Journal of Porphyrins and Phthalocyanines

Doubly N-confused dioxohexaphyrins were characterized by cyclic voltammetry and spectroelectrochemistry in the -2.5 to +2.0 V vsAg|Ag⁺ (0.10 M, in CH₃CN) range. Six reversible monoelectronic processes were found suggesting that the rich electrochemistry of porphyrin systems was preserved in that expanded macrocycle. However, the electronic and electrochemical properties of the free-base, Cu(II) and Ni(II) species were shown to be sensitive to the coordinated transition metal ions and solvent revealing a quite complex behavior, probably reflecting the higher flexibility and strong conformational effects on the energy levels and stability of those complexes.

We report the kinetics of CO binding to a series of substituted ferrous tetra(4-X-phenyl)porphyrins (X = CF₃, Cl, H, CH₃, OCH₃) in DMSO solvent using a mixture of 1,2-DMI/1-MeIm as proximal base. The CO dissociation rate constant increases with electron donation of the substituent X; the aggregate Hammett ρ value is -0.38. Using a Swain-Lupton analysis we determine the electronic effects to be transmitted 67% by through-bond or field effect and 33% by resonance. These results indicate that there is significant conjugation between the phenyl rings and the porphyrin core of iron tetraphenylporphyrin systems.

Six substituted tetrapyrazolylporphyrins (TAPyPH₂), meso-tetrakis(1-phenylpyrazol-4-yl)porphyrin (TPPyPH₂), meso-tetrakis[1-(p-tolyl)pyrazol-4-yl] porphyrin ((p-CH₃)TPPyPH₂), meso-tetrakis[1-(p-methoxyphenyl)pyrazol-4-yl]porphyrin ((p-CH₃O)TPPyPH₂), meso-tetrakis[1-(p-chlorophenyl) pyrazol-4-yl]porphyrin ((p-Cl)TPPyPH₂), meso-tetrakis[1-(p-bromophenyl)pyrazol-4-yl]porphyrin ((p-Br)TPPyPH₂) and meso-tetrakis[1-(m-tolyl)pyrazol-4-yl]porphyrin ((m-CH₃)TPPyPH₂), were synthesized by the condensation of pyrrole with the corresponding substituted formylpyrazole and used as the doping materials in the Organic Light-Emitting Diodes (OLEDs) with hole-transport materials of N,N'-diphenyl-N,N'-bis (4-methylphenyl)-[1,1'-biphenyl]-4,4'-diamine (TPD) within a tris(8-hydroxyquinoline) aluminum (Alq₃) host layer. Both the electroluminescence properties of these OLEDs and effects of the peripheral substituents of the tetrapyrazolylporphyrins on EL properties of the OLEDs were studied. The tests found that the OLEDs using substituted tetrapyrazolylporphyrins (TAPyPH₂) as the dopants had the saturated red emission at a concentration of 1.5 wt.%. The electron-donating groups of tetrapyrazolylporphyrins (for example, p-CH₃ and p-CH₃O) increased the luminance of OLEDs, while the electron-drawing groups (for example, p-Cl and p-Br) decreased the luminance. The OLEDs using meso-tetrakis(1-phenylpyrazol-4-yl)porphyrin (TPPyPH₂) as a dopant showed saturated red emission at 680 nm (CIE coordinates of x = 0.65, y = 0.31) with a luminance of 305 cd/m² at a driving voltage of 25 V at concentration of 1.5 wt.%. Compared with OLEDs doped by the free-base tetraphenylporphyrin (TPPH₂), the OLEDs doped by the tetrapyrazolylporphyrins had better luminance and higher emission efficiency. An explanation for these results was given based on the molecular structure and spectral properties of the porphyrin compounds.

Photodynamic therapy (PDT) has been reported to be effective for treating various tumors and induce apoptosis in many tumor cells. In this study, we examined a biological significance of PDT with a chlorin-based photosensitizer, Radachlorin^®, in a cervical cancer model, TC-1 cells. When TC-1 cells were exposed to varied doses of Radachlorin^® with light irradiation (6.25 J/cm²), PDT induced a dose-dependent growth inhibition of TC-1 cells. All of these cells were significantly damaged after light irradiation and categorized to be early and late apoptosis, as determined by annexin V staining. Radachlorin^® localized primarily into the Golgi apparatus of cells in 12 h of the treatment, and weak fluorescence intensity was also detected in mitochondria. On the other hand, in the in vivo experiments, following light irradiation (100 J/cm²), retarded tumor growth was significant in mice treated with Radachlorin^®, as compared to the control group. Taken together, we propose that PDT after the application of Radachlorin^® may induce the Golgi apparatus-mediated apoptosis of cervical cancer cells in vitro, and also be effective in the mice system.

