Parent Phthalocyanine Research Articles

Cobalt Tetracationic 3,4-Pyridinoporphyrazine for Direct CO2 to Methanol Conversion Escaping the CO Intermediate Pathway.

Molecular catalysts offer a unique opportunity to implement different chemical functionalities to steer the efficiency and selectivity for the CO2 reduction for instance. Metalloporphyrins and metallophthalocyanines are under high scrutiny since their most classic derivatives the tetraphenylporphyrin (TPP) and parent phthalocyanine (Pc), have been used as the molecular platform to install, hydrogen bonds donors, proton relays, cationic fragments, incorporation in MOFs and COFs, to enhance the catalytic power of these catalysts. Herein, we examine the electrocatalytic properties of the tetramethyl cobalt (II) tetrapyridinoporphyrazine (CoTmTPyPz) for the reduction of CO2 in heterogeneous medium when adsorbed on carbon nanotubes (CNT) at a carbon paper (CP) electrode. Unlike reported electrocatalysis with cobalt based phthalocyanine where CO was advocated as the two electron and two protons reduced intermediate on the way to the formation of methanol, we found here that CoTmTPyPz does not reduce CO to methanol. Henceforth, ruling out a mechanistic pathway where CO is a reaction intermediate.

Cobalt Tetracationic 3,4‐Pyridinoporphyrazine for Direct CO2 to Methanol Conversion Escaping the CO Intermediate Pathway

AbstractMolecular catalysts offer a unique opportunity to implement different chemical functionalities to steer the efficiency and selectivity for the CO2 reduction for instance. Metalloporphyrins and metallophthalocyanines are under high scrutiny since their most classic derivatives the tetraphenylporphyrin (TPP) and parent phthalocyanine (Pc), have been used as the molecular platform to install, hydrogen bonds donors, proton relays, cationic fragments, incorporation in MOFs and COFs, to enhance the catalytic power of these catalysts. Herein, we examine the electrocatalytic properties of the tetramethyl cobalt (II) tetrapyridinoporphyrazine (CoTmTPyPz) for the reduction of CO2 in heterogeneous medium when adsorbed on carbon nanotubes (CNT) at a carbon paper (CP) electrode. Unlike reported electrocatalysis with cobalt based phthalocyanine where CO was advocated as the two electron and two protons reduced intermediate on the way to the formation of methanol, we found here that CoTmTPyPz does not reduce CO to methanol. Henceforth, ruling out a mechanistic pathway where CO is a reaction intermediate.

Consequences of isosteric replacement of benzene for pyrazine in phthalocyanines

Tetrapyrazinoporphyrazines (TPyzPzs) likely represent the most investigated group of azaanalogs of phthalocyanines. This review highlights the author’s contributions in this field and summarizes the most important features of these interesting macrocycles with the aim of emphasizing the differences from the parent phthalocyanines. In particular, uniqueness in synthesis, spectral, photophysical and electrochemical properties are discussed. Thanks to systematic investigation of intramolecular charge transfer with TPyzPzs as electron acceptors, detailed structure-activity relationships of this ultrafast quenching process have been disclosed. This opened the door for the use of TPyzPzs as fluorescence sensors and quenchers in oligodeoxynucleotide probes, the latter being unique for TPyzPzs, which have not been investigated with phthalocyanines. These two applications seem to be much more suitable for TPyzPzs than photodynamic therapy, where the phthalocyanines typically have superior in vitro activities.

Novel phosphorus(V) tetrabenzotriazacorroles: synthesis, characterization, optical, electrochemical, and femtosecond nonlinear optical studies.

A series of three novel tetrabenzotriazacorroles (TBCs) designed with an alkyl substituent tert-butyl group (TBC-tert), an electron donor phenothiazine group (TBC-PTZ) and an energy donor carbazole group (TBC-CBZ) on the peripheral position with phosphorus metal in the cavity have been synthesized. All three compounds were characterized using various spectroscopic techniques and we assessed their femtosecond third-order nonlinear optical (NLO) properties. TBCs exhibit the properties of both phthalocyanines and corroles as they are derived from parent phthalocyanines. The optical studies revealed a new band at ∼450 nm, which was absent in the parent phthalocyanine molecules, and all three compounds obeyed Beer-Lambert's law. Singlet-state quantum yields were measured in different solvents and were found to be in the range of 0.3 to 0.6 for TBC-tert, 0.21 to 0.25 in the case of TBC-PTZ and 0.31 to 0.41 for TBC-CBZ. Time-resolved fluorescence studies revealed lifetimes in the ns regime (typically few ns). The redox properties of the TBCs suggest that they are easier to oxidize and harder to reduce and exhibit multiple oxidation and reduction potentials. Using the Z-scan technique, the third-order NLO properties were investigated with kilohertz and megahertz repetition rate femtosecond pulses at 800 nm. We report the first observation of strong three-photon absorption in these molecules with coefficients of ∼10-22 cm3 W-2 (∼10-13 cm3 W-2) with kHz (MHz) repetition rate fs pulse excitation.

