Synthesis and Optoelectronic Properties of <i>Janus</i>-Dendrimer-Type Multivalent Donor–Acceptor Systems

A convergent, multistep protocol was employed for the synthesis of a <i>Janus</i>-type multivalent donor–acceptor system. The synthetic approach is based on a Sonogashira cross-coupling of two differently ferrocene-(Fc) substituted dendrons and a final sixfold [2 + 2] cycloaddition−retroelectrocyclization (CA−RE) reaction with tetracyanoethene, which occurs regioselectively at only one of the rigidly linked dendrons. The structural and optoelectronic properties of the compounds were investigated by X-ray analysis, UV/vis spectroscopy, and electrochemistry. The target <i>Janus</i>-system displays redox-amphoteric behavior. The nonalkynylated Fc end groups in one dendron are readily and reversibly oxidized. The second dendron, in which the terminal Fc-activated alkynes underwent the CA−RE reaction to give tetracyanobuta-1,3-dienes in the final step of the synthesis, undergoes four reversible 3-e^– reductions in the very narrow potential range of 1 V. A spontaneous intramolecular charge transfer from the donor into the acceptor hemisphere was not observed. Furthermore, the oxidation potential of the Fc donors in one hemisphere is hardly perturbed by the push–pull acceptors in the other, which suggests that electronic communication along the π-system, with several <i>meta</i>-connectivities, is not efficient. Therefore, the charge-transfer bands seen in the <i>Janus</i>-type system originate from the interaction of the Fc donors with the directly connected tetracyanobuta-1,3-diene acceptors in the same hemisphere

Influence of Environment on the Measurement of Rates of Charge Transport across Ag^TS/SAM//Ga₂O₃/EGaIn Junctions

This paper investigates the influence of the atmosphere used in the fabrication of top electrodes from the liquid eutectic of gallium and indium (EGaIn) (the so-called “EGaIn” electrodes), and in measurements of current density, <i>J</i>(V) (A/cm²), across self-assembled monolayers (SAMs) incorporated into Ag/SR//Ga₂O₃/EGaIn junctions, on values of <i>J</i>(V) obtained using these electrodes. A gas-tight measurement chamber was used to control the atmosphere in which the electrodes were formed, and also to control the environment in which the electrodes were used to measure current densities across SAM-based junctions. Seven different atmospheresair, oxygen, nitrogen, argon, and ammonia, as well as air containing vapors of acetic acid or waterwere surveyed using both “rough” conical-tip electrodes, and “smooth” hanging-drop electrodes. (The manipulation of the oxide film during the creation of the conical-tip electrodes leads to substantial, micrometer-scale roughness on the surface of the electrode, the extrusion of the drop creates a significantly smoother surface.) Comparing junctions using both geometries for the electrodes, across a SAM of <i>n</i>-dodecanethiol, in air, gave log |<i>J</i>|_mean = −2.4 ± 0.4 for the conical tip, and log |<i>J</i>|_mean = −0.6 ± 0.3 for the drop electrode (and, thus, Δlog |<i>J</i>| ≈ 1.8); this increase in current density is attributed to a change in the effective electrical contact area of the junction. To establish the influence of the resistivity of the Ga₂O₃ film on values of <i>J</i>(V), junctions comprising a graphite electrode and a hanging-drop electrode were compared in an experiment where the electrodes did, and did not, have a surface oxide film; the presence of the oxide did not influence measurements of log |<i>J</i>(V)|, and therefore did not contribute to the electrical resistance of the electrode. However, the presence of an oxide film did improve the stability of junctions and increase the yield of working electrodes from ∼70% to ∼100%. Increasing the relative humidity (RH) in which <i>J</i>(V) was measured did not influence these values (across methyl (CH₃)- or carboxyl (CO₂H)-terminated SAMs) over the range typically encountered in the laboratory (20%–60% (RH))

‘I have given myself up to the study of the State’: Wyndham Lewis, Modernism, the Avant-garde, and the State

In his introduction to the recent Cambridge Companion to Wyndham Lewis, Tyrus Miller describes the modernist painter, novelist, and critic Wyndham Lewis (1882 - 1957) as an embodiment of ‘the boundary crossing nature of the avant - garde’ (2016, p. 6). In Miller’s account, the avant - garde of the early twentieth century ‘tore apar t the conventional boundaries between the various arts, between artistic and political activity, and between aesthetic works and conceptual discourse’ (2016 p. 6). The historical avant - garde — by which is meant the various groupings of artists of experimenta l artists and writers which emerged across Europe in the years prior to the First World War — can be broadly characterised by its vehement opposition to bourgeois society, and its conception of the potential of experimental art and literature to act as a cat alyst for radical social change

