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Charge-transfer complexes involving tetrathiafulvalene (TTF) and tetracyanoquinodimethane (TCNQ) derivatives are engineered in a 2D arrangement onto a carbon surface through the exposure of immobilized TTF units to TCNQ compounds. TTF molecules were immobilized as robust monolayers on carbon surfaces using the electrografting method followed by a click chemistry coupling. When the TTF monolayer is exposed to TCNQ, TCNQF2 (2,5-difluoro-TCNQ), and TCNQF4 (2,3,5,6-tetrafluoro-TCNQ), strong donor–acceptor complexes are formed onto the surface. A considerable decrease of the electrochemical response accompanies the formation of the charge-transfer complex. This observation is rationalized by the analysis of original crystal samples using an ultramicroelectrode cavity, confirming that charge-transfer complexes are electrochemically silent. A fine control of the degree of charge transfer with the judicious choice of different acceptors is evidenced through electrochemical and X-ray photoelectron spectroscopy (XP...

This work shows the electrocatalytic activity towards the oxidation of acetaminophen of a composite electrode PVC/TTF-TCNQ modified with gold nanoparticles. Owing to a good linear relationship between acetaminophen concentration and current response at lower oxidation potential it is proposed as a new alternative for amperometric determination of acetaminophen. Besides the good catalytic activity (Eapp = 0.425 V), the proposed sensor shows high reproducibility, long-term stability, low cost and can be used both in batch and in FIA systems. In batch, it was obtained a linear range for acetaminophen over a range of 1 to 800 μM with a detection limit of 0.66 μM and a correlation coefficient of 0.997 with a slope (sensitivity) of 53 mA M-1. In FIA, a sensitivity of 9.9 ± 0.15 mA M-1 and a linear regression coefficient (r) of 0.999 were obtained for a linear range for acetaminophen between 1 to 800 μM. The detection limit (s/n = 3) was 8.9 μM.

Understanding strongly correlated systems is one of the most challenging problems of physics. Their properties often sensitively depend on the delicate interplay of kinetic and Coulomb energy rendering them susceptible to external perturbations. To understand and predict experimental results we need methods to reliably describe these materials. In this thesis we tackled the problem from two different perspectives: the construction of appropriate models and the evaluation of dynamical lattice response functions. At first we derive realistic material-specific Hubbard model parameters for organic crystals. We extract the simplest parameters, the hopping integrals t, from the bonding/anti-bonding splitting of the relevant orbitals in a tight-binding dimer. The main challenge is the proper evaluation of the screening for the Coulomb integrals, which we tackle with a three-step approach. At first we calculate the Hartree-integrals. To assess the screening of the electrons within the molecules alone we calculate DFT total energies for additional charges in the molecules. The orbital relaxation effect in the self-consistent calculation yields the screening energy. The final step captures the effect of all molecules. With a quantum mechanical treatment being infeasible we resort to a classical electrostatic method which effectively describes a non-polar molecular crystal in terms of a microscopic point-dipole model. We apply this method to two organic crystals: TTF-TCNQ and (BEDT-TTF)_2 I_3. Having the parameters of the former we solve a long standing problem in the interpretation of its spectra. One of the most successful methods to treat strongly correlated systems is DMFT. It provides a good approximation to local correlations and direct access to quantities such as the local self-energy. While lattice spectral functions follow directly from the self-energy, general lattice susceptibilities are difficult to obtain. To make the evaluation feasible we rewrite the susceptibilities as ladder diagrams, where the vertex part is then approximated by the local DMFT vertex. From the vertex and the lattice bubbles we can evaluate arbitrary susceptibilities. We employ Padé approximants to analytically continue our Matsubara results to the real-frequency axis. Since accuracy is of paramount importance, we make up for the finite approximations to the infinite vertices by using a "roaming vertex" scheme which captures the most relevant part of the vertex. Moreover, we perform the computations for different matrix sizes and extrapolate to the infinite limit. As an application we choose a three-dimensional periodic Anderson model.

It was prepared a new polyvinyl chloride (PVC)/tetrathiafulvalene-tetracyanoquinodimethane (TTF-TCNQ) composite electrode which showed good physical and electrochemical characteristics. Different PVC/TTF-TCNQ-graphite proportions were tested and the relation 1/10 (p/p) PVC/TTF-TCNQ provided the best results in terms of sensitivity, coefficients of variation and mechanical resistance. This electrode has interesting applications as a working electrode. So, employment is remarkable in a flow injection system and had been satisfactory checked to detect ascorbic acid. Also, the electrode exhibits selective voltammetric behaviour in aqueous solution that affords its use as an ion detector. The proposed electrode showed good kinetics property with a low background current and a relatively reproducible signal. Moreover, the electrode can be prepared in a simple way and its surface easily recovered. Se ha preparado un electrodo compósito de cloruro de polivinilo (PVC)/tetratiofulvaleno-tetracianoquinodimetano (TTF-TCNQ) que presenta buenas características físicas y electroanalíticas. El estudio con distintas proporciones de PVC/TTF-TCNQ-grafito ha mostrado que la relación 1/10 (p/p) PVC/TTF-TCNQ es la que mejores resultados ofrece en términos de sensibilidad, coeficientes de variación y de resistencia mecánica. Este electrodo presenta interesantes aplicaciones como electrodo de trabajo. Así, destaca su empleo en sistemas de inyección de flujo, habiéndose aplicado satisfactoriamente a la determinación de ácido ascórbico. También ha mostrado su utilidad como sensor voltamperométrico de iones. El electrodo propuesto presenta buenas propiedades cinéticas, con una baja corriente de fondo y una señal relativamente reproducible. Además, puede ser preparado de una manera simple, y su superficie es fácilmente regenarable.

The optical properties of quasi-one-dimensional metallic LaTiO$_{3.41}$ are studied for the polarization along the $a$ and $b$ axes. With decreasing temperature modes appear along both directions suggestive for a phase transition. The broadness of these modes along the conducting axis might be due to the coupling of the phonons to low-energy electronic excitations across an energy gap. We observe a pronounced midinfrared band with a temperature dependence consistent with (interacting) polaron models. The polaronic picture is corroborated by the presence of strong electron-phonon coupling and the temperature dependence of the dc conductivity., 5 pages, 5 figures

Charge density waves (CDW) have been studied at the surface of a cleaved TTF-TCNQ single crystal using a low temperature scanning tunneling microscope (STM) under ultra high vacuum (UHV) conditions. All CDW phase transitions of TTF-TCNQ have been identified. The measurement of the modulation wave vector along the a direction provides the first evidence for the existence of domains comprising single plane wave modulated structures in the temperature regime where the transverse wave vector of the CDW is temperature dependent, as hinted by the theory more than 20 years ago., To appear in Phys.Rev.Rapid. Comm

We have thoroughly characterized the surfaces of the organic charge-transfer salts TTF-TCNQ and (TMTSF)2PF6 which are generally acknowledged as prototypical examples of one-dimensional conductors. In particular x-ray induced photoemission spectroscopy turns out to be a valuable non-destructive diagnostic tool. We show that the observation of generic one-dimensional signatures in photoemission spectra of the valence band close to the Fermi level can be strongly affected by surface effects. Especially, great care must be exercised taking evidence for an unusual one-dimensional many-body state exclusively from the observation of a pseudogap., 11 pages, 12 figures, v2: minor changes in text and figure labelling