Journal of Porphyrins and Phthalocyanines

The review aims at being an exhaustive summary of the use of Huisgen azide-alkyne dipolar addition in the synthesis of tetrapyrrolic compounds, mainly porphyrins, phthalocyanines, chlorins and bacteriochlorins.

An approach for information storage employs tetrapyrrole macrocycles as charge-storage elements attached to a (semi)conductor in hybrid chips. Anti-counterfeiting measures must cohere with the tiny amounts of such electroactive material and strict constraints on composition in chips; accordingly, the incorporation of typical anti-counterfeiting taggants or microcarriers is precluded. The provenance of the tetrapyrroles can be established through the use of isotopic substitution integral to the macrocycle. The isotopic substitution can be achieved by rational site-specific incorporation or by combinatorial procedures. The formation of a mixture of such macrocycles with various isotopic composition (isotopically unmodified, isotopologues, isotopomers) provides the molecular equivalent of an indelible printed watermark. Resonance Raman spectroscopic examination can reveal the watermark, but not the underlying molecular and isotopic composition; imaging mass spectrometry can reveal the presence of isotopologues but cannot discriminate among isotopomers. Hence, deciphering the code that encrypts the watermark in an attempt at forgery is expected to be prohibitive. A brief overview is provided of strategies for incorporating isotopes in meso-substituted tetrapyrrole macrocycles.

This review focus on the preparation of silica nanoparticles functionalized with porphyrins and related compounds. It is aimed to highlight their features as photosensitizers in the area of photodynamic therapy. In this field, photosensitizers have been covalently and non-covalently linked to silica nanoparticles, in order to study their photophysical and biological properties. Another fascinating scenario for photosensitizer-silica nanoparticles hybrids involves the possibility of including metal cores for conditioning the uptake in the target cells, allowing most of the times the combination of therapies and in certain conditions to facilitate the removal and reutilization of the photosensitizer in environmental applications.

A novel NCN type palladium pincer complex based on the porphyrin backbone was synthesized. The palladium atom bound to the meso-carbon of the porphyrin core was effectively supported by two imidazolyl groups. The product was characterized by spectroscopic and X-ray diffraction analysis. The structure of the porphyrinic macrocycle was revealed to be highly distorted by the coordination of the outer palladium center. The degree of deformation was found to be even larger than the analogous palladium pincer complexes in which pyridine groups were employed as the supporting ligands. The complex exhibited high catalytic activity in the Mizoroki-Heck reaction of iodobenzene with butyl acrylate with 0.005% of the catalyst loading.

The synthesis and characterization of two 18-crown-6 functionalized analogues of an extensively studied gadolinium texaphyrin derivative, motexafin gadolinium (1, MGd), are reported. These are the monomeric and dimeric species, compounds 2 and 3, respectively. Both crown ether functionalized species proved to be stable at physiological pH and revealed distinct shifts in the UV spectrum when treated with sodium-, potassium-, ammonium- or zinc(II)-salts. Zinc(II) is believed to play a major role regulating apoptosis mechanisms in cancerous cells. Therefore, cytotoxicity studies of 2 and 3 were carried out using the Ramos cell line in the presence and absence of zinc(II).

3,6-Dialkylphthalonitriles (6a) and (6b) with a fused TTF unit at 4,5-positions were prepared from dialkyltetrabromobenzenes via five step reactions (alkyl: butyl and octyl). Compounds 6a and 6b were treated with lithium in n-hexanol at 120 °C for 3 h to produce α-octaalkyltetrakis(tetrathiafulvaleno)phthalocyanines (8a) and (8b), respectively. The structure of the products was determined by ¹H NMR, FAB MS, and MALDI TOF MS. The ¹H NMR measurement was performed in chloroform-d at around 55 °C because of their higher aggregative property. Electrochemical and optical properties of 8a and 8b were examined by cyclic voltammetry and UV-vis and MCD spectroscopy. Molecular orbital calculations succeeded in reproducing the observed absorption spectrum of tetrakis(tetrathiafulvaleno)phthalocyanine.

This short communication describes the screening of various metal salts for the preparation of cyano-aqua cobinamides from vitamin B12 in methanol. ZnCl₂ and Cu(NO₃)₂·3H₂O have been identified as most active for this purpose and represent useful alternatives to the widely applied Ce(III) method that requires excess cyanide.

