Photoperoxidation of a Diamino Zinc Porphyrazine to the seco-Zinc Porphyrazine: Suicide or Murder?

Metal Complexes of Porphyrinoids Containing Nonpyrrolic Heterocycles

The replacement of one or more pyrrolic building block(s) of a porphyrin by a nonpyrrolic heterocycle leads to the formation of so-called pyrrole-modified porphyrins (PMPs), porphyrinoids of broad structural variability. The wide range of coordination environments (type, number, charge, and architecture of the donor atoms) that the pyrrole-modified frameworks provide to the central metal ions, the frequent presence of donor atoms at their periphery, and their often observed nonplanarity or conformational flexibility distinguish the complexes of the PMPs clearly from those of the traditional square-planar, dianionic, N₄-coordinating (hydro)porphyrins. Their different coordination properties suggest their utilization in areas beyond which regular metalloporphyrins are suitable. Following a general introduction to the synthetic methodologies available to generate pyrrole-modified porphyrins, their general structure, history, coordination chemistry, and optical properties, this Review highlights the chemical, electronic (optical), and structural differences of specific classes of metalloporphyrinoids containing nonpyrrolic heterocycles. The focus is on macrocycles with similar "tetrapyrrolic" architectures as porphyrins, thusly excluding the majority of expanded porphyrins. We highlight the relevance and application of these metal complexes in biological and technical fields as chemosensors, catalysts, photochemotherapeutics, or imaging agents. This Review provides an introduction to the field of metallo-PMPs as well as a comprehensive snapshot of the current state of the art of their synthesis, structures, and properties. It also aims to provide encouragement for the further study of these intriguing and structurally versatile metalloporphyrinoids.

Tuning the Acceptor Unit of Push-Pull Porphyrazines for Dye-Sensitized Solar Cells

A family of four push–pull porphyrazines of A₃B type, where each unit A contains two peripheral propyl chains and the unit B is endowed with a carboxylic acid, were prepared. The carboxylic acid was attached to the β-position of the pyrrolic unit, either directly (Pz 10), or through cyanovinyl (Pz 11) and phenyl (Pz 7) groups. The fourth Pz (14) consisted in a pyrazinoporphyrazine wherein the dinitrogenated heterocycle provided intrinsic donor–acceptor character to the macrocycle and contained a carboxyphenyl substituent. The direct attachment of the carboxylic acid functions and their linkers to the porphyrazine core produces stronger perturbation on the electronic properties of the macrocycle, with respect to their connection through fused benzene or pyrazine rings in TT112 and 14, respectively. The HOMO and LUMO energies of the Pzs, which were estimated with DFT calculations, show little variation within the series, except upon introduction of the cyanovinyl spacer, which produces a decrease in both frontier orbital energetic levels. This effective interaction of cyanovinyl substitution with the macrocycle is also evidenced in UV/Vis spectroscopy, where a large splitting of the Q-band indicates strong desymmetrization of the Pz. The performance of the four Pzs as photosensitizers in DSSCs were also investigated.

S-seco-porphyrazine as a new member of the seco-porphyrazine family - Synthesis, characterization and photocytotoxicity against cancer cells

An important subgroup within the porphyrazine (Pz) family constitutes seco-porphyrazines, in the chemical structure of which one pyrrole unit is opened in the oxidative process. So far, there are only limited data on N-seco- and C-seco-Pzs. Here, the synthesis of a novel member of the Pzs seco-family, represented by an S-seco-tribenzoporphyrazine analogue, 22,23-bis(4-(3,5-dibutoxycarbonylphenoxy)butylsulfanyl)tribenzo[b,g,l]-22,23-dioxo-22,23-seco-porphyrazinato magnesium(II), is reported, with moderate 34% yield. The new derivative was characterized using NMR spectroscopy, UV-Vis spectroscopy, and mass spectrometry. In the photochemical study performed following the indirect chemical method with 1,3-diphenylisobenzofuran, S-seco-Pz revealed a high singlet oxygen quantum yield of 0.27 in DMF. Potential photocytotoxicity of S-seco-Pz was assessed in vitro on three cancer cell lines - two oral squamous cell carcinoma cell lines derived from the tongue (CAL 27, HSC-3) and human cervical epithelial adenocarcinoma cells (HeLa). In the biological study, the macrocycle was tested in its free form and after loading into liposomes. It is worth noting that S-seco-Pz was found to be non-toxic in the dark, with cell viability levels over 80%. The photocytotoxic IC₅₀ values for free S-seco-Pz were 0.61, 0.18, and 4.1 µM for CAL 27, HSC-3 and HeLa cells, respectively. Four different liposomal compositions were analyzed, and the cationic liposomes revealed the highest photokilling efficacy, with the IC₅₀ values for CAL 27, HSC-3, and HeLa cells at 0.24, 0.25, and 0.31 µM, respectively. The results of the photocytotoxicity study indicate that the new S-seco-tribenzoporphyrazine can be considered as a potential photosensitizer in photodynamic therapy of cancer, along with the developed cationic liposomal nanocarrier.

