1,721,091 research outputs found
Energy Transfer in Nanotube-Perylene Complexes
No full textA functional surfactant designed to solubilize and individualize nanotubes efficiently in aqueous media and to form energy transfer complexes with the carbon nanotubes through π–π stacking is presented. Upon excitation of the adsorbed perylene unit an emission from the nanotubes is observed that indicates a successful excitation transfer. The efficiency of the indirect excitation via the adsorbant is of the same order of magnitude as the direct excitation of the nanotubes. Under optimized preparation conditions the pH independent perylene-imido-diester compound isolates and solubilizes carbon nanotubes in biocompatible aqueous environments without additional surfactants. The resulting solutions are stable over many months
Designing a spiropyran-based molecular switch for carbon nanotube functionalization: Influence of anchor groups and tube-switch separation
No full textMolecular switch compounds, consisting of aromatic anchoring groups connected to a spiropyran moiety, are exploited for carbon nanotube functionalization. The effect of the different anchor groups on sample distribution and debundling efficiency is investigated as well as the influence of the anchor–switch distance and hence tube–switch separation. Morphologically similar anchor groups result in similar chiral compositions of the sample. With smaller separation, the tube–switch interaction strength increases as well as the lifetime of the ring opened isomer
Non-Covalent Functionalization of Individual Nanotubes with Spiropyran-Based Molecular Switches
No full textSingle-walled carbon nanotubes (SWCNTs) are functionalized with a spiropyran derivative, which is attached non-covalently to the SWCNT's sidewall via a pyrene anchor group. Using this non-covalent functionalization strategy, individual SWCNTs can be stabilized in solution without the need for additional surfactants. Bright luminescence confirms the presence of individual tubes in the thus-prepared samples. In these samples, the majority of pyrene-spiropyran molecules are attached to the walls of the SWCNTs. Upon complex formation with the SWCNT, the switching moiety retains its ability to switch, i.e., to undergo reversible transformations between the closed spiropyran and the opened merocyanine form, and is stable over many cycles of operation
Functional Surfactants for Carbon Nanotubes: Effects of Design
No full textSurfactants are needed to create stable suspensions of carbon nanotubes. Increasingly, these surfactants are given additional functionalities, resulting in bigger and more complex molecules with several subunits. We investigate the effect of assembly of these subunits for a class of perylene-based functional surfactants. The subunits that all surfactants are based on are a perylene core, hydrophilic polyglycerol dendrons, and alkyl chains of different orientations and lengths. The assembly of these subunits affects both the molecules' performance as a surfactant and the efficiency of the energy-transfer complexes formed by the nanotube and surfactant through a π–π stacking mechanism. This results in a best practice guide for designing functional surfactants with π–π stacking cores, and affords more general insights that are applicable to non π–π stacking systems as well
Chirally enhanced solubilization through perylene-based surfactant
No full textRecently we introduced a rationally designed surfactant which forms energy transfer complexes with carbon nanotubes. We investigate the chiral selectivity of this compound, a perylene derived surfactant, through photoluminescence (PL) measurements, and find a strong enhancement of the luminescence intensity for one particular group of chiralities. The effect is striking, with luminescence increases of several hundred percent.
Chiral selectivity of the investigated surfactant compound as compared to solubilization through sodium cholate (SC). Small numbers indicate chirality, large numbers laola family
Excitation characteristics of different energy transfer in nanotube-perylene complexes
Full text linkWe report the properties of perylene-nanotube complexes that form efficient energy transfer systems. Most perylene-derivatives yield similar ratios between transfer and direct luminescence (0.66 ± 0.04). The photoluminescence spectra of the free compounds and the transfer complex are similar indicating that perylene and nanotubes act as separate systems. A further increase in interaction yields 40% higher transfer rates and luminescence excitation spectra that indicate a change in stacking of the perylene on the nanotube wall. All measurements are consistent with a transfer mechanism based on a dipole-dipole interaction at a distance much smaller than the Förster radius
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
- …
