[Show abstract][Hide abstract] ABSTRACT: We describe the production of graphene-based composites for energy storage, obtained by a combination of electrochemical and solution processing techniques. Electrochemically exfoliated graphene oxide sheets (EGO) are produced using an original setup that allows fast expansion of graphite flakes and efficient exfoliation of expanded graphite via an electrochemical route. The sheets are deposited on a sacrificial nickel foam together with an iron hydroxide colloidal precursor. Calcination treatment simultaneously renders the EGO foam conductive and transforms Fe(OH)3 into hematite (α-Fe2O3), yielding a nanoporous Fe2O3 layer on the surface of the mesoporous EGO foam, creating an ideal structure for lithium storage. The obtained graphene/metal oxide hybrid is a continuous, electrically conductive three-dimensional (3D) composite featuring a hierarchical meso-nano porous structure. A systematic study of these composites, varying the Fe2O3:EGO ratio, is then performed to maximize their performance as nanostructured electrodes in standard coin cell batteries.
[Show abstract][Hide abstract] ABSTRACT: By reacting 4,4′-bipyridine (bpy) with selected trinuclear triangular CuII complexes, [Cu3(μ3-OH)(μ-pz)3(RCOO)2(LL′)] [pz = pyrazolate anion; R = CH3, CH3CH2, CH2═CH, CH2═C(CH3); L, L′ = Hpz, H2O, MeOH] in MeOH, the substitution of monotopic ligands by ditopic bpy was observed. Depending on the stoichiometric reaction ratios, different compounds were isolated and structurally characterized. One- and two-dimensional coordination polymers (CPs), as well as two hexanuclear CuII clusters were identified. One of the hexanuclear clusters self-assembles into a supramolecular three-dimensional structure, and its crystal packing shows the presence of two intersecting channels, one of which is almost completely occupied by guest bpy, while in the second one guest water molecules are present. This compound also shows a reversible, thermally induced, single-crystal-to-single-crystal transition.
[Show abstract][Hide abstract] ABSTRACT: We report a successful chemical design strategy based on the even-odd alkyl end tailoring, which allows us to promote and control conformational polymorphism in single crystal and thin deposits of thienoimide-based molecular semiconductors (Cx-NT4N).
Chemical Communications 01/2015; 51(11). DOI:10.1039/c4cc09177a · 6.83 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: 2,3-Thieno(bis)imide (N) ended oligomers are emerging as valuable molecular materials for application in organic electronics. Here, we report the synthesis and characterization of three new 2,3-thieno(bis)imide ended oligothiophenes (T) bearing unsaturated ethylene (E), azomethine (I) and ethinyl (A) inner bridges (NTE, NTI and NTA respectively). The effect of the unsaturated bridge on the π-conjugation extent, molecular conformation and overall aromaticity is related to the functional optoelectronic and morphology properties and compared to the properties of the linear analogue (NTT) with a bithiophene inner moiety. Optical spectroscopy and cyclovoltammetry analysis show a strong red shift of the absorption and a decreased energy band gap on going from NTI to NTE to NTA. The HOMO level decreases in the order NTE>NTI>NTA. Moreover, while the LUMO of NTE and NTA have almost the same energy, NTI has a LUMO energy about 0.1 eV lower, likely due to the electron withdrawing effect of the azomethine moiety. Morphologic investigation of solution cast thin deposits shows that the unsaturated bridges promote the formation of concomitant polymorphs with simultaneous presence of microcrystals with different morphology and fluorescence properties. Moreover, irreversible conversion of one polymorph to the other was achieved by thermal treatments for NTA and NTE and by exploiting this feature we realized a time temperature integrator (TTI) device based on NTE material. This device allowed to monitor temperature evolutions in the range between RT and 200°C by means of a red to yellow fluorescence switch that was detectable by optical microscopy.
