Journal of Porphyrins and Phthalocyanines

Electron-transfer reaction of the newly synthesized light harvesting pentad composed of silicon phthalocyanine (SiPc) that is connected with two fullerene C₆₀ and two azobenzene units to form SiPc-(azobenzene)₂-(C₆₀)₂ pentad has been studied by laser flash photolysis and other complementary techniques. This combination between SiPc, azobenzene and C₆₀ in the examined SiPc-(azobenzene)₂-(C₆₀)₂ pentad leads to strong light absorption over the whole visible spectrum. Photoexcitation of the pentad results in rapid formation of the charge-separated state by photoinduced electron transfer from the singlet-excited state of the SiPc moiety to the C₆₀ moiety. The charge-separated state has a lifetime of 2.50 ns in benzonitrile.

The reaction of axial coordination of imidazole derivatives by (X)CrTPP in amphiprotic media was studied. The reaction includes two stages: consecutive substitution of the two alcohols molecules, first in the outer coordination sphere, and then in the inner sphere. For the reaction of the intrasphere substitution the solvolytic associative-dissociative mechanism has been found. The molecule of (chloro)chromium(III) porphyrin and its derivatives have been studied by density functional theory (DFT) computations utilizing the B3LYP hybrid method.

A convenient and regioselective synthesis of porphyrin diarylthiazoles is reported via the reactions of alkynyl(aryl)iodonium tosylates and porphyrin thioamides. Among the synthesized porphyrin diarylthiazoles, compounds 6d and 6f have shown significant interactions with ctDNA and exhibited efficient DNA photocleavage.

A homologous series of the phthalocyanine-fullerene dyads, C_n-PcM(OFbaC₆₀) (n = 6, 8, 10, 12; M = Cu, Ni, Co: 3a–3f) have been synthesized to obtain homeotropic alignment at rt and investigate the effects of spacer chain length (n = 6, 8, 10, 12) and central metal (M = Cu, Ni, Co) on the mesomorphism. Interestingly, the shorter-spacer-substituted (n = 6, 8; M = Cu) dyads 3a and 3b showed a hexagonal columnar mesophase (Col_h), whereas the longer-spacer-substituted (n = 10, 12; M = Cu, Ni, Co) dyads 3c–3f showed a tetragonal columnar mesophase (Col_tet). Moreover, each of the homologs 3a–3e shows perfect homeotropic alignment in both the Col_h and Col_tet mesophases at rt. More interestingly, these columnar mesophases gave a very unique XRD reflection peak denoted as Peak H in a very small angle region of 0.8 < 2θ < 2.0 degree. We have established at the first time from our developed two new XRD sample preparation techniques that the Peak H is due to the helical structure of fullerenes around columns formed by one-dimensionally stacked Pc cores. 1D nano array structure of donor and acceptor between two electrodes is recently proposed to obtain higher photoelectric conversion efficiency for organic thin film solar cells. This 1D nano array structure is almost compatible with the present homeotropically aligned Pc-C₆₀ dyads 3a–3f between two glass plates. Hence, these novel Pc-C₆₀ dyads 3a–3f may be very suitable to organic thin film solar cells.

