Relevance of the electron energy-loss spectroscopy for in situ studies of the growth mechanism of copper phthalocyanine molecules on metal surfaces: Al(100)

Reflection electron energy-loss spectroscopy (EELS) in specular and off specular geometry has been employed to study the early stage of the copper phthalocyanine (CuPc) growth on Al(100) substrate. EEL spectroscopy has been a useful tool in order to study the electronic structure of molecular films also in the submonolayer regime. The electronic structure of the first deposited layer of CuPc is strongly influenced by charge transfer from the Al substrate to the lowest unoccupied molecular orbital (LUMO). The strong molecule-substrate interaction gives rise to a coverage dependent frequency shift of the Al surface plasmon. Successive layers have essentially the electronic structure of the molecular solid. Momentum resolved EELS measurements reveal that, in the case of the thicker film investigated (22 Angstrom), the plane of the molecule is almost perpendicular to the surface of the substrate

Tetra-2,3-pyrazinoporphyrazines with externally appended pyridine rings. 2. Metal complexes of tetrakis-2,3-[5,6-di(2-pyridyl)pyrazino]porphyrazine: Linear and nonlinear optical properties and electrochemical behavior

A series of metal complexes of tetrakis-2,3-[5,6-di(2-pyridyl)pyrazino]porphyrazine, [Py8TPyzPzH2], having the general formula [Py8TPyzPzM]\ue2xH2O (M ) MgII(H2O), MnII, CoII, CuII, ZnII; x ) 3-8) were synthesized by reaction of the free-base macrocycle with the appropriate metal acetate in pyridine or dimethyl sulfoxide under mild conditions. Clathrated water and retained pyridine molecules for the MnII and CoII species are easily eliminated by heating under vacuum, the water molecules being recovered by exposure of the unsolvated macrocycles to air. Magnetic susceptibility measurements and EPR spectra of the materials in the solid state provide basic information on the spin state of the CuII, CoII, and MnII species. Colloidal solutions caused by molecular aggregation are formed in nondonor solvents (CH2Cl2, CHCl3), a moderately basic solvent (pyridine), and an acidic solvent (CH3COOH), with the extent of aggregation depending on the specific solvent and the central metal ion. UV-vis spectral monitoring of the solutions after preparation indicates that disaggregation systematically occurs as a function of time leading ultimately to the formation of clear solutions containing the monomeric form of the porphyrazine. Cyclic voltammetry and thin-layer spectroelectrochemistry show that each compound with an electroinactive metal ion undergoes four reversible one-electron reductions, leading to formation of the negatively charged species [Py8TPyzPzM]n- (n ) 1 - 4). The stepwise uptake of four electrons is consistent with a ring-centered reduction, but in the case of the cobalt complex a metal-centered (CoII f CoI) reduction occurs in the first process and only three additional reductions are observed. No oxidations are observed in pyridine or CH2Cl2 containing 0.1 M tetrabuthylammonium perchlorate (TBAP). The nonlinear optical properties (NLO) of the species [Py8TPyzPzM] (M ) 2HI, CuII, ZnII, MgII(H2O)) have also been examined with nanosecond pulses at 532 nm in dimethyl sulfoxide solution. Reverse saturable absorption is shown by all of the [Py8TPyzPzM] species, which exhibit distinct behavior depending on the nature of M and extent of aggregation

CuPc molecules adsorbed on Au(110)-(1 x 2): Growth morphology and evolution of valence band states

We present the growth morphology, the long-range ordering, and the evolution of the valence band electronic states of ultrathin films of copper phthalocyanine (CuPc) deposited on the Au(110)-(1 x 2) reconstructed surface, as a function of the organic molecule coverage. The low energy electron diffraction patterns present a (5 x 3) reconstruction from the early adsorption stages. High-resolution UV photoelectron spectroscopy data show the disappearance of the Au surface states related to the (1 x 2) reconstruction, and the presence of new electronic features related to the molecule-substrate interaction and to the CuPc molecular states. The CuPc highest occupied molecular orbital gradually emerges in the valence band, while the interface electronic states are quenched, upon increasing the coverage. (C) 2003 Published by Elsevier Science B.V

Excited state dynamics and nonlinear absorption of a pyrazinoporphyrazine macrocycle carrying externally appended pyridine rings

The multiphoton absorption properties of the tetrakis-2,3-[5,6-di(2-pyridyl)pyrazino]porphyrazinato(monoacquo)- Mg(II) complex [Py8TPyzPzMg(H2O)] (1) are reported and interpreted. The nonlinear optical behavior of 1 and the characterization of the excited states important for the nonlinear absorption process were studied at the pump frequency of the second harmonic generation of a Nd:YAG laser in the nanosecond time regime. It was found that complex 1 shows a very good optical limiting performance at 532 nm, which derives from two processes: (a) a reverse-saturable absorption process, which involves a triplet excited state at low intensities, and (b) a two-photon absorption process at higher intensities, which is due to the formation of the radical monoanion of 1, [Py8TPyzPzMg(H2O)]\ua5-, during the photoreduction of the triplet state. The participation of a monoanion in determining the overall nonlinear absorption behavior of 1 is found, for the first time, for a tetrapyrrolic system. One can deduce that the involvement of the monoanion derives from the electronwithdrawing effect of the dipyridinopyrazino fragments externally attached to the porphyrazine core which make the reduced form of 1 easily accessible. These results suggest a modification of tetrapyrrolic systems with new nonlinear absorption properties