Thermal and photoinduced electron transfer reactions of phthalocyanine complexes of Zn(II) and Cu(II) in acetonitrile.

Phthalocyanine that has four peripheral 2-methoxyphenyl substituents at the α-position and its Zn(II) and Cu(II) complexes were synthesized. Chemical oxidation by the Cu(II) ion and electrochemical oxidation of these metal complexes were investigated spectrophotometrically in acetonitrile. The UV-visible absorption spectra of these metal complexes and their one-electron oxidized π-cation radicals showed no concentration dependence, indicating that these species exist as monomers in solution. Kinetics of the thermal electron transfer reaction from each phthalocyanine complex to Cu2+ and the photoinduced electron transfer reaction of the Zn(II) phthalocyanine complex with V(V) and V(IV) Schiff base complexes were studied using conventional spectrophotometric and transient absorption techniques, and the electron transfer rate constants were analysed using the Marcus cross relationship. The obtained rate constants of the electron self-exchange reaction between the parent phthalocyanine complexes and their π-cation radicals were in the order of 109 to 1011 M-1 s-1 at T = 298.2 K. These large electron self-exchange rate constants are consistent with the phthalocyanine-centred redox reactions where small reorganization energies are required with little structural change during the electron transfer process.

Some donor-acceptor complexes of silicon phthalocyanine dianions

Studying the reaction of PcSiX2 (X = Cl, OH) with KOH in DMSO we first discovered red D-A complexes [(Pc2−)·PcSiX2] and [(Pc2−)·O2] in which silicon phthalocyanine dianion Pc2− is a donor, and the parent phthalocyanine silicon or oxygen are acceptors of electron density. The complexes were characterized by electron absorption, NMR, and ESR spectra. In the reactions with Me3SiCl, H2O, or CH3COOH the complexes regenerate phthalocyanine and O2. In O2 atmosphere the [(Pc2−)·O2] complex gradually degrades affording a product of unknown nature.

Enhancement of solubility via esterification: Synthesis and characterization of octakis (ester)-substituted phthalocyanines

Metal-free and metallophthalocyanines (M = Zn, Ni and ClFe) carrying eight hydroxyethylsulfanyl groups at peripheral positions were prepared from 4,5-bis(hydroxyethylsulfanyl)phthalonitrile. The reactivity of the hydroxyethyl groups was demonstrated by esterification of phthalocyanine derivatives with pyridine-4-carboxylic acid and also ferrocenecarboxylic acid in the presence of dicyclohexylcarbodiimide combined with N, N-dimethylaminopyridine or p-toluenesulfonic acid and acetic anhydride. Unlike the parent phthalocyanines, the symmetrically functionalized phthalocyanines with eight ester units were soluble in common organic solvents such as CHCl 3, THF, pyridine and DMF, sparingly soluble in ethanol and acetone and insoluble in water and hexane. The newly synthesized compounds were characterized by elemental analysis, IR, UV–vis, FAB-MS and 1H NMR spectroscopy.

Perylenophthalocyanines

The first perylenophthalocyanines have been synthesised using a Diels-Alder reaction between dialkylperylenes and fumaronitrile as the key step towards the dinitrile precursors. As expected the octaalkylperylenophthalocyanines show red-shifted absorption spectra. They are high melting solids that do not display mesophase behaviour at accessible temperatures. A 3:1 phthalocyanine/perylenophthalocyanine hybrid material, prepared by a mixed macrocyclisation reaction, presents an unusual board-like molecular profile. Its absorption maxima lie between those observed for the parent phthalocyanines and the symmetrical perylenophthalocyanines. The spectrum shows a characteristic split Q-band due to the reduced symmetry of the core. This material is non-mesogenic but is sufficiently soluble to permit processing and characterisation. The (1)H NMR spectrum indicates that at least two of the appended alkyl chains are displaced out of the macrocycle plane and lie in its shielding region--an arrangement that disfavours the face-to-face packing required for mesophase formation.

Studies on tetra-amine phthalocyanines

Metal(II) tetranitro phthalocyanines of cobalt, nickel and copper are synthesized in pure state by a novel modified method. The complexes are characterized using elemental, electronic and IR spectral studies. Pure metal(II) tetra-amino phthalocyanines of cobalt, nickel and copper are synthesized by reducing the nitro groups of the above complexes using sodium sulphide. These complexes are also characterized by elemental, electronic, IR spectral and magnetic susceptibility measurements. The nature of the electrical conductivities of the above three metal(II) tetra-amino phthalocyanine derivatives are studied in the temperature range 303–473 K and the data are presented. Among the effect of various substituent groups on the electrical conducting property of phthalocyanine, amine group substituent on the peripheral benzene ring of the phthalocyanine molecule has been found to increase electrical conductivity to a greatest extent. These complexes showed about 10 5–10 6 times higher electrical conductivities compared to their parent phthalocyanine compounds.

