Porphyrazine Core Research Articles

DFT and TDDFT study of Al(III), Ga(III), In(III) porphyrazinates and their perhalogenated derivatives

The effect of perhalogenation (F, Cl) of porphyrazine macrocycle on the molecular structure, electronic and spectral properties of AlIII, GaIII and InIII complexes bearing axial pentafluorophenoxy (C6F5O) group was investigated by DFT and TDDFT methods. Interactions between the axial pentafluorophenoxy group and porphyrazine core were carried out using the Symmetry-Adapted Perturbation Theory (SAPT0) method. According to the calculation results, the nature of the metal atom and peripheral halogenation slightly affect the geometry parameters. Analysis of the simulated spectra showed a bathochromic shift of the Q-band for perchlorinated complexes which correlates with narrowing of the HOMO-LUMO gap.

The Valence and Spin State Tuning of Iron(II/III) Porphyrazines with Bulky Pyrrolyl Periphery in Solution and Solid State.

Iron(III) porphyrazines containing peripheral 2,5-dimethyl-, 2-methyl-5-phenyl-, and 2,3,5-triphenyl-1H-pyrrol-1-yl substituents were synthesized and subjected to physicochemical characterization. This was accomplished by high-resolution mass spectrometry, nuclear magnetic resonance (as diamagnetic Fe(II) derivatives), HPLC purity analysis, and UV-Vis spectroscopy, accompanied by the solvation study in dichloromethane and pyridine. X-ray structure analysis was performed for a single crystal of the previously obtained 2,5-diphenyl-substituted derivative of porphyrazine complex (5d). The octahedral geometries of iron cation, present in the porphyrazine core, influenced the packing mode of molecules in the crystals. Mössbauer studies, performed for solid samples of iron porphyrazines, indicated that low-spin reduced iron states might occupy low- or high-symmetry binding sites. It was found that the hyperfine parameters and the subsequent contribution of the iron cations depend on the number of phenyl groups surrounding the pyrrolyl moiety. For iron(II) porphyrazine 2,3,5-triphenylpyrrol-1-yl substituents (5b), a high-spin ferrous state fraction was observed. Temperature-dependent measurements showed that the freed rotation of the peripheral porphyrazine ligands and the increased flexibility of the macrocycle ring result in the Fe2+ ion being stabilized in a diamagnetic state at a binding site of high symmetry at room temperature in the solid state. This process is most probably stimulated by the range of collective motions of the polymeric ribbons consisting of iron(II) porphyrazines observed in the X-ray.

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.

Optical properties of a series of pyrrolyl-substituted porphyrazines and their photoinactivation potential against Enterococcus faecalis after incorporation into liposomes

A series of porphyrazines substituted in the periphery with various pyrrolyl groups was studied regarding its optical properties and biological potential for antimicrobial photodynamic therapy towards Enterococcus faecalis. There were studied magnesium(II) porphyrazines with peripheral 2,5-dimethylpyrrol-1-yl, 2-methyl-5-phenylpyrrol-1-yl, 2,5-diphenylpyrrol-1-yl, 2,5-di(4′-chlorophenyl)pyrrol-1-yl, 2,5-di(biphenyl-4'-yl)pyrrol-1-yl, 2,3,5-triphenylpyrrol-1-yl substituents and zinc(II) porphyrazine substituted in the periphery with 2,5-dimethylpyrrol-1-yl groups. The studied photosensitizers revealed singlet oxygen quantum yield values in the range of 0.04–0.25, whereas fluorescence and photodecomposition quantum yield values were found between (0.45–4.55)·10−2 and (0.09–5.10)·10-4 respectively. For the studied group of porphyrazine randomers, it was noticed, that the non-alternating order of peripheral substituents can lead to the dramatic loss of their ability towards singlet oxygen formation and fluorescence emission. Replacing magnesium(II) with zinc(II) cation in the porphyrazine core also resulted in the significant improvement of the photoinactivation against Enterococcus faecalis with the log reduction value of >5.5 log. Magnesium porphyrazines revealed only weak or no activity against the studied bacterium.