Synthesis and Fluorescence Properties of Metalloporphyrazines Carrying 2-(Ethyl)-1,3-Dioxanethio-Groups

The synthesis, photophysical and spectroscopic properties of soluble 2-(ethyl)-1,3-dioxanethio-substituted metal-free and metalloporphyrazines containing Mg(II), Zn(II), Co(II) and Ni(II) are reported. The aggregation behaviour of these compounds was investigated in different solvents and concentrations. The effects of the substituent and the nature of the metal ion on the photophysical parameters of the Mg(II), Zn(II), Co(II) and Ni(II) porphyrazines are also reported.

Protonation of some non-transition metal phthalocyanines — spectral and photophysicochemical consequences

The photophysics and photochemistry of phthalocyanine complexes of magnesium (MgPc), aluminum chloride (ClAlPc) and zinc (ZnPc) are studied in N,N′-dimethylformamide (DMF). The values obtained for the photophysical and photochemical parameters are normal for simple metallophthalocyanine (MPc) complexes. Protonation of the azomethine bridges reduced the photoactivities of the complexes considerably; however the excited triplet states of the protonated species are more stable towards ground state oxygen. The interaction of the non-protonated MPcs with ground state oxygen is shown to be diffusion-assisted, with bimolecular rate constant values of the order of 1010 M-1.s-1. MgPc could not be protonated; it was easily demetalated by the protonating acid. The kinetics of the demetalation yielded the rate equation: Rate = 0.1[MgPc][H+]2/3

The renaissance in optical spectroscopy of phthalocyanines and other tetraazaporphyrins

Spectral properties of metallophthalocyanines and other tetraazaporphyrins are governed mainly by the Q band which originates from the π-π* transitions within the ring. The position and intensity of the Q band is important in tailoring new phthalocyanine derivatives for particular applications. Aggregation, the nature of the central metal, π conjugation, symmetry of the molecules, and axial, peripheral or non-peripheral substitutions affect the spectra and hence the properties of the phthalocyanine molecule. This review gives a brief outline on how optical spectroscopy provides useful informations on molecular and electronic structures, chemistry and physics of phthalocyanines and other tetraazaporphyrins.

The chemistry of porphyrazines: an overview

The main synthetic approaches for the preparation of porphyrazines are outlined. In addition, some structural and spectroscopic properties, especially the UV-vis absorption profiles emanating from their peripheral functionalization, the modification of the tetraazaporphyrin skeleton or the arrangement of macrocycles in a supramolecular manner, are discussed. Cyclotetramerization of appropriate dinitrile derivatives or modification of peripheral substituents on porphyrazines constitute the main synthetic routes. Moreover, the use of special templates, as well as different intermediates or nonpyrrolic precursors, are tools for the attainment of azaporphyrin analogues of distinct nature and unusual characteristics.

Synthesis and catalytic properties of a novel phthalocyanine covalently grafted onto silica

The iron complex of 2(3),9(10),16(17),23(24)-tetra[1,5-di(3-triethoxysilyl-propyl)biuryl]phthalocyanine (1) was prepared by reacting iron tetraaminophthalocyanine with 3-(triethoxysilyl)propyl isocyanate. This complex was directly grafted onto silica to give a supported catalyst without preliminary modification of silica support. This supported catalyst was successfully applied in clean catalytic oxidations by using molecular oxygen in combination with isobutyraldehyde. Cyclooctene, cyclohexene and styrene were oxidized to corresponding epoxides with 90, 78 and 74% yields, respectively. 2,3,6-Trimethylphenol was selectively oxidized to 2,2',3,3',5,5'-hexamethyl-4,4'-biphenol.