Octalkoxy-substituted phosphorus(V) triazatetrabenzcorroles via ring contraction of phthalocyanine precursors.

As part of efforts toward developing the synthesis of novel corrole analogues, the new triazatetrabenzcorrole (TBC) phosphorus(V) compounds (BuO)8(TBC)P(OCH3)2 (3), [(BuO)8(TBC)P(OH)]+OH- (4) ((BuO)8TBC=3,6,10,13,17,20,24,27-octabutoxytriazatetrabenzcorrolate), and [(BuO)8Cl8(TBC)P(OH)]+OH- (7) ((BuO)8Cl8TBC=3,6,10,13,17,20,24,27-octabutoxy-4,5,11,12,18,19,25,26-octachlorotriazatetrabenzcorrolate) were prepared. These TBCs were synthesized via a ring-contraction reaction mediated by PBr3 in pyridine in which a meso-nitrogen atom is extruded from an appropriate phthalocyanine precursor. Two of the compounds prepared, 3 and 4, are contracted analogues of the parent phthalocyanine (BuO8)PcH2 (1) 1,4,8,11,15,18,22,25-octabutoxy-29H,31H-phthalocyanine, which has been shown for the first time to be susceptible to ring-contraction despite the potential steric crowding imposed by the butoxy substituents. Likewise, the octachloro-substituted (BuO8)Cl8PcH2 (6), 1,4,8,11,15,18,22,25-octabutoxy-2,3,9,10,16,17,23,24-octachlorophthalocyanine, has also been shown to smoothly afford 7 via the same ring-contraction method. In addition, a rare example of a bona fide phosphorus(V) phthalocyanine, [(BuO)8(Pc)P(OCH3)2]+OH- (2), has been prepared for spectroscopic comparisons with the TBC compounds. These molecules are all extremely soluble in common organic solvents because of the octabutoxy substituents and have been characterized in detail by 1H NMR, 31P NMR, UV-vis, MALDI-MS, elemental analysis, and electrochemical studies. A clear trend in the phosphorus chemical shifts for 5 versus 6 coordination has been delineated: 31P NMR for 2, -179.8; 3, -186.1; 4, -105.1; and 7, -105.1. These data are compared to the 31P chemical shifts for related porphyrinoid(P(V)) molecules. The MALDI-MS data reveal the tendency of the TBC macrocycles to ionize as the radical cations (M(+*)) and has been useful in determining the axial ligands at phosphorus. A consequence of ring-contraction is reflected in the dramatic red-shifts (approximately 200 nm) observed for the Soret bands of the TBC compounds relative to the parent phthalocyanines. The magnitude of the red-shift is much greater than that reported for other TBCs. In addition, insertion of phosphorus causes a large red-shift in the Q-band of 2 found at 889 nm compared to 760 nm for 1. Cyclic voltammetry of the compounds in this study reveals multiple oxidation and reduction waves for each compound, and some interesting trends in redox potentials have been observed. The CV data for the octachloro-substituted compounds 6 and 7 show that the Cl substituents have an expected strong electron-withdrawing effect on the macrocycles. In general, the TBC compounds are significantly easier to oxidize and harder to reduce than the Pc counterparts, supporting the notion that corrole-type macrocycles favor higher oxidation states.

Ruthenium phthalocyanines with axial carboxylate ligands: Synthesis and function in solar cells based on nanocrystalline TiO2

The synthesis and characterization of phthalocyaninato-ruthenium ( PcRu ) complexes with potential functional axial ligands are described. The solubility of these PcRu complexes was much improved compared to their parent phthalocyanines without Ru , enabling purification by normal flash column chromatography and also NMR measurements in common solvents (e. g. DMSO - d 6 and CDCl 3). Adsorption of these phthalocyanine dyes onto the surface of a semiconductor through the carboxyl group(s) in the axial ligands prevents to some extent formation of H-aggregates, which is typical for phthalocyanines. It also prevents stacking of the dye molecules on the surface. The photovoltaic behavior of sandwich solar cells based on nanostructured TiO 2 films sensitized by these PcRu complexes was studied under irradiation with visible light. For a solar cell based on bis(4-carboxypyridine)-phthalocyaninato ruthenium(II) (1) sensitized nanoporous-nanocrystalline TiO 2, a monochromatic incident photon-to-current conversion efficiency (IPCE) of 21% was obtained at 640 nm. The overall conversion efficiency (η) was 0.61%, which is one of the best results for a solar cell based on a phthalocyanine dye. For a cell based on (4-carboxypyridine)-(4-(2-ethoxy)ethyloxycarbo-nylpyridine)-2,3,9,10,16,17,23,24-octa(n-pentyloxy)-phthalocyaninato ruthenium(II) (5) sensitized TiO 2, a IPCE of 6.6% at 640 nm and η of 0.58% were obtained.