Panchromatic Photosensitizers Based on Push-Pull, Unsymmetrically Substituted Porphyrazines.

A series of five push-pull porphyrazines of A3 B type, in which unit B is an isoindole 4-carboxylic acid, has been prepared. The units A have been endowed with thioether, amine, ether and alkyl functions, either directly attached to the β-position of the pyrrolic units, or connected to the porphyrazine core through p-substituted phenyl groups. Attaching the electron-donor functions to the porphyrazine periphery produces strong perturbations in the electronic and redox properties of the dyes. Their HOMO and LUMO energies, estimated from the optical and redox data, as well as with DFT calculations, raise upon functionalization with amines, while the corresponding frontier orbital energetic levels lower upon functionalization with thioethers, p-methoxyphenyl or p-tert-butylphenyl groups. The effective interaction of peripheral substitution with the macrocycle produces chromophores with panchromatic absorption between 300 and 750-850 nm.

Light-harvesting with panchromatically absorbing BODIPY–porphyrazine conjugates to power electron transfer in supramolecular donor–acceptor ensembles

Prerequisites for the design of efficient organic solar light converting systems are intense absorptions across the visible region, the ability to funnel excited state energy by intramolecular energy transfer, and the option to partake in photoinduced electron transfer processes. We have established a versatile synthesis platform for functionalized porphyrazines and present the synthesis of a light harvesting dibenzoquinoxalinoporphyrazine that is peripherally substituted with eight alkynyl-linked BODIPY chromophores. Photophysical investigation by means of time-resolved fluorescence and femtosecond transient absorption spectroscopy revealed efficient intramolecular energy transfer from the photoexcited BODIPY to the porphyrazine core. Coordination of a pyridyl-functionalized phenothiazine (PTZ) to the central metal ion of the porphyrazine generates a complex capable of an efficient electron transfer from the PTZ to the photoexcited porphyrazine core. The porphyrazine˙−/PTZ˙+ fingerprints in the visible and in the near-infrared regions as well as the electron transfer dynamics were determined using spectroelectrochemistry and femtosecond transient absorption spectroscopy. The findings form the basis for the development of supramolecular multichromophore ensembles as materials in solar light converting systems.

A perfluorous polyphenyl dendritic shell for the protection of a photosensitizing porphyrazine core

The implementation of thirty-two pentafluorophenyl groups in the periphery of a phthalocyanine analogue results in a photosensitizer with a pronounced resistance towards autophotooxidation. The synthesis relies on the microwave-assisted cycloaddition of terminal alkynes to tetrakis(pentafluorophenyl)cyclopentadienone, for which a new route was devised.

The origin of the unusual broad and intense visible absorption of tetrathiafulvalene-annulated zinc porphyrazine: A density functional theory study

The vertical excitation energies of tetrathiafulvalene (TTF)-annulated zinc porphyrazine (ZnPzTTF) were investigated using time-dependent density functional theory (TDDFT) calculations and compared to the experimental UV–vis spectra. To examine the effects of the aza substitutions and TTF groups on the molecular properties, zinc complexes of porphyrin (ZnP), porphyrazine (ZnPz) and tetraTTF-annulated porphyrin (ZnPTTF) were also selected for comparison. It was shown that numerous electronic transitions with TTF-to-porphyrin or porphyrazine charge transfer character exist and the Q band of ZnPzTTF is dominated by TTF-to-porphyrazine charge transfer transition mixed with porphyrazine core unit itself except for classic porphyrazine π → π* transitions. The Q band of ZnPzTTF mixes with other configurations, which breaks down the Gouterman's classic four-orbital model for the spectral interpretation. The data suggest that TDDFT/SAOP performs best for Q and B bands of ZnPzTTF with the maximum error in excitation energy being 0.17 eV. The CAM-B3LYP, ωB97XD and M06-2X calculations qualitatively predict that the low-lying electronic transitions of ZnPzTTF with TTF-to-porphyrazine charge transfer character located below the Q band. The broad and intense red-shifted Q band suggests that ZnPzTTF can be a candidate for dye-sensitized solar cells.

