Journal of Porphyrins and Phthalocyanines

In the present review, we show how the chemical variability of phthalocyanines allowed to synthesize a broad range of hybrid materials. The combination of phthalocyanines or related derivatives with polymers or carbonaceous materials led to efficient chemical sensors. It is shown how the incorporation of macrocyclic molecules in hybrid materials highly modifies the structural and morphological characteristics of the materials. Rugosity, specific surface and porosity being key parameters in the analyte-sensing material interactions, these modifications highly improve the performance of chemical sensors. This is the reason why they are particularly promising materials for the development of new chemical sensors, associated with electrochemical, conductometric or optical transducers.

In this work, we investigated the nonlinear optical absorption properties of chloroaluminum, chlorogallium, chloroindium, zinc and lead octaphenoxy phthalocyanines in a dimethyl sulphoxide solution using 5 ns pulses at 532 nm. Using the Z-scan technique, the nonlinear optical properties and the excited state absorption cross-sections were determined by fitting the Z-scan data. The k value was the highest for Pb derivative at 211, making it the best nonlinear optical material. In terms of hyperpolarizability, Pb derivative (containing a larger central metal) also gave the largest value followed by aluminum derivative (containing a small central metal). The distortion of the ring caused by the central metal is used to explain the hyperpolarizability values. Large nonlinear absorption coefficient values, β_eff, in the range of 3.558–4.763 × 10^-9 cm.W^-1 and low saturation fluence values, F_sat between 21.5–38.5 mJ.cm^-2, were obtained for these samples.

A one step chemical reduction process was used for the preparation of hydrophilic silver nanoparticles (AgNP) using silver nitrate, sodiumborohydride and polyvinylpyrolidone as stabilizer. In the case of hydrophobic silver nanoparticles reduced silver ions were stabilized with cetyl trimethylammonium bromide (CTAB). The resultant nano particles were characterized by absoption spectra and their interactions with cationic cobalt (QCoPz) and neutral magnesium (MgPz) porphyrazines in water and in organic medium were investigated by using UV-vis spectroscopy and zeta potential techniques. It is confirmed that both metalloporphyrazine molecules interact with silver nanoparticles in an effective manner. The possible arrangement of the porphyrazines on the surfaces of the hydrophilic and hydrophobic AgNPs has been also discussed according to obtained spectroscopic results. These well-characterized novel AgNP-metalloporphyrazine composites are expected to be useful in optical and catalytic applications.

In the present work, the optical response of CoPcF₁₆ films upon exposure to ammonia vapor in the concentration range 50 to 1000 ppm was measured by total internal reflection ellipsometry. It was demonstrated that the sorption of NH₃ molecules causes substantial shift of the Δ(λ) spectrum which is determined by the increase in film thickness and change of its optical parameters. It was found that the CoPcF₁₆ films deposited at substrate temperature of 220 °C are characterized by larger grains and more developed surface demonstrating higher optical response than films deposited at substrate temperature of 60 °C. In order to gain an insight into the sorption mechanism at molecular level, we have studied the interaction of ammonia vapor with hexadecafluorinated cobalt phthalocyanine using infrared spectroscopy. It was shown that the detection of ammonia was found to be governed primarily by coordination to the metal center.

A series of hydroxyl-substituted free-base tetraphenylporphyrins was synthesized and characterized by UV-vis spectroscopy, ¹H NMR and mass spectrometry. The porphyrins are represented as (HOPh)_n(tBuPh)_4-nPH₂, where Ph presents a phenyl group, HO and tBu are substituents on the para-positions of the phenyl rings of the macrocycle, n = 0–4 and P represents the dianion of tetraphenylporphyrin. The UV-visible properties of each porphyrin were examined in dichloromethane (DCM), N,N′-dimethylformamide (DMF) and dimethyl sulfoxide (DMSO) before and after addition of trifluoroacetic acid (TFA) or sodium hydroxide (NaOH) to solution. Equilibrium constants for protonation (logβ_n) and deprotonation of each compound were determined using standard equations. The protonations occur in a single step involving a simultaneous two proton addition at the porphyrin central nitrogens. The phenolic protons on (HOPh)_n(tBuPh)_4-nPH₂ are easier to deprotonate than the core nitrogen protons of the porphyrins and this reaction occurs in a single step involving the simultaneous loss of 1–4 protons on the hydroxyl groups followed by a loss of two protons from the central nitrogens. The effect of HO substituents on UV-visible spectra and the magnitude of the protonation/deprotonation constants (logβ_n and ) are discussed. Two of the porphyrins, (tBuPh)₄PH₂ and trans-(HOPh)₂(tBuPh)₂PH₂, are also characterized by a single-crystal X-ray analysis.

