Journal of Porphyrins and Phthalocyanines

Metal-free phthalocyanine derivatives have been synthesized in very short times with high yields in the presence of 1,1,3,3-tetramethylguanidinium trifluoroacetate (TMGT) as an ionic liquid or tetrabutylammonium bromide (TBAB) as a phase transfer reagent under both classical heating conditions and using microwave irradiation. The best results were obtained with ionic liquid. Both the ionic liquid and phase transfer reagent can be recycled for subsequent reactions and reused without appreciable loss of efficiency.

We are investigating the properties of corrole-sensitized TiO₂ solar cells. The TiO₂-adsorbed free base and Ga^III corroles display cell efficiencies under AM 1.5 illumination that are about half that of a standard N3-sensitized cell (N3 = cis-bis(4,4'-dicarboxy-2,2'-bipyridine)dithiocyanato ruthenium(II)), while that of the Sn^IV-based cell is much lower. The properties of the corrole-TiO₂ solar cells, along with results obtained with electrodes of lower conduction band energies clearly reveal that the reducing power of the singlet excited states of the free base and Ga^III corrole, but not of the Sn^IV derivative, is sufficiently high for efficient injection into the TiO₂ conduction band.

2,9,16,23-tetra(4-amino-3-nitrophenoxy)phthalocyanines were synthesized from 4-(4-amino-3-nitrophenoxy)phthalonitrile which was obtained from 4-nitro-1,2-dicyanobenzene and 4-amino-3-nitrophenol. 2,9,16,23-tetra(4-ferrocenylimino-3-nitrophenoxy)phthalocyanine and 2,9,16,23-tetra(4-ferrocenylimino-3-nitrophenoxy)phthalocyaninatocobalt(II) were synthesized in a one-step condensation reaction of ferrocenylaldehyde with 2,9,16,23-tetra(4-amino-3-nitrophenoxy)phthalocyanine and 2,9,16,23-tetra(4-amino-3-nitrophenoxy)phthalocyaninatocobalt(II), respectively. The novel compounds were characterized by elemental analysis, Inductively Coupled Plasma (ICP-MS), UV-vis, IR and ¹H NMR spectroscopy. The effects of temperature and frequency on the conduction properties (a.c. and d.c.) and the dielectric constant were studied on pellet samples of 2,9,16,23-tetra(4-amino-3-nitrophenoxy)phthalocyanine, 2,9,16,23-tetra(4-ferrocenylimino-3-nitrophenoxy)phthalocyanine, 2,9,16,23-tetra(4-amino-3-nitrophenoxy)phthalocyaninatocobalt(II) and 2,9,16,23-tetra(4-ferrocenylimino-3-nitrophenoxy)phthalocyaninatocobalt(II), with evaporated, ohmic gold electrodes in the frequency range 40-10⁵ Hz. and within the temperature range 290-400 K. Unlike many metallophthalocyanines, a variable-range hopping model is found to most appropriately fit the experimental conductivity data of 2,9,16,23-tetra(4-ferrocenylimino-3-nitrophenoxy)phthalocyanine and 2,9,16,23-tetra(4-ferrocenylimino-3-nitrophenoxy)phthalocyaninatocobalt(II), while for 2,9,16,23-tetra(4-amino-3-nitrophenoxy)phthalocyanine and 2,9,16,23-tetra(4-amino-3-nitrophenoxy)phthalocyaninatocobalt(II), thermally activated conduction with single activation energy is valid. Frequency and temperature dependence of the a.c conductivity were analyzed in terms of existing theory for 2,9,16,23-tetra-(4-amino-3-nitrophenoxy)phthalocyanine, 2,9,16,23-tetra(4-ferrocenylimino-3-nitrophenoxy)phthalocyanine, 2,9,16,23-tetra(4-amino-3-nitrophenoxy)phthalocyaninatocobalt(II) and 2,9,16,23-tetra(4-ferrocenylimino-3-nitrophenoxy)phthalocyaninatocobalt(II). It was found that the a.c. conductivity of the compounds depends on the frequency, obeying the empirical formula, σ_ac = A(T)ω^s. The model parameters calculated are reasonable and consistent with the prediction of the correlated barrier hopping model for 2,9,16,23-tetra(4-ferrocenylimino-3-nitrophenoxy)phthalocyanine and 2,9,16,23-tetra(4-ferrocenylimino-3-nitrophenoxy)phthalocyaninatocobalt(II) and the quantum mechanical tunneling model for 2,9,16,23-tetra(4-amino-3-nitrophenoxy)phthalocyanine and 2,9,16,23-tetra(4-amino-3-nitrophenoxy)phthalocyaninatocobalt(II). The dielectric constant of the compounds increased with temperature and decreased with frequency in the investigated range.

The redox behavior of iron porphycenes using the sodium mirror contact technique is reported. The resonance Raman spectra are obtained for each redox state, in order to explore the vibrational characteristics of these species in different redox states. The observed resonance Raman behavior of Fe^II porphycene anion radical and its dianion is interpreted using the vibrational analysis of free-base porphycene anion radical and dianion. For the first time, a species generated in the fourth reduction step, is confirmed by UV-vis spectroscopy and is assigned to Fe^I porphycene π dianion. The dependence of resonance enhancements of Raman bands for the Fe^I porphycene π dianion on excitation laser reveals structural distortion along the NC_aC_aN or C_bC_aC_aC_b segments of the pyrrole-pyrrole direct connection in the excited electronic state.