[Show abstract][Hide abstract] ABSTRACT: In this contribution a new class of aliphatic poly(butylene succinate) (PBS)-based poly(ester urethane)s has been synthesized and characterized from the molecular, thermal and mechanical point of view. Hydrolytic degradation studies under physiological conditions have been conducted to assess their biodegradation rate. To obtain copolymers showing both thermoplastic and elastomeric properties, the chain-linking strategy has been considered. In particular, two hydroxyl-terminated oligomers have been synthesized by melt polycondensation: poly(butylene succinate) (PBS), as “hard segment”, and two poly(butylene adipate/diglycolate) (P(BAmBDGn) random copolymers as “soft segment”. The introduction of ether-linkages along the PBA chain permitted to depress its crystallinity degree and to enhance the wettability. Multiblock copolymers were finally obtained by chain extending with hexamethylene diisocyanate each P(BAmBDGn) copolymer with two different mass percentages of PBS: 30% and 50%. All copolymers maintained good thermal stability and were characterized by melting temperatures above 100°C. Elastic modulus (E) and stress at break (σb) varied with the chemical composition: the higher the PBS amount, the higher E and σb. No yield and very high elongations at break were observed. Hydrolytic degradation studies highlighted an increase of the degradation rate with the increase of the BDG content.
[Show abstract][Hide abstract] ABSTRACT: Herein is described a multidisciplinary approach to understand the performance limitations of small molecule organic light emitting transistors (OLETs) based on a layered architecture, an innovative architecture potentially competitive with the state of the art and more flexible for spectral emission control. The processes of charge injection and field-effect transport at metal/organic and organic/organic interfaces are analysed using microscopic and spectroscopic techniques in coordination. Atomic force microscopy and ultrasonic force microscopy are employed to characterize the interface morphology and the initial growth stages of organic films where charge transport actually occurs. X-ray diffraction and near edge X-ray dichroic absorption with linearly polarised light allow to determine the unit cell packing and the molecular orientation at the active organic interfaces, as well as the amount of non-ordered domains. Moreover, chemical reactivity at the interfaces are measured by X-ray photoelectron spectroscopy. It is found that a strong reaction occurs at the metal-organic interfaces, with molecular fragmentation. Additionally, the transport properties strongly depend on the nature of the materials forming the organic stack. Specifically, amorphous conjugated films as bottom layers can promote an increased molecular disorder in the upper active layer, with a concomitant deterioration of the conduction properties.
[Show abstract][Hide abstract] ABSTRACT: Polymorphic crystalline microfibers from an achiral octithiophene with one S-hexyl substituent per ring are separately and reproducibly grown with the same characteristics on various solid surfaces, including the interdigitated electrodes/SiO2 surface of a bottomcontact field-effect transistor. The arrangement of the same molecule in two diverse supramolecular structures leads to markedly different electronic, optical, and charge mobility properties. The microfibers—straight and yellow emitting or helical and red emitting—exhibit p-type charge transport characteristics, with the yellow ones showing a charge mobility and on/off current ratio of one and three orders of magnitude, respectively, greater than the red ones. Both forms show circular dichroism signals with significant differences from one form to the other. DFT calculations show that the octithiophene exists in two different quasi-equienergetic conformations aggregating with diverse orientations of the substituents. This result suggests that the observed polymorphism is conformational in nature. The self-assembly, driven by sulfur–sulfur non-bonding interactions, amplifies the small property differences between conformers, leading to quite different bulk properties.
[Show abstract][Hide abstract] ABSTRACT: In this study, we propose a new class of multiblock copolyesters containing butylene 1,4-cyclohexanedicarboxylate (BCE) and diethylene glycol 1,4-cyclohexanedicarboxylate (DGCE) sequences. The two parent homopolymers were prepared by the usual two-stage melt polycondensation. On the other hand, the multiblock copolyesters, characterized by the same chemical composition but different block lengths, were synthesized by reactive blending. Physicochemical characterization (DSC, WAXS, tensile tests, WCA, hydrolysis experiments) demonstrated that the block length controls the polymer crystallinity, the thermal and mechanical properties, the wettability and the degradation rate. The copolymers displayed different stiffnesses, mainly depending on the crystallinity degree and macromolecular chain flexibility, a tunable range of degradation rates, and different surface hydrophilicity. Biocompatibility assays showed the absence of potentially cytotoxic products released into the culture medium by the investigated samples, and demonstrated that our substrates support a physical environment where cells can adhere and proliferate, confirming their potential for biomedical applications.