“Molecular Metals” Based on Copper(II) 2,9,16,23-tetrahalo Substituted Phthalocyanine Derivatives

Pure copper(II) 2,9,16,23-symmetrically tetrahalo substituted phthalocyanine complexes, CuPTX (where X = F, CI, Br and I) were synthesized. Elemental analyses, electronic, IR, magnetic susceptibility measurements, ESR, X-ray diffraction and TGA studies were carried out on the above complexes both before and after iodine doping, to characterize and investigate the effect of substituents as well as the iodine doping on the electrical properties of the copper phthalocyanine complexes. Variations in the electrical conductivity of the complexes depend on the nature of the substituents and were found to show ∼105 times improved electrical conductivity in comparison to the parent phthalocyanine. It is interesting to note that substitution and iodine doping showed remarkably increased electrical conductivity, nearly 1012 times the electrical conductivity of copper phthalocyanine. This may be due to a decrease in the metal-metal bond distance, increase in the approach of an ideal eclipsed system or due to the combined effects of both.

Theoretical determination of the molecular and solid-state electronic structures of phthalocyanine and largely extended phthalocyanine macrocycles

The molecular and solid-state electronic structures of metal-free phthalocyanine and a series of linearly benzoannulated phthalocyanines have been investigated using the valence effective Hamiltonian (VEH) quantum-chemical method. Geometry optimizations show that, from the molecular structure standpoint, phthalocyanine-based macrocycles are the result of joining four polyacenic units to the C8N8 central ring. The electronic structure calculated for the parent phthalocyanine is compared with that of porphyrin, and the consequences of benzoannulation and meso-tetraaza substitution on the optical properties of phthalocyanines are discussed. The VEH results obtained for extended phthalocyanines are in agreement with available photoemission, cyclic voltammetry and optical absorption data and help to rationalize the evolution of the electronic properties. The first ionization energy is predicted to decrease with linear benzoannulation and asymptotically converges to an extrapolated value of –5.7 eV. Strikingly, a non-convergent behaviour is obtained for the HOMO–LUMO energy gap and very low excitation energies are predicted for extended phthalocyanines. Band-structure calculations have been performed for one-dimensional stacks of the molecules investigated. The variation of the bandwidth with the staggering angle and the intermolecular separation provides a coherent picture of the electrical conductivities observed experimentally in crystals and polymers. Very small bandgaps lower than 0.5 eV are predicted for extended phthalocyanines.

The photochemical properties of rhodium(III) phthalocyanine cation radicals

Stable rhodium(III) phthalocyanine cation radicals, Rh(pc) (CH/sub 3/OH)X/sup +/ with X = Cl or Br, were generated by one-electron chemical or electrochemical oxidations of the corresponding rhodium(III) phthalocyanines, Rh(pc) (CH/sub 3/OH)X, and characterized by means of their EPR and optical spectra. Some transitions in the optical spectra of the radicals were assigned by comparison with similar transitions in the spectra of the parent phthalocyanines. Moreover, the photochemical properties of the radicals were investigated by continuous, laser, and flash photolysis. Irradiations in the UV bands, lambda/sub excit/ = 250 or 320 nm, induce the photoreduction of the radicals (back to the parent phthalocyanine) by abstraction of hydrogen. Photolysis in the visible region, lambda/sub excit/ = 525 nm, induces the photodecomposition of the macrocycle. The mechanisms of these photoprocesses are discussed by comparison with known photochemical transformations of related compounds. 28 references, 3 figures, 1 table.

Phthalocyanines of metals of the first transition series. Part I. Nitrosyl derivatives: synthesis and properties

The action of nitric oxide on the β crystalline forms of the metal phthalocyanines of the first transition series from chromium to copper, and on vanadyl phthalocyanine, has been investigated. It has been found that the β modifications of Cr–pc, Mn–pc, and Co–pc (pc = phthalocyanine) react with nitric oxide, as previously reported for the β form of Fe–pc, to form the corresponding mononitrosyl derivatives. In contrast, no reaction of nitric oxide has been observed with the β form of Ni–pc or Cu–pc, or with VO–pc. The reaction of the nitrosyl derivatives of Cr–β–pc and Mn–β–pc with air and with pyridine is also described, and the properties and stability of the various nitrosyl derivatives are discussed in comparison with those of the parent phthalocyanines.