Journal of Porphyrins and Phthalocyanines

The effective 'one-pot' microwave-assisted synthesis of several substituted 5,10,15,20-tetraarylporphyrins is reported. The microwave-assisted insertion of five different transition metals into the 5,10,15,20-tetraphenylporphyrin, 5,10,15,20-tetrakis(4-chlorophenyl)porphyrin and 5,10,15,20-tetrakis(3-hydroxyphenyl)porphyrin core was also achieved with high yields. In addition to their simplicity, both these straightforward, experimental protocols were also characterized by extremely short reaction times and quite small quantities of solvents employed.

Non-covalent porphyrin dyads and triads containing N₃S porphyrin and RuN₄ porphyrin subunits were synthesized by treating meso-pyridyl-21-thiaporphyrin with RuTPP(CO)(EtOH) in toluene at refluxing temperature. The dyads and triads were characterized by various spectroscopic techniques and the properties were compared with the reported dyad containing N₄ and RuN₄ porphyrin subunits. The ¹H NMR study of dyads and triads indicated that the inner NH, β-heterocycle and meso-pyridyl protons of the 21-thiaporphyrin unit experienced large upfield shifts as compared to their corresponding monomeric meso-pyridyl-21-thiaporphyrins due to the ring current effect of RuTPP(CO) subunit. The singlet state photophysical properties of N₃S porphyrin subunit in dyads and triads showed 50-80% quenching of fluorescence as observed previously for N₄-RuN₄ dyad due to heavy ruthenium ion(s).

Two complexes of ruthenium(II) carbonyl tetraphenyl- and tetramesytilporphyrins were used as catalysts for epoxidation of olefins using metachloroperbenzoic acid and iodosylbenzene, as oxidants. Better results were obtained with the (TPP)RuCO catalyst in the presence of metachloroperbenzoic acid; however, iodosylbenzene showed higher yields than metachloroperbenzoic acid for some aromatic olefins. The effect of imidazole axial base was also investigated. Two different pathways are proposed based on these two oxygen atom transfer agents.

A series of tris[2,3,9,10,16,17,23,24-octakis(octyloxy)phthalocyaninato] rare earth(III) complexes M₂[Pc(OC₈H₁₇)₈]₃ [M = Eu, Gd, Y, Lu] has been prepared by the reaction of corresponding bis[2,3,9,10,16,17,23,24-octakis(octyloxy)phthalocyaninato] rare earth complexes with M(acac)₃·nH₂O in refluxing 1,2,4-trichlorobenzene. These liquid crystalline sandwich, triple-decker complexes were characterized by elemental analysis and various spectroscopic methods including ¹H NMR, UV-vis, IR and mass spectroscopies. Their liquid crystal phase transition behavior was studied by Polarized Optical Microscope, Differential Scanning Calorimeter and X-ray diffraction. The complexes, with octyloxy attached as side chains, showed rectangular columnar liquid crystal phases in a liquid crystal temperature range between 83 and 305°C. In addition to the rare earth contraction, both the transition temperature and the wide temperature range of the mesophase show a slight but obvious trend to decrease, respectively, in the same order. In contrast, the molecular packing of these complexes as revealed by X-ray diffraction was found to be almost independent of the ionic size of the central rare earth.

This work reports on the microwave synthesis of tetrasulfonated tin phthalocyanine and tetrasulfonated tin α,β,γ-tetrabenzcorrole. The latter was only formed at low ratios (<1:8) of 4-sulfophthalic acid to urea. Both complexes are aggregated in aqueous media, but can be partly or fully disaggregated by the addition of Triton X-100. The α,β,γ-tetrabenzcorrole complex has lower triplet life times and yields, while the binding constant and quenching (of bovine serum albumin) constant are lower for α,β,γ-tetrabenzcorrole compared to tetrasulfonated tin phthalocyanine.

Metallophthalocyanines have been assembled in MCM-41 channels by microwave irradiation of a mixture of ion-exchanged MCM-41, and 1,2-dicyanobenzene under solvent-free conditions in a considerably short period of time. The prepared materials have been characterized by diffuse reflectance UV-vis spectroscopy, X-ray powder diffraction XRD, differential scanning calorimetry DSC, and Brunauer-Emmett-Teller BET nitrogen adsorption desorption techniques. The X-ray diffraction and Brunauer-Emmett-Teller results showed that the textural properties of MCM-41 were preserved during microwave irradiation.

