Structure and Electrical Conductivity of Hybrid Langmuir–Blodgett Films from BEDO-TTF and Fatty Acid

Conducting Langmuir–Blodgett films are one of the candidates for molecular electronics. We investigated the structural and electrical properties of Langmuir–Blodgett films built up as a mixed molecular system of bis­(ethylenedioxy)­tetrathiafulvalene, in short BEDO-TTF, and fatty acid, as a function of (a) the alkyl chain length of the fatty acid and (b) the fatty acid: BEDO-TTF molar ratio in the starting solution from which the Langmuir film is prepared. The Langmuir–Blodgett films deposited from mixtures with molar ratio 1:2 showed better quality in terms of crystallinity and electrical conduction. Moreover, LB films with longer alkyl chain fatty acids were better ordered even at lower molar ratio

Electrochemical Write and Read Functionality through Oxidative Dimerization of Spiropyran Self-Assembled Monolayers on Gold

In contrast to their photochromism, the electrochemistry of spiropyrans in self-assembled monolayers has attracted only modest attention in recent years. In this contribution the electrochemical oxidation of self-assembled monolayers (SAMs) of 6-nitro-BIPS spiropyran (SP) prepared on polycrystalline gold surfaces is described. The SAMs were characterized with cyclic voltammetry, X-ray photoelectron spectroscopy (XPS), surface-enhanced Raman scattering (SERS), and UV/vis absorption spectroelectrochemistry. The electrochemical oxidation of spiropyrans in solution results in aryl C–C coupling of the indole units and thereby the formation of a symmetric spiropyran dimer. Comparison of spectroscopic data obtained for electrochemically oxidized spiropyran dimers in solution with data from monolayers confirms that a similar oxidative coupling occurs in the SAMs on gold also. The dimer formed can be oxidized electrochemically to monocationic and dicationic states and shows remarkably good stability in UHV and ambient conditions in all three redox states. In addition, the dimerized spiropyran self-assembled monolayer show photochromism, which was characterized by XPS and SERS spectroscopy

The Dynamics of Complex Formation between Amylose Brushes on Gold and Fatty Acids by QCM‑D

Amylose brushes were synthesized by enzymatic polymerization with glucose-1-phosphate as monomer and rabbit muscle phosphorylase b as catalyst on gold-covered surfaces of a quartz crystal microbalance. Fourier transform infrared (FT-IR) spectra confirmed the presence of the characteristic absorption peaks of amylose between 3100 cm^–1 and 3500 cm^–1. The thickness of the amylose brushesmeasured by Spectroscopic Ellipsometrycan be tailored from 4 to 20 nm, depending on the reaction time. The contour length of the stretched amylose chains on gold surfaces has been evaluated by single molecule force spectroscopy, and a total chain length of about 20 nm for 16.2 nm thick amylose brushes was estimated. X-ray photoelectron spectroscopy (XPS) was employed to characterize the amylose brushes before and after the adsorption of fatty acids. The dynamics of inclusion complex formation between amylose brushes and two fatty acids (octanoic acid and myristic acid) with different chain length was investigated as a function of time using a quartz crystal microbalance with dissipation monitoring (QCM-D) immersed in the liquid phase. QCM-D signals including the frequency and dissipation shifts elucidated the effects of the fatty acid concentration, the solvent types, the chain length of the fatty acids and the thickness of the amylose brushes on the dynamics of fatty acid molecule adsorption on the amylose brush-modified sensor surfaces

UV/Vis and NIR Light-Responsive Spiropyran Self-Assembled Monolayers

Self-assembled monolayers of a 6-nitro BIPS spiropyran (SP) modified with a disulfide-terminated aliphatic chain were prepared on polycrystalline gold surfaces and characterized by UV/vis absorption, surface-enhanced Raman scattering (SERS), and X-ray photoelectron spectroscopies (XPS). The SAMs obtained are composed of the ring-closed form (i.e., spiropyran) only. Irradiation with UV light results in conversion of the monolayer to the merocyanine form (MC), manifested in the appearance of an N⁺ contribution in the N 1s region of the XPS spectrum of the SAMs, the characteristic absorption band of the MC form in the visible region at 555 nm, and the C–O stretching band in the SERS spectrum. Recovery of the initial state of the monolayer was observed both thermally and after irradiation with visible light. Several switching cycles were performed and monitored by SERS spectroscopy, demonstrating the stability of the SAMs during repeated switching between SP and MC states. A key finding in the present study is that ring-opening of the surface-immobilized spiropyrans can be induced by irradiation with continuous wave NIR (785 nm) light as well as by irradiation with UV light. We demonstrate that ring-opening by irradiation at 785 nm proceeds by a two-photon absorption pathway both in the SAMs and in the solid state. Hence, spiropyran SAMs on gold can undergo reversible photochemical switching from the SP to the MC form with both UV and NIR and the reverse reaction induced by irradiation with visible light or heating. Furthermore, the observation of NIR-induced switching with a continuous wave source holds important consequences in the study of photochromic switches on surfaces using SERS and emphasizes the importance of the use of multiple complementary techniques in characterizing photoresponsive SAMs

New Magnetic Thin Film Hybrid Materials Built by the Incorporation of Octanickel(II)-oxamato Clusters Between Clay Mineral Platelets

