1,720,968 research outputs found
Fluorinated Styrene-Based Monomers for Cyclopolymerizations
No full textThe synthesis of versatile fluorine compounds and monomers for conducting polymer research and cyclopolymerizations is presented. Semiprotected 2,3,5,6-tetrafluoroterephthaldehyde 1 could be elaborated through Wittig olefination chemistry, deprotection and reduction to the previously unknown 4-vinyl-2,3,5,6-tetrafluorobenzylalcohol 8 in good yields. Compound 8 can be reacted to form the malonate ester, and then alkylation on the malonate moiety in mild conditions affords difunctional monomer 3. Through sequential esterifications on the malonate moiety, and subsequent alkylation, compound 4, a difunctional monomer for cyclopolymerization bearing one styrene and one perfluoroaryl styrene moiety, has been obtained. Preliminary experiments show that it is possible to cyclopolymerize 4 under free radical conditions
Mild Preparation of Functionalized [2.2]Paracyclophanes via the Pummerer Rearrangement
No full text[2.2]Paracyclophanes, incorporating functional groups in
the aliphatic bridges, suitable for elimination to give
[2.2]paracyclophanedienes, are synthesized through a novel
approach. It relies on a double Pummerer rearrangement on
dithiacyclophane precursors, followed by ring contraction
through a photochemical sulfur extrusion, and it is compatible
with aryl moieties possessing very different electronic
properties
Nanostructuring with chirality: binaphthyl-based synthons for the production of functional oriented nanomaterials
No full textChirality is a powerful tool for the generation of order, directionality, and, as such, of function, in assembled nanoscale chemical devices. Axially chiral binaphthyls have been widely used in organic synthesis; the stability of the enantiomers enables their use as robust chirality inducers and catalysts in asymmetric reactions, and they are nowadays industrially applied in a variety of organic transformations. Applications of these compounds in the field of nanosciences are more recent, and not yet fully explored. The integration of such a robust class of chiral compounds, capable of efficient transfer of stereochemical information, into functional aggregates and nanoarchitectures is of great current interest. We will discuss preeminent examples of applications of these synthons in several fields of nanoscience, such as reticular chemistry, non-linear optical materials and imaging, and liquid crystals
Controlled RAFT Cyclopolymerization of Oriented Styrenic Difunctional Monomers
No full textWe describe the first example of controlled free radical cyclopolymerization of difunctional styrenic monomers. The newly designed monomers are obtained from the introduction of two 4-vinylbenzyl moieties as malonate or dialkylated malonate esters. The more sterically hindered monomer is particularly efficient in the cyclization and propagation processes, giving cyclopolymers, in diluted solvent conditions, in good yields and degrees of polymerization. In the presence of a suitable RAFT mediator, and, upon careful optimization of the solvent, temperature and monomer concentration, linear increase of number average molecular weight with conversion and low polydisperisity indexes can be achieved
Polystyrene-based self-aggregating polymers based on UPy units
No full textThe synthesis and characterization of a series of polystyrene (PS)-based copolymers, bearing 2-ureido-4[1H]-pyrimidinone (UPy) units pendant from the polymer backbone, is reported. The PS-based copolymers are efficiently synthesized by RAFT-mediated free radical polymerization performed on styrene and protected 4-vinylbenzylamine, and post-modification with suitable UPy-derived isocyanates to give the target polymers. Analysis of the samples in solution reveals that the polymer chains aggregate to give organic nanoparticles of discrete and uniform dimensions, whose direct visualization when deposited on surfaces can be achieved using AFM
Spectroscopic and Electrochemical Sensing of Lanthanides with p-Extended Chromophores Incorporating Ferrocenes and a Coordinative End
No full textIn this study, we report the synthesis and characterization of three novel “push-pull” chromophores, in which multiple phenylenevinylene units are endcapped by ferrocene as donor units and malonate moieties as acceptor units. These chromophores have spectroscopic and electrochemical characteristics which consistently change according to the extension of the conjugated bridge, thus to the variation of the HOMO-LUMO band gap. The 1,3-dicarbonyl units, directly incorporated into the conjugated molecular structures, are able to coordinate Lewis acid-like cations, such as lanthanides, as confirmed by UV/Vis, 1H NMR and cyclic voltammetry studies. The UV/Vis spectroscopic response upon complexation with Sc3+ or Eu3+ as the triflate salts is rather unselective and nonlinear in going from the least to the most -extended chromophore. Binding studies in MeCN, analyzed via equilibrium-restricted factor analysis, give values between log Ka = 1.21 and 3.07 and affirm a 1:1 stoichiometry of the host:guest complexes in all cases. On the other hand, cyclic voltammetry reveals a selectivity in the response to Sc3+ coordination over Ln3+ (Eu3+, but also Lu3+ and Er3+ were tested) for the two shorter chromophores, whereas the ligand with the longest -bridge is able to sense Er3+ (E1/2 complexed/uncomplexed chromophore = 20 mV) selectively over the other lanthanides
Switching of Emissive and NLO Properties in Push-Pull Chromophores with Crescent PPV-like Structures
Get PDFWe report on a series of novel homologous push-pull compounds, in which identical donor (a dimethylamino) and acceptor (a malonate ester) functionalities endcap crescent PPV fragments, bearing respectively 1, 2 and 3 p-phenylenevinylene units in direct linear conjugation (compounds 7-9). The three compounds exhibit striking differences in their linear and nonlinear optical properties. The shorter compound 7 exhibits aggregation-induced emission with a strong luminescence in the solid state (blue emission, photoluminescence quantum yield 38%), and it is nonemissive in solution; the more extended conjugated systems 8 and 9 show classical aggregation-caused quenching in the solid state, while high quantum yield photoluminescence (21 and 93% in toluene) is restored in diluted solutions, through mechanisms involving intramolecular charge transfer in the excited states. EFISH measurements in solutions demonstrate a strong solvent and concentration dependence. As rationalized with the aid of molecular modelling, compound 8 and, more markedly 9, aggregate in stable centrosymmetric dimers in solution
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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