Journal of Porphyrins and Phthalocyanines

While investigating the destruction of the cyanobacterial hepatotoxin microcystin-LR in the presence of phycocyanin pigment via semiconductor photocatalysis, it became apparent that the pigment was catalysing the toxin decomposition. The mechanism of this process in terms of phycocyanin acting as a photo-oxygenation sensitizer via singlet oxygen and superoxide attack is explored. The absorption and fluorescence spectra of phycocyanin have been obtained and data on the properties of the excited state calculated. The established photo-oxygenation sensitizer rose bengal was also used as a catalyst for the photolytic decomposition of microcystin-LR to help elucidate the decomposition mechanism.

The investigation of the degradation of two commercially available dyes (Remazol Turquoise Blue and Everzol Turquoise Blue) by the lignin-degrading fungus Phanerochaete chrysosporium and comparison with that of a phthalocyanine whose structure is known (Heligon Blue) are presented. Atomic absorption showed a large release of copper from the biomass at day 7. Polarography served to speciate the copper present in the supernatant. Day 5 sees the complete disappearance of the main dye peak with the release of free copper into the supernatant. Day 7 sees a large increase in the free copper signal with two other electroactive species also present in the supernatant, all of which are seen to decrease at day 8. Visible spectroscopy shows that the main decolourization takes place between day 4 and day 6, with complete decolourization occurring at day 7. HPLC analysis again confirms the above results, with possible degradation products detected at 254 nm occurring at 3.621 and 4.170 min at day 7 which may well correlate with those found in polarographic analysis at –1050 and –1150 mV. Day 7 also sees a large increase in a peak at 2.744 min.

Unsymmetrically substituted binuclear phthalocyanine derivatives 8 and 9 have been synthesized by mixed condensation of nickel(II) dicyanophthalocyanine 6 with dioctyloxyphthalonitrile 7 in the presence of either nickel(II) or zinc(II) chloride. In addition, a heterotrinuclear phthalocyanine–triazolehemiporphyrazine–phthalocyanine complex 16 has been obtained using the methodology described earlier for the preparation of heterobinuclear phthalocyanine–triazolehemiporphyrazine systems (13a–13e). All these compounds exhibit in their UV-vis spectra broad and split Q bands that are shifted to the near-IR in comparison with mononuclear phthalocyanines as a consequence of the enlargement of the π conjugation.

The synthesis of three novel porphyrins (that are models for mesoporphyrin) requires the synthesis of eight new pyrroles, one new alkyl-3-oxohexanoate and two new dipyrromethanes. The new porphyrin free bases have hydrophobic substitution patterns different from that in mesoporphyrin. We are seeking amphilic porphyrins that will form Langmuir–Blodgett (LB) multilayers without recourse to either long-chain alkyl substituents or fatty acid additives. In this way the influence of the conjugated tetrapyrrole unit on the properties of the multilayer films can be maximized. We report multilayer deposition for porphyrins having the following substituents: CH₃, C₂H₅, n-C₃H₇, (CH₂)₂COOMe; no additives such as stearic acid, cadmium stearate or mesitylene are required, Y-type deposition being exhibited by the simply substituted pure methyl esters. The variations in proton NMR chemical shift with concentration are reported and the action spectrum of an LB film of a porphyrinato-Zn(II) complex is described. Our observations and conclusions are in sharp (and optimistic) contrast with those of H. Chou et al. (J. Phys. Chem. 98, 383 (1994)), who found that in the absence of steric constraints from bulky aliphatic chains the Langmuir films are so rigid that either no multilayers or multilayers of poor quality are given. We obtain good-quality multilayers (60 layers) for porphyrins bearing eight small substituents.

A polymorph of perfluoro-vanadyl-phthalocyanine was found to be formed epitaxially on a potassium iodide monocrystalline surface by vacuum deposition. The molecular orientation and molecular packing of the polymorph were analysed by a combination of several electron microscopic methods, namely electron diffraction, high-resolution imaging and electron energy loss spectroscopy. The polymorph is different from the tetragonal polymorph previously obtained on potassium chloride and potassium bromide single crystals. The molecular packing of the new polymorph on potassium iodide was found to be orthorhombic with a = 1.48 nm, b = 0.37 nm and c = 27 nm, the ab-plane being parallel to the substrate surface.

This is a review of the recent studies done by the authors in the area of catalysis and photocatalysis by phthalocyanines and related compounds. Several examples of catalytic processes are given. Special attention is paid to the design of new types of photocatalytic systems for photodynamic therapy of cancer and to the development of novel catalytic methods of cancer treatment.

