Journal of Porphyrins and Phthalocyanines

Adsorption of phthalocyanines lacking conventional attaching substituents onto nanostructured TiO₂ electrodes has been studied, and some of the important factors for sensitisation have been identified. Tetra-dimethoxyphenyl phthalocyanine (2) and tetra-phenyl phthalocyanine (3), derived from 4-(2,5-dimethoxyphenyl)phthalonitrile and 4-phenylphthalonitrile, respectively, are shown to successfully sensitise nanostructured TiO₂ electrodes, with IPCE_max of 9 and 5% at λ = 650 nm. The dye-oxide systems have been characterised by UV-vis spectroscopy, cyclic voltammetry and photoelectrochemical methods, and the dye–surface interactions are discussed.

Phthalocyaninatosilicon(IV), germanium(IV) and tin(IV) dihydroxides react with potassium hydroxide in o-xylene in the presence of crown ether 15-cr-5 initially forming paramagnetic compounds of dark-blue color with absorption bands at 580–590 nm and 620–625 nm and then diamagnetic compounds of red color with an absorption band at 518–523 nm. The red compounds are very reactive towards proton donors, restoring the initial phthalocyanines, and oxidation agents under decomposition of the phthalocyanines. The color changes are due to the formation of the mono- and dianions, (PcMO₂)^2- and (PcMO₂)^-, accompanied with transfer of electrons from oxygen atoms to the tetrapyrrol macrocycle.

Thallium(I) complexes of 2,3,7,8,12,13,17,18-octaethylporphyrin and 5,10,15,20-tetraphenylporphyrin are shown to have two thallium(I) ions per porphyrin ligand. Syntheses, spectroscopic characteristics (UV-vis, MS, NMR), chemistry, and an X-ray crystal structure of bis-thallium(I) porphyrins are presented.

The formation of a sitting-atop complex of a N-alkylporphyrin, containing a 6-hydroxyhexyl group, with Al³⁺ was studied in moist acetonitrile by equilibrium and kinetic measurements. A sandwich type of metalloporphyrin, where a metal ion binds two N-alkylporphyrins, appears to be formed under the conditions that porphyrins exist in excess over a metal ion. When a large excess of metal ion was used, a 1:1 type of sitting-atop complex of Al(III)N-alkylporphyrin was produced through formation of the sandwich type of Al(III)N-alkylporphyrin.

The fluorescence quenching of a Zn(II) porphyrin linked to Cu(I)catenates relative to a model compound without Cu(I) was attributed to energy transfer from the Zn(II) porphyrin to the metal-to-ligand charge transfer (MLCT) state of the Cu(I)(phenanthroline)₂ center at the core of the molecules. The similarity of the fluorescence spectra and fluorescence decays of a Zn(II) porphyrin linked to an Au(III) porphyrin, a Zn(II) porphyrin or a benzoate moiety through the catenate framework suggested that no fluorescence quenching by electron transfer to the Au(III) porphyrin occurred and that the copper(I) (phenanthroline)₂ center acts as an energy sink. The value of the critical distance for Förster type energy transfer, determined from spectral data is compatible with the observed rate constants for energy transfer and dimensions of the macrocycle. The multi-exponential nature of the fluorescence decay is attributed to the presence of different slowly interconverting conformations of the macrocycle to which the porphyrins are attached.

Four recently synthesized cationic zinc(II)-benzonaphthaporphyrazines 1–4 were studied in vitro and in vivo for their photodynamic therapy (PDT) effectivity. The photophysical measurements showed that in solution and in Cremophor micelles all examined compounds exhibit very high absorption intensity in the spectral range between 680 to 750 nm. The fluorescence emission for 3 and 4 was very well expressed in different media, as well as in cell culture. The dark toxicity examinations on invasive human bladder carcinoma cell line EJ did not show any traces of toxicity. The investigations connected with the detection of their phototoxic capacity on the same cell line demonstrated very promising results especially with photosensitizers 3 and 4. The in vivo studies with these two compounds demonstrating high cell-phototoxic effect were carried out against Lewis lung carcinoma in mice after incorporation in Cremophor micelles. The excitation was done at the respective maximum absorption wavelength for each of the sensitizers at a fluence rate of 380 mW cm^-2 and a fluence of 360 J cm^-2. The phototherapeutic effect was evaluated through macroscopic observations (tumour growth delay) and by electron microscopy detection. According to these approaches the best effect (including tumour destroyment) was detected after PDT treatment with the cationic tribenzonaphthoporphyrazinato-zinc(II) 3. Typical features of random, but not of programmed, cell death necrosis were observed.

Aggregation of 5,10,15,20-tetrakis(m-hydroxyphenyl)chlorin (m-THPC) is observed not to occur in methanol or in ethanol:polyethyleneglycol 300:water = 2:3:5 (v/v) in the concentration range of 0.46–73.4 × 10^-5M and 0.92–29.4 × 10^-5M, respectively. However, aggregation occurs for 4.59 × 10^-5M solutions in methanol–water mixtures for compositions >50% water (v/v). The Soret band broadens and ε_max decreases; λ_max shows a red shift, consistent with a J-type structure. Possible aggregate structures are considered based on the known hydrogen bonding patterns in crystalline solvates of the closely related 5,10,15,20-tetrakis(3,5-dihydroxyphenyl)porphyrin. Spectrophotometric titration of m-THPC in methanol–buffer mixtures gives apparent pK_a values of pK₃ = 3.45 and pK₄ = 1.45. The phenolic groups have pK_a = 10.0. Comparisons are made with the corresponding porphyrin and with literature values on related systems. Singlet oxygen chemistry. The photobleaching of bilirubin is shown to be accelerated fivefold in the presence of a 0.05 mol proportion of m-THPC. The accelerated reaction is slowed down in the presence of 2,5-dimethylfuran and of β-carotene, providing further evidence by chemical reaction for the ability of m-THPC to photogenerate singlet oxygen. The relevance of these observations to clinical usage is discussed briefly.