13 research outputs found
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<sup>–1</sup> and 3500 cm<sup>–1</sup>. The thickness of
the amylose brushesmeasured by Spectroscopic Ellipsometrycan
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<sup>+</sup> 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 Ni<sub>8</sub> 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)<sub>6</sub>]<sup>4–</sup> Substitutions on the Spin-Flop Transition of a Layered Nickel Phyllosilicate
A 3 to 1 Ni/Si antiferromagnetic layered phyllosilicate,
Ni<sub>3</sub>Si(C<sub>3</sub>H<sub>6</sub>NH<sub>3</sub>)F<sub>0.65</sub>O<sub>1.9</sub>(OH)<sub>4.45</sub>(CH<sub>3</sub>COO)<sub>1.1</sub>·<i>x</i>H<sub>2</sub>O, was modified with K<sub>4</sub>[Fe(CN)<sub>6</sub>]·3H<sub>2</sub>O. This compound retained
its ordering as proved by X-ray diffraction, while infrared spectra
revealed the presence of [Fe(CN)<sub>6</sub>]<sup>4–</sup> 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><sub>1</sub> = 24 kOe, <i>H</i><sub>2</sub> = 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