The design and synthesis of Aviram-Ratner-type molecular rectifiers, featuring an anilino-substituted extended tetracyanoquinodimethane (exTCNQ) acceptor, covalently linked by the σ-spacer bicyclo[2.2.2]octane (BCO) to a tetrathiafulvalene (TTF) donor moiety, are described. The rigid BCO spacer keeps the TTF donor and exTCNQ acceptor moieties apart, as demonstrated by X-ray analysis. The photophysical properties of the TTF-BCO-exTCNQ dyads were investigated by UV/Vis and EPR spectroscopy, electrochemical studies, and theoretical calculations. Langmuir-Blodgett films were prepared and used in the fabrication and electrical studies of junction devices. One dyad showed the asymmetric current-voltage (I-V) curve characteristic for rectification, unlike control compounds containing the TTF unit but not the exTCNQ moiety or comprising the exTCNQ acceptor moiety but lacking the donor TTF part, which both gave symmetric I-V curves. The direction of the observed rectification indicated that the preferred electron current flows from the exTCNQ acceptor to the TTF donor.

This paper investigates the influence of the interface between a gold or silver metal electrode and an n-alkyl SAM (supported on that electrode) on the rate of charge transport across junctions with structure Met(Au or Ag)(TS)/A(CH2)nH//Ga2O3/EGaIn by comparing measurements of current density, J(V), for Met/AR = Au/thiolate (Au/SR), Ag/thiolate (Ag/SR), Ag/carboxylate (Ag/O2CR), and Au/acetylene (Au/C≡CR), where R is an n-alkyl group. Values of J0 and β (from the Simmons equation) were indistinguishable for these four interfaces. Since the anchoring groups, A, have large differences in their physical and electronic properties, the observation that they are indistinguishable in their influence on the injection current, J0 (V = 0.5) indicates that these four Met/A interfaces do not contribute to the shape of the tunneling barrier in a way that influences J(V).

A convergent, multistep protocol was employed for the synthesis of a Janus-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 Janus-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 meta-connectivities, is not efficient. Therefore, the charge-transfer bands seen in the Janus-type system originate from the interaction of the Fc donors with the directly connected tetracyanobuta-1,3-diene acceptors in the same hemisphere.

This paper investigates the influence of the atmosphere used in the fabrication of top electrodes from the liquid eutectic of gallium and indium (EGaln) (the so-called "EGaln" electrodes), and in measurements of current density, J(V) (A/cm(2)), across self-assembled monolayers (SAMs) incorporated into Ag/SR//Ga2O3/EGaln junctions, on values of J(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 n-dodecanethiol, in air, gave log vertical bar J vertical bar(mean) = -2.4 +/- 0.4 for the conical tip, and log vertical bar J vertical bar(mean) = 0.6 +/- 0.3 for the drop electrode (and, thus, Delta log vertical bar J vertical bar approximate to 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 J (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 vertical bar J(V)vertical bar, 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 similar to 70% to,similar to 100%. Increasing the relative humidity (RH) in which J(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)).

Self-assembled monolayers (SAMs), prepared by reaction of terminal n-alkynes (HC≡C(CH2)nCH3, n = 5, 7, 9, and 11) with Au(111) at 60 °C were characterized using scanning tunneling microscopy (STM), infrared reflection absorption spectroscopy (IRRAS), X-ray photoelectron spectroscopy (XPS), and contact angles of water. In contrast to previous spectroscopic studies of this type of SAMs, these combined microscopic and spectroscopic experiments confirm formation of highly ordered SAMs having packing densities and molecular chain orientations very similar to those of alkanethiolates on Au(111). Physical properties, hydrophobicity, high surface order, and packing density, also suggest that SAMs of alkynes are similar to SAMs of alkanethiols. The formation of high-quality SAMs from alkynes requires careful preparation and manipulation of reactants in an oxygen-free environment; trace quantities of O2 lead to oxidized contaminants and disordered surface films. The oxidation process occurs during formation of the SAM by oxidation of the -C≡C- group (most likely catalyzed by the gold substrate in the presence of O2).

We report the rise and fall of third-order optical polarizabilities in donor-acceptor substituted molecules featuring a systematically varied conjugation path. We identify the optimum conjugation length that optimizes the non-linear response in small molecules.

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.

The mechanism (or mechanisms) of enthalpy-entropy (H/S) compensation in protein-ligand binding remains controversial, and there are still no predictive models (theoretical or experimental) in which hypotheses of ligand binding can be readily tested. Here we describe a particularly well-defined system of protein and ligands--human carbonic anhydrase (HCA) and a series of benzothiazole sulfonamide ligands with different patterns of fluorination--that we use to define enthalpy/entropy (H/S) compensation in this system thermodynamically and structurally. The binding affinities of these ligands (with the exception of one ligand, in which the deviation is understood) to HCA are, despite differences in fluorination pattern, indistinguishable; they nonetheless reflect significant and compensating changes in enthalpy and entropy of binding. Analysis reveals that differences in the structure and thermodynamic properties of the waters surrounding the bound ligands are an important contributor to the observed H/S compensation. These results support the hypothesis that the molecules of water filling the active site of a protein, and surrounding the ligand, are as important as the contact interactions between the protein and the ligand for biomolecular recognition, and in determining the thermodynamics of binding.

It's the water that matters. Pairs of benzo- and perfluorobenzoarylsulfonamide ligands bind to human carbonic anhydrase with a conserved binding geometry, an enthalpy-driven binding, and indistinguishable binding affinities (see picture). These data support the pervasive theory that the lock-and-key model disregards an important component of binding: the water, which fills the binding pocket of the protein and surrounds the ligand.