Recent experimental studies of Liu and Groves (J. Am. Chem. Soc. 2010; 132: 12847) on dioxomanganese(V) porphyrin complexes implicated substrate halogenation in good yield. Currently, little is known of this unique mechanism, therefore to gain understanding on the halogenation mechanism and the chemical features of this oxidant we decided to do a computational (density functional theory) study. We show that the dioxomanganese(V) complex has considerably different molecular (valence) orbitals as compared to monooxomanganese(V) porphyrin due to mixing of the metal 3d orbitals with 2p orbitals on both oxygen atoms. This results in a set of three pairs of orbitals of which the bonding and nonbonding pairs are doubly occupied and the antibonding orbitals are vacant. As a consequence, the bonding character along the Mn–O bond is less in dioxomanganese(V) as compared to monooxomanganese(V) complexes and therefore this bond can formally be described as a double bond rather than a triple bond. The differences in orbital interactions and orbital energies also affect the intrinsic chemical properties of the oxidants, such as the electron affinity and pK_a values, which result in enhanced catalytic potential for dioxomanganese(V) porphyrin. Our calculations predict a halogenation mechanism in line with that proposed by experiment with an initial hydrogen atom abstraction followed by ligand exchange and halogen transfer.

Three differently substituted Pd-tetraphenyl-porphyrins complexes were synthesized and their X-ray crystal and photophysical properties were studied. All compounds display intense phosphorescence in de-aerated solutions at room temperature with decay time in the μs range. An efficient spin transfer to oxygen in aerated solutions was monitored using singlet oxygen (¹O₂) luminescence at 1275 nm. For all compounds, the quantum efficiency for generating singlet oxygen was found to be close to unity. Interesting differences in the pathways from the excited singlet state to singlet oxygen via the intermediate triplet state were observed. The excitation spectra obtained while recording the phosphorescence at 1275 nm closely matched the absorption spectra with two bands: the Soret (or B) band near 410–420 nm and a split Q-band at 510–520 nm. Noticeable differences in the B/Q intensity ratio between the absorption and excitation spectra (for both phosphorescence and singlet oxygen luminescence) were determined, indicating different S_x → T₁ pathways.

The reaction of 4-(2′,3′,4′,5′,6′-pentafluorobenzyloxy)phthalonitrile with 2,2,3,3,4,4,5,5-octafluoropentanol leads to the formation of 4-[2′,3′,5′,6′-tetrafluoro-4′-(octafluoropentoxy) benzyloxy]-phthalonitrile. The reaction was achieved by regioselective substitution reaction of the p-fluorine atoms of pentafluorobenzyloxy group by perfluoroalkoxy group. The tetramerization of the new dinitrile derivative in the presence of zinc, cobalt, copper or manganese salts results in the corresponding phthalocyanines. The prepared compounds have been characterized by elemental analyses, FT-IR, UV-vis, ¹H NMR, ¹³C NMR, ¹⁹F NMR and mass spectroscopies, consistent with the proposed structures. The influence of solvent and concentrations on the aggregation of the phthalocyanine complexes was studied by electronic spectroscopy.

The design, synthesis and theoretical calculations of a mononuclear and its corresponding annulated dinuclear hydrophilic zinc(II) phthalocyanines (ZnPcs) are reported here, the hydrophilic substituent being 1,3-bis((2,2-dimethyl-1,3-dioxolan-4-yl)methoxy)propan-2-ol. These novel compounds have been characterized by UV-vis spectroscopy in ethanol and ethanol:water (50:50) solutions. The electronic spectra of the mononuclear derivatives retain the main spectral features of ZnPc with a strong Q-band absorbance at 678 nm in ethanol and a less intense B-band at 370 nm. The annulated dinuclear derivatives show a broad Q-band absorbance with main wavelength maxima between 600 and 720 nm. From time-dependent density functional (TDDFT) UV-vis spectra simulation performed on selected isomers, Q-band absorption maxima of the non-peripherally substituted forms are more red-shifted compared to those of peripheral forms.

Water pollution by pesticides as the result of intensive agriculture and horticulture has brought many negative consequences to humans and ecosystems. Among others, chemical sensor systems are under intense development for direct pesticide analysis in aqueous samples as a cost effective and simple alternative analytical method. In this work, a set of zinc phthalocyanines is studied in its liquid sensing properties using quartz crystal microbalances. Four different species selected from the two most common organophosphorus and carbamate classes of pesticides are used as test analytes. The phthalocyanines are chemically modified with different fluorinated substituents to increase sensor sensitivity and govern pesticide selectivity in order to create sensors with widely diverging analyte responses. By this means, sensors with a general high sensitivity and selectivity for the two pesticide classes were obtained and detection limits down to 0.03 mg.L^-1 could be achieved. The response data of the sensors are analyzed in detail using exploratory multivariate data evaluation methods. The results show that phthalocyanine based sensors are a truly capable platform for chemical analysis systems of aqueous samples.

