Journal of Porphyrins and Phthalocyanines

An efficient route to meso-β doubly connected fused porphyrin dimers was developed. Synthesis of the dimers incorporated two successive C–C bond-forming steps selectively coupling unsubstituted meso- and β-positions. Using Cu(BF₄)₂ as an oxidant in nitromethane solvent, the radical coupling of Cu(II)-porphyrins occurred in high yield and without side-products, allowing chromatography-free purification. Efficient demetalation of the product yielded free-base derivatives and the possibility to incorporate other metals into the macrocycles. The absorption and electrochemical properties vary with the inserted metal, showing broad UV-visible-NIR absorption and multiple one-electron oxidations/reductions in a relatively narrow electrochemical window.

The dicobalt complex [Co₂(L²)] of a Schiff-base pyrrole macrocycle adopts a Pacman structure in solution and the solid state and shows much greater catalytic activity and selectivity for the four-electron oxygen reduction reaction (ORR) than the mononuclear cobalt phthalocyanine (CoPc) counterpart. Soft X-ray absorption spectroscopy (XAS) shows that the Co center in Co₂(L²) is of the same valence as mononuclear CoPc. However, the former complex shows higher unoccupied Co 3d density which is believed to be beneficial for electron transfers. Furthermore, the XAS data suggests that the crystal fields for Co₂(L²) and CoPc are different, and that an interaction remains between two Co atoms in Co₂(L²). DFT calculations imply that the sterically hindered, cofacial structure of the dicobalt complex is critical for the operation of the four-electron reaction pathway during the ORR.

Iron porphyrin and cobalt porphyrin were respectively modified on glassy carbon (GC) electrodes together with multiwalled carbon nanotubes (MWCNTs), and the modified electrodes were characterized by X-ray photoelectron spectroscopy (XPS). Their electrochemical performance for the reduction of oxygen (O₂), proton (H⁺) and carbon dioxide (CO₂) were respectively investigated and compared by cyclic voltammetry (CV). The results showed that iron porphyrin-MWCNT modified electrode always had a better performance than cobalt porphyrin-MWCNT modified electrode. It is proposed that iron porphyrin-MWCNT modified electrode will have promising application in electrochemical architectures like microbial fuel cells (MFCs) and microbial electrolysis cells (MECs) for its good biocompatibility, easy availability, as well as excellent electrochemical performance.

In our previous work, we could successfully synthesize the 1:1 phthalocyanine-fullerene (Pc-C₆₀) dyads, (OFbaC₆₀)PcCu(OCH₃)2, in very high yields (81 ~ 96%) by using Prato reaction. In this study, we have prepared novel Pc-C₆₀ dyads, (OFbaC₆₀)PcM (M = Co (a), Ni (b), Cu (c), metal free (d)) 3a–3d without the methoxy group. The target Pc-C₆₀ dyads 3a–3d could be successfully synthesized in good yields also by Prato reaction. It is surprising for us that removal of a very small methoxy group from the big (OFbaC₆₀)PcCu(OCH₃) molecule (2) significantly lowers the cp of (OFbaC₆₀)PcCu (3c) by about 70 °C in comparison with that of 2 having the methoxy group. Very interestingly, each of the novel dyads 3a–3d synthesized here shows perfect homeotropic alignment in the tetragonal columnar phase (Col_tet). Moreover, it is noteworthy that 3c and 3d show only one Col_tet.o mesophase having ordered stacking distance with perfect homeotropic alignment. Such simple phase transition can contribute to maintain stable performance in wide temperature range, when they will be applied to organic thin film solar cells.

It is known that among other applications porphyrin aggregates can be used in the detection of volatile organic compounds (VOC) and gases and vapors in general. However, the use of porphyrins for this purpose has been limited by the fact that usually the porphyrin and the polymer employed as a matrix are soluble in different media, such as polyvinyl alcohol and tetraphenylporphyrin, respectively. In this paper, we discuss how starting from stable aqueous solutions of hydrophobic porphyrins one can use the drop coating method to prepare polyvinyl alcohol polymer matrices containing porphyrin aggregates. The resulting solid films were characterized by optical techniques, and we have used UV-vis absorption spectroscopy to analyze how they interact with vapors of HCl, NO₂ and NH₃.