[Show abstract][Hide abstract] ABSTRACT: Poly(hexane dodecanoate) (PHD) based random copolyesters containing ether-linkages (P(HDxTEDy)) have been synthesized and characterized from the molecular and thermomechanical point of view. Gas permeability and biodegradability in compost have been also evaluated. The polymers showed good thermal stability and appeared as semicrystalline materials at room temperature. The main effect of copolymerization was a lowering in the crystallinity degree and a decrease of Tm with respect to homopolymers. Different surface hydrophilicity has been also displayed: water contact angle decreased with TED increasing mol %. Moreover, all the copolymers showed very high elongation at break, while the elastic modulus (E) and the stress at break (σb) were found strictly dependent on the composition: E and σb decreased with the increase of the TED content. Both permeability to CO2 and O2 and biodegradation rate evidenced a relationship with the chemical composition: the higher the TED mol %, the higher the permeability and the biodegradation extent.
[Show abstract][Hide abstract] ABSTRACT: A series of novel random copolymers of poly(butylene 1,4-cyclohexanedicarboxylate) (PBCE) containing triethylene glycol sub-unit (P(BCEmTECEn)) were synthesized and characterized in terms of molecular and solid-state properties, among these barrier properties to different gases (oxygen and carbon dioxide). In addition, biodegradability studies both in soil and in compost and ecotoxicological analysis, by means of the Lepidium sativum test, have been conducted.
The copolymers displayed a high and similar thermal stability with respect to PBCE. At room temperature, all the copolymers appeared as semicrystalline materials: the main effect of copolymerization was a lowering of crystallinity degree (χc) and a decrease of the melting temperature compared to the parent homopolymer. The Baur’s equation well described the Tm-composition data. Final properties and biodegradation rate of the materials under study were strictly dependent on copolymer composition and χc. As a matter of fact, hydrophilicity regularly increased with the increasing of TECE mol%, due to the PEG-like portion. The elastic modulus and the elongation to break decreased and increased, respectively, as TECE unit content was increased. As to the barrier properties, the selectivity ratios for the examined samples increased with the increasing of TECE mol%, confirming the correlation between the permeability and the chemical composition. The copolymers with lower TECE unit content (up to 30 mol%) showed improved barrier properties with respect to polylactide films tested under the same conditions.
Lastly, the biodegradation rate of P(BCEmTECEn) copolymers increased with the increasing of TECE mol%, while PBCE remained almost undegraded in the explored conditions.
[Show abstract][Hide abstract] ABSTRACT: The influence of the simultaneous presence of the two inhibitors of bone degradation, strontium and zoledronate, on the direct synthesis of hydroxyapatite was explored in the range of Sr concentration up to 50 atom% at two different bisphosphonate concentrations (ZOL7 and ZOL14). The results of structural analysis indicated that HA can be obtained as a single crystalline phase up to a Sr concentration in solution of 20 and 10 atom% within the ZOL7 and ZOL14 series respectively. Both Sr substitution and ZOL incorporation affect the length of the coherently scattering crystalline domains and the dimensions of HA nanocrystals. At greater Sr content, XRD full profile fitting data indicate that zoledronate provokes the segregation of Sr in two crystalline apatitic phases, at different strontium content. Co-cultures of osteoblast-like MG63 cells and human osteoclast show that ZOL displays a greater inhibitory influence than Sr on osteoclast proliferation and activity. On the other hand, the results obtained on osteoblast surnatant and on gene expression indicate that Sr exerts a greater promotion on osteoblast proliferation and differentiation. The co-presence of Sr and ZOL has a combined effect on the differentiation markers, so that HA containing about 4 wt% ZOL and 4 Sr atom%, and even more HA containing about 4 wt% ZOL and 8 Sr atom%, result the best compromise for osteoblast promotion and osteoclast inhibition.