Donor-Substituted Octacyano[4]dendralenes: Investigation of π‑Electron Delocalization in Their Radical Ions

Symmetrically and unsymmetrically electron-donor-substituted octacyano[4]­dendralenes were synthesized and their opto-electronic properties investigated by UV/vis spectroscopy, electrochemical measurements (cyclic voltammetry (CV) and rotating disk voltammetry (RDV)), and electron paramagnetic resonance (EPR) spectroscopy. These nonplanar push–pull chromophores are potent electron acceptors, featuring potentials for first reversible electron uptake around at −0.1 V (vs Fc⁺/Fc, in CH₂Cl₂ + 0.1 M <i>n</i>-Bu₄NPF₆) and, in one case, a remarkably small HOMO–LUMO gap (Δ<i>E</i> = 0.68 V). EPR measurements gave well-resolved spectra after one-electron reduction of the octacyano[4]­dendralenes, whereas the one-electron oxidized species could not be detected in all cases. Investigations of the radical anions of related donor-substituted 1,1,4,4-tetracyanobuta-1,3-diene derivatives revealed electron localization at one 1,1-dicyanovinyl (DCV) moiety, in contrast to predictions by density functional theory (DFT) calculations. The particular factors leading to the charge distribution in the electron-accepting domains of the tetracyano and octacyano chromophores are discussed

Filter-Based Assay for Escherichia coli in Aqueous Samples Using Bacteriophage-Based Amplification

This paper describes a method to detect the presence of bacteria in aqueous samples, based on the capture of bacteria on a syringe filter, and the infection of targeted bacterial species with a bacteriophage (phage). The use of phage as a reagent provides two opportunities for signal amplification: (i) the replication of phage inside a live bacterial host and (ii) the delivery and expression of the complementing gene that turns on enzymatic activity and produces a colored or fluorescent product. Here we demonstrate a phage-based amplification scheme with an M13KE phage that delivers a small peptide motif to an F⁺, α-complementing strain of Escherichia coli K12, which expresses the ω-domain of β-galactosidase (β-gal). The result of this complementationan active form of β-galwas detected colorimetrically, and the high level of expression of the ω-domain of β-gal in the model K12 strains allowed us to detect, on average, five colony-forming units (CFUs) of this strain in 1 L of water with an overnight culture-based assay. We also detected 50 CFUs of the model K12 strain in 1 L of water (or 10 mL of orange juice, or 10 mL of skim milk) in less than 4 h with a solution-based assay with visual readout. The solution-based assay does not require specialized equipment or access to a laboratory, and is more rapid than existing tests that are suitable for use at the point of access. This method could potentially be extended to detect many different bacteria with bacteriophages that deliver genes encoding a full-length enzyme that is not natively expressed in the target bacteria

Donor-Substituted Octacyano[4]dendralenes: Investigation of π‑Electron Delocalization in Their Radical Ions

Symmetrically and unsymmetrically electron-donor-substituted octacyano[4]­dendralenes were synthesized and their opto-electronic properties investigated by UV/vis spectroscopy, electrochemical measurements (cyclic voltammetry (CV) and rotating disk voltammetry (RDV)), and electron paramagnetic resonance (EPR) spectroscopy. These nonplanar push–pull chromophores are potent electron acceptors, featuring potentials for first reversible electron uptake around at −0.1 V (vs Fc⁺/Fc, in CH₂Cl₂ + 0.1 M <i>n</i>-Bu₄NPF₆) and, in one case, a remarkably small HOMO–LUMO gap (Δ<i>E</i> = 0.68 V). EPR measurements gave well-resolved spectra after one-electron reduction of the octacyano[4]­dendralenes, whereas the one-electron oxidized species could not be detected in all cases. Investigations of the radical anions of related donor-substituted 1,1,4,4-tetracyanobuta-1,3-diene derivatives revealed electron localization at one 1,1-dicyanovinyl (DCV) moiety, in contrast to predictions by density functional theory (DFT) calculations. The particular factors leading to the charge distribution in the electron-accepting domains of the tetracyano and octacyano chromophores are discussed