Francesco Tassinari

Chiral Conductive Polymers as Spin Filters

DOI: 10.1002/adma.201405249 electrode. By controlling the direction of the magnetization of nickel, it is possible to inject electrons that have mainly one spin orientation and to verify their transport through the PCT by monitoring the cyclic voltammetry (CV) curve in the electrochemical cell in which the redox couple is not chiral. The CV curves refl ect a steady state in which a double layer is formed near the working electrode. Another method to monitor the spin selectivity is by chronoamperometry, in which one monitors time-dependent current at a fi xed potential. At the beginning, when the potential is turned on, the current is high, but it is reduced with time due to the formation of the double layer. [ 18,19 ]

Control of Electrons’ Spin Eliminates Hydrogen Peroxide Formation During Water Splitting

The production of hydrogen through water splitting in a photoelectrochemical cell suffers from an overpotential that limits the efficiencies. In addition, hydrogen-peroxide formation is identified as a competing process affecting the oxidative stability of photoelectrodes. We impose spin-selectivity by coating the anode with chiral organic semiconductors from helically aggregated dyes as sensitizers; Zn-porphyrins and triarylamines. Hydrogen peroxide formation is dramatically suppressed, while the overall current through the cell, correlating with the water splitting process, is enhanced. Evidence for a strong spin-selection in the chiral semiconductors is presented by magnetic conducting (mc-)AFM measurements, in which chiral and achiral Zn-porphyrins are compared. These findings contribute to our understanding of the underlying mechanism of spin selectivity in multiple electron-transfer reactions and pave the way toward better chiral dye-sensitized photoelectrochemical cells.

Electric-field-driven alignment of chiral conductive polymer thin films.

We investigated the effect of an electric field on the alignment and structural properties of thin films of a chiral polybithiophene-based conductive polymer, functionalized with a protected l-cysteine amino acid. Thin films were obtained by exploiting both drop-casting and spin-coating procedures. The electric properties, the polarized Raman spectrum, the UV-vis spectrum, and the CD spectra were measured as a function of the electric field intensity applied during film formation. It was found that beyond the enhancement of the conductivity observed when the electric field aligns the polymer, the electric field significantly affects the chiral properties and the effect depends on the method of deposition.

On the Hybrid Glassy Carbon Electrode/OligoThiophene/Ag(NP) Interface

GC/OligoThiophene/Ag(NP) hybrid interfaces are synthesized and characterized: GC is the glassy carbon surface; OligoThiophene stands for both an ultrathin bithiophene grafted film and a 4-Br-Bithiophene grafted polymer; Ag(NP) stands for silver nanoparticles. The hybrid interface preparation involves different steps: first, the electrode surface is functionalized through a combination of electrochemically assisted grafting (under reduction regime) and polymerization (under oxidation regime); then, silver nanoparticles are chemisorbed by dipping. In particular, an ultrathin film of grafted bithiophene can be obtained by applying one cyclic voltammetry reduction cycle (GC/BT surface), while subsequent cyclic voltammetry cycling under oxidation regime yields an immobilized 4Br-Bithiophene polymer (GC/4BrBT surface). AFM and TEM images were recorded to investigate the morphology and chemical composition of the Ag(NP). Fe(II)/Fe(III) cyclic voltammetry, Zn underpotential deposition (UPD), XPS, LA-ICP-MS, and Raman techniques were exploited to characterize both the GC/OligoThiophene and GC/OligoThiophene/Ag(NP) interfaces. Theoretical calculation, at the B3LYP/6-311G** level of the theory, enabled rationalization of the electroreduction mechanism and the Raman results.

Π-Stacking Signature in NMR Solution Spectra of Thiophene-Based Conjugated Polymers

Studies on conjugated polymers seldom report on their NMR characterization in solution. This paper shows how NMR experiments, both 1H NMR and routine 2D NMR spectra, can help in gaining a further insight into the aggregation behavior of conjugated polymers and could be used to flank the more employed solid-state NMR and other spectroscopy and microscopy techniques in the understanding of the aggregation processes. NMR spectroscopy allows distinguishing, within the class of poorly solvatochromic conjugated polymers, those highly prone to form π-stacked aggregates from the ones that have a low tendency toward π-stacking.

On the co-adsorption process of sodium dodecyl sulfate and sodium dodecylbenzenesulfonate on a 1-decanethiol-functionalized Au electrode, as a corrosion inhibiting mimic process

The co-adsorption of sodium dodecyl sulfate (SDS) and sodium dodecylbenzenesulfonate (SDBS), on the 1-decanethiol self-assembled monolayer (SAM)-functionalized polycrystalline gold surface, is investigated by electrochemical techniques. The peak current (cyclic voltammetry) and charge transfer resistance (impedance spectra) variations are measured, concerning the [Fe(CN)6]3−/[Fe(CN)6]4− couple redox process. SDBS is found to yield a more efficient inhibiting barrier (towards the charge transfer process), when compared to the SDS one. Thus, it is suggesting that a higher tendency of SDBS to be co-adsorbed within the 1-decanethiol SAM with respect to SDS.

Chapter 15 – Chiral Polythiophenes

This review reports the synthesis and the properties of chiral polythiophenes (PTs) and in particular it is focused on PTs bearing a sulfur atom directly bonded to the thiophene ring. These polymers show remarkable properties, related to their chirality and electrical conductivity and to the ability to interact with chiral molecules opening the possibility for using them in new potential applications, like chiral sensors, chiral resolution and electrodes.