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This review analyses the results obtained through the Electron Spin Resonance (ESR) spectroscopy on multilayer Langmuir-Blodgett films fabricated with metal derivatives (mainly Cu 2+ , VO 2+ and low-spin CO 2+ ) of polyazamacrocycles (porphyrins, tetraazaannulenes, phthalocyanines). These metal ions are particularly suitable for an ESR analysis because of their relatively long electron spin relaxation times that render possible their observation even at room temperature and in all co-ordination symmetry. This allows us to obtain valuable data on both mobility and orientation of the metal-macrocycle systems adsorbed onto a solid support. The preliminary characterisation of the spreading monolayer obtained from the systems considered, as it is typically done by surface pressure/area isotherms, optical (UV-Vis) and ESR spectroscopies, is also reviewed.

By surface tension and ellipsometric measurements, we studied how 2D crystallization of fatty alcohol monolayers is influenced by the presence in the subphase of a short chain carboxylic acid, whose surface activity is dependent upon pH. The surface crystallization of the alcohol monolayer was appreciably perturbed for pH values smaller than the pK a of the acid, that is when the protonated form of the acid was predominant in the bulk solution. On the contrary, for pH values above the pK a of the acid, the monolayer was not influenced by the presence of the acid in the subphase. The effect was greatly dependent on the acid concentration in the subphase, at a fixed pH. We also studied the effect of the acid chain length (C 6 -C 10 ) on a decanol monolayer, the effect of the alcohol chain length with octanoic acid in the subphase, and the effect of the lateral surface pressure of the monolayer.

The spreading monolayers at the air-water surface of the mesogenic, discotic copper(II) derivatives of 2,3,7,8,12,13,17,18-octakis(alkylthio)porphyrin (CuTAP) have been characterized with the aim of finding the best experimental conditions for fabricating Langmuir-Blodgett (LB) films with columnar aggregates having significant mono- and/or bidimensional properties. The spreading isotherms of pure metal compounds were interpreted in terms of inhomogeneous, rigid surface films, not suitable for LB film deposition. A better transfer was reached with mixtures (e.g. 1 20 molar ratio) of Cu-TAP with the film forming stearic acid, thus obtaining stable and reproducible LB films with more than 300 layers. The film maintained a disordered state of columnar aggregates as proved by electron spin resonance and UV-visible spectroscopy.

We studied the properties of the monolayers and deposition behaviour of a new member of the group of bis-porphyrin complexes of rare earth metals, namely the newly fabricated lutetium(III) bis-2,3,7,8,12,13,17,18-octakis(butylthio) tetraazaporphyrinato, as a pure compound and in mixture with cadmium stearate, in the light of their magnetic, semiconducting and gas sensing properties. In both cases the molecules assumed a tilted edge-on orientation at the liquid-air interface, with the molecular rings perpendicular to the water surface, as deduced from π−A isotherms. Multilayer Langmuir-Blodgett (LB) films were successfully built up only when the bis-porphyrin molecules were mixed with cadmium stearate. Electronic absorption spectra using plane-polarized light indicated isotropy in the plane of the film, i.e. the axes of the molecules were randomly oriented in this plane. The peak width at half-height for the Q band increased on passing from the chloroform solution to the LB films of pure and mixed compounds, indicating different degrees of molecular packing. A single electron spin resonance line was given by the chloroform solution of the molecule and it was also maintained in the mixed LB film.

The properties of monolayers and multilayers of nickel(II) compounds with the dinaphtho derivative of the macrocycle ligand dinaphtho{ b,i }5,7,12,14-tetramethyltetraaza[14]annulene with one and two hexadecanoyl chains on the water surface and onto a solid support have been studied from a thermodynamic and spectroscopic point of view and the results were compared with those from the dibenzo analogues. The molecular plane showed a tilted edge-on orientation at the air-water interface. The spreading monolayers were stable with time and their stability was almost independent of the compound used. The presence of hysteresis in the compression-expansion-compression cycles indicated an incomplete reversibility. Films prepared with the monohexadecanoyl macrocycle metal derivatives were regular and homogeneous whereas the occurrence of two alkyl chains on the ring resulted in a monolayer too viscous to be transferred. The effect of the film iodination was investigated through UV-visible and electron spin resonance spectroscopies.

The synthesis and the physico-chemical properties of the bis(2,3,7,8,12,13,17,18-octakis-(octhylthio)-5,10,15,20-tetraazaporphyrinato)lutetium(III) double-decker complex, Lu(OOTTAP)2, are described, ESR, 1H and 13C NMR, UV-visible and NIR studies show that radical nature of this compound and suggest that the unpaired electron cannot be assigned to a specific tetra-azaporphyrinic ring on the time scales available. Some relevant UV-visible spectroscopic and redox features of Lu(OOTTAP)2 resemble closely those of diphthalocyanine complexes, while the intensity and vibrational structure of the NIR spectra are rather reminiscent of those of bis-porphyrin systems.

