Journal of Porphyrins and Phthalocyanines

Peripheral and non-peripheral tetra(13,17-dioxanonacosane-15-hydroxy) substituted metal free-, Ni(II) and Zn(II) phthalocyanines have been synthesized from the corresponding phthalonitrile derivatives in the presence of the anhydrous metal salt (NiCl₂ and Zn(OOCCH₃)₂) or a strong organic base. The new compounds have been characterised by elemental analyses, IR, NMR, mass spectra and electronic spectroscopy. The mesogenic properties of these new materials were studied by differential scanning calorimetry (DSC), optical polarised microscopy and X-ray investigations. The effects of peripheral or non-peripheral substitution of (13,17-dioxanonacosane-15-hydroxy) to the phthalocyanine ring are also investigated. It is found out that non-peripheral substituted phthalocyanine derivatives (4a-c) are liquid at room temperature whereas, peripheral substituted phthalocyanine derivatives (7a-c) exhibit ordered discotic hexagonal columnar mesophases (Col_h) at room temperature.

Lanthanide(III) complexes with acetylacetonate and meso-tetraalkyltetrabenzoporphyrin (TATBP) having the general formula Ln(TATBP)acac (where Ln = Tb, Dy, Ho, Er, Tm, Yb; A = C₁₂H₂₅; Hacac = acetylacetone) are reported. These compexes have been studied by elemental analyses, ultraviolet visible spectra, infrared spectra, molar conductance, ¹H NMR spectra, cyclic voltammetry, surface photovoltage spectroscopy (SPS), and luminescence spectroscopy. The infrared spectral bands of the ligand and complexes were assigned. In dimethylformamide (DMF), 0.1 M tetrabutylammonium perchlorate (TBAP), the synthesized TATBP exhibit two one-electron reversible redox reactions, and Ln(TATBP)acac shows three redox reactions respectively, within the accessible potential window of the solvent. The absorption bands of the complexes appear in the range 431-433 (Soret band), 578-580 (Q band) and 627-631 (Q band) nm. The photovoltaic properties and charge transfer process of these compounds were investigated by surface photovoltage spectroscopy (SPS) and electric-field-induced surface photovoltage spectroscopy (EFISPS) techniques, which reveal that the ligand TATBP and the complexes Er(TATBP)acac are p-type semiconductors. The spectral bands of TATBP correspond to π → π* transitions. Quantum yields of the S₁ → S₀ fluorescence are in the region 0.25-0.27 and the fluorescence lifetimes are in the region 0.014-0.022 ms at room temperature. The phosphorescence bands of the complex at 77 K appears 714 nm.

The degradation rate constants of the tetracations 5,10,15,20-tetrakis(N-methylpyridinium-4-yl)porphyrin and 5,10,15,20-tetrakis(N,N,N-trimethylanilinium-4-yl)porphyrin as well as their manganese(III) complexes toward the oxidants H₂O₂, t-BuOOH, and NaOCl were measured at various pH values, I = 0.2 M and 30°C. The free-base and manganese porphyrins showed high structural stabilities toward H₂O₂ and t-BuOOH in strong acidic solutions and their degradation constants were on the order of 10^-6 min^-1 or no porphyrin degradation was observed at all. As the pH increased, their stability towards these peroxides decreased and in basic solutions, they showed almost no stability toward H₂O₂ and a moderate stability toward t-BuOOH. When NaOCl was employed as the oxidant, they showed only moderate stabilities in strong basic solutions and almost no stability in slightly basic, neutral or acidic solutions. The degradation rate constants in the presence of NaOCl in strong basic solutions varied from 10^-2 min^-1 to 10^-4 min^-1.

A new route to the synthesis of 4-chloro-5-alkyl-phthalonitrile derivatives was shown by the displacement reaction of 4,5-dichloro-phthalonitrile and diethylmalonate, a CH-acidic precursor, in the presence of K₂CO₃. Cyclotetramerization of 1-chloro-3,4-dicyano-6-(1,1-dicarbethoxy-methyl)benzene and the metal salt without any solvent gave the corresponding metallophthalocyanines (M = Co, CuorPd). Transesterification occurred when the reaction was carried out in hexanol in the presence of DBU to obtain the metal-free derivative. Treatment of 1-chloro-3,4-dicyano-6-(1,1-dicarbethoxy-methyl)benzene with sodium ethoxide at ambient temperature and further acidification resulted in 2,9,16,23-tetra(carboxymethyl)-3,10,17,24-tetrachloro-phthalocyaninatopalladium(II) with partial decarboxylation. Its electronic spectrum in aqueous solution indicated no appreciable change over a pH range from 7 to 12.