[Show abstract][Hide abstract] ABSTRACT: The formation of gold nanoparticles (GNPs) within mesoporous silica matrices by means of irradiation
techniques is reported. The xerogels were impregnated with solutions of two different gold precursors:
(Ph3P)AuCl for Au(I) and [nBu4N]AuCl4 for Au(III). The irradiations were performed with two continuous
wave laser sources (266 and 532 nm), with a femtosecond pulsed laser (800 nm), and with a mercury
vapour lamp emitting in the UV region. It has been shown that no reducing agent was ever required to
obtain GNP formation. XRD data exhibited the typical patterns of fcc gold, except for two cases involving
the Au(I)-doped matrices, where a preferential crystallographic orientation was observed. Excluding the
case of the UV irradiations performed on Au(III)-doped samples, we always obtained the formation of
roughly spherical and well dispersed GNPs of relatively small size (6–60 nm). The gold-reduction
mechanisms proposed depend on the chosen irradiation technique. Moreover, when laser sources are
employed, GNP formation can be selectively limited to the irradiated areas, thus making it possible to
obtain reproducible patterns of GNPs.
[Show abstract][Hide abstract] ABSTRACT: The relationships between the molecular structure, packing modalities, charge mobility and light emission in organic thin films is a highly debated and controversial issue, with both fundamental and technological implications in the field of organic optoelectronics. Thieno(bis)imide (TBI) based molecular semiconductors provide an interesting combination of good processability, tunable self-assembly, ambipolar charge transport and electroluminescence, and are therefore an ideal test base for fundamental studies on the structure-property correlation in multifunctional molecular systems. Herein, we introduce a new class of thieno(bis)imide quaterthiophenes having alkyl side chains of different shapes (linear, cyclic, branched) and lengths (C1-C8). We found that contrarily to what is generally observed in most molecular semiconductors, the length of the alkyl substituent does not affect the optical, self-assembly and charge transport properties of TBI materials. However, different electroluminescence powers are observed by increasing the alkyl side, this suggesting a potential tool for the selective modulation of TBI functionalities. A deep experimental and theoretical investigation on this new family of TBI materials is provided.
[Show abstract][Hide abstract] ABSTRACT: The variation of the drift mobility of positive and negative charge carriers in fi lms of anthracene-
containing poly( p -phenylene-ethynylene)- alt- poly( p -phenylene-vinylene)s ( AnE-PVs ),
differently substituted, is investigated as a function of the
applied electric fi eld. Branched 2-ethylhexyl and linear alkoxy
side chains of different lengths are considered, as well as
well-defi ned and random distributions of lateral substituents.
The same conditions are used both for the deposition of the
polymer fi lms and for their characterization, which allows for
the establishment of a clear relationship between the chemical
structure and the charge carrier mobility.
[Show abstract][Hide abstract] ABSTRACT: The synthesis of two new thieno(bis)imide (TBI, N) end functionalized oligothiophene semiconductors is reported. In particular, trimer (NT3N) and pentamer (NT5N) have been synthesized and characterized. Two different synthetic approaches for their preparation were tested and compared namely conventional Stille cross coupling and direct arylation reaction via C–H activation. Theoretical calculations, optical and electrochemical characterization allowed us to assess the role of the π-conjugation extent, i.e., of the oligomer size on the optoelectronic properties of these materials. In both TBI ended compounds, due to the strong localization of the LUMO orbital on the TBI unit, the LUMO energy is almost insensitive to the oligomer size, this being crucial for the fine-tailoring of the energy and the distribution of the frontier orbitals. Surprisingly, despite its short size and contrarily to comparable TBI-free analogues, NT3N shows electron charge transport with mobility up to μN = 10−4 cm2 V−1 s−1, while increasing the oligomer size to NT5N promotes ambipolar behavior and electroluminescence properties with mobility up to μN = 0.14 cm2 V−1 s−1 and to μP = 10−5 cm2 V−1 s−1.