Magnetic circular dichroism (MCD) spectroscopy and TD-DFT calculations are used to analyze the electronic structure and optical properties of low-symmetry acenaphthoporphyrins with AAAB, ABAB and AABB structures. Evidence for dual fluorescence caused by tautomerism has been identified in the emission spectra of the AAAB and ABAB compounds. The sign sequences observed for the Q and B bands in the MCD spectra have been used to validate the results of the TD-DFT calculations. An anomalous +/- sign sequence is observed in the B band region with ascending energy similar to that reported previously for metal tetraphenyltetraacenaphthoporphyrin complexes.

Four new zinc phthalocyanines (ZnPcs 1–4) peripherally substituted with fully conjugated 6b,10b-dihydrobenzo[j]cyclobut[a]acenaphthylene (DBCA) have been synthesized and chemically characterized. In (DBCA)₄ZnPc1 and ^tBu₃(DBCA)ZnPc2 the DBCA units are directly connected to the phthalocyanine core, meanwhile in (VDBCA)₄ZnPc3 and ^tBu₃(VDBCA)ZnPc4 DCBA units are connected through a vinyl spacer. We describe the effect of the substituents on optical spectra, fluorescence lifetimes and quantum yields.

A new tricationic subphthalocyanine was synthesized and employed as light-harvesting and donor material in an ionic solid state organic photovoltaic cell. The incorporation of ionic dyes in organic photovoltaics aims to take advantage of ionic movement in order to enhance the charge transport properties of these materials. In this preliminary study, we report the results obtained in the fabrication of a partially solution-processed device with a cationic dye, where an effiency of 0.5% was reached.

The first push-pull μ-nitrido diiron phthalocyanine complex was prepared and characterized. The EPR spectrum confirms the Fe^+3.5–N–Fe^+3.5 formalism. The stability of this dimer in oxidant media (up to 1000 equivalent of H₂O₂) was studied by UV-vis spectroscopy. The push-pull μ-nitrido diiron phthalocyanine exhibited excellent stability because of the delocalization of an unpaired electron.

The triple-decker complexes of symmetrical type [mBr₄TPP]Ln[(15C5)₄Pc]Ln[mBr₄TPP] (Ln-mTD; Ln = La, Nd; [(15C5)₄Pc] = tetra-(15-crown-5)-phthalocyaninato-ligand; [mBr₄TPP] = tetrakis-meso-(3-bromophenyl)-porphyrinato-ligand) are synthesized for the first time with 43% and 36% yield. The applicability of the previously developed selective one-step synthetic approach for the preparation of the mentioned complexes is demonstrated and the limitations, determined by meta-substitution of meso-aryl-fragments, are revealed. The spectral features of the obtained complexes is determined by means of UV-vis and NMR spectroscopy. The hindered rotation of porphyrin meso-substituents in the obtained complexes and formation of statistical set of atropisomers are demonstrated.

The electrochemical and spectroelectrochemical properties of two β-phosphorylated Zn porphyrins, [2-diethoxyphosphoryl-5,10,15,20-tetraphenylporphyrinato]zinc (1) and [2-diisopropoxyphosphoryl-5,10,15,20-tetraphenylporphyrinato]zinc (2), are reported in CH₂Cl₂ and PhCN containing tetrabutylammonium perchlorate (TBAP) or tetrabutylammonium hexafluorophosphate (TBAPF₆) as supporting electrolyte. Under certain solution conditions, three one-electron reductions are observed, with the last process being attributed to the product of a chemical reaction following formation of the porphyrin dianion. Two or three oxidations are observed for the same compounds, again depending upon the solution conditions. In some cases, two well-defined and well-separated one electron oxidations are observed but in others the first one-electron abstraction to give the porphyrin radical cation is split into two redox processes, separated from each other by 110–140 mV. This splitting of the first oxidation into two processes is attributed to linking of the two porphyrins which results when a P=O unit of the phosphoryl substituent on one porphyrin binds to the Zn(II) center of a second porphyrin, resulting in dimer formation. The interaction between the two macrocycles is discussed in terms of the difference in potentials between the two split redox processes (ΔE_1/2) and the overall data is compared with that for other porphyrin dimers and bis-macrocycles reported in the literature.

In this study, the novel tetra-substituted Zn(II)(3), Co(II)(4) and In(III)acetate (5) phthalocyanines were synthesized by cyclotetramerization reactions of 7-(2,3-dicyanophenoxy)-8-methylcoumarin-4-acetic acid (2) with corresponding metal salts. All the new compounds have been characterized by MALDI-TOF mass, FT-IR and UV-vis spectra, and elemental analysis as well. The electrochemical, in situ spectroelectrochemical and photochemical properties of tetra-substituted Zn(II), Co(II) and In(III)acetate phthalocyanines were also investigated.