Giovanna Pennesi

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.

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.

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.

Dioxygen activation and catalytic oxidation of triphenylphosphine by iron phthalocyanine compounds

Abstract The oxidation of PPh3 by molecular oxygen in toluene has been investigated through the use of phthalocyaninatoiron(II), (PcFe), and its corresponding bis-adducts of formula PcFe(N-base)2 (N-base = pyridine, 4-methylpyridine, piperidine, N-methylimidazole and imidazole) as catalysts. No oxidation was observed at 1 atm pressure, whereas both homogeneous and heterogeneous catalytic oxidation of PPh3 occurred at po2 = 60 - 70 atm at room temperature. Heterogeneous catalysis was observed with PcFe and PcFe(imidazole)2 which are both insoluble in toluene. Homogeneous catalysis in toluene solution was observed in all the other cases studied. The Nbase appears to play an important role in maintaining the conditions required for the Fe(II) ⇌ Fe(III) redox reaction. μ-Oxobis(phthalocyaninatoiron(III)), i.e. (PcFe)2O, appears to be the final oxygen-containing species formed by PcFe and its N-base adducts during the irreversible reaction involved. An ‘oxenic’ species of formula pyPcFeO is proposed as the intermediate active ‘oxygen atom transfer agent’ in the catalytic process, which seems to proceed via a non-radical pathway.

Bridged Phthalocyanine Systems for Sensitization of Nanocrystalline TiO 2 Films

Phthalocyanines based-dyes represent attractive alternatives to the expensive and polluting pyridyl based Ru complexes because of their photochemical and thermal stability, they do show in fact intense absorption in the UV/blue (Soret band) and the red/near IR (Q band) spectral regions and appear very promising as sensitizer dyes for DSSC. In this contribution we review the state of the art and the recent progress in the application of these materials as dyes for DSSC and present three new dyes which are bridged derivatives of Iron phthalocyanine. Synthesis, optical properties, electrochemical characterization and device performances are discussed with regard to the different substitution degree of the macrocycle.

Oxygen atom transfer in the oxidation of triphenylphosphine by µ-oxo-bis[phthalocyaninatoiron(III)]

It has been shown that µ-oxo-bis[phthalocyaninatoiron(III)] can oxidize triphenylphosphine to triphenylphosphine oxide in the presence of pyridine under mild conditions, resulting in the formation of the corresponding FeII-bis adduct; this reaction is a rare example of O atom transfer by a µ-oxo FeIII oligomer.