Ludovico Valli

A sensitivity-enhanced field-effect chiral sensor

Organic thin-film transistor sensors have been recently attracting the attention of the plastic electronics community for their potential exploitation in novel sensing platforms. Specificity and sensitivity are however still open issues: in this respect chiral discrimination-being a scientific and technological achievement in itself--is indeed one of the most challenging sensor bench-tests. So far, conducting-polymer solid-state chiral detection has been carried out at part-per-thousand concentration levels. Here, a novel chiral bilayer organic thin-film transistor gas sensor--comprising an outermost layer with built-in enantioselective properties-is demonstrated to show field-effect amplified sensitivity that enables differential detection of optical isomers in the tens-of-parts-per-million concentration range. The ad-hoc-designed organic semiconductor endowed with chiral side groups, the bilayer structure and the thin-film transistor transducer provide a significant step forward in the development of a high-performance and versatile sensing platform compatible with flexible organic electronic technologies.

Synthesis of N-acylated fulleropyrrolidines: New materials for the preparation of Langmuir-Blodgett films containing fullerenes

The synthesis of a series of new C60 derivatives of interest for their potential in the study of LB properties of fullerenes is reported. Besides that of compounds 4b and 4c, featuring fatty acid chains, the preparation of the well-characterized, perfluorinated fulleropyrrolidine 4d is described. A preliminary investigation of LB behavior of the N-acetyl compound 4a gives very promising results.

Optochemical vapour detection using spin coated thin films of metal substituted phthalocyanines

Spin coated layers of metallophthalocyanines have been used as chemically interacting materials and a discussion concerning the data obtained with optical absorbance measurements in UV-Vis spectral range in controlled atmosphere is presented. Glass substrates coated with metallophthalocyanines show good sensitivity and selectivity depending on both the central metal ion of the molecules and the peripheral substituents of the macrocycles. A promising sensitivity towards tert-butylamine, diethylamine, dibutylamine, 2-butanone and acetic acid vapours has been monitored. Moreover, a structural characterisation by using scanning electron microscopy has been performed and a different morphology of the sensitive layers obtained from different materials has been evidenced.

Langmuir–Blodgett and layer-by-layer films of photoactive fullerene–porphyrin dyads

The fabrication of high quality, robust and photoactive ITO electrodes—in the form of well-defined two- and three-dimensional films—is reported following the Langmuir–Schafer (LS) and the layer-by-layer (LBL) methods. In the LS approach C60-NiP multilayers were transferred from the air–water interface, while the LBL approach utilizes electrostatic and van der Waals interactions for the step-by-step deposition of individual C60-NiP molecules out of solution. These complementary techniques allow control over the thickness and composition of the films at a molecular level and guarantee the specific alignment and the orientation of the incorporated donor–acceptor system. Modified ITO electrodes were probed in photocurrent experiments, in which the LBL-modified electrodes reveal smaller photon to current conversion efficiencies relative to the LS-modified electrodes.

State of art in porphyrin Langmuir–Blodgett films as chemical sensors

Porphyrins are tetrapyrrolic macrocycles with a fascinating and multifarious variegation of properties of essential significance in up-to-date and leading technologies. From a different point of view, the Langmuir-Blodgett technique allows the immobilisation of films with an accurate regulation of molecular organisation and thickness. As a logical upshot, this manuscript concerns a substantial object of consideration in contemporary research, the utilisation of Langmuir-Blodgett multilayers of porphyrins in sensing elements for the detection of analytes in different matrices. Investigations on the morphological, optical, structural and surface characteristics of these films are remarkably related to the significant properties of sensors with the ultimate goal of rationalising the innermost intercourses between the sensing behaviour and the peculiarities and molecular organisation brought about by the deposition method. The integration of the typical electrical and optical characteristics of porphyrins with the potentialities of the Langmuir-Blodgett multilayer has originated not only encouraging projects but has afforded also certainties on the accomplishment of operative chemical sensors.