Synthesis and photophysical properties of a covalently linked porphyrin-phthalocyanine conjugate

The synthesis of a phthalocyanine-porphyrin heteropentamer (zinc(II) tetra(5-phenoxy-10,15,20-triphenylporphyrin)) zinc(II) phthalocyanine, ( ZnPc -( ZnTPP )4), containing four units of zinc tetraphenylporphyrin linked to a central zinc phthalocyanine macrocycle via an ether linkage is reported. The photophysical parameters of the pentamer are reported in toluene and dimethyl sulfoxide ( DMSO ). The observed differences in the fluorescence behavior of the pentamer in the two solvents is explained in terms of emission from different states; charge transfer state in DMSO and locally excited state in toluene. The rate constants for fluorescence, intersystem crossing, internal conversion, and of charge and energy transfer are reported for the pentamer. Quantum yields for fluorescence, internal conversion, triplet state and of charge and energy transfer are also reported for the pentamer, ZnPc -( ZnTPP )4 and the mixture of ZnPc and ZnTPP . The latter two parameters are higher in the pentamer compared to a mixture containing ZnPc and ZnTPP .

Photophysical, photochemical and bovine serum albumin binding studies on water-soluble gallium(III) phthalocyanine derivatives

Spectral, photophysical, photochemical and bovine serum albumin binding studies on some gallium(III) derivatives - {1,(4)-(tetrapyridyloxyphthalocyaninato)gallium(III), (α GaPc ); 2,(3)-(tetrapyridyloxyphthalocyaninato)gallium(III), (β GaPc ); and their quaternized derivatives: Q α GaPc and Q β GaPc )} are hereby presented. β-Substituted complexes are more fluorescent, but show lower tendencies to undergo intersystem crossing than the α-substituted, as judged by their fluorescence and triplet quantum yield values. The quaternized derivatives ( QGaPc ) are water-soluble and non-aggregated, which makes them potential photosensitizers of choice for photodynamic therapy applications; these amphiphilic compounds also bind strongly to bovine serum albumin in 1:1 stoichiometries, and with binding constants ( Kb) in the order of 106M−1.

Effects of central metal on the photophysical and photochemical properties of non-transition metal sulfophthalocyanine

The photophysical and photochemical properties and quenching (by 1,4-benzoquinone) of metallophthalocyanine sulfonates of aluminium ( AlPcSmix), zinc ( ZnPcSmix), silicon ( SiPcSmix), germanium ( GePcSmix) and tin ( SnPcSmix) are presented. The quantum yield values of fluorescence (ΦF), triplet state (ΦT), singlet oxygen (ΦΔ) and photodegradation (Φd) were determined and the observed trends in their variation among the complexes discussed in terms of aggregation and the heavy atom effect. 1,4-benzoquinone effectively quenched the fluorescence of the complexes. Quenching analyses gave positive deviations from Stern-Volmer behavior, suggesting the existence of static quenching in addition to dynamic quenching. The static and dynamic components of the quenching were separated using a modified Stern-Volmer equation and the “sphere of action quenching model”. The quenching constant was found to be a function of the radius of the central metal ion.

Potential aluminium(III)- and gallium(III)-selective optical sensors based on porphyrazines

Porphyrazines possessing non-coordinating alkyl (propyl) and aralkyl (4-tert-butylphenyl) groups in the periphery were studied as optical sensors for a set of mono-, di- and trivalent cations. Investigated porphyrazines in the UV-Vis monitored titrations revealed significant responses towards aluminium and gallium cations, unlike other metal ions studied. Additionally, porphyrazine possessing 4-tert-butylphenyl peripheral substituents showed sensor property towards ruthenium cation and was chosen for further investigation. The presence of isosbestic points in absorption spectra for its titration with aluminium, gallium and ruthenium cations, accompanied by a linear Benesi-Hildebrand plot, proved complex formation. The continuous variation method was used to determine binding stoichiometry in 1:1 porphyrazine-metal ratio. X-Ray studies and density functional theory calculations were employed to investigate octa(4-tert-butylphenyl)porphyrazine structure. The results helped to explain the observed selectivity towards certain ions. Interaction between ion and porphyrazine meso nitrogen in a Lewis acid-Lewis base manner is proposed.