A series of 11 low melting ionic liquids based on meso-substituted A₃B-porphyrins and A₂B₂-porphyrins containing one or two pyridyl substituents have been synthesized in high yields. Three of them are liquids at room temperature. All these porphyrinic salts were characterized by ¹H NMR, ¹⁹F NMR, MALDI-TOF mass spectrometry, elemental analysis and UV-visible spectroscopy. The thermal properties and conductivity values of these salt derivatives have been also measured. A specific conductivity value of up to 4 mS.cm^-1 could be obtained for a compound having the counter-anion B(C₆F₅)₄^-.

A new route to N-phenylquinolino[2,3,4-at]porphyrins is described and the electrochemical and photochemical properties of the synthesized derivatives were investigated. The electrochemical studies (cyclic voltammetry and rotating disk voltammetry) of the free-base and the corresponding Ni, Cu and Pd complexes have shown that the presence of the phenyl group is responsible for the formation of stable radical cations. The capacity of the N-phenylquinolino[2,3,4-at]porphyrins to generate singlet oxygen was evaluated and some of them have promising features as photosensitizers.

The syntheses and spectroscopic properties of new μ-nitrido-[2,3,9,10,16,17,23,24-octa(n-pentoxy)phthalocyaninato]diiron complexes in Fe(IV)Fe(IV) and Fe(+3.5)Fe(+3.5) oxidation states are reported. UV-vis spectra of both dimers demonstrate a strong solvatochromic behavior. UV-vis and ¹H NMR data reveal the presence of two different forms for both oxidation states in apolar and polar solvents. Fe K-edge X-ray absorption near-edge structures (XANES) spectra of two Fe(IV)Fe(IV) forms also show a significant difference: pre-edge feature in toluene is shifted to higher energy compared to that in tetrahydrofuran. The difference of properties between two forms is explained by solvent-dependent mutual orientation of two phthalocyanine rings. A strong sharp Q-band in UV-vis spectrum at 642 nm and small splitting of aromatic protons (0.18 ppm) in ¹H NMR spectrum observed in apolar solvents (toluene, benzene, cyclohexane) imply that the green form is in more symmetric D_4d configuration. In turn, a broad multipreaked Q-band and relatively high splitting of aromatic protons (0.56 ppm) observed in THF and CH₂Cl₂ for the blue form are in agreement with less symmetric D₄ conformation. The Fe(μ-N)Fe structure is relatively rigid showing no free rotation at room temperature in NMR time scale. Tuning of the structure of N-bridged diiron macrocyclic complexes by introduction of substituents and modification of electronic properties of the complexes via conformation changes might be useful for optimization of their catalytic properties as well as for their potential application in sensors.

We describe the spectroscopic characterization of a supramolecular trisporphyrin complex that is heterogeneously self-assembled onto mesoporous Al₂O₃ films and can be used as efficient light harvesting complex. The parameters for an efficient complexation process, such as dye loading, are evaluated and discussed. In addition, the heterosupramolecular complex is tested on TiO₂ nanoparticles and the charge transfer process elucidated.

Amorphous hexadecafluoro(phthalocyaninato)ruthenium(II) F₁₆PcRu (1) has been studied with EXAFS spectroscopy. It has been shown that F₁₆PcRu has a dimeric structure in the solid state.

The preparation of two chiral porphyrin ligands 7 and 9 and of their ruthenium and cobalt complexes is reported. These new complexes have been used as catalysts in cyclopropanation reactions. Both 7-Ru and 9-Ru complexes showed a catalytic activity in the enantiomeric cyclopropanation of α-methylstyrene by ethyldiazoacetate whereas amination of ethylbenzene by arylazide in the presence of 7-Ru or 9-Ru did not stop at the corresponding benzylamine stage but instead afforded the corresponding benzylimine.

