Francesca Bonosi

Synthesis and physico-chemical properties of the bis(2,3,7,8,12,13,17,18-octakis-(octhylthio)-5,10,15,20-tetraazaporphyrinato)lutetium(III) complex

Abstract 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.

Monolayers and Langmuir-Blodgett films of a new lutetium(III)-bis-octakis(alkylthio)tetraazaporphyrin

Abstract 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.

Interactions between monolayers and metal ions at the water-air interface : conditions for the transferability as Langmuir-Blodgett multilayers

Abstract 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.

DODAC in bidimensional states monolayers, Langmuir—Blodgett films and vesicles

Abstract 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.

Mesogenic metal alkylthioporphyrins for the formation of Langmuir-Blodgett films

Abstract 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.

Electron paramagnetic resonance and thermodynamics of Langmuir—Blodgett films of manganese arachidate and of its mixtures with methyl arachidate

Abstract 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.

A study of the bidimensional miscibility of ceramide and dioleoylphosphatidylcholine

Abstract 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.

Langmuir-Blodgett films of pure long-chain nitroxides, their mixtures and mixtures with stearic acid studied by electron spin resonance

Abstract 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.

Synthesis, structure, magnetic, spectroscopic and electrochemical behaviour of chloro-iron(III) and -manganese(III) complexes of 2,3,7,8,12,13,17,18-octakis(ethylsulfanyl)-5,10,15,20-tetraazaporphyrin

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.

Monolayer and multilayer films of differently substituted metal tetraazaannulene complexes

Abstract 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.