Metal substituted octachloro-, hexadecachloro- and tetranitrophthalocyanine were synthesized by exposure to microwave irradiation under solvent free and reflux conditions and the products were purified by a new route.

Adjacent phthalocyanines with a binaphthalo backbone and phenoxy substituents were synthesized and their photochemical properties were investigated. The adjacent phthalocyanines are the binaphthalophthalocyanines, with the phenoxy, 4-tert-butylphenoxy and the sulfophenoxy substituents, respectively and bis-binaphthalophthalocyanine which has an extended π conjugation system and larger singlet oxygen quantum yield compared to the other compounds. The presence of the phenoxy substituents as well as the binaphthalo bridge does not cause a marked difference on the fluorescing properties of these complexes when compared to zinc phthalocyanine. The binaphthalo backbone allowed the molecules to photoswitch during photolysis affording them very high photostability.

The selective meso-monobromination of 5,15-diarylporphyrins is difficult to achieve and extensive chromatography is required to obtain pure products. A sequence of (i) dibromination, (ii) selective monoinsertion of Pd(dppe) (dppe = 1,2-bis(diphenylphosphino)ethane) and (iii) hydrodepalladation using methanolic base affords pure monobromoporphyrins in typically ≥ 60% overall yield without isolation of the organopalladium porphyrin. Monobromo derivatives of even highly lipophilic 5,15-diarylporphyrins are thus readily available without tedious, expensive and environmentally undesirable chromatography.

A way of anchoring unsymmetrical phthalocyaninato-metal complexes (metal ion: zinc and ruthenium) is described. The synthesis and characterization of these complexes are presented. In case of the zinc complex, the obtained product is an aggregate, while only the monomer is obtained in the case of the ruthenium derivative. Both complexes could be attached onto the TiO₂ surface by using the reported method. Both dyes are expected to form monolayers with dye molecules standing on the surface of nano-structured TiO₂, forming higher-order aggregates with the zinc but not with the ruthenium complex. A highest monochromatic incident photo-to-current conversion efficiency (IPCE) of 1.6% at 690 nm was obtained for a solar cell based on the Pc-Zn sensitized nano-structured TiO₂ electrode, while an IPCE of 23% at 630 nm was obtained for the Pc-Ru sensitized electrode. Overall conversion efficiencies (η) at a simulated AM 1.5 (100 W.m^-2) of 0.03% and 0.40% for the zinc and ruthenium complexes were achieved, respectively. The difference in efficiencies could be due to the formation of face-to-face aggregation in the former case. This work shows that the ruthenium complex, with two axial methylpyridine ligands, does not form aggregates in solution nor on the surface of TiO₂, making it possible for further construction of supramolecular systems with such types of phthalocyanine.

Electrochemical and spectroelectrochemical studies are presented for nine copper corroles with electron-withdrawing or electron-donating substituents on the three meso-phenyl rings of the compounds or on the eight β-pyrrole positions of the macrocycle. Up to three reversible oxidations can be seen for each Cu(III) corrole in CH₂Cl₂ containing 0.1 M TBAP. Unlike the case of (OEC)Cu, no dimer is electrochemically detected upon the first oxidation of these compounds at room temperature. However, a dimer forms at low temperature (< -50°C) for compounds having strong electron-donating groups. Two reductions are observed for all nine corroles at low temperature in CH₂Cl₂, 0.1 M TBAP, but only one reduction is detected at room temperature for four of these compounds which have weak electron-withdrawing or electron-donating groups. The neutral, reduced or oxidized Cu corroles were also characterized by thin-layer UV-visible spectroelectrochemistry and ESR. The resulting data indicates that eight of the nine neutral complexes contain a Cu(III) center while only one complex, [Br₈(C₆F₅)₃Cor]Cu, exists in its Cu(II) form in CH₂Cl₂ containing 0.2 M TBAP.