We report on a new method based on the combination of Langmuir–Schaefer deposition with self-assembly to insert highly anisotropic Ni₈ molecules in a hybrid organic–inorganic nanostructure. Spectroscopic, crystallographic, and magnetic data prove the successful insertion of the guest cationic molecule between templating clay platelets. These results open a new route toward the highly controlled fabrication of tailored functional organic–inorganic nanomaterials

Mixed Monolayers of Spiropyrans Maximize Tunneling Conductance Switching by Photoisomerization at the Molecule–Electrode Interface in EGaIn Junctions

This paper describes the photoinduced switching of conductance in tunneling junctions comprising self-assembled monolayers of a spiropyran moiety using eutectic Ga–In top contacts. Despite separation of the spiropyran unit from the electrode by a long alkyl ester chain, we observe an increase in the current density <i>J</i> of a factor of 35 at 1 V when the closed form is irradiated with UV light to induce the ring-opening reaction, one of the highest switching ratios reported for junctions incorporating self-assembled monolayers. The magnitude of switching of hexanethiol mixed monolayers was higher than that of pure spiropyran monolayers. The first switching event recovers 100% of the initial value of <i>J</i> and in the mixed-monolayers subsequent dampening is not the result of degradation of the monolayer. The observation of increased conductivity is supported by zero-bias DFT calculations showing a change in the localization of the density of states near the Fermi level as well as by simulated transmission spectra revealing positive resonances that broaden and shift toward the Fermi level in the open form

DataSheet1_Graphene growth from photo-polymerized bi-phenylthiol self-assembled monolayers.docx

We present an enhanced methodology for the synthesis of graphene, from photo-polymerized self-assembled monolayers (SAMs) of 1,1ʹ-biphenyl-4-thiol on both electropolished and oxidized copper substrates. The SAMs were subjected to a two-step process involving light-induced polymerization followed by annealing in a vacuum furnace to yield the two-dimensional solid. Comprehensive characterization using contact angle measurements, X-ray photoelectron spectroscopy, and Raman spectroscopy, as well as scanning electron and transmission electron microscopy, provided conclusive evidence of growth of single-layer graphene. Notably, our findings revealed superior quality graphene on oxidized copper substrates compared to their electropolished counterparts, highlighting the impact of substrate choice on the quality of the resultant material.</p

A Simple Road for the Transformation of Few-Layer Graphene into MWNTs

We report the direct formation of multiwalled carbon nanotubes (MWNT) by ultrasonication of graphite in dimethylformamide (DMF) upon addition of ferrocene aldehyde (Fc-CHO). The tubular structures appear exclusively at the edges of graphene layers and contain Fe clusters. Fc in conjunction with benzyl aldehyde, or other Fc derivatives, does not induce formation of NT. Higher amounts of Fc-CHO added to the dispersion do not increase significantly MWNT formation. Increasing the temperature reduces the amount of formation of MWNTs and shows the key role of ultrasound-induced cavitation energy. It is concluded that Fc-CHO first reduces the concentration of radical reactive species that slice graphene into small moieties, localizes itself at the edges of graphene, templates the rolling up of a sheet to form a nanoscroll, where it remains trapped, and finally accepts and donates unpaired electron to the graphene edges and converts the less stable scroll into a MWNT. This new methodology matches the long held notion that CNTs are rolled up graphene layers. The proposed mechanism is general and will lead to control the production of carbon nanostructures by simple ultrasonication treatments

Effect of [Fe(CN)₆]^4– Substitutions on the Spin-Flop Transition of a Layered Nickel Phyllosilicate

A 3 to 1 Ni/Si antiferromagnetic layered phyllosilicate, Ni₃Si­(C₃H₆NH₃)­F_0.65O_1.9(OH)_4.45(CH₃COO)_1.1·<i>x</i>H₂O, was modified with K₄[Fe­(CN)₆]·3H₂O. This compound retained its ordering as proved by X-ray diffraction, while infrared spectra revealed the presence of [Fe­(CN)₆]^4– groups and X-ray photoelectron spectroscopy showed that the latter partially substitute the acetate groups. Both the parent and the modified compound are canted antiferromagnets with an anisotropy perpendicular to the layers and show spin-flop transitions. For the parent compound, a single step spin-flop occurs at <i>H</i> = 24 kOe. The modified compound shows increased antiferromagnetic canting and a two-step transition (<i>H</i>₁ = 24 kOe, <i>H</i>₂ = 48 kOe). These results testify to the existence of competing interactions that depend sensitively on the grafted species

Data_Sheet_1_Hybrid Nanomaterials of Magnetic Iron Nanoparticles and Graphene Oxide as Matrices for the Immobilization of β-Glucosidase: Synthesis, Characterization, and Biocatalytic Properties.pdf

<p>Hybrid nanostructures of magnetic iron nanoparticles and graphene oxide were synthesized and used as nanosupports for the covalent immobilization of β-glucosidase. This study revealed that the immobilization efficiency depends on the structure and the surface chemistry of nanostructures employed. The hybrid nanostructure-based biocatalysts formed exhibited a two to four-fold higher thermostability as compared to the free enzyme, as well as an enhanced performance at higher temperatures (up to 70°C) and in a wider pH range. Moreover, these biocatalysts retained a significant part of their bioactivity (up to 40%) after 12 repeated reaction cycles.</p