Synthesis, characterization, electrochemistry and spectroelectrochemistry of novel soluble porphyrazines bearing unsaturated functional groups

Metalloporphyrazines with a 2-methyl-2-pentenyl group fused to each pyrrole unit were synthesized starting with the corresponding unsaturated dicarbonitrile derivative. The new compounds were characterized by elemental analysis together with FTIR, 1H-NMR, and UV–Vis spectroscopy and via voltammetric and spectrochemical methods. Electrochemical and spectroelectrochemical measurements demonstrate that while metal-free and magnesium porphyrazines gave common porphyrazine (Pz) ring-based electron-transfer reactions, incorporating redox active metal center, Co II, into the porphyrazine core extended the redox activity of the ring system with reversible metal-based reduction and oxidation couples of the metal center in addition to the common Pz ring-based electron transfer processes. The unsaturated functional groups of the porphyrazines did not alter the common electrochemical behavior of the complexes. An in situ electrocolorimetric method, based on the 1931 CIE (Commission Internationale de l’Eclairage) system of colorimetry, was applied to investigate the color of the electro-generated anionic and cationic forms of the complexes for possible electrochromatic applications.

Synthesis, characterization and thermal properties of a novel star polymer consisting of poly( ε-caprolactone) arms emanating from an octa-functional porphyrazine core

Octaarmed star-shaped poly( ε-caprolactone) (OSPCL) was successfully synthesized via the ring-opening polymerization (ROP) of ε-caprolactone ( ε-CL) with a magnesium porphyrazine as the multisite initiator and tin(II) 2-ethylhexanoate (Sn(Oct 2)) as the catalyst in bulk at 115 °C. The star polymer has a central Mg-porphyrazine surrounded by ε-CL arms. OSPCL was characterized by 1H NMR, FTIR, GPC and UV–vis, and fluorescent spectroscopy. The effect of the molar ratio of the monomer to the initiator on molecular weight of the polymer was also investigated. The molecular weight of the polymer linearly increased with increasing molar ratio of the monomer to the initiator. The crystallization behavior of OSPCL was studied using differential scanning calorimetry (DSC) and polarizing optical microscopy (POM). OSPCL displayed an interrupted crystal morphology owing to its highly branched architecture, and consequently, the degree of crystallinity was lower in comparison with the linear analogue. Thermogravimetric analysis (TGA) clearly indicated that incorporation of porphyrazine core enhanced the thermal stability of the resulting polymers.

5-Hexylthiophene-fused porphyrazines: new soluble phthalocyanines for solution-processed organic electronic devices

5-Hexylthiophene-fused porphyrazines were designed and synthesized as novel soluble phthalocyanine derivatives. Single-crystal X-ray structural analyses indicated that they have a well-ordered structure in the solid state in spite of the existence of disorder in the thiophene-fused porphyrazine core. Due to the high solubility and improved molecular ordering, the present 5-hexylthiophene-fused porphyrazines showed comparable performance to vapor-processable phthalocyanines as solution-processable organic semiconductors: solution-processed OFETs showed mobility of up to 0.2 cm2V−1 s−1.