A series of donor-acceptor-substituted alkynes, 2 a-f, was synthesized in which the length of the π-conjugated polyyne spacer between the N,N-diisopropylanilino donor and the 1,1,4,4-tetracyanobuta-1,3-diene (TCBD) acceptor was systematically changed. The effect of this structural change on the optoelectronic properties of the molecules and, ultimately, their third-order optical nonlinearity was comprehensively investigated. The branched N,N-diisopropyl groups on the anilino donor moieties combined with the nonplanar geometry of 2 a-f imparted exceptionally high solubility to these chromophores. This important property allowed for performing INADEQUATE NMR measurements without (13) C labeling, which, in turn, resulted in a complete assignment of the carbon skeleton in chromophores 2 a-f and the determination of the (13) C-(13) C coupling constants. This body of data provided unprecedented insight into characteristic (13) C chemical shift patterns in push-pull-substituted polyynes. Electrochemical and UV/Vis spectroscopic studies showed that the HOMO-LUMO energy gap decreases with increasing length of the polyyne spacer, while this effect levels off for spacers with more than four acetylene units. The third-order optical nonlinearity of this series of molecules was determined by measuring the rotational averages of the third-order polarizabilities (γrot ) by degenerate four-wave mixing (DFWM). These latter studies revealed high third-order optical nonlinearities for the new chromophores; most importantly, they provided fundamental insight into the effect of the conjugated spacer length in D-A polyynes, that can be exploited in the future design of suitable charge-transfer chromophores for applications in optoelectronic devices.

We present linear and nonlinear optical properties of small donor-acceptor substituted molecules for third-order nonlinear optics and of their dense assemblies created by molecular beam deposition in high vacuum. The molecules are variations on the DDMEBT molecule, obtained by varying the structure of the electron donating groups around a compact conjugated core derived from a tetracyanobutadiene (TCBD) group. We discuss the optical properties, lifetime, losses, and robustness of vapor-deposited DDMEBT thin films and the influence of the different end-groups on both the linear and nonlinear optical properties of the molecules and the resulting supramolecular assemblies. (C) 2012 Optical Society of America

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 n-Bu4NPF6) and, in one case, a remarkably small HOMO-LUMO gap (ΔE = 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.

Double [2+2] cycloaddition/retro-electrocyclisation reactions between tetracyanoethene (TCNE) and various anilino-capped buta-1,3-diynes furnished a series of octacyano[4]dendralene derivatives featuring intense, low-energy intramolecular charge-transfer absorptions. These novel chromophores are strong electron acceptors and undergo facile one-electron reductions at potentials (–0.09 to –0.17 eV vs.Fc+/Fc, in CH2Cl2–0.1 M nBu4NPF6) lower than those reported for the benchmark organic acceptors, such as TCNE (–0.32 eV) and 7,7,8,8-tetracyanoquinodimethane (TCNQ) (–0.25 eV). The electron-accepting power of one octacyano[4]dendralene, as expressed by the computed adiabatic electron affinity (EA), compares to that of the reference acceptor 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4-TCNQ) used as a p-type dopant in organic light-emitting diodes (OLEDs) and solar cells. Gas-phase density functional theory (DFT) calculations predict a stretched-out conformation as the global energy minimum for octacyano[4]dendralenes. In the solid state however, folded conformations were observed for two structures by X-ray analysis. Taking the solid state environment approximately into account calculations predict a energetical degeneracy between the stretched-out and folded conformation. Therefore conformational preference probably is a result of supramolecular dimer formation, mediated by two pairs of intermolecular, antiparallel dipolar CN⋯CN interactions.

We report the synthesis and properties of two series of homologous donor-acceptor (D-A) chromophores in which N,N-dimethylanilino (DMA) or N,N-dihexylanilino (DHA) donors and dicyanovinyl acceptors are separated by up to four C C triple-bond spacers or up to three C=C double-bond spacers. The intramolecular charge-transfer (CT) interactions of the new D-A oligoynes and the known all-trans D-A oligoenes were investigated by X-ray crystallography, electrochemistry, UV/Vis spectroscopy, and theoretical calculations. In both series, the optical and electrochemical HOMO-LUMO gaps decrease with increasing spacer length. The HOMO-LUMO gaps for the D-A oligoynes and oligoenes with a given spacer length are nearly identical. The effect of the spacer length was found to level-off for spacers with more than six carbon atoms. The third-order optical nonlinearity of both series of molecules was determined by measuring the rotational averages of the third-order polarizabilities gamma(rot) by degenerate four-wave mixing.

We determine the optical losses of DDMEBT planar waveguides and characterize the shelf-life and robustness of DDMEBT thin films used for ultra-fast all optical data processing.

Related Article: B.B.Frank, P.R.Laporta, B.Breiten, M.C.Kuzyk, P.D.Jarowski, W.B.Schweizer, P.Seiler, I.Biaggio, C.Boudon, J.-P.Gisselbrecht, F.Diederich|2011|Eur.J.Org.Chem.||4307|doi:10.1002/ejoc.201100378

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

We demonstrate ultrafast optical signal processing up to bitrates of 170 Gbit/s. Silicon-on-insulator waveguides are defined by CMOS technology. In addition, an organic cladding pro-vides either X(3) or X(2)-nonlinearities that are not impaired by two-photon absorption. With a proper waveguide design, the influence of two-photon absorption in silicon is greatly reduced.

All-optical wavelength conversion of 56 Gbit/s NRZ-DQPSK based on four-wave mixing is demonstrated in a silicon-organic hybrid strip waveguide operated in TM mode.