L. Gaffo

Resonant Nonlinear Absorption in Zn-Phthalocyanines

In this work, we investigate the nonlinear absorption dynamics of Zn phthalocyanine in dimethyl sulfoxide (DMSO). We used single pulse and pulse train Z-scan techniques to determine the dynamics and absorption cross-sections of singlet and triplet states at 532 nm. The excited singlet state absorption cross-section was determined to be 3.2 times higher than the ground state one, giving rise to reverse saturable absorption. We also observed that reverse saturable absorption occurs from the triplet state, after its population by intersystem crossing, whose characteristic time was determined to be 8.9 ns. The triplet state absorption cross-section determined is 2.6 times higher than the ground state one. In addition, we used the white light continuum Z-scan to evaluate the singlet excited state spectrum from 450 to 710 nm. The results show two well-defined regions, one above 600 nm, where reverse saturable absorption is predominant. Below 600 nm, we detected a strong saturable absorption. A three-energy-level diagram was used to explain the experimental results, leading to the excited state absorption cross-section determination from 450 nm up to 710 nm.

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.

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.

Electrochemically induced orientation of copper phthalocyanine thin films

The dependence of the electrochromic and organizational behaviors of copper phthalocyanine (CuPc) evaporated thin films on oxidation level have been investigated. UV-vis experiments with CuPc thin film obtained before cyclic voltammetry display two Q bands in the region between 600 and 700 nm, which correspond to the α form of CuPc. The FTIR spectra show an improved molecular orientation of CuPc molecules, obtained after the electrochemical process. Molecules in the film in the oxidized state (1.27 V) display a plane parallel to the film surface, indicating a flat-on molecular orientation. Spectrum changes observed after one complete voltammetric cycle (between −0.5 and 1.5 V) show an evolution from a mixed molecular organization to an edge-on organization.

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.

Reversible electrochromical response of thin MEH-PPV films

A reversible electrochromical response of thin poly(2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene) (MEH-PPV) films spin-coated on ITO substrates was observed during spectroelectrochemical experiments. The polymer layer changes its coloration from reddish-orange (neutral form) to brownish-green (oxidized form) upon varying the applied potential. The oxidized form showed to be stable even after removing the film from the electrochemical cell, returning to its original form only after electrochemical reduction. The color transitions at different potentials were studied by UV-vis-NIR absorption spectroscopy.