We report on the use of a copper compound of 2,3,7,8,12,13,17,18-octakis (octylthio)-5,10,15,20-tetraazaporphyrin for the fabrication of a spreading monolayer and Langmuir-Blodgett Films. This compound, as a free ligand or metal substituted, gives mesogenic material with a discotic, columnar structure. Its structural and magnetic properties have been characterized by optical and ESR spectroscopies. The spreading monolayer was not homogeneous and use of a typical film-forming amphiphile, such as stearic acid, was necessary for obtaining stable, reproducible surface films, which were easily transferred onto quartz plates treated with dimethyldichlorosilane. The properties of the film were also analyzed with both UV-vis and ESR spectroscopies

The Langmuir—Blodgett technique has been used for the preparation of magnetic multilayer films of manganese arachidate either as a pure component or in mixture with the diamagnetic methyl arachidate. The mutual surface miscibility of both compounds was verified from the spreading isotherms of their mixtures. The spreading isotherms allowed us to find the optimum conditions for the transfer of monolayers onto silanized quartz plates and to prepare LB films with more than 100 layers. Electron paramagnetic resonance spectroscopy has been used to characterize the magnetic properties of the films. The typical shape anisotropy of quasi-two-dimensional magnets was observed from the orientation dependence in the magnetic field of the linewidth and from the changes of both linewidth and resonance position with temperature at T 5 the usual isotropic properties were observed.

Some parameters related to the bidimensional interactions between ceramide (CER) and diolcoylphosphatidylcholine (DOPC) molecules, alone and in mixtures of different weight fractions, were deduced from the study of spreading monolayers at the air-water interface. Spreading isotherms were recorded using both 0.1 M NaCl (pH 5.6) and a phosphate buffer solution (pH 7) as subphases in the 15–30°C temperature range. The bidimensional phases of the two components were obtained and their bidimensional miscibility was deduced as a consequence of positive deviations of the surface areas from the additivity relationship and by applying the phase rule at the collapse pressure. Excess surface Gibbs energies, enthalpies and entropies of mixing were also computed. The results obtained showed that the two components were miscible under the experimental conditions at all temperatures investigated, using both the Na + -ion-containing subphase and the buffered one.

The interactions between monolayers of behenic acid or dihexadecylphosphoric acid (DHP) with mono- and multivalent metal ions in the aqueous subphase were studied tp find the best conditions for the layer transferance on solid supports as LB films. The thermodynamic parameters, the ellipsometric and spectroscopic data allowed us to assess that condensed phases of the monolayer and appreciable surface association between metal ions and ionized amphiphilic were the main requirements to be fulfilled.

An investigation is reported on mono- and multilayers of metal behenates to show the importance of a detailed characterization of the spreading monolayers to find the best conditions for transfer and deposition under the form of Langmuir-Blodgett films. A comparison was made between the properties of copper and manganese behenates as Langmuir-Blodgett forming materials.

The spreading isotherms of DODAC at the water—air interface were determined as a function of temperature. We verified that a study of the spreading film is the starting point for a better understanding of the most suitable conditions to obtain more complex aggregates, such as Langmuir-Blodgett (LB) films or vesicles. When the DODAC monolayer was in a liquid-condensed phase, this resulted in the optimum conditions for obtaining LB multilayers. In contrast, when the monolayer was in a liquid-expanded phase, multi- and unilamellar vesicles were obtained after sonication. Vesicles were also obtained when the system was below the gel-liquid crystal transition temperature ( T c =37°C), but a greater fraction of multilamellar vesicles were formed, as indicated by turbidimetric data.

The surface and the aggregation properties of the nickel(II) compounds with the dibenzo- and dinaphtho-tetraazal[14]annulene (TAA) macrocycles have been investigated by their spreading isotherms and electronic spectra. The possibility to form LB films was checked for both compounds. Homogeneous, reproducible LB films were obtained with the dibenzo-TAA derivatives, whereas the high surface viscosity prevented a good multilayer overlapping with the dinaphtho-compound.

Electron spin resonance spectroscopy of doxylstearic acids with the paramagnetic unit inserted in the 5, 6, 7, 9, 12, and 16 carbon position was used to analyze the dynamic and structural features of dioleoylphosphatidylcholine (DOPC) vesicles in the presence and in the absence of ceramide (CER) and as a function of temperature. The sizes and the homogeneity of these lipid aggregates were checked by electron microscopy and turbidimetry

The effect of the presence of the sphingolipid ceramide (CER) on the properties of vsicles of dioleoxylphosphatidylcholine (DOPC) has been investigated by electron paramagnetic resonance (EPR) of doxyl stearic acid (DXSA) with the oxazolidinyl ring in different positions on the alkyl chain. CER acted as a condensing agent at temperature near the gel-liquid crystal phase transition temperature (T c ), whereas it acted as a fluidizer at T well above T c . This occurred in the double-layer region from the water-lipid interface down to the double-bond system of the oleoyl residues of DOPC. Spreading isotherms of DOPC and DOPC/CER mixtures at T ∼ T c confirmed the ESR results.

