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Enantiorecognition of a chiral analyte usually requires the ability to respond with high specificity to one of the two enantiomers of a chiral compound. However, in most cases, chiral sensors have chemical sensitivity toward both enantiomers, showing differences only in the intensity of responses. Furthermore, specific chiral receptors are obtained with high synthetic efforts and have limited structural versatility. These facts hinder the implementation of chiral sensors in many potential applications. Here, we utilize the presence of both enantiomers of each receptor to introduce a novel normalization that allows the enantio-recognition of compounds even when single sensors are not specific for one enantiomer of a target analyte. For this purpose, a novel protocol that permits the fabrication of a large set of enantiomeric receptor pairs with low synthetic efforts by combining metalloporphyrins with (R,R)- and (S,S)-cyclohexanohemicucurbit[8]uril is developed. The potentialities of this approach are investigated by an array of four pairs of enantiomeric sensors fabricated using quartz microbalances since gravimetric sensors are intrinsically non-selective toward the mechanism of interaction of analytes and receptors. Albeit the weak enantioselectivity of single sensors toward limonene and 1-phenylethylamine, the normalization allows the correct identification of these enantiomers in the vapor phase indifferent to their concentration. Remarkably, the achiral metalloporphyrin choice influences the enantioselective properties, opening the way to easily obtain a large library of chiral receptors that can be implemented in actual sensor arrays. These enantioselective electronic noses and tongues may have a potential striking impact in many medical, agrochemical, and environmental fields.

Two zinc oxide (ZnO) nanomaterials, exhibiting distinct morphologies, were synthesized in wurtzite phase through chemical precipitation. The elongated shape rod-like ZnO (R-ZnO) exhibited more pronounced piezoelectric characteristics compared to the more compact flower-like ZnO (F-ZnO). Detailed characterization including piezoforce microscopy, finite element simulation, revealed that the remarkable piezoelectric properties of R-ZnO are due to its strongly anisotropic structure, enabling significant mechanical deformation under ultrasound in aqueous suspension. The piezocatalytical degradation of these materials was assessed using methylene blue as a test organic dye across various ultrasound frequencies, with R-ZnO consistently outperforming F-ZnO. This highlighted the impact of structural deformability on piezocatalytic efficiency. Additionally, the capability of R-ZnO to facilitate oxygen evolution from water through ultrasound-induced stress was explored in an oxygen-free environment. Our findings demonstrate that R-ZnO can effectively catalyze water oxidation and produce oxygen directly, showcasing its potential as a standalone catalyst for environmental remediation and sustainable chemical processes.

Perylene bisimide derivatives show peculiar physical chemical features, such as a highly conjugated system, high extinction coefficients and elevated fluorescence quantum yields, making them suitable for the development of optical sensors of compounds of interest. In particular, they are characterized by the tendency to aggregate into π–π stacked supramolecular structures. In this contribution, the behavior of the PBI derivative N,N′-bis(2-(trimethylammonium)ethylene)perylene bisimide dichloride was investigated both in aqueous solution and on solid support. The electronic communication between PBI aggregates and biogenic amines was exploited in order to discriminate aromatic amines down to subnanomolar concentrations by observing PBI fluorescence variations in the presence of various amines and at different concentrations. The experimental findings were corroborated by density functional theory calculations. In particular, phenylethylamine and tyramine were demonstrated to be selectively detected down to 10–10M concentration. Then, in order to develop a surface plasmon resonance (SPR) device, PBI was deposited onto a SPR support by means of the layer-by-layer method. PBI was deposited in the aggregated form and was demonstrated to preserve the capability to discriminate, selectively and with an outstanding analytical sensitivity, tyramine in the vapor phase and even if mixed with other aromatic amines.

