Using Electrochemical Data to Obtain Energy Diagrams for Layer-by-Layer Films from Metallic Phthalocyanines (original) (raw)
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Phthalocyanine thin films as semiconductor electrodes
Journal of the American Chemical Society, 1979
Metal-free, zinc, and nickel phthalocyanines ( H~P c , ZnPc, and NiPc) have been studied electrochemically. The electrode assemblies involved a glass substrate overlaid by a gold contact layer, which in turn was covered by the phthalocyanine at nominal thicknesses of 40-3000 A. Interfacial capacitances were determined as functions of potential and frequency. Plots of capacitance vs. potential showed sharp rises for potentials more positive than 0.3 V vs. SCE and (for HzPc and ZnPc) peaks at more negative potentials. The capacities were linear with the inverse square root of frequency in the negative potential regime. Cyclic voltammetric studies of six nonlabile complexes of Fe(ll) were carried out. and chronocoulometry was used to measure their standard heterogeneous rate constants. The complexes with very negative standard potentials could be oxidized irreversibly on H2Pc but could not be reduced again. Systems with more positive standard potentials were reversiblq oxidized and reduced. The irreversible systems could be reduced on H2Pc at potentials more negative than 0.35 V vs. SCE when the electrode was irradiated by light at 6328 A. The observations have been rationalized by considering the phthalocyanines as relatively well behaved p-type semiconductor electrodes. Band edges and interfacial states have been mapped and the nature of interfacial charge transfer has been discussed in terms of Gerischer's model modified by inclusion of surface states in the gap region.
Journal of Physical Chemistry C, 2007
A judicious combination of materials and molecular architectures has led to enhanced properties of layerby-layer (LbL) films, in which control at the molecular level can be achieved. In this paper we provide one such example by showing that supramolecular effects in electroactive LbL films comprising tetrasulfonated metallophthalocyanines (NiTsPc or FeTsPc) alternated with poly(allylamine hydrochloride) (PAH) may depend on both the choice of material and the film-forming technique. Indeed, though some properties such as film growth were common to both types of LbL film, those containing NiTsPc displayed unique features. PAH/ NiTsPc films assembled onto ITO (indium tin oxide) showed two redox processes, with E 1/2 at 0.54 and 0.80 V (vs SCE) attributed to the phthalocyanine unit ([TsPc] 6-/[TsPc] 5-) and Ni 2+ /Ni 3+ redox couple, respectively. In contrast, only one redox process was observed for PAH/FeTsPc films, with E 1/2 at 0.45 V assigned to the [TsPc] 6-/[TsPc] -5 couple. For both systems, the anodic peak current versus scan rate increased up to 500 mV‚s -1 , indicating that the electrochemical response of NiTsPc and FeTsPc in LbL films is governed by charge-transport mechanism. Interestingly, the second redox process for PAH/NiTsPc became totally reversible at high scan rates, showing fast charge transfer. The influence from the film-forming technique was proven by comparison with results from an electrodeposited film of NiTsPc on ITO, which was less stable than its LbL counterpart. It is envisaged that the high electrochemical stability, reversibility, and unique features arising from the supramolecular structure of PAH/NiTsPc LbL films may be exploited in applications such as electrochromic and sensing devices.
Spectroscopic and electrochemical studies of transition metal tetrasulfonated phthalocyanines
Journal of Electroanalytical Chemistry and Interfacial Electrochemistry, 1985
phthalocyanine (TsPc) and Co-phthalocyanine (PC) have been carried out on ordinary pyrolytic graphite and silver electrodes at different solution pH ranging from 1 to 13. Many voltammetric peaks were found to be pH dependent with a slope of -59 mV/unit pH. In some instances this dependence was observed in alkaline or acid solutions only. The influence of oxygen has been also examined. l Permanent address: Faculty of Technology and Metallurgy, University of Belgrade, Belgrade, Yugoslavia. 0022-0728/85/$03.30 0 1985 Elsevier Sequoia S.A.
Study of phthalocyanines in aqueous solutions and adsorbed on electrode surfaces
Journal of Electroanalytical Chemistry and Interfacial Electrochemistry, 1983
The in-situ surface enhanced Raman spectra and voltammetry curves have been examined Tar meml-free. cobalt and iron tenasulfonated phthalocyanines (Hz-. Co-and Fe-TSPc) adsorbed on sdver in aad. neutral and alkaline electrolytes_ The aqueous solutions of these species have also been examined with UV-visible absorpuon and Raman spectroscopy. 0, has been round to prculuce significant changes in the Raman spectra of the adsorbed and solution phase species
Physicochemical Properties and Sensing Ability of Metallophthalocyanines/Chitosan Nanocomposites
The Journal of Physical Chemistry B, 2006
Electroactive nanostructured films of chitosan (Ch) and tetrasulfonated metallophthalocyanines containing nickel (NiTsPc), copper (CuTsPc), and iron (FeTsPc) were produced via the electrostatic layer-by-layer (LbL) technique. The multilayer formation was monitored with UV-vis spectroscopy by measuring the increase of the Q-band absorption from metallophthalocyanines. Results from transmission and reflection infrared spectroscopy suggested specific interactions between SO 3groups from metallophthalocyanines and NH 3 + from chitosan. The electroactive multilayered films assembled onto an ITO electrode were characterized by cyclic voltammetry, with Ch/NiTsPc films showing higher stability and well-defined voltammograms displaying reversible redox peaks at 0.80 and 0.75 V. These films could be used to detect dopamine (DA) in the concentration range from 5.0 × 10 -6 to 1.5 × 10 -4 mol L -1 . Also, ITO-(Ch/NiTsPc) n electrodes showed higher electrocatalytic activity for DA oxidation when compared with a bare ITO electrode. On the other hand, only the Ch/FeTsPc and Ch/CuTsPc modified electrodes could distinguish between DA and ascorbic acid. These results demonstrate that versatile electrodes can be prepared by incorporation of different metallophthalocyanine molecules in LbL films, which may be used in bioanalytical applications.
