Wania C. Moreira

Electrochromic and redox properties of Langmuir–Blodgett films of ytterbium bisphthalocyanine

Abstract Langmuir–Blodgett (LB) films from pure ytterbium bisphthalocyanine (YbPc 2 ) and mixtures of YbPc 2 and stearic acid have been produced, whose cyclic voltammetric response displays a redox activity strongly dependent on the scan rate and film thickness. Successive redox reactions are accompanied by color variations upon small changes in the electrode potential range which make these films promising for multi-color devices.

Surface-enhanced Raman scattering and micro-Raman imaging of Langmuir–Blodgett films of rhodium phthalocyanine

Rhodium phthalocyanine (RhPc) was synthesized and ultra thin Langmuir-Blodgett (LB) films of RhPc were successfully fabricated. The LB film characterization was carried out using both UV-vis absorption spectra and Raman scattering. The Raman spectroscopy was carried out using 633 and 780 nm laser lines. LB films were deposited onto Ag nanoparticles to achieve the surface-enhanced pre-resonance Raman scattering (pre-SERRS) and surface-enhanced Raman scattering (SERS) for both laser lines, respectively, which allowed the characterization of the RhPc ultra thin films. The morphology of the LB RhPc neat film is extracted from micro-Raman imaging.

Electroactive Layer-by-Layer Films of Iron Tetrasulfonated Phthalocyanine

Electroactive films of iron tetrasulfonated phthalocyanine (FeTsPc) were assembled via the electrostatic layer-by-layer technique (LBL), in which FeTsPc layers were alternated with the polycationic poly(allylamine hydrochloride) (PAH). The multilayer formation was monitored via UV-Vis spectroscopy by measuring the increase in the Q Band of FeTsPc at 676 nm. Film thickness was estimated by profilometry as ca. 10 A per bilayer. Fourier transform infrared and UV-Vis absorption spectroscopy suggested specific interactions between FeTsPc and PAH. Cyclic voltammograms showed reproducible pairs of oxidation-reduction peaks at 0.92 mV and 0.70 mV, respectively, for a 50-bilayer PAH/FeTsPc film at 50 mV/s (vs Ag/AgNO 3 ).

Spectroscopic, electrochemical, and microgravimetric studies on palladium phthalocyanine films

The optical properties of palladium phthalocyanine in dimethylformamide, toluene, acetonitrile, and dichloromethane solutions were studied in the visible range of energy. Palladium phthalocyanine in organic medium presented itself as a mixture of monomeric and dimeric species in equilibrium, and it was only in dichloromethane that the monomeric, non-aggregated form predominated. Palladium phthalocyanine films were prepared by casting, and studied by cyclic voltammetry and spectroelectrochemistry. The films showed an electrochromic response from blue to purple, and stability that depended on the applied potential. Electrochemical quartz crystal microbalance experiments indicated that the film exfoliates into solution after applying high values of final potentials. Raman spectroscopy was used to structurally characterize the palladium phthalocyanine film, which showed a central metal with +2 oxidation state that is not affected even when the film is oxidized.

The effect of cyclic voltammetry on the crystalline order of PdPc thin films

The degree of crystalline order of evaporated and cast palladium phthalocyanine films was investigated before and after they were submitted to a voltammetric process. X-ray diffraction and UV-vis spectroscopy measurements demonstrated that the electrochemical treatment improves the crystalline quality of the films. The X-ray results revealed an increase of the average size of the crystallites composing the films as well as a decrease in the spacing between the lattice planes in the direction perpendicular to the surface of the film. Optical measurements showed that the electrochemical treatment also introduces an appreciable degree of in-plane ordering. These improvements of crystalline order are observed in both types of films, cast and evaporated, which indicates that the ordering is a direct consequence of the electrochemical treatment and not of the method used for the film deposition.

Optical properties of ytterbium bis-phthalocyanine solution

We describe the optical properties of ytterbium bis-phthalocyanine (YbPc 2 ) dissolved in chloroform. A six-energy-level diagram is proposed to establish the population dynamics when laser pulses at 532nm are employed.

Langmuir films of ytterbium and samarium phthalocyanines

Abstract Monolayer characteristics of ytterbium and samarium phthalocyanines (YbPc 2 and SmPc 2 ) have been investigated by surface pressure and surface potential isotherms. It has been shown that the metal ion in the phthalocyanines can cause marked differences in the monolayer properties. The different monolayer characteristics of YbPc 2 and SmPc 2 may possibly be ascribed to either the extent of aggregation or the symmetry of the metallophthalocyanines.

Heteroarray of cobalt(II)tetrasulfophthalocyanine and cobalt(II) tetrakis(N-methyl-4-pyridyl)porphyrin: synthesis, isolation and electronic properties

Porphyrin and phthalocyanine macrocycles with ionic substituents can form mixed assemblies with interesting electronic properties for potential application on the development of new devices. This paper reports the synthesis, isolation and purification of heteroaggregate formed by cobalt(II) 4,4′,4″,4‴-tetrasulfophthalocyanine (CoTsPc) and cobalt(II) tetrakis(N-methyl-4-pyridyl)porphyrin (CoTMPyP), followed by its spectroscopic characterization. Spectroscopic titration, performed with a CoTsPc water/acetone solution, allowed the use of Jobs method for determination of the heteroaggregates stoichiometry. The Jobs plot revealed the formation of only one predominant heterocomplex in solution, containing two CoTsPc molecules in terminal positions and a central CoTMPyP one. For the first time, a method for isolation and purification of a mixed ionic array has been reported in the literature. The triads electronic spectrum is quite different from the sum of the macrocycles isolated spectra, due to the overlap of their electronic densities and a charge transfer process between CoTsPc and CoTMPyP.