Journal of Porphyrins and Phthalocyanines

Chlorophyll (Chl) and bacteriochlorophyll (BChl) pigments, which are crucial cyclic tetrapyrroles in photosynthesis, generally have a chiral center in their exo-cyclic five-membered E-ring. Although $S$-epimers (primed-type) of (B)Chl pigments are rarely present in photosynthetic organisms, they play key roles in photosynthetic reaction center complexes. The epimerization mechanism of (B)Chl pigments in vivo has not been unraveled. The structural effects on the physicochemical properties of (B)Chl epimerization reactions provide useful information to tackle this question. We analyzed epimerization of three pigments, BChl $a$, Chl $a$, and 3-acetyl Chl $a$, to elucidate the structural factors that are responsible for epimerization reactions. We compared the epimerization kinetics of the three pigments and concluded that the bacteriochlorin skeleton (7,8,17,18-tetrahydroporphyrin) significantly retarded the epimerization kinetics. Thus, BChl $a$ exhibited slower epimerization kinetics than Chl $a$ in spite of the presence of the electron-withdrawing 3-acetyl group that accelerates epimerization. In contrast to the large structural effects of (B)Chl molecules on epimerization kinetics, the thermodynamic properties at equilibrium in the epimerization of the three pigments were barely influenced by their molecular structures. This study also demonstrates that a semi-synthetic pigment, 3-acetyl Chl $a$, is appropriate for comparative analyses of the structural effects of BChl $a$ and Chl $a$ on their physicochemical properties.

Surfactant-assisted self-assembly of porphyrin molecules in aqueous solutions sometimes leads to the formation of hybrid supramolecular structures with unusual photophysical properties resulting from the dipole–dipole interactions between the neighboring aromatic systems. The macrocycle orientation and interchromophore distance in such assemblies are determined by the dye–surfactant interactions, and hence, strongly depend on the molecular structure of both surfactant and porphyrin molecules. In this paper we studied the influence of the number and position of the peripheral alkyl chains of amphiphilic meso-aryl-substituted porphyrins on their aggregation behavior and intermolecular interactions with different surfactants in aqueous solutions. The studies revealed a crucial role of the local acidity on the micellar surface in the protolytic equilibrium of the porphyrin derivatives, as well as the influence of the macrocycle hydrophilic–lipophilic balance on its solubilization site within a micellar system. These findings enable prediction of the photophysical properties of amphiphilic porphyrin derivatives in the presence of different solubilizing agents and membrane-mimetic systems, and hence, selection the most suitable drug delivery systems for the novel amphiphilic porphyrin-based photosensitizers.

In this Part 1 of our two part study, 1D-linear oligomeric phthalocyanine zinc(II) with fully annulated (fused) phthalocyanine macrocycles are described. By semi-empirical and DFT computational methods the UV-vis and near infrared spectra, including energy gaps, are thoroughly evaluated. The long-wavelength Q band of the oligophthalocyanines is compared with the long wavelength absorption band of analogous oligoacenes consisting of annulated benzene rings. In addition, graphene nanoribbons are considered. The aromaticity is especially interesting when considering Clar’s rule. Therefore it is the aim to get information about the extent of $\pi$-electron delocalization in linear or semi-linear systems. Finally, the results of linear oligophthalocyanines are extrapolated to estimate the energy gap of 1D linear polyphthalocyanine by DFT, and the result is compared to the DFT calculation of the periodic structure with a plane-wave basis set. Part 2 will describe non-linear oligo- and two-dimensional polyphthalocyanines.

The practical potential of petroleum porphyrins still remains underestimated because of the absence of satisfactory simple and effective methods for their isolation in pure form. Our work aims to provide a solution for this problem via use of sulfuric acid loaded macroporous silica as an unprecedentedly effective adsorbent for deep petroporphyrin purification. Using chromatographic columns of reduced volume (4 cm³), a series of experiments on optimization of chromatographic conditions for silica-based sulfocationite were carried out. As a source of petroleum porphyrins, the primary concentrates of vanadyl porphyrins isolated on silica gel column from DMF extracts of heavy oil asphaltenes have been used. UV-vis and MALDI-TOF mass-spectrometric methods were employed for vanadyl porphyrin analysis and identification. We established that in a narrow range of water and acid content equal to $\sim$25 and $\sim$15 wt.%, respectively, silica-based sulfocationite becomes able to retain a bulk of polar petroleum components with exception of porphyrins, which thus leave the column first. A preparative-scale purification of vanadyl porphyrins by the sulfocationite-based method was performed for the first time and 18.5 mg of excellently pure product were obtained. Considering the extremely simple preparation and excellent purification performance of our novel sulfocationite, it could greatly facilitate access to high-purity petroleum porphyrins.

In this study two pairs of novel zinc-porphyrin complexes (ZnP1 ZnP2 ZnP3 and ZnP4) were synthesized as sensitizers for DSSC and their photophysical, computational studies and photovoltaic properties were investigated. Structures of proposed dyes are based on a molecular design that relies on donor/$\pi$-bridge/acceptor interactions. Compounds differ by anchoring mode to the titanium dioxide surface: ZnP2 and ZnP4 porphyrins possess carboxyl anchoring groups while ZnP1 and ZnP3 porphyrins have similar structure but without anchors and attached to the surface by isonicotinic acid ligands. All the zinc-porphyrin derivatives bear hexyloxy-chains at the para-positions of their phenyl rings and ZnP3 and ZnP4 contain 1,3,5-triazine fragments as efficient electron transfer bridges. Electron density distribution of the frontier molecular orbitals was calculated based on the density functional theory (DFT). The test DSSC was manufactured and its parameters were measured to compare the effectiveness of the proposed sensitizers. Our results reveal that dyes with an anchoring group directly in their structure demonstrated several times higher efficiency. The use of the triazine fragment proved effective for the introduction of acceptor substituents bearing anchor groups. As a result, the highest efficiency of 4.33% was achieved using the dye ZnP4.