Reaction between H₂TFcP (TFcP^2- is a dianion of 5,10,15,20-tetraferrocenylporphyrin) with tin(II) chloride results in formation of the trans-Cl₂SnTFcP complex, which was characterized by UV-vis, MCD, ¹H and ¹³C NMR, and APCI MS methods. X-ray single crystal analysis was used to determine the structure of the target compound. Crystallography reveals a very unusual α,α,β,β-conformation of the ferrocene groups and largely planar structure of the porphyrin macrocycle. Density functional theory calculations predict that the HOMO in trans-Cl₂SnTFcP is predominantly ferrocene centered, while LUMO is primarily localized over the porphyrin core. Redox properties of the trans-Cl₂SnTFcP complex were investigated using electrochemical (CV and DPV), spectroelectrochemical, and chemical oxidation approaches. Electrochemical experiments conducted in low-polarity solvent using non-coordinating electrolyte reveal the sequential oxidation of ferrocene substituents along with porphyrin-based single-electron oxidation and reduction processes. The first ferrocene oxidation process is separated by 130 mV from the next three ferrocene based oxidations, which are more closely spaced. Mixed-valence [trans-Cl₂SnTFcP]⁺ was generated in situ by spectroelectrochemical and chemical oxidation approaches and characterized by UV-vis-NIR spectroscopy.

A new type of rhenium(I) tricarbonyl porphycene complex is reported based on a reaction between free-base 2,3,6,7,12,13,16,17-octaethylporphycene (H₂OEPc) and Re(CO)₅Cl. As is the case with tetraphenylporphyrin (TPP), a complex containing only one Re(CO)₃ groups, which retains a pyrrole proton, can be isolated and characterized in addition to a bis-Re(I) complex. The Re^I(HOEPc)(CO)₃ complex was characterized by ¹H NMR, ¹³C NMR, MS, IR, UV-visible, and MCD spectroscopy and cyclic voltammetry. A single crystal was successfully obtained, which enabled the determination of the X-ray structure.

Ethylenediamine-N,N′-diacetic acid complexes of the covalent conjugates of octacarboxy-substituted cobalt phthalocyanine with one, two and three platinum atoms (3a–c) were synthesized and characterized by elemental analysis, electronic absorption, infrared and mass spectra data.

A series of free-base and zinc porphyrin hexamers, where six porphyrin units are linked to a triphenylene core through amide or ester linkage, was designed and synthesized in an effort to study their spectroscopic and electrochemical properties, and aggregate formation. The distances between triphenylene core and porphyrin moieties are tuned by changing the lengths of spacer alkyl chains. The absorption spectral studies indicates that the porphyrin units in a hexamer behave like monomeric porphyrins, while a strong fluorescence quenching of triphenylene core was observed suggesting the deactivation of the excited state of triphenylene. The redox potentials of porphyrin units in a hexamer were estimated by differential pulse voltammetry (DPV). These values are very similar to those of the corresponding monomer. Consequently, absorption and electrochemical data demonstrate that six porphyrin units of (H₂PAC₅)₆TPh behave like monomers independently in the ground state. The hexamers undergo supramolecular aggregation spontaneously in different fashions based on the solvent systems as well as spacer lengths. Highly ordered and aligned monolayer-based patterns are formed when hexamers are allowed to aggregate from toluene solution onto carbon-coated copper films. In contrast, hexamers undergo aggregation to nanoparticles in toluene/acetonitrile mixed solvent system and the particle sizes increase with increasing the spacer alkyl chain lengths.

Microwave irradiation is a powerful tool in organic synthesis allowing for instance, to reduce reaction times and to obtain the desired products in better yields. Contrary to what is reported in literature, the first Vilsmeier-Haack formylation of Ni(II) and Cu(II) complexes of meso-tetraarylporphyrins by using microwave irradiation is described here. Different solvents, irradiation powers and reaction times were studied using the Ni(II) and Cu(II) complexes of 5,10,15,20-tetraphenylporphyrin and the best found conditions were extended to a series of other meso-substituted tetraarylporphyrins. The products, namely the new ones were isolated in good to excellent yields and with a significant reduction on the reaction times. Scaled-up studies have shown that the efficiency of the process is not affected by increasing the amount of porphyrin.

High molecular weight poly(p-phenylenenevinylene) PPV copolymers laterally substituted with zinc (II) phthalocyanines (Zn(II)Pc-PPV 1 and 2) have been synthesized by means of post-polymerization functionalization reactions through DCC-mediated esterifications between hydroxy-phthalocyanines 4 and 6 and carboxy-bearer PPV copolymers, comprising 2-methoxy-5-(3,7-dimethyloctyloxy)-1,4-phenylenevinylene (MDMO-PPV) and 1,4-(2-(5-carboxypentyloxy)-5-methoxyphenylenevinylene (CPM-PPV) units in a 9:1 (3) and 1:1 (5) ratio, respectively. The resulting copolymer 1 contains a 7 mol % of Pc molecules, while copolymer 2, which is isolated as the soluble fraction of the reaction with the starting 1:1 copolymer (namely having around 50% of COOH-containing monomeric units), holds a 9 mol % of zinc(II) phthalocyanines. 1 and 2 were fully characterized by ¹H NMR, UV-vis and FT-IR spectroscopies.