The interest of the scientific community toward carbon-based nanostructures is justified by the wide range of applications of such multifaceted structures. In the present work, carbon nanoparticles (CNPs) were synthesized, in mild conditions, by using spent coffee grounds as the carbon source. Green-emitting CNPs of about 40 nm were obtained, and they were characterized by X-ray photoelectron spectroscopy, energy-dispersive X-ray spectroscopy, fluorescence spectroscopy, and Fourier transform infrared spectroscopy, highlighting that they are naturally doped with N, K, Mg, and P. Such intrinsic doping promotes the characteristic green emission; furthermore, the N- and P-doping prompted us to evaluate their ability to photoproduce 1O2for PDT applications. The presence of heteroatoms in the CNP structure was also used to electrochemically promote the oxygen reduction reaction and hydrogen evolution reaction catalysis.

ZnO@Ag patchy nanostructures were demonstrated to be efficient and stable photocatalysts for the photodegradation of organic contaminants in aqueous solutions. The photoinduced charge transfer from the conduction band of ZnO toward the Fermi level of the noble metal was favored and exploited to enhance the photocatalytic efficiency of ZnO, with a mechanism based on hole stabilization. Naked ZnO and ZnO@Ag patchy nanostructures were demonstrated to degrade methylene blue, a model compound, in aqueous solution under 370–800 nm light irradiation (100 mW cm–2); in particular, the introduction of silver nanoparticles allowed one to increment twice the constant rate of the reaction when fitted as pseudo-first-order kinetics. Furthermore, the degradation of 2,4-dichlorophenol under direct sunlight irradiation was studied. The photo-oxidation catalyzed by patchy nanostructures was noticeably increased. In fact, the observed half time (t1/2) was reduced by almost 4 times in comparison with the value observed for bare ZnO.

A supramolecular adduct formed by the interaction among octadecylamine (ODA) and zinc oxide nanostructures was promoted. A stable dispersion of the ZnO@ODA adduct was obtained and characterized by means of thermogravimetric analysis and infrared and Raman spectroscopy. Then, the supramolecular adduct was spread at the air/water interface of a Langmuir trough. The presence of octadecylamine gave amphiphilic features to the ZnO@ODA adduct that was transferred from the air/water interface to solid substrates by Langmuir–Schaefer (LS) method. The transferred film was characterized by tunnel electron microscopy that highlighted rectangular well-shaped structures assembled by nanostructure of ZnO arranged in an ODA matrix. Piezoelectric feature of large LS film (1 cm2) was tested and a very promising response was observed as a consequence of the application of a pressure of 1 kPa.

The mechanisms of interaction between a tetrapyridyl-substituted porphyrin and Hg(II) and Cu(II) ions have been investigated by means of different spectroscopic techniques. Reflection spectroscopy investigations of the porphyrin Langmuir floating film and by polarization modulation infrared (IR) reflection adsorption spectroscopy at the air–water interface provided evidence of the active role played by the pyridyl substituents of the porphyrin in the interaction with the analyte. Such behavior seems to be very selective toward Cu2+and Hg2+ions, as demonstrated by the IR measurements in difference mode. UV–vis and IR characterizations suggest a deeply different interaction between the active molecules and the two analytes. In fact, the interaction of Hg2+ions with the tetrapyrrolic derivative molecules involves both the pyridyl substituents and the central bite of the ring. On the other hand, in the case of Cu2+ions, spectroscopic evidence suggests that the cupric ions interact with only the porphyrin peripheral substituents. A relevant fluorescence quenching of the Langmuir–Schaefer (LS) film is observed when even a 0.5 nM HgCl2or 0.5 nM CuCl2aqueous solution is fluxed on the LS film.

Single-walled carbon nanotubes (SWCNTs) were suspended in 1,2-dichloroethane by noncovalent functionalization with a low-band-gap conjugated polymer 1alternating dialkoxyphenylene–bisthiophene units with benzo[c][2,1,3]thiadiazole monomeric units. The suspended 1/SWCNT blend was transferred onto different solid substrates by the Langmuir–Schaefer deposition method, resulting in films with a high percentage of aligned nanotubes. Photoelectrochemical characterization of 1/SWCNT thin films on indium–tin oxide showed the benefits of SWCNT alignment for photoconversion efficiency.