Tetrapyridotetraazaporphyrinatozinc (TPyTAPZn) can be looked at as a substituted phthalocyanine. Thin films of TPyTAPZn were prepared on quartz glass by physical vapour deposition under high-vacuum conditions. During the deposition, island growth was observed by a characteristic change in the electrical conduction, indicating an increasing number of conduction pathways along the film. Deposition conditions could be optimized to yield an ordered rather than amorphous growth as detected by a characteristic absorption band in the visible range, strongly red-shifted from the absorption of the monomeric molecule in solution. A negative Seebeck coefficient confirmed n-type conduction for TPyTAPZn. In temperature-dependent measurements of the electrical conductivity and thermopower across the samples an activation energy of 0.31 eV was established for the conductivity and of 0.04 eV for charge carrier generation. From this difference it is concluded that a thermally activated charge carrier transport mechanism (hopping) rather than delocalized conduction (band model) is dominant in TPyTAPZn. Photoconduction turned out to be rather small in these samples, although light was absorbed quite efficiently. The time dependence of photoconduction indicated a significant trap density. Interaction with ammonia or triethylamine in the gas phase led to an increase in the conductivity; oxygen or water led to a decrease. The time dependence of these interactions indicated that triethylamine and water were only reacting with the surface region, whereas NH₃ and O₂ were also diffusing into the bulk of the films.

We review here the self-assembly, electrochemical and spectroelectrochemical properties of 2,3,9,10,16,17,23,24-octa(2-benzyloxyethoxy) phthalocyaninato copper (CuPc(OC₂OBz)₈), where terminal benzyl groups on the eight ethylene oxide side chains assist in forming unusually ordered, mechanically rigid thin films. New spectroscopic characterization of cast CuPc(OC₂OBz)₈ films is discussed in comparison with cast films of its metal-free analogue H₂Pc(OC₂OBz)₈ and similar copper and dihydrogen phthalocyanines with benzyl — terminated triethylene oxide substituents, CuPc((OC₂O)₃Bz)₈, and H₂Pc((OC₂O)₃Bz)₈, which do not demonstrate the same degree of ordering as CuPc(OC₂OBz)₈. AFM studies of horizontally transferred LB films of CuPc(OC₂OBz)₈ show column–column distances of ca 2.8 nm and confirm the high degree of ordering previously surmised from spectroscopic characterization of multilayer thin films. The oxidative electrochemistry of multilayer thin films prepared from these Pcs is strongly dependent on the chemical identity of the supporting electrolyte anion and on annealing of the thin films. Compliance of the films to counter-ion transport limits the extent of electrochemical doping. Preliminary studies of the oxidative electrochemistry of isolated CuPc(OC₂OBz)₈ aggregates (diluted into an electroinactive methyl arachidate thin film) on an electroactive, integrated optic waveguide (EA-IOW) are also presented. Monitoring the change in absorbance at 633 nm on the waveguide surface allows the determination of the onset potential for oxidation of the isolated aggregates, which appears to be less positive in potential versus that observed for multilayer Pc assemblies.

Octakis(alkoxymethyl) cobalt phthalocyanines with relatively short side chains were synthesized which exhibited no thermotropic liquid crystalline behaviour. The final products as well as the intermediates have been characterized by proton magnetic resonance, infrared and electron spectra and elemental analysis. Cyclic voltammograms were measured for octakis(alkoxymethyl) cobalt phthalocyanines in order to examine their electron transfer properties. The electron transfer properties of octakis (alkoxymethyl) cobalt phthalocyanines depend on the kind and number of substituents and are due to the interaction between the phthalocyanine ring, the central metal which is influenced by the conjugated π electron current of the porphyrazine ring.

Copper phthalocyanines are commercially important organic pigments for blue shades of colour. They are dispersed by mechanical means as tiny molecular crystals (of dimensions 0.02—0.5 μm) into a wide range of commercial media to form products such as printing inks, paints and coloured plastics. Many important technological properties of copper phthalocyanine pigments, including colour strength and dispersion performance, depend on the physical properties of their crystals, notably crystal lattice type, crystal size and crystal shape. The roles which these crystal properties play in determining a copper phthalocyanine pigment's technological performance are briefly reviewed. The reduction of crystal aggregation during the manufacture of a copper phthalocyanine pigment and the control of flocculation in an application medium are also highlighted.

