simulation results are presented to show the effectiveness of the proposed chaos synchronization technique over the existing methodologies. 相似文献
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Convective heat transfer within circular microchannels in a rectangular solid substrate with heat generation due to imposed
magnetic field was studied. A detailed parametric study was performed by varying Reynolds number, magnetic field strength,
working fluid, and the diameter of the channel. It was found that the heat transfer coefficient decreases downstream along
the channel. Nusselt number increased with Reynolds number. The tube diameter, properties of the working fluid, and magnetic
field strength affected the temperature distribution and heat transfer rate at the solid-fluid interface. 相似文献
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Algebras and Representation Theory - We introduce the concept of a prime band in a string algebra Λ and use it to associate to Λ its finite bridge quiver. Then we introduce a new... 相似文献
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Ujjwal Mandal Subhadip Ghosh Dibyendu Kumar Das Aniruddha Adhikari Shantanu Dey Kankan Bhattacharyya 《Journal of Chemical Sciences》2008,120(1):15-23
Fluorescence resonance energy transfer (FRET) from Coumarin 153 (C153) to Rhodamine 6G (R6G) in a secondary aggregate of a
bile salt (sodium deoxycholate, NaDC) is studied by femtosecond up-conversion. The emission spectrum of C153 in NaDC is analysed
in terms of two spectra-one with emission maximum at 480 nm which corresponds to a non-polar and hydrophobic site and another
with maximum at ∼530 nm which arises from a polar hydrophilic site. The time constants of FRET were obtained from the rise
time of the emission of the acceptor (R6G). In the NaDC aggregate, FRET occurs in multiple time scales — 4 ps and 3700 ps.
The 4 ps component is assigned to FRET from a donor (D) to an acceptor (A) held at a close distance (R
DA ∼ 17 ?) inside the bile salt aggregate. The 3700 ps component corresponds to a donor-acceptor distance ∼48 ?. The long (3700
ps) component may involve diffusion of the donor. With increase in the excitation wavelength (λ
ex) from 375 to 435 nm, the relative contribution of the ultrafast component of FRET (∼4 ps) increases from 3 to 40% with a
concomitant decrease in the contribution of the ultraslow component (∼3700 ps) from 97 to 60%. The λ
ex dependence is attributed to the presence of donors at different locations. At a long λ
ex (435 nm) donors in the highly polar peripheral region are excited. A short λ
ex (375 nm) ‘selects’ donor at a hydrophobic location. 相似文献