Self-Assembled Monolayers of Molecular Conductors with Terpyridine-Metal Redox Switching Elements: A Combined AFM, STM and Electrochemical Study

Self-assembled monolayers (SAMs) of terpyridine-based transition metal (ruthenium and osmium) complexes, anchored to gold substrate via tripodal anchoring groups, have been investigated as possible redox switching elements for molecular electronics. An electrochemical study was complemented by atomic force microscopy (AFM) and scanning tunneling microscopy (STM) methods. STM was used for determination of the SAM conductance values, and computation of the attenuation factor β from tunneling current–distance curves. We have shown that SAMs of Os-tripod molecules contain larger adlayer structures compared with SAMs of Ru-tripod molecules, which are characterized by a large number of almost evenly distributed small islands. Furthermore, upon cyclic voltammetric experimentation, Os-tripod films rearrange to form a smaller number of even larger islands, reminiscent of the Ostwald ripening process. Os-tripod SAMs displayed a higher surface concentration of molecules and lower conductance compared with Ru-tripod SAMs. The attenuation factor of Os-tripod films changed dramatically, upon electrochemical cycling, to a higher value. These observations are in accordance with previously reported electron transfer kinetics studies

Modelování spektrálních a fotochemických vlastností diiminových karbonylových komplexů přechodových kovů s diiminy

The felxibility pf the coordination sphere of mixed valence carbonyl complexes enables to tune spectral and protochemical properties. The variety of excited states in ilustrated on Ru, Re and W mixed ligand carbonyl complexed. The lowest excited states of [W(CO)4L] and [W(CO)5L’] (L=N,N'-di-methyl-1,4-diazabutadiene, ethylenediamine, 2,2’-bipyridine, phenantroline; L’= pyridine, 4-CN-pyridine, piperidine) ckomplexes were found to be either W -> pi*(L) or W -> pi*(CO) in charakter, depending on the type of the heteroligands

Raman spectroscopy and DFT calculations of PEDOT:PSS in a dipolar field

The conductive polymer-electrolyte interface plays an important role in many electrochemical devices. An unusual situation arises when a solvent-free ionic liquid (SF-IL) is used as the electrolyte because it behaves as a molten salt rather than an electrolyte solution. On the basis of Raman spectra, it was found that the presence of ion pairs of SF-IL in the vicinity of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) results in a decrease in the oxidation level of the polymer and an increase in the HOMO-LUMO gap. The process of polymer “dedoping” and the modification of the electronic structure of the polymer are illustrated by quantum chemical calculations

Self-Assembled Monolayers of Molecular Conductors with Terpyridine-Metal Redox Switching Elements: A Combined AFM, STM and Electrochemical Study

Self-assembled monolayers (SAMs) of terpyridine-based transition metal (ruthenium and osmium) complexes, anchored to gold substrate via tripodal anchoring groups, have been investigated as possible redox switching elements for molecular electronics. An electrochemical study was complemented by atomic force microscopy (AFM) and scanning tunneling microscopy (STM) methods. STM was used for determination of the SAM conductance values, and computation of the attenuation factor β from tunneling current–distance curves. We have shown that SAMs of Os-tripod molecules contain larger adlayer structures compared with SAMs of Ru-tripod molecules, which are characterized by a large number of almost evenly distributed small islands. Furthermore, upon cyclic voltammetric experimentation, Os-tripod films rearrange to form a smaller number of even larger islands, reminiscent of the Ostwald ripening process. Os-tripod SAMs displayed a higher surface concentration of molecules and lower conductance compared with Ru-tripod SAMs. The attenuation factor of Os-tripod films changed dramatically, upon electrochemical cycling, to a higher value. These observations are in accordance with previously reported electron transfer kinetics studies

Interaction of selected gases with zinc phthalocyanine thin films: theoretical and experimental studies

In this work we studied both theoretically and experimentally interactions between zinc phthalocyanine (ZnPc) and selected gases (Ar, He, N2, O2, H2, NO2). Specifically, we focused on electrical conductivity as important macroscopical physical parameter reflecting ZnPc/gas complexes interaction states. To interpret the measured data and determine the main parameters that influence the resistivity/charge transport ability of ZnPc in a specific gas atmosphere, the density functional theory (DFT) has been used. Combining experimental results and DFT modeling we were able to characterize states/parameters influencing charge transport conditions from new and comprehensive perspectives

Impact of nucleic acid self-alignment in a strong magnetic field on the interpretation of indirect spin-spin interactions

Heteronuclear and homonuclear direct (D) and indirect (J) spin-spin interactions are important sources of structural information about nucleic acids (NAs). The Hamiltonians for the D and J interactions have the same functional form; thus, the experimentally measured apparent spin-spin coupling constant corresponds to a sum of J and D. In biomolecular NMR studies, it is commonly presumed that the dipolar contributions to Js are effectively canceled due to random molecular tumbling. However, in strong magnetic fields, such as those employed for NMR analysis, the tumbling of NA fragments is anisotropic because the inherent magnetic susceptibility of NAs causes an interaction with the external magnetic field. This motional anisotropy is responsible for non-zero D contributions to Js. Here, we calculated the field-induced D contributions to 33 structurally relevant scalar coupling constants as a function of magnetic field strength, temperature and NA fragment size. We identified two classes of Js, namely 1JCH and 3JHH couplings, whose quantitative interpretation is notably biased by NA motional anisotropy. For these couplings, the magnetic field-induced dipolar contributions were found to exceed the typical experimental error in J-coupling determinations by a factor of two or more and to produce considerable over- or under-estimations of the J coupling-related torsion angles, especially at magnetic field strengths >12 T and for NA fragments longer than 12 bp. We show that if the non-zero D contributions to J are not properly accounted for, they might cause structural artifacts/bias in NA studies that use solution NMR spectroscopy

HERMES – A Software Tool for the Prediction and Analysis of Magnetic-Field-Induced Residual Dipolar Couplings in Nucleic Acids

Field-Induced Residual Dipolar Couplings (fiRDC) are a valuable source of long-range information on structure of nucleic acids (NA) in solution. A web application (HERMES) was developed for structure-based prediction and analysis of the (fiRDCs) in NA. fiRDC prediction is based on input 3D model structure(s) of NA and a built-in library of nucleobase-specific magnetic susceptibility tensors and reference geometries. HERMES allows three basic applications: (i) the prediction of fiRDCs for a given structural model of NAs, (ii) the validation of experimental or modeled NA structures using experimentally derived fiRDCs, and (iii) assessment of the oligomeric state of the NA fragment and/or the identification of a molecular NA model that is consistent with experimentally derived fiRDC data. Additionally, the program's built-in routine for rigid body modeling allows the evaluation of relative orientation of domains within NA that is in agreement with experimental fiRDCs