Dithallium phthalocyanine (Tl₂Pc) was synthesized by direct reaction of Tl metal with 1,2-dicyanobenzene. A thin film of the product was prepared by vacuum deposition on KCl single-crystalline substrate and its structure and epitaxy were examined by electron microscopy. The crystal structure of the thin film was the same as the orthorhombic structure reported previously. The film grew epitaxially on KCl substrate as expected from point-on-line coincidence. The UV-vis spectrum of the film was measured and compared with that of an as-synthesized powder sample. The UV-vis spectrum of the thin film of Tl₂Pc showed some differences from that of the powder in the visible region, which may result from the difference in molecular orientation. The electrical resistance of a Tl₂Pc thin film deposited on mica was about 10¹⁰Ω in our measuring set-up, which means that the film does not show high conductivity.

Intermediates of the cobalt tetrasulfophthalocyanine (CoTSPc)-catalyzed thiol autoxidation were studied by UV-vis spectroscopy. All thiolates react with CoTSPc resulting in the formation of 1:1 complexes. Three major factors control both the stability and aggregation of the complexes: thiolate basicity, metal-to-ligand charge transfer (MLCT) and π stacking. Basic thiolates partially reduce Co^IITSPc, whereas CoTSPc complexes with low-basicity aliphatic thiolates (pK_a < 4) do not exhibit Co(II) reduction, based on the absence of the characteristic Co(I) charge transfer band at 450 nm. CoTSPc complexes with aliphatic and bulky aromatic thiolates appear to be aggregated in aqueous solutions and are characterized by a broad band at 650 nm. Non-bulky aromatic thiolates of low basicity (pK_a < 6) form unique stable monomeric Co^IITSPc complexes. This unique spectral feature can be attributed to π stacking between the phthalocyanine ring and thiolate. Comparison of binding constants shows that the partial reduction of Co(II) significantly contributes to the thiolate binding. A combination of aromatic π stacking and MLCT appears to be responsible for the observed 1000-fold stronger binding of non-basic aromatic thiolates as compared with aliphatic ligands of similar basicity. Kinetic studies confirm the importance of the thiolate binding type for catalysis.

The electron mobility of hexadecafluorophthalocyaninato-copper (F₁₆PcCu) films was evaluated based on field effect measurements in vacuum and in various gas atmospheres. An Arrhenius plot of the mobility showed that the carrier transport followed a thermally activated hopping mechanism with an activation energy of 0.28 eV. The mobility evaluated for freshly prepared films in ultrahigh vacuum was 2.0 × 10⁻³cm²V⁻¹s⁻¹ at room temperature. The electrical conductivity and carrier density were 4.4 × 10⁻⁵S cm⁻¹ and 1.4 × 10¹⁷cm⁻³ respectively. The high carrier density indicated the existence of impurities acting as electron donors in the films. The field effect carrier mobility increased to 5.7 × 10⁻³cm²V⁻¹s⁻¹ in NH₃ atmosphere (100%, 1 atm) and decreased by 75% in the presence of O₂ gas (100%, 1 atm). A quick recovery of mobility was observed when the gas molecules were evacuated, indicating a low capability of gas adsorption.

It is shown that it is possible to obtain structural information from small (<100 nm) phthalocyanine crystals by using crystallographic direct phasing methods applied to electron diffraction data. This technique is both quantitative and does not suffer from the difficulties associated with high-resolution electron microscopy. Structural information has been obtained from both tetra- and octa chloro-copper phthalocyanines, and the results compared with the hydrogenated and perchloro members of the series.

Polyaniline (PA) and aniline black (AB) were prepared in powder form by the chemical method of oxidative polymerization, from which free-standing thin films were obtained by solvent evaporation using N-methyl pyrrolidinone (NMP). The thin films contained 2, 4, 6 or 8 wt% AB. Electrical measurements showed that the samples containing 4% AB exhibited the highest photoconductivity of the four concentrations. Thus there appears to be a critical ratio of PA to AB for maximum photoconductivity. Annealing up to 570 K has little effect on the conductivity. Upon adding a small quantity of copper phthalocyanine (CuPc) to the PA + AB, the electrical conductivity increased considerably and the optical absorption was extended from the UV to the near IR. The electrical conductivity mechanism is a consequence of a redox process, since AB is the oxidized state of PA and, upon illumination, there is an exchange of charge carriers. The extension of the range of optical absorption upon addition of CuPc is interpreted to suggest that CuPc photosensitizes the material and enhances the carrier transport process in the redox couple. The activation energy from the temperature-dependent conductivity and the band gap from the electrolyte electroreflectance method were determined. The activation energy for 0.4% CuPc is lowest (0.52 eV) and the corresponding band gap is determined to be 3.0 eV. This organic compound could be a good candidate for inexpensive, reliable and efficient solar energy-converting devices.