Electroactive LbL films of metallic phthalocyanines and poly(0-methoxyaniline) for sensing
Journal of Solid State Electrochemistry, 2007
Multilayered nanostructured films have been widely investigated for electrochemical applications as modified electrodes, including the layer-by-layer (LbL) films where properties such as thickness and film architecture can be controlled at the molecular level. In this study, we investigate the electrochemical features of LbL films of poly (o-methoxyaniline; POMA) and tetrasulfonated phthalocyanines containing nickel (NiTsPc) or copper (CuTsPc). The films displayed well-defined electroactivity, with redox pairs at 156 and 347 mV vs SCE, characteristic of POMA, which allowed their use as modified electrodes for detecting dopamine and ascorbic acid at concentrations as low as 10 −5 M.
Electrochemical and electrical properties of novel mono and ball-type phthalocyanines
Polyhedron, 2013
New mononuclear Co(II) phthalocyanine 3 and ball-type homobinuclear Cu(II)-Cu(II) and Zn(II)-Zn(II) phthalocyanines, 4 and 5 respectively, were synthesized using the corresponding metal salts and the 4,4 0-(methane-5-methyl-3-(1-methylcyclohexyl)-2,2 0-phenoxy)diphthalonitrile ligand 2, which was prepared from the reaction of 4-nitrophthalonitrile with bis[2-hydroxy-5-methyl-3-(1-methylcyclohexyl)phenyl]methane (1). The novel compounds 3-5 have been characterized using their elemental analysis data and UV-Vis, IR, 1 H NMR and MALDI-TOF mass spectra. The redox properties of the complexes were investigated by cyclic voltammetry in a non-aqueous medium. The electrochemical measurements showed that complex 5 forms a mixed-valence reduction species, due to the strong intramolecular interactions between the two phthalocyanine rings. Complex 4 displayed Pc ring-based redox signals with very high peak currents, which were attributed to the adsorption of the complex on the working electrode. Dc and ac electrical properties of films of 3, 4 and 5 were also investigated as a function of temperature (295-523 K) and frequency (40-10 5 Hz). From the dc conductivity measurements, activation energy values of the films were found, being 0.70, 0.66 and 0.68 eV for films of 3, 4 and 5, respectively. From impedance spectroscopy measurements, it was observed that the bulk resistance decreases with increasing temperature, indicating semiconductor properties.
Structure and Electronic Properties of Phthalocyanine Films on Metal and Semiconductor Substrates
Http Www Theses Fr, 2014
The current thesis presents fundamental studies of phthalocyanines (Pcs), a group of organic macro-cycle molecules. The use of phthalocyanine molecular films in devices with a variety of possible technological applications has been the reason of the many studies dedicated to such molecules during the last decades. Core and valence photoelectron spectroscopies (PES), X-ray absorption spectroscopy (XAS) and scanning tunneling microscopy (STM) techniques are used to study phthalocyanine molecules in gas phase and adsorbed on gold (111) and silicon Si(100)-2x1 substrates. Density functional theory (DFT) is used to obtain further insights in the electronic structure of the phthalocyanines. The aim of our studies is to get a deeper understanding into the molecule-molecule and molecule-substrate interactions, a fundamental requirement for improving the devices based on such molecular materials. Gas phase PES and XAS studies and single molecule DFT calculations are performed on the valence band (VB) of iron phthalocyanine (FePc), manganese phthalocyanine (MnPc) and metal-free phthalocyanine (H 2 Pc). The VB simulations have shown how the metal atom of the Pc influences the inner valence states of the molecules. The HOMO of the H 2 Pc and FePc is formed by mostly C2p states, whereas the HOMO of MnPc has mainly Mn3d character. PES studies of H 2 Pc on Au(111) have revealed the influence of the surface on the adsorption of the monolayer. XAS studies indicate formation of ordered monolayer with the Pc ligands parallel to the surface and the change of the molecular tilt angle with increasing thicknesses. For LuPc 2 adsorbed on Au(111), STM study demonstrates a formation of bilayer instead of a monolayer. A comparison between the results of LuPc 2 adsorbed on pristine or passivated Si(100)-2x1 confirmes the different reactivities of these surfaces: LuPc 2 retains many molecular-like characters, when adsorbed on the innert passivated Si. Instead, on the more reactive pristine Si surface, the spectroscopic results have indicated a more significant interaction, possible hybridization and charge redistribution between the molecules and the surface. Moreover, STM images show a modification of the geometrical shape of the molecules, which are proposed to adsorb in two different geometries on the pristine Si surface.