Journal of Porphyrins and Phthalocyanines

A series of four new porphyrin-rhodanine dyads were synthesized having the rhodanine acetic acid group either at the meso- or the pyrrole-β position of a free-base/zinc porphyrin. These dyads were fully characterized by UV-visible, ¹H NMR, MALDI-MS and fluorescence spectroscopies and cyclic voltammetry. Both the Soret and Q-bands were red-shifted in the case of pyrrole-β substituted dyads. The redox potentials of all four dyads were altered in comparison with their individual constituents. The dyads were tested in dye sensitized solar cells and the zinc metalated dyads gave a better performance in comparison with the corresponding free-base dyads.

A facile synthesis of free-base and metalated stilbene-linked porphyrin dimers via the Wittig reaction is reported. 5-(4-chloromethylphenyl)-10,15,20-triphenyl porphyrin was prepared by direct chloromethylation of meso-tetraphenylporphyrin as the useful precursor for both the porphyrin-derived Wittig reagent and the monoformylporphyrin. It was found that the stilbene-linked porphyrin dimers were formed with a remarkable sterochemical preference in the cis-form. Their absorption and emission spectra were measured.

In this study we report the preparation, physical characterization and electrochemistry of peripherally functionalized substituted ionophore double-decker lanthanide phthalocyanines, lanthanide bis-[(4,4″,4″,4‴)-tetrakis-(6-hydroxyhexylthio)phthalocyaninates], {M[Pc(S-C₆H₁₃OH)₄]₂} (M = Pr^III, Yb^III, and Lu^III). All benzenes on the double-decker phthalocyanines are functionalized with hydroxyhexylsulfanyl moieties for potential use as metal ion binding and surface anchors. The double-decker phthalocyanines synthesized from the anhydrous metal salts {Ln(acac)₃} and the corresponding 4-(6-hydroxyhexylthio)-1,2-dicyanobenzene exhibit ion-specific optical changes in the presence of Ag⁺ and Pd²⁺. Thio donors of the complexes coordinate to Ag⁺ and Pd²⁺ to give 4:1 metal-phthalocyanine complexes. Newly synthesized lanthanide double-decker phthalocyanines are soluble in methanol (MeOH), ethanol (EtOH), tetrahydrofuran (THF), dimethylformamide (DMF), dimethylsulfoxide (DMSO), chloronapthalene, quinoline and less soluble in i-PrOH and acetonitrile. Electrochemical studies reveal that all lanthanide-base complexes undergo ligand-based redox processes. The smaller HOMO-LUMO gaps of the complexes indicate the existence of strong π-orbital interactions between the rings of the sandwich. The newly synthesized compounds have been characterized by elemental analysis, FTIR, ¹H and ¹³C NMR, MS (ESI and Maldi-TOF), UV-vis and EPR spectral data.

Mass spectrometric studies of the composition of the gaseous phase for solid compounds of hexadecafluorinated phthalocyanines MPcF₁₆, M = Cu, Zn, VO and their unsubstituted MPc analogs were performed in a temperature range up to 600°C. It has been shown that phthalocyanines sublime into the form of monomers without thermal decomposition. The vapor pressure of these phthalocyanines was determined as a function of temperature by the Knudsen effusion method, in which the rate of effusion of the equilibrium vapor through a small orifice was measured. The thermodynamic parameters of the sublimation process for phthalocyanines were calculated.

The synthesis, spectral and photophysical properties including fluorescence quenching of the following octa-substituted oxotitanium phthalocyanines are reported: 2,3,9,10,16,17,23,24-octaphenoxyphthalocyaninato titanium(IV) oxide, 2,3,9,10,16,17,23,24-[octakis(4-t-butylphenoxyphthalocyaninato)]titanium(IV) oxide, 2,3,9,10,16,17,23,24-{octakis[(4-benzyloxy)phenoxy]phthalocyaninato}titanium(IV) oxide and 2,3,9,10,16,17,23,24-octaphenylthiophthalocyaninato titanium(IV) oxide. The complexes are characterized by ¹H NMR, IR and UV-vis spectroscopies. Their photophysical properties are presented where moderate fluorescence quantum yields (0.14-0.19) and lifetimes were determined. Varied triplet quantum yields were obtained and the triplet lifetimes (40-100 μs) were short.

