Recent studies in phthalocyanine chemistry (original) (raw)
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Oxygen Reduction Reaction at Penta-Coordinated Co Phthalocyanines
Frontiers in Chemistry
From the early 60s, Co complexes, especially Co phthalocyanines (CoPc) have been extensively studied as electrocatalysts for the oxygen reduction reaction (ORR). Generally, they promote the 2-electron reduction of O 2 to give peroxide whereas the 4-electron reduction is preferred for fuel cell applications. Still, Co complexes are of interest because depending on the chemical environment of the Co metal centers either promote the 2-electron transfer process or the 4-electron transfer. In this study, we synthetized 3 different Co catalysts where Co is coordinated to 5 N atoms using CoN4 phthalocyanines with a pyridine axial linker anchored to carbon nanotubes. We tested complexes with electro-withdrawing or electro-donating residues on the N4 phthalocyanine ligand. The catalysts were characterized by EPR and XPS spectroscopy. Ab initio calculations, Koutecky-Levich extrapolation and Tafel plots confirm that the pyridine back ligand increases the CoO 2 binding energy, and therefore promotes the 4-electron reduction of O 2. But the presence of electron withdrawing residues, in the plane of the tetra N atoms coordinating the Co, does not further increase the activity of the compounds because of pull-push electronic effects.
Polyhedron, 2000
We have studied the metal-centered redox chemistry of unsubstituted cobalt phthalocyanine (Co Pc) and the cobalt complexes of the substituted ligands, cobalt octaethylhexyloxyphthalocyanine (CoOEHPc), cobalt tetramethoxyphthalocyanine (CoMeOPc), cobalt tetraneopentoxyphthalocyanine (CoTNPPc), cobalt tetraaminophthalocyanine (CoTAPc), cobalt tetrasulfonatophthalocyanine (CoTSPc) and cobalt hexadecafluorophthalocyanine (CoPcF 16 ) adsorbed on ordinary pyrolytic graphite (OPG). These complexes exhibit two distinct metal-centered reversible redox processes attributed to the Co(II)/Co(I) and Co(III)/Co(II) couples. The redox potentials of these couples are shifted according to the electron withdrawing or donating character of the groups located at the periphery of the phthalocyanine ligand, as seen by comparison to molecular orbital theoretical calculations. Correlations between the redox potential and the Hammett parameters of the substituents provide good linear correlations. The slopes of the linear free energy correlations give values of 0.41 and 0.49 V | − 1 for the Co(III)/Co(II) and Co(II)/Co(I) redox couples, respectively. We have also tested the electrocatalytic activity of these adsorbed phthalocyanines for the reduction of 2-hydroxyethyldisulfide. A plot of log i (current density at constant potential) versus the Co(II)/Co(I) redox potential gives a linear correlation where the rate of the reaction increases with the driving force of the catalyst, suggesting that that the reaction takes place via an outer-sphere mechanism.
Unoccupied electronic structure of phthalocyanine films
The Journal of Chemical Physics, 1990
The unoccupied molecular orbitals of metal-free phthalocyanine (H2PC), nickel-phthalocyanine (NiPC), and copper-phthalocyanine (CuPC) adsorbed on single crystal surfaces have been studied by inverse photoemission spectroscopy (IPES) and near-edge x-ray absorption spectroscopy (NEXAFS). The features observed in the experimental data are assigned by reference to molecular orbital calculations. Carbon and nitrogen 1s NEXAFS measurements of NiPC adsorbed on Cu(110) surface indicates that the phthalocyanine molecular planes are parallel to the surface. X-ray absorption data recorded at the Ni LIII and LII edges show that the unoccupied Ni 3d level is located in the plane of the phthalocyanine rings.
The synthesis and electrochemistry of novel, symmetrical, octasubstituted phthalocyanines
Synthetic Metals, 2013
In this study, the preparation of new phthalocyanines with eight dialkylaminophenoxy or trialkylaminophenoxy substituents on periphery of the phthalocyanines was achieved by the cyclotetramerization of 1,2-dicyano-4,5-bis[3-(diethylamino)phenoxy]benzene (2). All of the synthesized compounds have been characterized by using elemental analysis, UV-vis, FT-IR, 1 H NMR and MS spectroscopic data. Aggregation behaviors of phthalocyanines were investigated in different solvents. The electrochemistry and in situ spectroelectrochemical properties of neutral and electrogenerated complexes were also characterized. All complexes coated on the working electrodes with electropolymerization process, which is a desired property for the functional materials for their practical applications. Dialkylamine groups on the substituents cause to electropolymerization of the complexes on the working electrode. Number of the substituents and the metal center of the complexes alter the character of the electropolymerization processes.
The Journal of Physical Chemistry, 1985
The oneelectron oxidations of cobalt(II), cobalt(III), copper(II), and nickel(I1) tetrasulfophthalocyanine have been investigated by using stop-flow, pulse radiolysis, and photolysis techniques. The optical and ESR spectral data obtained in all cases are consistent with the primary formation of the ligand-centered radical cation. The rate constants for the oxidation of the Cu(II), Ni(II), and Co(II1) complexes with Ce(IV) have been determined to be around lo6 M-' s-I. In the case of the Co(I1) complex, spectral changes detected in stop flow and pulse radiolysis experiments are consistent with the formation of the cobalt(I1) phthalocyanine radical and its rapid conversion to the stable Co(II1) species. The cobalt(III), copper(II), and nickel(I1) phthalocyanine radicals disproportionate, resulting in the regeneration of the parent phthalocyanine, M"+(aq), and ligand degradation products.