The reaction of the starting materials [Co^II(Porph)] (Porph = α,α,α,α-tetrakis(o-pivalamidophenyl)porphyrin (TpivPP) and the meso-tetraphenylporphyrin (TPP)) with an excess of 4,4′-bipyridine in chlorobenzene leads to the creation of two cobalt(II) derivatives: [Co^II(α,β,α,β-TpivPP)(4,4′-bpy)₂]·C₆H₅Cl·C₆H₁₄(1) and [Co^II(TPP)(4,4′-bpy)₂]·2bpy(2). These compounds have been characterized by UV-vis, IR, ¹H NMR and MALDI-TOF spectroscopy. The proton NMR spectra of (1) and (2) clearly indicated that these derivatives are paramagnetic while the UV-vis data confirmed creation of a new six-coordinated or penta-coordinated Co(II)-meso-porphyrin complexes by displaying red shifted Soret bands. The determined X-ray structures of (1) and (2) show that in the solid state these species are considered as coordination polymers which consist of 1D chains of alternating [Co^II(Porph)] and 4,4′-bipyridine molecules located at the axial positions of the cobalt(II) coordination sphere. The coordination geometry of Co(II) in (1) and (2) is octahedral; the porphyrin (TpivPP or TPP) acts as a tetradentate chelating ligand with four nitrogen atoms from the pyrrole moieties occupying the equatorial positions along the porphyrin core. The N-donor atoms of the 4,4′-bipyridine create the axial ligands. It is noteworthy that for complex (1) the starting porphyrin is the α,α,α,α-TpivPP atropisomer but the final coordination polymer contains the α,β,α,β-TpivPP conformer.

The selective oxidation of sulfides with hydrogen peroxide to give sulfoxides was carried out in aqueous solution by water-soluble manganese porphyrin as mimics of cytochrome P450-like catalyst. Different factors that influencing the selective oxidation of sulfides, for example, catalyst, amount of catalyst, solvent and reaction temperature were investigated. MnTE4PyP (meso-tetrakis(N-ethylpyridinium-4-yl) manganese porphyrin) was efficient and selective catalyst for oxidation of various sulfides. The reaction showed first-order dependence in both [sulfide] and [H₂O₂], and a fractional order respect to catalyst. Oxygen atom transfer mechanism involves high-valence intermediate was proposed, which was supported by kinetic orders and spectrophotometric evidences.

Three imidazolyl-appended porphyrins were synthesized and characterized by ¹H NMR, elemental analyses, MS and UV-vis spectra. Anticancer activities of porphyrins have been evaluated against cutaneous squamous cell carcinoma (A431 cells) in vitro. The results indicate that the porphyrins have high selective cytotoxicity towards A431 cells in the absence of light and improved phototoxic activity upon exposure to UV light. The yield of singlet oxygen generated by porphyrins were also evaluated by measuring the absorption decay of 1,3-diphenylisobenzofuran (DPBF) in DMF. The phototoxicities of porphyrins against A431 cells were enhanced along with the increase of singlet oxygen.

Demetalation kinetics of zinc chlorophyll derivative 1 possessing two formyl groups directly linked to the A- and B-rings of the chlorin macrocycle, which was synthesized from chlorophyll b, was examined under acidic conditions and compared with those of Zn chlorins 2 and 3 possessing a single formyl group in the A- and B-ring, respectively, as well as Zn chlorin 4 lacking any formyl group to unravel the substitution effects on demetalation properties of chlorophyllous pigments. Demetalation kinetics of diformylated Zn chlorin 1 was slower than those of monoformylated Zn chlorins 2 and 3, indicating that the effect of the electron-withdrawing formyl group on demetalation kinetics was amplified by introduction of two formyl groups to the chlorin macrocycle. High correlations were observed between demetalation rate constants of Zn chlorins 1–4 and the sum of Hammett σ parameters of the 3- and 7-substituents on the chlorin macrocycle, indicating that the combination of electron-withdrawing abilities of the substituents linked directly to the cyclic tetrapyrrole was responsible for demetalation properties of zinc chlorophyll derivatives.

Free base porphyrin in chloroform solution irradiated with focused laser beam, in an open Z-scan set-up, changed color from purple to green, which was associated with protonation of the porphyrin with protonic species from photodegradation of the solvent. Protonation is demonstrated as a simple means to improve the optical limiting performance of free base porphyrin nonlinear optical (NLO) materials.

The synthesis and spectral properties of the metal-free and the Mg complex derivatives of crown-substituted tetraquinoxalinoporphyrazine are described. Porphyrazine 4 and 5 have satisfactory solubility in chlorinated hydrocarbons, THF and toluene, but are practically insoluble in alcohols. Porphyrazine 5 generally did not show aggregation in CHCl₃ but aggregate in DMF.