This work presents a complete vibrational analysis of iron [Fe(II) and Fe(III)] and nickel [Ni(II)] complexes with 5,10,15,20-tetraphenyl-21-oxaporphyrin [OTPPH] and 5,20-bis(p-tolyl)-10,15-diphenyl-21-oxaporphyrin [ODTDPPH]. In these porphyrins, a furan ring replaces one of the pyrrole rings. The six-coordinate (OTPP)Fe^IIICl₂ and (ODTDPP)Fe^IIICl₂ as well as the five-coordinate (OTPP)Fe^IICl and (OTPP)Ni^IICl complexes were investigated using experimental and theoretical methods. The experimental part of this work involved Fourier-transform absorption infrared (FT-IR), resonance Raman (RR), and electron absorption (UV-vis) measurements for all of the investigated complexes. In the theoretical section, optimized geometries and vibrational frequencies for model compounds are provided. The theoretical calculations were performed at the B3LYP level with the LANL2DZ basis set. Good agreement was achieved between the experimental and theoretical vibrational spectra. In addition, charge distributions (GAPT) and geometrical aromaticity indices (Bird's I₅ and HOMA) were calculated and discussed.

Two protoporphyrin derivatives were prepared by a facile method using inexpensive hemin as starting material. They were added to cigarette filters to reduce the carcinogenic tobacco specific N-nitroamines (TSNAs), especially toward NNK (4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone) and NNN (N-nitrosonornicotine) for environment protection and public health. The reduction level of TSNAs was reached to 37.6% from MSS, with greater reductions when more porphyrin was included in the filter. The decrease level for NNK by protoporphyrin derivatives is more effective than NNN. The interaction between protoporphyrin derivatives and TSNAs (NNK and NNN) were investigated by fluorescence spectra and UV-visible titration. The correlation coefficients were 0.978~0.997 and the binding constants was the scope from 1.26 × 10³ to 4.04 × 10⁴. The interaction mechanisms between protoporphyrin derivatives and, NNK and NNN are possibly the co-interaction of hydrogen bond binding and strong π–π stacking.

Iron(II) 2,3- and 3,4-tetrapyridinoporphyrazine complexes (2,3-PyD and 3,4-PyD) were synthesized and characterized as to their electrochemistry, UV-visible spectroelectrochemistry and catalytic properties towards the reductive dechlorination of 1,1-bis(4-chlorophenyl)-2,2,2-trichloroethane (p,p′-DDT) in pyridine, dimethyl sulfoxide (DMSO), N,N′-dimethylacetamide (DMA) and N,N′-dimethylformamide (DMF). These properties were compared with those of the unsubstituted iron(II) phthalocyanine ((Pc)Fe). Electrochemistry indicates that there are up to three reductions and one oxidation in the three investigated derivatives. The easiest reduction takes place for 3,4-PyD while the most difficult one occurs for (Pc)Fe in all of the solvents investigated. The first reduction is metal-centered corresponding to the formation of [P(-2)Fe(I)]^- while the second and third reductions are ring-centered leading stepwise to the generation of [P(-3)Fe(I)]^2- · and [P(-4)Fe(I)]^3-, where P = phthalocyanine or tetrapyridinoporphyrazine rings. Aggregation exists in the solutions of all three iron complexes and its extent depends upon the nature and concentration of the iron compounds and the binding property of each solvent. The order of the extent of aggregation for the three iron derivatives is 3,4-PyD > 2,3-PyD > (Pc)Fe. Stronger binding solvents such as pyridine and DMSO do not favor the aggregation. The singly and doubly reduced species of investigated complexes, [P(-2)Fe(I)]^- and [P(-3)Fe(I)]^2- ·, are active in DDT reductive dechlorination, the latter of which has better catalytic performance. As a result, three products, 1,1-bis(4-chlorophenyl)-2,2-dichloroethane (p,p′-DDD), 1,1-bis(4-chlorophenyl)-2,2-dichloroethylene (p,p′-DDE), and 1,1-bis(4-chlorophenyl)-2-chloroethylene (p,p′-DDMU), were obtained after the dechlorination of DDT catalyzed by each iron complex. The increasing order of catalytic performance is 3,4-PyD < 2,3-PyD < (Pc)Fe in pyridine, which is superior to DMSO and DMA for the DDT dechlorination reaction. An overall electrocatalytic mechanism is proposed for DDT reductive degradation based on the electrochemical and UV-visible spectroelectrochemical results.