[Show abstract][Hide abstract] ABSTRACT: The role of lipids in controlling water exchange is fundamentally a matter of molecular organization. In the present study we have observed that in snake molt the water permeability drastically varies among species living in different climates and habitats. The analysis of molts from four snake species: tiger snake, Notechis scutatus, gabon viper, Bitis gabonica, rattle snake, Crotalus atrox, and grass snake, Natrix natrix, revealed correlations between the molecular composition and the structural organization of the lipid-rich mesos layer with control in water exchange as a function of temperature. It was discovered, merging data from micro-diffraction and micro-spectroscopy with those from thermal, NMR and chromatographic analyses, that this control is generated from a sophisticated structural organization that changes size and phase distribution of crystalline domains of specific lipid molecules as a function of temperature. Thus, the results of this research on four snake species suggest that in snake skins different structured lipid layers have evolved and adapted to different climates. Moreover, these lipid structures can protect, "safety", the snakes from water lost even at temperatures higher than those of their usual habitat.
[Show abstract][Hide abstract] ABSTRACT: The coating of substrate materials with different geometry (gauze, plate, foam) and composition (Pt and FeCrAlloy) with Layered Double Hydroxides (lNi/A1, Mg/Al) was performed using the base electrogeneration method. The pH established by the cathodic reduction of nitrates in the proximity of a Pt gauze was measured with a glass electrode. In order to study the morphology, composition, and structure of the electrodeposited solids, at first Pt plates were used as substrates; the characterization was performed by SEM/EDS and XRD. Lastly, the study was focused on the FeCrAlloy foam more complex substrate. The more negative the applied potential was, the higher the pH values measured were; however, very negative potentials (-1.1 to -1.3 V vs SCE) promoted the formation of H-2 bubbles. Optimum potential for precipitating Layered Double Hydroxides depended on their chemical composition and even if the potential applied was adequate for the formation of pure phases, SEM/EDS analyses revealed that a sequential precipitation occurred at long synthesis times.
[Show abstract][Hide abstract] ABSTRACT: A squaraine dye functionalized with a bulky trialkoxy phenyl moiety through a flexible diamide linkage (GA-SQ) capable of undergoing self-assembly has been synthesized and fully characterized. Rapid cooling of a hot solution of GA-SQ to 0 °C results in self-assembled precipitates consisting of two types of nanostructures, rings and ill-defined short fibers. The application of ultrasound modifies the conditions for the supersaturation-mediated nucleation, generating only one kind of nuclei and prompting the formation of crystalline fibrous structures, inducing gelation of solvent molecules. The unique self-assembling behavior of GA-SQ under ultrasound stimulus has been investigated in detail by using absorption, emission, FT-IR, XRD, SEM, AFM and TEM techniques. These studies reveal a nucleation growth mechanism of the self-assembled material, an aspect rarely scrutinized in the area of sonication-induced gelation. Furthermore, in order to probe the effects of nanoscale substrates on the sonication-induced self-assembly, a minuscule amount of single-walled carbon nanotubes was added, which leads to acceleration of the self-assembly through a heterogeneous nucleation process that ultimately affords a supramolecular gel with nanotape-like morphology. This study demonstrates that self-assembly of functional dyes can be judiciously manipulated by an external stimulus and can be further controlled by the addition of carbon nanotubes.
Chemistry - A European Journal 09/2013; 19(39). DOI:10.1002/chem.201301539 · 5.73 Impact Factor