Glucose-based fluorescent low-molecular mass compounds: creation of simple and versatile supramolecular gelators

Five novel glucose-based naphthalene derivatives with linkers containing hydrazine, ethylenediamine, 1,3-propanediamine, 1,4-butanediamine, and 1,6-hexanediamine, respectively (1, 2, 3, 4, and 5) were designed and prepared. The gelation test revealed the following points: (1) within the 30 solvents tested, 1 gels water only; (2) in contrast, 2 gels not only water, but also 11 of the organic solvents tested, a typical "ambidextrous gelator"; (3) 3, 4, and 5, however, gel organic solvents only, and the numbers of solvents gelled are 11, 11 and 13, respectively. Clearly, these compounds are effective low-molecular mass gelators, and show transitions from a low-molecular mass hydrogelator to an ambidextrous gelator and then to low-molecular mass organogelators with a slight increase in the length of the spacers. Interestingly, 5 is a super gelator to acetonitrile, of which the minimum gelation concentration is only 0.07%, w/v. The morphology, microstructure and molecular aggregation of the system strongly depend on the transition, as revealed by SEM, contact angle, energy dispersive X-ray spectroscopy, and XRD measurements. More interestingly, an aggregation-induced enhanced emission was observed along with gelation. Furthermore, the system appeared as a supramolecular chiroptical switch in the sol-gel process that is the chirality disappeared when the gel was heated to solution, whereas it reappeared when cooled to a gel.

ROM Polymerization-Capture-Release Strategy for the Chromatography-Free Synthesis of Novel Unsymmetrical Porphyrazines

[reaction: see text] Crossover-Linstead macrocyclization reactions of two norbornenyl-tagged diaminomaleonitriles with dipropylmaleonitrile gave access to crude mixtures of porphyrazines containing diamino-hexapropyl-porphyrazine magnesium complexes. The mixtures were subjected to ring-opening metathesis polymerization to yield the insoluble diaminoporphyrazine-functionalized polymers. Acid-mediated cleavage from the polymer backbone followed by acylation of the resultant sensitive macrocyclic diamines gave monoacetyl-, monotrifluoroacetyl-, and ditrifluoroacetyl-substituted porphyrazinediamines. Conversion of these amido-porphyrazines to the corresponding zinc macrocycles and studies of their electronic absorption and emission spectra, electrochemistry, and photophysics are described.

Photophysicochemical consequences of bovine serum albumin binding to non-transition metal phthalocyanine sulfonates

The interactions between bovine serum albumin (BSA) and sulfonated metallophthalocyanine (MPc) complexes of aluminum (AlPcS(mix)), zinc (ZnPcS(mix)), silicon (SiPcS(mix)), germanium (GePcS(mix)) and tin (SnPcS(mix)) are studied using fluorescence quenching of BSA by MPc complexes. The fluorescence quantum yields of the non-aggregated MPc complexes (AlPcS(mix), GePcS(mix) and SiPcS(mix)) decreased in the presence of BSA, but increased for the aggregated ZnPcS(mix) and SnPcS(mix) complexes. The BSA: MPc conjugates were less stable than the corresponding MPc complexes. The quenching constants were much higher for the non-aggregated complexes. The aggregated nature of the complexes also affected the rate constants (k(F), k(IC), k(ISC)) for the deactivation of the excited singlet state.

Synthesis and reactions of aminoporphyrazines with annulated five- and seven-membered rings

The novel five- and seven-membered ring appended aminoporphyrazines 3 and 12 have been prepared via mixed Linstead macrocyclization. The structures of both have been unequivocally established by X-ray crystallographic studies. Reductive deselenation of selenadiazole 3 in the presence of 9,10-phenanthrenequinone or 2,3-butanedione results in the formation of pyrazines 6a,b, whereas oxidation of porphyrazine 12 gave the corresponding seco derivative 14. seco-Porphyrazine 14 mediates the generation of singlet oxygen with a quantum yield of 0.74.

Peripherally metalated secoporphyrazines: a new generation of photoactive pigments

Base-catalyzed cross condensation of dipropylmaleonitrile 1 with bis(dimethylamino)maleonitrile 2 in an equimolar ratio afforded the porphyrazines 3a, 4a, 5a, 6a and 7a. Subsequent demetalation of 5a with TFA followed by remetalation with Zn(OAc)(2) gave ligand 5c in good yield. Compound 5c was, in turn, selectively oxidized and further peripherally functionalized using Pt(PhCN)(2)Cl(2) and PdCl(2) to yield the novel seco solitaire porphyrazines 10a and 10b. The photophysical profiles of the seco solitaire porphyrazines 10a and 10b were evaluated by means of absorption, emission, and transient absorption spectroscopy. The new pigments 10a and 10b were found to be photochemically more stable than the solitaire complexes 3d and 3e and mediated the generation of singlet oxygen with quantum yields of 0.59 and 0.45, respectively.