Structural and spectroscopic characterization of Cu(II) [tetrakis-(3,3-dimethyl-l-butoxycarbonyl)] phthalocyanine thin films deposited by the Langmuir—Blodgett technique

Abstract Langmuir-Blodgett (LB) films of Cu(II) [tetrakis(3,3-dimethyl-l-butoxycarbonyl]phthalocyanine were prepared and characterized by X-ray diffraction, and polarized UV-Vis and electron paramagnetic resonance (EPR) spectroscopies. It was found that the phthalocyanine molecules deposited on quartz and polyethylene terephthalate (pet) are arranged edge-on on the substrate with the normal to the molecular plane that lies close to the plane of the film. Polarized UV-Vis spectra of films show in-plane anisotropy in the orientation of molecules for LB films deposited on quartz and on pet. EPR spectra also, assigned to Cu 2+ interacting species, were detected for the LB films deposited on pet. The spectra show a marked in-plane anisotropy of the Zeeman interaction when the magnetic field lies in the support plane. The analysis of their angular dependence confirms that the plane of the phthalocyanine molecule is almost perpendicular to the film plane and gives evidence that the in-plane orientation anisotropy arises from two different distributions of orientations pinned around two average orientations having an angle of 68 ° between them.

Supramolecular amplification of amyloid self-assembly by iodination

Amyloid supramolecular assemblies have found widespread exploitation as ordered nanomaterials in a range of applications from materials science to biotechnology. New strategies are, however, required for understanding and promoting mature fibril formation from simple monomer motifs through easy and scalable processes. Noncovalent interactions are key to forming and holding the amyloid structure together. On the other hand, the halogen bond has never been used purposefully to achieve control over amyloid self-assembly. Here we show that single atom replacement of hydrogen with iodine, a halogen-bond donor, in the human calcitonin-derived amyloidogenic fragment DFNKF results in a super-gelator peptide, which forms a strong and shape-persistent hydrogel at 30-fold lower concentration than the wild-type pentapeptide. This is remarkable for such a modest perturbation in structure. Iodination of aromatic amino acids may thus develop as a general strategy for the design of new hydrogels from unprotected peptides and without using organic solvents.

Gas-sensing properties of porphyrin dimer Langmuir-Blodgett films

Abstract Langmuir–Blodgett films of a 1:4 mixture of meso,meso′-buta-1,3-diyne-bridged Ni(II) octaethylporphyrin dimer and arachidic acid have been deposited onto various substrates. The isotherm at the air/water interface and absorbance measurements using polarised light are consistent with a planar statistical orientation of the porphyrin dimers which are probably prone onto the arachidic acid tails. The presence in the dimer of the acetylenic linking group allows the formation of a large and highly conjugated molecular structure; this has suggested the use of the films in gas sensing apparatus. Electrical characterisation in controlled atmosphere and with the simultaneous presence of interfering gaseous species, such as C2H5OH, NH3, and CO, suggest that this porphyrin dimer is a promising selective NO gas sensing material.

Kinetic behavior analysis of porphyrin Langmuir–Blodgett films for conductive gas sensors

Meso, meso′-buta-1,3-diyne-bridged Ni (II) octaethylporphyrin dimer thin films have been deposited by the Langmuir–Blodgett method and, for the first time, have been considered as the active layer in resistive gas sensors. In particular, the electrical conductivities of these films undergo a remarkable variation due to exposure to small concentrations of NO in air at an operating temperature of 50 °C. To interpret the behavior of such organic films, a model has been built up and the conductivity variation as a function of test gas concentrations and time has been derived. The fitting of theoretical and experimental behavior allows us to determine the number of adsorbed gas molecules per porphyrin dimer, response and recovery times, adsorption and desorption coefficients. The reliability of the model is proved by obtained results. In particular, the determined adsorption and desorption coefficients depend only on test gas species but are unaffected by other experimental conditions such as gas concentration.

Effects of NO2 oxidizing gas on a novel phthalocyanine Langmuir-Blodgett thin film

Abstract In the last two decades there has been considerable interest in the study of optical and electrical properties of metal-substituted phthalocyanines with the goal of their possible applications in technology. In particular, these compounds have been proposed as new materials for gas sensors [1–3]. The deposition of these macrocycles by the Langmuir-Blodgett thin films is a method with significant potential [4].