Applied Organometallic Chemistry, 2015
Benzylpiperidin-4-yl)oxy]-substituted cobalt(II) and iron(II) phthalocyanine complexes were synthesized and their catalytic activity towards various phenolic compounds was investigated. Converting from environmentally harmful phenolic compounds into less harmful oxidation products using phthalocyanines makes this study attractive. This catalysis is feasible and timesaving in terms of procedure and the best oxidation conditions determined. Electrochemical studies were also carried out using cyclic voltammetry and square wave voltammetry techniques. Voltammetric analyses of the synthesized phthalocyanine complexes supported their proposed structures.
Dalton Transactions, 2012
The new ball-type metallo bisphthalocyanines (Co 2 Pc 2 and Zn 2 Pc 2) were synthesized from the corresponding [4,4′-bis(dicoumaroylphthalonitrile)] which can be obtained from the reaction of 3,3′-methylenebis(4-hydroxy-2H-chromen-2-one) and 4-nitrophthalonitrile. The structures of the newly synthesized compounds have been confirmed and characterized by elemental analysis, UV/Vis, IR and 1 H NMR spectroscopies and MALDI-TOF mass spectrometry. Solar cells of the configuration ITO/ Co 2 Pc 2 /C60/Al and ITO/Zn 2 Pc 2 /C60/Al were fabricated. The effect of the thickness of the active Pc layer the thickness of the Pc layer was varied from 15 to 80 nmon solar cells parameters has been investigated. A nearly thickness independent open circuit voltage was observed in both structures. The maximum photovoltaic conversion efficiency, short circuit current and fill factor were observed in ITO/ Zn 2 Pc 2 /C60/Al cell with 80 nm Pc layer to be 0.255%, 1 mA cm −2 and 0.38, respectively. The redox properties of the ball-type complexes were investigated by cyclic voltammetry, controlled-potential coulometry and in situ spectroelectrochemistry in DMSO-TBAP. The electrochemical measurements showed that the complexes form ring-based and/or metal-based mixed-valence species, due to the remarkable intramolecular interactions between the two metal phthalocyanine units. The Vulcan XC-72 (VC)/Nafion(Nf)/Co 2 Pc 2 modified glassy carbon electrode showed much higher catalytic performance towards oxygen reduction, compared to the VC/Nf/Zn 2 Pc 2 modified one. It was found that the VC/Nf/ Co 2 Pc 2 catalyst is nearly insensitive to the presence of methanol. In the presence of 1 M methanol in the electrolyte, the catalytic performance of the Co 2 Pc 2-based catalyst in oxygen reduction was much better than that of the Pt-based one. Thus, it was shown that the VC/Nf/Co 2 Pc 2 catalyst can be a good alternative to VC/Nf/Pt as a cathode catalyst in direct methanol fuel cells. † Electronic supplementary information (ESI) available: absorption spectra of compounds 4 and 5 in DMSO and 1 H-NMR spectrum of compound 5 in DMF. See
Synthesis, structure, and properties of new phthalocyanines
Journal of Porphyrins and Phthalocyanines, 2004
Many low symmetry and/or deformed phthalocyanines (Pcs) have been synthesized, separated, and their spectroscopic and electrochemical properties elucidated in the last decade, mainly because of improvement in separation techniques of reaction mixtures and development of instruments and computers. In this overview, some advances in the chemistry of Pcs are surveyed. In recent years, many types of alkynyl Pcs, various isomers of low symmetry Pcs, severely sterically deformed Pcs, and chiral Pcs have been prepared and some of their properties are reproduced by quantum mechanical calculations, which have not been achieved previously. Also, in the field of Pc sandwich complexes, properties of hetero double- and triple-decker complexes can be compared, since many types of compounds are now available. Some hetrodinuclear planar dimers have also been reported in the last decade.
The Journal of Physical Chemistry B, 2001
Ultraviolet photoelectron spectroscopy was performed on phthalocyanine samples in the gas phase and as thin vapor-deposited solid films. The results are compared to those of molecular orbital calculations and electrochemical redox experiments in solutions and as solid films. Electron-withdrawing groups or substituents are introduced to the phthalocyanine system to increase the ionization potential and electron affinity. An almost parallel shift of photoelectron spectra is obtained. Unsubstituted phthalocyaninatozinc (PcZn), complexes of tetrapyridotetraazaporphyrins (TPyTAPZn, TPyTAPVO) and hexadecafluorophthalocyanines (F 16 PcZn, F 16 PcVO, F 16 PcAlF) have been studied. The alignment of energy levels in organic heterojunctions prepared from the substituted phthalocyanines and the unsubstituted zinc complex is discussed in detail. The offset between the highest occupied electronic levels, the establishment of a surface dipole, and the redistribution of charge in the heterointerface region beyond molecular contact is shown.