A bis(terpyridine)ruthenium(II) complex ([Ru]²⁺) was covalently connected via a floppy -OCH₂CH₂O- spacer to the free-base porphyrin (H) or zinc(II) porphyrin (Zn) or both, to obtain dyads ([HRu]²⁺, [ZnRu]²⁺) and triads ([HRuH]²⁺, [ZnRuH]²⁺, [ZnRuZn]²⁺). These compounds have been fully characterized by MALDI, UV-vis, ¹H NMR (1D and ¹H-¹H COSY) spectroscopies, and also by the cyclic and differential pulse voltammetric techniques. Absorption spectroscopy of these newly synthesized compounds shows that significant exciton coupling exists in non-polar solvents (cyclohexane and toluene) between the porphyrin ring and the bis(terpyridine)ruthenium(II) complex. Upon excitation within the Soret band of [HRu]²⁺/[HRuH]²⁺, free-base porphyrin fluorescence was found to be strongly quenched in non-polar and weakly quenched in polar solvents, probably due to ‘singlet-triplet’ energy transfer from the free-base porphyrin to the [Ru]²⁺ complex. Whereas, in [ZnRu]²⁺/[ZnRuZn]²⁺, zinc(II) porphyrin fluorescence was quantitatively and reasonably quenched in non-polar and polar solvents, respectively by mainly electron transfer from the zinc(II) porphyrin to the [Ru]²⁺ complex. The solvent plays a crucial role in the photophysical properties of these compounds, since the energy of the triplet metal-to-ligand charge-transfer (³MLCT) excited state is influenced by the polarity of the medium. Finally, [ZnRuH]²⁺ exhibits the combined fluorescence properties of [HRu]²⁺ and [ZnRu]²⁺ but the observed additional quenching in non-polar solvents for the zinc(II) porphyrin component is explained by energy transfer from the zinc(II) porphyrin to the free-base porphyrin and/or the bis(terpyridine)ruthenium(II) complex.

A new zinc phthalocyanine peripherally substituted with methacrylic groups was synthesized to be employed as a functional monomer in the formation of molecularly imprinted polymers as nucleoside receptors. The binding affinity and selectivity of the synthesized phthalocyanine towards nucleosides were evaluated by UV-vis titration experiments in CH₂Cl₂ at 298 K. The binding constant (K_a) and Gibbs free energy changes (-ΔG₀) were calculated according to the modified Benesi-Hildebrand equation. Binding experiments showed that K_a of phthalocyanine with tri-O-acetyladenosine (TOAA) is 1.35 × 10⁴, 500 times that of phthalocyanine with tri-O-acetyluridine (TOAU), indicating a high selectivity of the synthesized phthalocyanine derivative.

The dehalogenation activities of cobalt porphyrin catalysts with dendritic phenylazomethine units on the meso-positions were studied. Tetrachloroethylene was used as a substrate. By applying samarium iodide as a reducing agent, the tetrachloroethylene conversion into trichloroethylene and dichloroethylene was observed in the presence of the cobalt porphyrin catalyst. The turnover frequency was 1.70 min⁻¹ when a cobalt porphyrin connected with dendritic phenylazomethines (3 generations) was employed as the catalyst. While the turnover frequency was almost the same as that for a non-dendritic porphyrin catalyst (1.57 min⁻¹ by cobalt tetraphenylporphyrin), a significant increase in the turnover frequency was observed when samarium (3.43 min⁻¹) or terbium trifluoromethane sulfonate (8.57 min⁻¹) binds to the phenylazomethine units of the dendrimer. Because these metal ions (Sm³⁺ or Tb³⁺) are positioned in a space between the encapsulated catalytic center and the solvent phase, they can act as electron mediators that relay electrons from the reducing agent (samarium iodide) to the catalytic center (cobalt porphyrin). This facile electron transfer would provide an enhancement in the catalytic activity for the tetrachloroethylene reduction leading to dehalogenation.

This paper deals with the synthesis of a new hybrid meso-tetraarylporphyrin-cardanol with the cardanol bearing an unsaturated chain. Cardanol is a renewable, natural, widely available and relatively low-cost material obtained as a by-product of the cashew industry which provides cashew kernels for edible use. The unsaturation in the chain in the new hybrid meso-tetraarylporphyrin-cardanol leads to chemical and physico-chemical properties which are different from the saturated derivatives. The unsaturation also allows preparation of the corresponding epoxy compounds as well as self-metathesis derivatives.