The spreading monolayers at the air-water interface of ceramide (CER) and dioleoylphosphatidylcholine (DOPC), as pure compounds and in mixtures, in the 15–30°C temperature range, were studied using two different subphases, containing NaCl (0.1 M) and a phosphate buffer (pH 7), respectively. The bidimensional phases of the pure compounds, their miscibility and the excess free energy of mixing, ΔGmix, were determined. The results showed a surface compatibility of the two components over the whole range of temperatures, either using the Na+ ion-containing subphase or the buffered subphase.

A two-pulse electron spin echo experiment has been carried out on a Langmuir Blodgett film of stearic acid-doxyl stearic acid mixture. The proton nuclear modulation of the signal has been analyzed by computer simulation.

The application of the ESR to the study of the Langmuir-Blodgett films is discussed by reference to copper stearate films (as an example of material with peculiar magnetic properties) and to films of nitroxide derivatives of stearic acid (as very simple examples of membrane mimetic). Particular emphasis is given to the need of a preliminary, detailed study on the film-forming monolayers, whose physical and structural properties determine both reproducibility and homogeneity of the film. The different condensation of the copper stearate monolayers in the presence and in the absence of a condensing ion such as Ba2+ has allowed us to recognize that the formation of a Cu-Cu dimer at the water/air interface is the kinetic parameter which determines the film stability. The spin triplet doublet state of the film has been investigated by ESR of the S=1/2 monomer adduct formed after treatment of [Cu2(St)4] with ammonia vapours. On the other hand, the ESR signals obtained from LB films of pure nitroxides or from nitroxides diluted in stearic acid have given details on the spin-spin interactions and on the shape anisotropy. The motional parameters evaluated from the lineshape are of the correct order of magnitude expected for multilayer systems such as the membranes.

The complexes [M(oespz)Cl][M = MnIII or FeIII; oespz = 2,3,7,8,12,13,17,18-octakis(ethylsulfanyl)-5,10,15,20-tetraazaporphyrinate dianion] have been prepared and their structures determined. The isomorphous structures consist of stacked dimers. Monomers, within each dimer, are slipped and faced in trans fashion respect to the M–Cl bond. Weak interdimer interactions arise from Cl ⋯ S contacts. Intradimer interactions are provided by relatively long M ⋯ S and N (pyrrole)⋯ S contacts. Magnetic susceptibility measurements revealed that [Mn(oespz)Cl] is a high-spin (S= 2) complex with weak antiferromagnetic coupling between the MnIII. The toluene frozen-glass EPR spectrum of [Fe(oespz)Cl] seems to be consistent with a S= ground state, whereas the polycrystalline powder EPR spectrum at 4.2 K and magnetic susceptibility data are better rationalized in terms of a S=5//2 and ½ admixture. The crowding of the UV/VIS spectra of both complexes and the red shift of the Soret and Q bands of [Fe(oespz)Cl] are related to the effects of the peripheral ethylsulfanyl groups on the porphyrazinato ring. Both compounds show characteristic NIR absorptions. Voltammetric data are consistent with the tendency of the porphyrazinate ligand to stabilize the lower oxidation states of metals relative to phthalocyanines and porphyrins.

In this paper we report information on the spreading isotherms and the electron spin resonance (ESR) spectra of mono- and multilayer films built up with long hydrocarbon chain nitroxides (namely doxyl stearic acid and hexadecanoyl- piperidine-oxyl radicals). These ultrathin molecular assemblies were prepared from (i) single components, (ii) nitroxide binary mixtures, and (iii) a diluted solution of the paramagnetic components in a diamagnetic (stearic acid) host. The spreading isotherms allowed us to establish that the presence of a five- or six-membered ring in the hydrocarbon chain rendered the film more expanded, and this effect depended on the substituent position in the chain. The ESR spectra of undiluted nitroxides were characterized by strong spin-spin (dipole-dipole and Heisenberg spin exchange) magnetic interactions whose extent also depended on the nitroxide type and mixture. The calculation of the parameters of motion governing the ESR lineshape allowed accurate evaluation both of the degree of order and of the chain flexibility, particularly for diamagnetically diluted systems.

Preparation et caracterisation par spectrometrie RPE des couches monomoleculaires d'acide doxylstearique