Anna Maria Paoletti

Two phthalocyanine units ‘stapled’ by carbon–carbon σ bonds in a new sandwich-type molecule: {5,5′;19,19′-bi[phthalocyaninato (2–)]}titanium(IV). Synthesis, X-ray crystal structure, and properties

{5,5′;19,19′-Bi[phthalocyaninato(2–)]}titanium(IV)–1-chloronaphthalene(1/1 ), [TiL]·C10H7Cl, is obtained by the reaction of [Ti(pc)Cl2](pc = phthalocyaninato dianion, [C32H16N8]2–) with Na2(pc) in 1-chloronaphthalene at 190 °C, An X-ray single-crystal structure (monoclinic, space group C/2c, a= 16.327(3), b= 18.568(4), c= 19.022(4)A; β= 94.50(1)°, Z= 4) indicates for this complex a sandwich-type structure with the titanium atom in the centre of the molecule and the two phthalocyaninato units ‘stapled’ by two inter-ring C–C σ bonds [C(11)–C(11′) 1.556(6) and C(31)–C(31′) 1.575(6)A]. Due to the staggered orientations of the two macrocyclic rings (relative rotation 45°) the planes of the two inner N4 systems (each of which is slightly distorted from planarity) form a square-antiprism, with an average interplane distance of 2.32 A(much shorter than that found in similar ‘unstapled’ complexes), and Ti–N bond distances in the range 2.17–2.26 A. The complex shows high thermal stability and can be oxidized by nitric acid to give the species [TiL]NO3. The complexes [TiL] and [TiL]NO3 show differing solid-state electrical conductivity properties.

Titanium and Ruthenium Phthalocyanines for NO2 Sensors: A Mini-Review

This review presents studies devoted to the description and comprehension of phenomena connected with the sensing behaviour towards NO2 of films of two phthalocyanines, titanium bis-phthalocyanine and ruthenium phthalocyanine. Spectroscopic, conductometric, and morphological features recorded during exposure to the gas are explained and the mechanisms of gas-molecule interaction are also elucidated. The review also shows how X-ray reflectivity can be a useful tool for monitoring morphological parameters such as thickness and roughness that are demonstrated to be sensitive variables for monitoring the exposure of thin films of sensor materials to NO2 gas.

Time-resolved energy dispersive x-ray reflectometry measurements on ruthenium phthalocyanine gas sensing films

The energy dispersive (ED) variant of the conventional x-ray reflectivity (XR) provides an atomic scale determination of the morphological characteristics of thin films, such as their thickness and surface roughness. We report on the in situ EDXR measurements of the (minimal) morphological changes of ruthenium phthalocyanine gas sensing thin films. A series of reflectivity spectra have been collected, during the exposure of the films to a gas flux of nitrogen oxides (NOx) molecules. The measurements allowed a very high density time sampling of the evolution of the two morphological parameters, providing important information on the gas-film interaction.

Effect of nitrogen dioxide on titanium bisphthalocyaninato thin films

Thin films of Titanium bis-phthalocyaninato (TiPc2) are deposited on interdigital electrodes by evaporation under vacuum and have been investigated as semiconducting gas sensors. Oxidation of the films by NO2 is studied by visible absorption spectroscopy and IR spectroscopy of neutral and oxidised films. The variation at room temperature (RT) of electrical conductivity with different concentrations of NO2 has been investigated. The results describe the existence of a conductivity maximum during the oxidation. The analysis of the optical spectra of TiPc2 during NO2 adsorption and desorption gives the possibility to explain the change of the conductivity in terms of concentration of species present in the reaction.

Experimental evidence of a two-step reversible absorption/desorption process in ruthenium phtalocyanine gas sensing films by in situ energy dispersive x-ray reflectometry

An in situ energy dispersive x-ray reflectivity technique was used to study the morphological changes of gas sensing thin films of ruthenium phtalocyanine (RuPc)2 induced by gas absorption/desorption processes. The time-resolved collection of reflectivity spectra during the exposure of each film to a gas flux of nitrogen oxides provided the evolution of the morphological parameters (thickness and roughness). The gas absorption process develops in two stages: The first induces morphological changes characteristic of a surface (adsorption) process, while the second is dominated by a bulk effect. This two-step behavior is also observed in the desorption process: When the thermal treatment is performed at 130°C, the gas is released from the bulk only. Conversely, at higher temperatures, the gas is fully released, i.e., also from the surface, and the initial film thickness is regained. Finally, a further in situ study upon a second absorption treatment was carried out: In this case, only the film bulk diffusio...