Copper-phthalocyanine ultra thin films grown onto Al(100) surface investigated by synchrotron radiation

In this work X-ray photoemission spectroscopy (XPS) and X-ray absorption spectroscopy (XAS) are employed to study the CuPc/Al(1 0 0) organic-inorganic interface. The C ls core level, investigated for three different coverages, shows sharp differences in passing from bulk to monolayer range CuPc film: in particular the shake-up satellite is not visible in the early stages of adsorption, suggesting a strong molecule-substrate interaction. XAS at the Cu L-3 edge was employed to study the molecular orientation with respect to the substrate. In the case of a 40 Angstrom CuPc film the molecular plane was found to be almost perpendicular to the substrate surface. (C) 2004 Elsevier B.V. All rights reserved

Synthesis, X-ray crystal structure, UV/Visible linear and nonlinear (optical limiting) spectral properties of symmetrical and unsymmetrical porphyrazines with annulated 1,2,5-thiadiazole and 1,4-diamyloxybenzene moieties

Co-cyclization of 1,2,5-thiadiazole- 3,4-dicarbonitrile and 3,6-diamyloxyphthalodinitrile in the presence of magnesium or lithium amylate in amyl alcohol leads to mixtures containing the Mg derivatives of the symmetrical species tetrakis(1,2,5-thiadiazolo)- porphyrazine, (S4)PzH2 , and tetrakis( 1,4-diamyloxybenzo)porphyrazine, (A4)PzH2 , and the low-symmetry macrocycles bearing peripheral 1,2,5-thiadiazole and 1,4-dipentyloxybenzene rings in the ratio 3:1, 2:2 (cis and trans), and 1:3, that is, (SA3)PzH2, (S2A2)PzH2 , (SASA)PzH2 , and (S3A)PzH2 , respectively. The basic Mg materials were converted to the corresponding freebase macrocycles by treatment with CF3COOH. The species were separated from the mixtures by chromatography, either as Mg complexes or demetalated materials. With results on (S4)PzH2 and (SA3)PzH2 in hand, including crystallographic work on the latter, a general chemical physical investigation has been carried out of all the symmetrical and unsymmetrical free-base macrocycles. The structures of the species (S2A2)PzH2 and (A4)PzH2 . were elucidated by single- crystal X-ray crystallography. The effect of the progressive variation of the macrocyclic structure along the series, from the symmetrical (S4)PzH2 to its symmetrical partner (A4)PzH2 via the low-symmetry 3:1, 2:2 (cis and trans), and 1:3 macrocycles, was studied by IR, 1H NMR, and UV/Vis linear and nonlinear (optical limiting) measurements. The results are interpreted on the basis of intra- and intermolecular interactions between the electron-deficient 1,2,5- thiadiazole and the electron-donating 1,4-dipentyloxybenzene moieties

Multiple established forms of palladium acetate binding to the four N-atom donor 2,3-dicyano-5,6-di(2-pyridyl)-pyrazine, [(CN)2dpp]

The reaction of the ligand 2,3-dicyano-5,6-di(2-pyridyl)-pyrazine, [(CN)2dpp], with Pd(OAc)2, in CH3CN leads to the formation of three novel complexes which were characterized by thermogravimetric analysis, single crystal and powder X-ray measurements, MALDI-TOF mass spectra, IR and UV–visible spectroscopy as well as electrochemistry. As established by crystallographic work, the complex of formula [(CN)2dppPd(OAc)2]⋅H2O (molar ratio ligand/Pd(II) 1:1; species 3) shows a single Pd(OAc)2 unit coordinated to each nitrogen of the two pyridyl (py) groups of [(CN)2dpp]. i.e. the “py-py” mode of coordination previously established for the analogs [(CN)2dppMCl2] (M = Pd(II), Pt(II)). The second isolated species is a highly insoluble dinuclear Pd(II) complex of formula [(CN)2dpp{Pd(OAc)2}2]⋅5H2O (molar ratio ligand/Pd(II) 1:2; species 1), where the two Pd(OAc)2 units are each coordinated to one pyrazine nitrogen and one N atom of a pyridyl group on [(CN)2dpp] (“py-pyz” binding). Based on crystallographic work, the third isolated species is assigned the formula [(CN)(CONH)dppPd(OAc)] (molar ratio ligand/Pd(II) 1:1; species 2), which is formed by hydrolysis of a CN substituent on [(CN)2dpp] giving a –CONH- group and characterized by a “py-pyz” type of coordination. Electrochemical and spectroelectrochemical data of complexes 1, 2, and 3 in DMF and DMSO were used to assign the sites of electron transfer