The readily prepared 2,3,9,10,16,17,23,24-octamethyl-1,4,8,11,15,18,22,25-octaoctyloxyphthalocyanine (Pc 1) adopts a non-planar conformation in the crystalline state as indicated by a dihedral angle of 27.2° formed between isoindole subunits on opposite sides of the core. The ring distortion can be attributed to a combination of steric congestion of the side-chains and the stabilization of the saddle-shaped conformation via pairing of molecules to give the so-called 'overlap effect'. The ring distortion is compared to that found in other metal-free phthalocyanines. Pc 1 adsorbs strongly in the near-IR region, is highly soluble and gives robust spin-coated films of excellent optical clarity.

Electron spin resonance spectra of copper phthalocyanine doped with alkaline metals (A_xCuPc) have been investigated. The temperature dependence of ESR spectra indicates ferromagnetic behavior. The Curie-Weiss temperature varies from 30 to 115 K depending on the stoichiometry x of the samples. Some particles of polycrystalline samples were attracted to a weak magnet at temperatures slightly higher than 77 K. The observed magnetism is caused by unpaired π-electrons of phthalocyanine anions on the eg doubly degenerated molecular orbital. The observed ferromagnetism can be understood within the framework of the McConnell-2 model proposed for organic ferromagnetic charge-transfer complexes. The high-temperature magnetism in A_xCuPc is considered to be a result of the Zener mechanism of double exchange between phthalocyanine molecular anions of different valence.

The 5,10,15,20-tetrakis(4-sulfophenyl)porphyrin (TPPS₄) and 5-phenyl-10,15,20-tris(4-sulfophenyl)porphyrin (TPPS₃)] were obtained for the first time as the pure sulfonic acid derivatives and characterized for their constitutional structure in the solid state and in water solution. The zwitterionic species in water solutions, above a critical micellar concentration, are stabilized by side-to-side homoassociation to J-aggregates (B-band: 490 nm), but in solids they only give the J-aggregates when water is present in enough amount. Severe dried solids show a zwitterionic species, stabilized by side-to-side interactions, that probably corresponds to the dimer (B-band: 455 nm). The monomeric zwitterion (B-band: 434 nm) is detected in dilute water solutions and its acid/base properties (concentration pK_a(1/2) ≈ 5.0) are not significantly different from those of the acidified solutions of their sodium sulfonate derivatives. However, pure water solutions of TPPS_n, in contrast to those of their sodium salts, show important interactions with hydrophilic surfaces: e.g. TPPS₄ adsorbs on fused quartz forming a monolayer of the free-base porphyrin together with its counter cations. Dilution of the title porphyrins in a solid matrix (e.g.KBr) leads to a free-base porphyrin species with a red-shifted B-band (424 nm) that points to a side-to-side homoassociation, which is in contrast with the typical π-stacked aggregates of the corresponding alkaline metal sulfonato salts.

The X-ray structure, electrochemistry, and optical spectroscopy of the porphycene analog of a benzochlorin, octaethylbenzochloracene (OEBzC) are reported. The OEBzC macrocycle is easier to oxidize and harder to reduce than octaethylporphycene (OEPc). The optical spectra of OEBzC and of the diacid salt are also reported. The optical spectrum for the one-electron oxidation of OEBzC is indicative of π-cation radical formation. In porphyrins, saturation of one pyrrole ring and addition of an exocyclic benzene ring progressively red-shifts the first absorption band. For porphycenes, saturation of one pyrrole ring results in a 35 nm blue shift in the first absorption relative to OEPc. Compared to 2,3-dihydroporphycene (DHPc), the first absorption band in OEBzC is red-shifted 24 nm. These studies further illustrate how the fused exocyclic benzene ring influences the macrocycle conformation, chemical and physical properties of porphycenes.

Lead(II) phthalocyanine (PbPc); lead(II) tetranitrophthalocyanine (PbTNP) and lead(II) tetraaminophthalocyanine (PbTAP) were synthesized in pure state by microwave irradiation and conventional heating methods. The procedures for their synthesis by the microwave technique are standardized and reported for the first time. PbPc and PbTNP were synthesized in dry conditions and PbTAP complex was synthesized in aqueous medium. All the compounds are obtained in very high yield (~90%). The synthesized complexes are characterized with respect to elemental analysis, UV-visible, IR-spectroscopy and X-ray diffraction study. The microwave methods are advantageous over the conventional method of synthesis with respect to higher yield, rapidity and simplicity.

The synthesis of various axially substituted titanium phthalocyanines in high yield using microwave irradiation without an added solvent is reported. The times of reaction, as expected, are short and generally less than 10 minutes. The products were obtained in high purity after chromatography.