This work reports on the structural and spectroscopic properties, as well as the gas-sensing performance, of ethane-bridged Zn porphyrin dimers (ZnPP) in Langmuir–Schäfer (LS) thin films toward volatile organic compounds in a magneto-optical surface plasmon resonance (MOSPR) configuration. Structural and spectroscopic properties of ethane-bridged ZnPP thin films deposited onto proper Au/Co/Au magneto-optical substrates were inspected in dry air conditions and after exposure to amine vapors by means of IR spectroscopy, scanning probe microscopy, and MOSPR techniques. The molecular organization of the thin films deposited by the LS technique is investigated. The overall results suggest the presence in all cases of mainly the anti-conformer of the investigated porphyrin dimers. The strong interaction between n-butylamine vapors at high concentration and Zn porphyrin thin layers leads to a great conformational change in the porphyrin structure, which is linked to a change in the optical anisotropy of the realized LS layer.

An alkoxy‐substituted poly(phenylene thiophene) is used in order to suspend single‐walled carbon nanotubes in an organic solvent. The suspension is spread on the air–water interface of a Langmuir trough and the floating film is characterized by means of Brewster angle microscopy and UV‐visible reflection spectroscopy and the compression isotherm is recorded. The polymer/carbon‐nanotube blend is transferred onto different substrates using the Langmuir–Blodgett technique. AFM measurements indicate the formation of globular structures for the samples transferred at low surface‐pressure values and a tubular morphology for high‐pressure‐deposited samples. AFM analysis is repeated on a sample exposed to soft X‐rays for about 5 h and a highly organized structure of bundles of carbon nanotubes rises up. Samples with different numbers of layers are transferred onto ITO substrates by means of the Langmuir–Blodgett method and are tested as photocathodes in a photo‐electrochemical cell. A Vocof 0.18 V, an Iscof 85.8 mA, FFof 40.0%, and ηof (6.23 × 10−3)% are obtained.

The synthesis of novel functional amphiphilic dipodal NiII1 and ZnII2 Schiff base complexes and the preparationcharacterization and optical properties of Langmuir–Schäfer LS multilayer films are reported. The existence of stacked 3D aggregates is observed for all films, as established by the combination of reflection spectroscopy and Brewster angle microscopy. Although aggregate formation does not involve major electronic changes, as evidenced by analysis by absorption spectroscopy, fluorescence emission is much more sensitive to the chemical environment, and complete quenching is observed in the multilayer LS aggregates. However, in the limit of negligible interchromophore interactions, achieved by means of mixed LS multilayer films the fluorescence is restored by using arachidic acid as a spacer diluent, and LS layers of 2behave as related selfassembled monolayers. © WileyVCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008

Solution processed Langmuir−Schäfer and cast thin films of regioregular poly(2,5-dioctyloxy-1,4-phenylene-alt-2,5-thienylene) are investigated as transistor active layers. The study of their field-effect properties evidences that no transistor behavior can be seen with a cast film channel material. This was not surprising considering the twisted conformation of the polymer backbone predicted by various theoretical studies. Strikingly, the Langmuir−Schäfer (LS) thin films exhibit a field-effect mobility of 5 × 10-4 cm2,5·s, the highest attained so far with an alkoxy-substituted conjugated polymer. Extensive optical, morphological, and structural thin-film characterization supports the attribution of the effect to the longer conjugation length achieved in the Langmuir−Schäfer deposited film, likely due to an improved backbone planarity. This study shows that a technologically appealing deposition procedure, such as the LS one, can be exploited to significantly improve the inherently poor field-effect properties of twisted conjugated backbones. This achievement could promote the exploitation for electronic, and possibly sensing, applications of the wealth of opportunities offered by the alkoxy substitution on the phenylene units for convenient tailoring of the phenylene−thienylene backbone with molecules of chemical and biological interest.