Porphyrins have been studied as photosensitizers in photodynamic therapy. DNA is one of the most important targets of the sensitizer. In the present study, we have examined the photosensitized DNA damage caused by dihydroxoP(V) tetraphenylporphyrin (P(V)TPP), a cationic water-soluble porphyrin. P(V)TPP photosensitized guanine-specific damage to the DNA fragment. P(V)TPP induced severe photodamage to single-stranded rather than to double-stranded DNA. High performance liquid chromatography measurements confirmed the formation of 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxo-G), an oxidized product of 2'-deoxyguanosine, and showed that the content of 8-oxo-G in single-stranded DNA is larger than that in double-stranded DNA. The effects of reactive oxygen scavengers on DNA damage suggested the involvement of singlet oxygen (¹O₂). Photosensitized ¹O₂ formation was confirmed by near-infrared emission measurements. The results showed that ¹O₂ formation mainly contributes to the mechanism of DNA photodamage by P(V)TPP. Absorption spectrum measurements showed the interaction between P(V)TPP and DNA. This interaction is expected to enhance the ¹O₂-mediated DNA damage since the lifetime of ¹O₂ in a cell is very short. On the other hand, P(V)TPP induced DNA damage at the consecutive guanines in double-stranded DNA. Because the consecutive guanines act as a hole trap, this DNA-damaging pattern suggests the partial involvement of photo-induced electron transfer. The fluorescence of P(V)TPP was quenched by DNA, supporting the electron transfer mechanism. However, DNA damage by electron transfer was not a main mechanism possibly due to reverse electron transfer. In conclusion, P(V)TPP binds to DNA and induces guanine-specific, photo-oxidation mainly via ¹O₂ generation.

The reactions of dodecahydro-closo-dodecaborate oxonium derivatives with various phenols resulted in phenoxy-undecahydro-closo-dodecaborates in high yields. Using this method, a phthalocyanine zinc(II) complex containing four (B₁₂H₁₂)^2- species was prepared in high yield. The compound shows good photocatalytic activity. The combination of boron cages and phthalocyanines makes this compound useful for boron neutron capture therapy for cancer and photodynamic tumor therapy.

The Zn(quinoline)₂Cl₂ complex is found to be a convenient reagent for the direct synthesis of amino-substituted, zinc azaphthalocyanines. Octa(4-thiomorpholinyl)- and octa(1-pyrazolyl)- substituted zinc azaphthalocyanines were synthesized from pyrazines, 5,6-bis(4-thiomorpholinyl)pyrazine-2,3-dicarbonitrile and 5,6-bis(1-pyrazolyl)pyrazine-2,3-dicarbonitrile, respectively and dry Zn(quinoline)₂Cl₂. Two zinc azaphthalocyanines, both mixtures of four constitutional isomers, were synthesized by the same method, from 6-(2-thienyl)-5-(4-thiomorpholinyl)pyrazine-2,3-dicarbonitrile and from 6-(2-thienyl)-5-(1-pyrazolyl)pyrazine-2,3-dicarbonitrile respectively. The octa(4-thiomorpholinyl)- and octa(1-pyrazolyl)-substituted zinc azaphthalocyanines and the zinc azaphthalocyanines with mixed substituents were characterized by elemental analyses, TOF-SIMS, ¹H and ¹³C NMR, and UV-vis spectroscopic methods. Q-bands for octa(4-thiomorpholinyl)- and octa(1-pyrazolyl)-substituted zinc azaphthalocyanines and the zinc azaphthalocyanines with mixed substituents are found at respectively 655 and 670 nm (ɛ: 100 000-180 000 M^-1.cm^-1).

The application of mono-triazole-annulated phthalocyanine and benzoporphyrazine complexes for the functional unsymmetrical modification of the macrocycle's periphery is discussed. The peculiarities of the synthesis of some metal complexes with aryloxy-substituted mono-triazole-annulated Pc are described. Alkylation by ω-alkenylbromide of the triazole ring in accordingly prepared novel mono-triazole-annulated phthalocyaninato nickel, as well as in mono-benzotriazole-annulated porphyrazinato zinc, is studied. The terminal double bond in the formed derivatives could be successfully converted into acetylsulfanyl function only in the case of phthalocyaninato nickel complex due to the instability of porphyrazinato zinc under the reaction conditions.

A panel of nitro substituted 5,15-diaryl-porphyrins, featuring nitro groups either on the phenyl rings or on one of the two free meso-positions, was synthesized. In the former category, compounds 5-(3-nitrophenyl)-15-phenylporphyrin, 5,15-di(3-nitrophenyl)porphyrin and 5-(4-nitrophenyl)-15-phenylporphyrin were obtained following standard procedures by reacting dipyrromethane and aromatic aldehydes. In the latter category, porphyrins 10-nitro-5,15-diphenylporphyrin, 10-nitro-5-(3-methoxyphenyl)-15-phenylporphyrin and 10-nitro-5,15-di(3-methoxyphenyl)porphyrin were generated by nitration of 5,15-diarylporphyrins with trifluoroacetic acid/sodium nitrite under particularly mild conditions. The new molecules bearing one or two nitro-groups were tested as photosensitizers during in vitro experiments on a human colon adenocarcinoma cell line (HCT116), and their effects were compared with those induced by temoporfin, porfimer sodium and by some previously published electron-rich diarylporphyrins. The results, expressed as IC₅₀ values obtained by the MTT test following 24 h incubation with the photosensitizers and 2 h irradiation with a 500 W tungsten-halogen lamp, indicate that the presence of an electron withdrawing substituent, on a meso-position, decreases the photodynamic activity of the compound. Conversely, 5-(3-nitrophenyl)-15-phenylporphyrin, a non symmetrically substituted diarylporphyrin bearing both one electron-deficient and one lipophilic moiety, resulted in high phototoxic activity.