In this study, the synthesis and characterization of novel 4-chloro-5-((2,3-dihydrobenzo-1,4-benzodioxin-2-yl)methoxy)phthalonitrile (1) and its peripherally octa-substituted Zn(II) (Pc-Zn), In(III) (PcInCI) and Mg(II) (Pc-Mg) phthalocyanine (Pc) derivatives are reported for the first time. FT-IR, elemental analysis, UV-vis, NMR and MS techniques were used for characterization studies of the compounds. Aggregation properties of the compounds were evaluated in DMF, DMSO and THF solvents in different concentrations, and the compounds did not tend to aggregate in these solvents. In addition, photophysicochemical properties such as fluorescence, photodegradation and singlet oxygen quantum yield of the compounds were examined in DMSO, DMF and THF solvents to show the potential use of these novel compounds as photosensitizers for photodynamic therapy (PDT). The effects of zinc, indium and magnesium metals, octa substitutions in peripheral positions and different types of solvents on photophysicochemical properties were investigated. The singlet oxygen quantum yield values of compounds ranged from 0.27 to 0.77 in different solvents. As a result of the photophysicochemical properties, these compounds can be considered as potential candidates for PDT, applications.

We have synthesized a novel series of four flying-seed-like liquid crystals (1Ph-PhO)₄PcM [5-M: M = Co (5-Co), Ni (5-Ni), Cu (5-Cu) and Zn (5-Zn)] which are based on a phthalocyanine core having peripheral bulky groups without long alkyl chains, in order to clarify the precise mechanism inducing their mesomorphism. For comparison, we have also synthesized a long alkyl-chain-substituted liquid crystal ($m-$C${}_{20}$OPhO)₈PcCu (7o) having the same phthalocyanine core with long alkyl chains in the periphery. Each of the derivatives 5-M and 7o showed a hexagonal ordered columnar (Col_ho) mesophase. Very interestingly, the halo positions in the X-ray diffraction patterns for the Col_ho mesophases of the flying-seed-like liquid crystals 5-M and the long alkyl-chain-substituted liquid crystal 7o were quite differently given at 5.7–6.2 Å and 4.6–4.7 Å, respectively. The halo positions of the representative derivatives 5-Cu and 7o having the same copper phthalocyanine (PcCu) core were finely measured at various temperatures by using the temperature-variable small angle X-ray diffraction technique. As the result, the derivatives 5-Cu and 7o showed sudden jumps of halo position from 5.5 to 5.7 Å and from 4.2 to 4.6 Å, respectively, at the phase transition from the crystalline phase to the liquid crystalline phase (Col_ho). This means that the volume changes ($\mathrm{\Delta }$V) corresponding to these halo jumps originate from two different kinds of mechanisms by sudden free rotation of the bulky substituents and by sudden melting of the long alkyl chains. Thus, in this work we have unambiguously clarified these two different mechanisms inducing mesomorphism.

In this work, metal free, zinc and copper tetraphenyl porphyrin thin films were employed as substrates to study their interaction with glycine, serine, glutamate, lysine and argynine amino acids in order to investigate the effect of the metallic center and the amino acid characteristics in the adsorption phenomena. The amount of amino acid adsorbed on the films was quantified by using the Ruhemann method. Adsorption isotherms were obtained and analyzed in order to predict the adsorption mechanism for each case. In addition, the morphology of the films was investigated before and after the amino acid immersion by using scanning electron and atomic force microscopies. On the other hand, dynamic contact angle measurements were performed to monitor the spreading phenomena and changes in the hydrophobic nature of the surfaces after the amino acid interaction. From the results, it was observed that the largest deposited amino acid on all three surfaces corresponded to the positively charged compounds, while serine was the lowest adsorbed amino acid in all cases. These results can be attributed to electronic interactions between the amino acids’ lateral chains and the electronic $\pi$ distribution of the porphyrin macrocycle ring, and they provide important information regarding the amino acid selectivity of adsorption on tetraphenyl porphyrin films.

The optical limiting properties of crown-ether-substituted scandium(III) phthalocyaninate complexes, bis-tetra-15-crown-5-phthalocyaninates Sc[(15C5)₄Pc]${}_2^{•0}$ (I) and Sc[(15C5)₄Pc]${}_2^{-}$ (Ia), together with monophthalocyaninate [(15C5)₄Pc]Sc(OAc) (II) were measured by using the Z-scan technique (532 nm laser and pulse rate of 10 ns). It was revealed that expansion of the $\pi$-system on moving from the monomeric Sc complex II to sandwich compound I and changing the electronic state of the sandwich compound from the anionic Ia species to the neutral radical I improves the optical limiting properties. The Im[${\chi }^{(3)}$] values obtained lie in the 10${}^{-12}$–10${}^{-10}$ esu range that is consistent with those reported previously for other organic chromophores. The crystal structure of sandwich Sc(III) complex I was elucidated by means of single-crystal X-ray diffraction analysis and was used to guide a series of theoretical calculations. It was demonstrated that the application of simplified time-dependent density functional theory (sTD-DFT) calculations can provide reasonably accurate predictions for compounds of this type when the geometries of the complexes are clearly defined.