Thin films consisting of a fulleropyrrolidine derivative 1and a novel water‐soluble porphyrin 2were prepared by the Langmuir–Shäfer (LS, horizontal lifting) method. In particular, a solution of 1in chloroform and dimethyl sulfoxide was spread on the water surface, while porphyrin 2(bearing peripheral anionic groups) was dissolved into the aqueous subphase. To the best of our knowledge, such a versatile method of film fabrication for fullerene/porphyrin mixed composite films has never been used before. Evidence of the effective interactions between the two moieties at the air–water interface was obtained from the analysis of the floating layers by means of surface pressure versus area per molecule Langmuir curves, Brewster angle microscopy and UV‐visible reflection spectroscopy. The characterisation of the LS films by UV‐visible spectroscopy reveals that the two constituents behave as discrete and weakly interacting π systems. The use of polarised light suggests the existence of a preferential direction of the macrocyclic rings with an edge‐on arrangement with respect to the substrate surface. Finally, photoaction spectra were recorded from films deposited by only one horizontal lifting onto indium–tin–oxide (ITO) electrodes and the observed photocurrent increased notably with increasing transfer surface pressure.

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–Schäfer LS and the layer-by-layer LBL methods. In the LS approach C60-NiPmultilayers 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-NiPmolecules 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.

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–Schäfer (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.

A new calix[4]pyrrole-based macrocycle, meso-tetra(methyloctyl)calix[4]pyrrole (MTP), has been synthesized and fully characterized. Thin films of MTP have been transferred onto hydrophobized quartz and silicon oxide sheets by using the Langmuir–Schäfer (LS) method (horizontal lifting). Scanning force microscopy (SFM) investigation showed that the LS films are almost homogeneous and are consistent with the X-type configuration with the hydrophobic tails of MTP disposed almost perpendicularly with respect to the substrate. Induced circular dichroism (ICD) measurements have been performed in the presence of chiral alcohol vapours, such as (−)-(R)-2-butanol, (−)-(R)-2-pentanol and (−)-(R)-2-hexanol. The results showed that although not chiral by themselves the MTP molecules within the film exhibit chirality induced by binding with the chiral guests. The appearance of ICD signals is accounted for by the close proximity of the alcohol molecules to the pyrrole moieties of MTP. The reversibility of the binding event, coupled with the differentiated response observed towards the alcohols investigated, makes the LS films promising active layers for the chemical recognition of short-chain polar neutral molecules.

Novel [2,3,9,10,16,17,23,24-octakis(3,3-dimethyl-1-butoxycarbonyl) phthalocyaninato] copper(II) thin films were prepared by the Langmuir-Blodgett technique. Unlike for the symmetrical tetrasubstituted analogue, polarized light UV-visible measurements do not show inplane anisotropy of the orientation of molecules in the films. Transmission electron microscopy methods were applied in order to investigate the morphology and the structure of the deposited films. Dynamic response characteristics of the electrical conductance to 250 ppm NH3 in dry air are presented. The sensitivity as a function of temperature was analysed.

A Langmuir film of cubane-bridged bisporphyrin (H2por-cubane-H2por) at the air/water interface was developed and characterized. The floating film was successfully employed for the chiral discrimination between l- and d-histidine. The enantioselective behavior persisted after the deposition of the film on a solid support using the Langmuir–Schaefer method. Distinct absorption and reflection spectra were observed in the presence of l- or d-histidine, revealing that conformational switching was governed by the interaction between H2por-cubane-H2porand the histidine enantiomer. The mechanism of chiral selection was investigated using an ad hocmodified nulling ellipsometer, indicating the anti-conformation was dominant in the presence of l-histidine, whereas the presence of d-histidine promoted the formation of tweezerconformation.