An Arylazopyrazole‐Based N‐Heterocyclic Carbene as a Photoswitch on Gold Surfaces: Light‐Switchable Wettability,Work Function,and Conductance

A novel photoresponsive and fully conjugated N‐heterocyclic carbene (NHC) has been synthesized that combines the excellent photophysical properties of arylazopyrazoles (AAPs) with an NHC that acts as a robust surface anchor (AAP‐BIMe). The formation of self‐assembled monolayers (SAMs) on gold was proven by ToF‐SIMS and XPS, and the organic film displayed a very high stability at elevated temperatures. This stability was also reflected in a high desorption energy, which was determined by temperature‐programmed SIMS measurements. E‐/Z‐AAP‐BIMe@Au photoisomerization resulted in reversible alterations of the surface energy (i.e. wettability), the surface potential (i.e. work function), and the conductance (i.e. resistance). The effects could be explained by the difference in the dipole moment of the isomers. Furthermore, sequential application of a dummy ligand by microcontact printing and subsequent backfilling with AAP‐BIMe allowed its patterning on gold. To the best of our knowledge, this is the first example of a photoswitchable NHC on a gold surface. These properties of AAP‐BIMe@Au illustrate its suitability as a molecular switch for electronic devices.     

Association behavior of linear ω-functionalized polybutadienes in cyclohexane

The dilute solution properties of linear polybutadienes with dimethylamine and zwitterionic end groups were studied by membrane osmometry (MO), low-angle laser light scattering (LALLS), viscometry, and dynamic light scattering (DLS) in cyclohexane. The polymers were prepared by anionic polymerization, under high vacuum conditions using [3-(dimethylamino)propyl]lithium as initiator. The dimethylamine groups were converted to zwitterions by reaction with cyclopropane sultone. No evidence of association was found for the amine-capped polymers, whereas the zwitterionic samples exhibited strong association in cyclohexane. The degrees of association increase by decreasing molecular weight of the base polymer due to the excluded volume repulsions. These aggregation numbers are of the same order as those found for ω-functionalized polyisoprenes, with the same polar groups in the same solvent. The hydrodynamic properties, measured by viscometry and dynamic light scattering, supported the conclusions drawn by LALLS and provide strong evidence that the aggregates behave hydrodynamically as star polymers. Comparison with theoretical models shows that the association behavior is best described by the linear head packing model. © 1996 John Wiley & Sons, Inc.     

Surface Tension of the 4-Methyl-2-Pentanone/Ethyl Benzoate Binary System in the Temperature Range from 278.15 to 308.15K

Surface tensions (σ) and densities (ρ) of 4-methyl-2-pentanone/ethyl benzoate binary mixtures have been measured over the entire composition range at 278.15, 288.15, 298.15, and 308.15 K. Values of the excess surface tensions (σ^E) and excess molar volumes (V^E) have been calculated. The σ^E and V^E values were fitted by to the Redlich–Kister polynomial equation and the A_k coefficients have been derived. The standard deviations between the calculated and the experimental excess properties have also been derived. The surface tension values have been further used to calculate the surface entropies (S^S) and surface enthalpies (H^S) per unit surface area. The lyophobicity (β) and the surface mole fractions (x₁^S) of the surfactant 4-methyl-2-pentanone have been derived using the extended Langmuir model. The obtained results are discussed from the viewpoint of the existence of specific interactions between unlike molecules in the bulk region and the surface.     

Amino acid functionalisation of water soluble carbon nanotubes

High solubility of SWNTs and MWNTs in water is obtained by organic functionalisation; derivatisation with N-protected glycine is also easily achieved.     

Sidewall functionalization of single-walled carbon nanotubes through electrophilic addition

Electrophilic addition of chloroform to SWNTs followed by hydrolysis resulted in the addition of hydroxy groups to the surface of the nanotubes; further esterification with propionyl chloride led to the corresponding ester derivatives, which allowed us to identify their structure, also providing better solubility in organic solvents.     

Compatibility of poly(ethylene oxide)–poly(vinyl acetate) blends

The compatibility of poly(ethylene oxide)–poly(vinyl acetate) (PEO-PVA) blends was examined at five compositions covering the complete range. Samples were prepared by coprecipitation and solution casting. Dynamic mechanical properties were studied at 110 Hz between ?120 and 65°C for dry, quenched, and annealed samples. The study also included tensile testing at 25°C, examination of blend morphology, and DSC measurements at elevated temperatures. Optical microscopy revealed that crystallization of PEO proceeds essentially unhindered at up to 25% poly(vinyl acetate) content by weight. Higher levels of this component drastically reduce spherulite size, and at the highest PVA compositions there was no evidence of crystallization. Thermomechanical spectra of quenched and annealed samples indicate limited mixing of the two components except for the higher (>75%) PVA compositions. Tensile properties show a mutual reinforcement at 10-25% PVA content due to possible polymer segment association. The melting-point depression of PEO is significant above 25% PVA and has been attributed to morphological changes of the PEO crystalline phase.     

The structure of strongly stationary systems

Motivated by a problem in ergodic Ramsey theory, Furstenberg and Katznelson introduced the notion of strong stationarity, showing that certain recurrence properties hold for arbitrary measure preserving systems if they are valid for strongly stationary ones. We construct some new examples and prove a structure theorem for strongly stationary systems. The building blocks are Bernoulli systems and rotations on nilmanifolds.     

On the nature of the BOLD fMRI contrast mechanism

Since its development about 15 years ago, functional magnetic resonance imaging (fMRI) has become the leading research tool for mapping brain activity. The technique works by detecting the levels of oxygen in the blood, point by point, throughout the brain. In other words, it relies on a surrogate signal, resulting from changes in oxygenation, blood volume and flow, and does not directly measure neural activity. Although a relationship between changes in brain activity and blood flow has long been speculated, indirectly examined and suggested and surely anticipated and expected, the neural basis of the fMRI signal was only recently demonstrated directly in experiments using combined imaging and intracortical recordings. In the present paper, we discuss the results obtained from such combined experiments. We also discuss our current knowledge of the extracellularly measured signals of the neural processes that they represent and of the structural and functional neurovascular coupling, which links such processes with the hemodynamic changes that offer the surrogate signal that we use to map brain activity. We conclude by considering applications of invasive MRI, including injections of paramagnetic tracers for the study of connectivity in the living animal and simultaneous imaging and electrical microstimulation.     

Observation of discrete solitons in optically induced real time waveguide arrays

We report the first experimental observation of discrete solitons in an array of optically induced waveguides. The waveguide lattice is induced in real time by illuminating a photorefractive crystal with a pair of interfering plane waves. We demonstrate two types of bright discrete solitons: in-phase self-localized states and the staggered (pi out-of-phase) soliton family. This experiment is the first observation of bright staggered solitons in any physical system. Our scheme paves the way for reconfigurable focusing and defocusing photonic lattices where low-power (mW) discrete solitons can be thoroughly investigated.     

Anion recognition by functionalized single wall carbon nanotubes

Amidoferrocenyl-functionalised single wall carbon nanotubes (Fc-SWNT) are efficient exoreceptors for the redox recognition of H2PO4-.