A complete assignment of ¹³C NMR resonance peaks in the spectrum of heteroleptic triple-decker (porphyrinato)(phthalocyaninato) lanthanum of type [Br₄TPP]La[(15C5)₄Pc]La[Br₄TPP] (Br₄TPP = 5,10,15,20-tetrakis-(4-bromophenyl)-porphyrinato-ligand, (15C5)₄Pc = tetrakis-(15-crown-5)-phthalocyaninato-ligand) is performed. Application of set of gradient-enhanced homonuclear ¹H-¹H-correlation techniques (COSY and NOESY) allowed the unambiguous interpretation of proton spectrum of the complex. Application of INEPT polarization transfer technique allowed to separate quaternary carbon resonances from proton-bound carbon ones. Gradient-enhanced proton-detected HMQC and HMBC techniques allowed to correlate all the resonances in ¹³C-spectrum.

meso-diethylmalonylidene-(1,4-naphthi)thiaporphyrin containing exocyclic C–C double bonds at meso-positions has been synthesized and characterized. The compound undergoes initial protonation at the α-position of the diethylmalonyl group with large red shifted absorption maxima. The second protonation occurs at a meso-position to give a species with broken cross-conjugation.

New porphyrin-(cyanine dye) composites, in which two porphyrins are bridged by a cyanine dye through triple bonds, were synthesized. In the UV-vis absorption spectra of the composites, the Soret band and Q-band were red-shifted to 436 and 575–640 nm, respectively. The absorption originating from the cyanine dye portion was also red-shifted from 710 nm to 764 nm, suggesting the expansion of πconjugation over the porphyrin and cyanine dye parts. Fluorescence studies suggested that energy transfer from the porphyrin portion to the cyanine dye moiety occurred. The fluorescence intensity decreased with increasing dielectric constants of solvents, suggesting intramolecular photoinduced electron transfer from the porphyrin to the cyanine dye parts. The effective two-photon absorption (2PA) cross-section values were measured using a nanosecond open aperture Z-scan method. The maximum effective 2PA cross-section and two-photon excited fluorescence cross-section values were 33,000 GM and 4,800 GM, respectively, at 860 nm in toluene/pyridine (95:5).

We report the synthesis and crystal structure of a novel phthalocyanine-calixarene conjugate (Pc-Calix) derived from a calixarene-based phthalonitrile (Pn-Calix). Crystal structures confirm the retention of the full cone configuration of the calixarene unit, which is thus suitable for the binding of appropriate chemical species. This new conjugate may find application as a molecular sensor in which the calixarene acts as the binding site and the perturbations of the optical properties of the phthalocyanine reports the presence of the binding species.

The reaction of Ni(II) complexes of etioporphyrins I, octaethylporphyrins, coproporphyrinsI tetramethylester, methyl pyrroporphyrin XXI ethylester and mesoporphyrin IX dimethyl ester derivatives with N-bromosuccinimide and triethylamine trihydrofluoride gave mono- through tetra-meso-brominated derivatives as the principal products. β-brominated products were also detected with the simultaneous loss of the β-alkyl substituents. Reaction of octaethylporphyrin Cu(II) was slow yielding meso-mono and dibromo derivatives as major products. Prolongation of the reaction time resulted in the formation of tri- and tetrabromo products substituted at both meso- and β-positions. Our results show that the central metal ion plays a major role in these bromination reactions.

Bicyclo[2.2.2]octadiene(BCOD)-fused diazaporphyrin was synthesized by the reaction of BCOD-fused dipyrromethane with sodium nitrite in acetic acid/ethanol in the presence of copper(II) acetylacetonate. This soluble precursor was converted into the semiconducting thin film of (tetrabenzodiazaporphyrinato)copper(II) by heating after fabrication via spin-coating.