The inhibition of the formation of J-aggregates of meso-tetra(4-sulfonatophenyl)-porphyrin (H₄TPPS) by urea is investigated spectroscopically by absorbance, fluorescence, and fluorescence lifetime techniques. In 8 M urea at pH 2 with 0.1 M NaCl, diacid TPPS (H₄TPPS) exists as a monomer up to 75 μM H₄TPPS where the absorbance is linearly dependent on porphyrin concentration. The extinction coefficient of monomeric H₄TPPS in 8 M urea at pH 2 with 0.1 M NaCl at 438 nm is 4.43 × 10⁵M^-1.cm^-1. No aggregation peaks at 491 nm and 708 nm are found in the 0.5-75 μM concentration range. Aggregated H₄TPPS (10 μM) molecules in pH 2 buffer dissociate to monomers when the temperature is raised to 65°C. In D₂O at pH 2, no aggregation is observed. These spectral observations suggest that the H₄TPPS aggregation involves intermolecular hydrogen bonding.

Magnesium and zinc complexes of azaphthalocyanines (AzaPc) with eight peripheral aromatic (phenyl) or heteroaromatic (pyridyl, thienyl, furyl) substituents are studied from the point of view of their singlet oxygen (Φ_Δ) and fluorescence (Φ_F) quantum yields, and UV-vis absorption spectra. Zn complexes have higher Φ_Δ than Mg complexes by a factor of two, whereas the Mg complexes have higher Φ_F than Zn complexes, also by a factor of two. Thienyl AzaPc have the highest Φ_Δ among all studied substances (0.635 for Zn complex) followed by phenyl and pyridyl derivatives. The order of Φ_F values is then reversed - the highest values were reached for pyridyl and phenyl derivatives followed by thienyl AzaPc. Both furyl AzaPc were unstable towards light and decomposed giving very low Φ_Δ and Φ_F. The Q-bands of the furyl and thienyl AzaPc were red-shifted for approx. 20 nm compared to phenyl and pyridyl derivatives indicating lower sterical hindrance between five-membered rings and thus allowing better conjugation of π-systems. Pyridyl-, thienyl- and furyl-substituted pyrazino[2,3-b]pyrazine-2,3-dicarbonitriles were also prepared but decomposed during attempted cyclotetramerizations.

The association behavior of tetrakis(N,N',N″,N‴-tetramethyltetra-3,4-pridino)porphyrazine cobalt(II) ([Co(II)3,4-TMTPPA]⁴⁺) was investigated in aqueous solution at 25°C and various ionic strengths using optical absorption and resonance light scattering spectroscopies. The results show that [Co(II)3,4-TMTPPA]⁴⁺ does not have any affinity for aggregation due to increasing salt concentration and exists as the monomer form even in homogeneous aqueous solutions at high ionic strengths (more than 1 M concentration of NaCl). The interaction of [Co(II)3,4-TMTPPA]⁴⁺ with calf thymus DNA in aqueous solution has also been studied in 5 mM phosphate buffer pH 7.2, by optical absorption and resonance light scattering spectroscopies, and thermal denaturation experiments. The appearance of hypochromicity of less than 10% and a bathochromic shift of Δλ ≤ 8 nm in the UV-vis spectra of [Co(II)3,4-TMTPPA]⁴⁺, an increase in the thermal melting point of DNA, and no enhancement in resonance light scattering spectra of porphyrazine due to interaction with DNA, indicates the minor outside-groove binding mode without any stack aggregate formation. The thermodynamics of the binding of [Co(II)3,4-TMTPPA]⁴⁺-DNA has also been studied. The binding constant (K) was obtained by analysis of optical absorption spectra of the above-mentioned complex at various DNA concentrations using SQUAD software. The value of K was estimated as 1.31 × 10⁶ ± 1.174 M^-1 at 25°C. The thermodynamic parameters were calculated by van't Hoff equation. The enthalpy and entropy changes were 48.77 ± 2.50 kJ.mol^-1 and 280.77 ± 9.62 J.mol^-1.K^-1 at 25°C, respectively. The results indicate that the process is entropy driven suggesting that hydrophobic interactions are the main driving forces for complex formation. The increase of ionic strength due to the addition of NaCl, destabilized porphyrazine-DNA complexes, which indicates the competition of Na⁺ ions with porphyrazine complexes for occupation of minor groove binding sites.