Structural and morphological characterisation of ruthenium phthalocyanine films by energy dispersive X-ray diffraction and atomic force microscopy

Abstract Ruthenium phthalocyanine (RuPc)2, deposited as a film by vacuum sublimation onto a variety of substrates, was structurally and morphologically investigated by energy dispersive X-ray diffraction (EDXD) and atomic force microscopy (AFM) techniques. The attempt to apply the EDXD technique to amorphous films was successful and the reported results show the preservation of the Ru-Ru bond between two phthalocyanines units while transferring from the bulk to the film. The unidimensional arrangement of the dimeric phthalocyanine units in the film was observed to a larger extent than in the bulk; indeed 10 dimers were superimposed along the stacking direction (parallel to the RuRu bonds), while six units were found in the bulk material, the higher order being also supported by conductivity measurements. The amorphous nature of the film, anomalous in respect of the generally microcrystalline films of other metal phthalocyanines, was not changed by annealing the films at 170–200°C for more than 10 h. Reproducible and uniform deposition is identified by both EDXD and AFM data.

Effect of molecular packing on the solid state spectra of ruthenium phthalocyanine: anomalous behaviour of a monodimensional stacked assembly

The ruthenium phthalocyanine molecule has never been isolated as a single unit in the solid phase. Any attempt to obtain it leads to the dimeric form (RuPc)2 with a double bond between Ru–Ru atoms. Owing to the amorphous nature of this compound, its structural characterisation was previously investigated by LAXS (Large Angle X-ray Scattering) and EXAFS (Extended X-ray Absorption Fine Structure) studies. Magnetic and conductivity properties were also discussed in the light of the found structure. The optical spectra of the material in the solid phase and as evaporated films are reported in the present contribution. The obtained results show a marked red shifting absorption when passing from solution to film. Such anomalous behaviour can be explained taking into account the considerable molecular distortion presented by the two macrocycles within the dimer and, overall, considering the strong π–π interactions throughout the molecular stack. The attempt to apply the coupling exciton theory in order to clarify the optical data was not successful for the molecular assembly assumed by (RuPc)2 dimeric units. The EXAFS investigation on films, which supports the suggested interpretation, also shows some degree of flexibility of the molecule which somehow influences the whole molecular packing. Depth profile analysis of (RuPc)2 films, studied by the XPS (X-ray Photo-emission spectroscopy) technique, clearly indicates a homogeneity and a stable chemical composition throughout the thickness.

Artificially layered films of CuBa2 (Ca1−xSrx)n−1CunOy grown using pulsed laser deposition

We have shown that the pulsed laser deposition technique (PLD) can be successfully used to grow artificially layered films of the CuBa2(Ca1−xSrx)n−1CunOy compound using only two targets having nominal composition BaCuOy and (Ca1−xSrx)CuOy, respectively. n was varied between 2 and 5. We have demonstrated, by a kinematic analysis of the x-ray diffraction spectra that the average random discrete thickness fluctuations which affect both the BaCuOy and (Ca1−xSrx)CuOy layers are much smaller than one atomic layer. Such features are confirmed by the appearance of sharp peaks even for the n=2 artificially layered structure where only one (Ca1−xSrx)CuOy cell is deposited in the stacking sequence. These results show that truly new structures can be obtained by a layer by layer deposition technique with a low interfacial disorder and give strong support to the idea of synthesizing new artificial high Tc structures by the PLD technique.

Evidence of a rearrangement of the surface structure in titanium phthalocyanine sensors induced by the interaction with nitrogen oxides molecules

Thin-film samples of titanium phthalocyanine, a sensor of environmental pollutants, were studied by time resolved energy-dispersive x-ray reflectivity (EDXR). This original method demonstrated to be an ideal tool to follow the evolution of the films morphology upon gas exposure, in situ, also allowing an unexpected response of the sensors to be detected. Indeed, while the increase in thickness showed the characteristic feature of a “breathing-like” expansion, already observed in other metal-Pc, the curve of roughness versus exposure time exhibited a peak. This effect, in some cases evident by observation with the naked eye the EDXR data, was attributed to a surface structure rearrangement process.

Third-order optical non-linearities in titanium bis-phthalocyanine/toluene solutions

Abstract We report Z-scan experiments performed on titanium bis-phthalocyanine (TiPc 2 )/toluene solutions as a function of the molar concentration. The TiPc 2 cubic molecular hyperpolarizability, γ hyper , has been found to be (−70±30)×10 −32 esu at 800 nm, approximately 10 5 times larger in magnitude than the third-order susceptibility of the standard reference molecule CS 2 . Given the non-proximity of the laser wavelength to the main electronic bands of this molecule and its unusual molecular structure, we compare our results with previous measurements in other phthalocyanine systems. We also discuss the most probable factors influencing the non-linear optical response of our molecular system. The results indicate that the large non-linear optical response observed for TiPc 2 cannot be explained using optical-pumping, resonance-enhancement or electronic delocalization arguments.