The DNA-binding modes and nuclease activity of methylpyridiniumyl/phenyl-hydroxamic acid porphyrin adducts (PHAs) have been studied. These compounds are derived from the tetracationic meso-tetrakis(N-methyl-4-pyridiniumyl)porphyrin (H₂TMPyP-4) by replacing one or two pyridinium rings by a phenyl group. A hydroxamic acid function was connected by a polymethylenic chain of 3 to 5 carbon atoms to the meta or para position of the phenyl group. Different DNA-interaction modes were observed depending on the number of charges and hydroxamic acid functions. The nuclease activity in the presence of lanthanides was shown to be depending on the 1/r₀ ratio and the nature of the lanthanide ion, and the optimum conditions are depicted after a systematic study.

New heterogeneous photosensitizers were synthesized, in which phthalocyanines of zinc and aluminum, tetrasubstituted at non-peripheral positions with modified thiophenyl groups, were grafted to aminopropyl silica gel. The absorption and fluorescence spectra, and the quantum yields of fluorescence and photosensitized singlet oxygen generation were estimated for aqueous suspensions of these sensitizers. It is shown that upon photoexcitation, silica gel-bound phthalocyanines produce singlet oxygen and display photobactericidal activity against bacteria E. coli.

Sterically bulky substituents at the β-carbons of the pyrrole rings of porphyrins are sufficient to cause large out-of-plane porphyrin distortions even in the absence of substituent groups at the meso carbons. It is well established that substituents at the meso-positions only or at both the β-pyrrole and the meso-positions are sufficiently bulky to result in large non-planar distortions of the macrocycle. However, no systematic studies of the effects of bulky β-pyrrole substituents alone have been reported. Herein, molecular simulations and X-ray crystallography of nickel(II) 2,3,7,8,12,13,17,18-octa(isopropyl)porphyrin reveal that large out-of-plane distortions (>1.5 Å) are induced by the steric repulsion of the β-isopropyl groups but fail to lead to a single strongly energetically favored conformer. The molecular simulations indicate that multiple conformers differing in the orientation of the isopropyl groups and the macrocycle conformation coexist in solution and this is confirmed by resonance Raman spectroscopy. Large downshifts in the structure-sensitive lines result from the non-planar distortion, and line broadenings result from structural heterogeneity. The heterogeneity originates from tradeoffs between energy contributions from steric repulsion and macrocycle distortion. Simulations for 5-nitro-2,3,7,8,12,13,17,18-octa(isopropyl)porphyrin suggest two possible orientations of the nitro group with respect to the macrocycle mean plane — one nearly vertical (as in the crystal structure) and another that is nearly parallel. INDO/S semiempirical calculations indicate an orbital of the NO₂ group resides between the porphyrin frontier orbitals with significant mixing of the nitro and porphyrin orbitals.KEYWORDS: porphyrin, non-planar, resonance Raman, X-ray crystallography, crystal structure, isopropyl, nitro, conformer, molecular mechanics, molecular simulations, density functional theory, steric crowding, conformational heterogeneity.

Phenylboronic acid esters of an unsaturated precursor 1,2-dicyano-1,2-bis(2-hydroxy- ethylthio)ethylene and the magnesium porphyrazine derived from it have been prepared either by refluxing a mixture of the reagents in chloroform in the presence of molecular sieve or by solvent-free heating in an oven under reduced pressure. The two novel compounds have been characterized by elemental analysis together with ultraviolet-visible, infrared spectroscopy, proton nuclear magnetic resonance, carbon-13 nuclear magnetic resonance, boron-11 nuclear magnetic resonance, and mass spectra.

Hemi and amphi-substituted μ-carbido iron diphthalocyanine having general formula (t-bu)₄PcFe-C-FePc and (t-bu)₄PcFe-C-FePc(t-bu)₄ have been oxidized with I₂. The oxidized compounds have been characterized and their physicochemical properties have been studied; the results obtained lead to assign them the formula [(t-Bu)₄PcFe-C-FePc] (I₅)_0.66 and [[(t-Bu)₄PcFe]₂C]] (I₅)_0.66 respectively. The conduction properties, related to the role played by the pushing groups inserted in the peripheral macrocycles, are discussed. Moreover, an effective purification method for improving the yield and purity of iron tetra-tert-butyl phthalocyanine is described, the difficulty being able to obtain this precursor with a high purity grade.