Excited State Dynamics and Nonlinear Absorption of a Pyrazinoporphyrazine Macrocycle Carrying Externally Appended Pyridine Rings

The multiphoton absorption properties of the tetrakis-2,3-[5,6-di(2-pyridyl)pyrazino]porphyrazinato(monoacquo)-Mg(II) complex [Py(8)TPyzPzMg(H(2)O)] (1) are reported and interpreted. The nonlinear optical behavior of 1 and the characterization of the excited states important for the nonlinear absorption process were studied at the pump frequency of the second harmonic generation of a Nd:YAG laser in the nanosecond time regime. It was found that complex 1 shows a very good optical limiting performance at 532 nm, which derives from two processes: (a) a reverse-saturable absorption process, which involves a triplet excited state at low intensities, and (b) a two-photon absorption process at higher intensities, which is due to the formation of the radical monoanion of 1, [Py(8)TPyzPzMg(H2O)](.-), during the photoreduction of the triplet state. The participation of a monoanion in determining the overall nonlinear absorption behavior of 1 is found, for the first time, for a tetrapyrrolic system. One can deduce that the involvement of the monoanion derives from the electron-withdrawing effect of the dipyridinopyrazino fragments externally attached to the porphyrazine core which make the reduced form of 1 easily accessible. These results suggest a modification of tetrapyrrolic systems with new nonlinear absorption properties.

Probing Surface-Porphyrazine Reduction Potentials by Molecular Design

This manuscript reports electrochemical and angle-resolved X-ray photoelectron spectroscopy measurements of surface-bound porphyrazine monolayers in which the molecule-surface distance and molecular orientation of the porphyrazine are controlled through the design of the adsorbates. This system has allowed us to probe the importance of molecule-surface interaction in determining the shift in reduction potential upon binding to a gold surface. This quantity currently is in theoretical dispute, with one computation indicating that a porphyrazine/porphyrin exhibits an extremely large covalent binding energy ( approximately 10 eV) to a gold surface, whereas a more recent one finds the binding energy to be only a fraction of an electronvolt. Our study indicates that the shift in reduction potential upon surface binding is not a discontinuous function of the molecule-surface distance, as would be the case if covalent interaction of the porphyrazine core with the gold surface were controlling, but rather varies smoothly. This, therefore, rules out the possibility that the large potential shift seen for a porphyrazine whose macrocyclic core lies approximately 3.9 A above the gold surface, relative to one that lies approximately 8.9 A above the surface, DeltaDeltaE = 340 mV, is caused by direct covalent binding of the pi-system to the metal surface.

Synthesis, Characterization and EPR Studies of Supramolecular Porphyrazines

Supramolecular porphyrazines with eight pyridine donor groups bound through ethylthio ester bridges on the periphery have been prepared. The pyridine donors were quaternized with iodomethane to octacationic porphyrazine. The nonanuclear supramolecular porphyrazine was prepared by the coordination of peripheral pyridine donors with VO(acac)2. The paramagnetic nonanuclear structure was studied in powder and in solution form by EPR. EPR studies together with the other spectral data confirmed the presence of identical pyridine-coordinated VO(acac)2 paramagnetic centers attached to the peripheral positions of the porphyrazine core.

Theoretical AM1 study of acidity of porphyrins, azaporphyrins and porphyrazines

The structure-acidity relationship in the series of non-substituted, meso- or β-substituted and β,β-annulated porphyrins and porpyrazines have been studied using the AM1 method with unrestricted Hartree-Fock basis set. With this purpose, heats of formation have been determined for the geometry optimized structures of the free base macrocycles and corresponding monoanions and dianions formed by deprotonation. Calculated first deprotonation enthalpy values show correlation with available experimental p K1avalues and can be used for prediction of acidity. For porphyrazines bearing electron-withdrawing substituents or π-deficient annulated heteroarens the dianions have lower heats of formation than the corresponding neutral species and such porphyrazines are easily deprotonated upon dissolution in basic solvents (pyridine, DMF). For porphyrazines with annulated 5-member heteroarens it is predicted that deprotonation of peripheral NH groups should occur more easily than deprotonation of the internal NH groups. The influence of different types of annulation of 5- and 6-membered heteroarens to the porphyrazine core on the stability of the macrocyclic system and its acidity are also discussed.

Synthesis and Characterisation of Unsymmetrical Porphyrazines Containing Bis(hydroxyethylthio) Substituents

Unsymmetrical porphyrazines bearing a single peripheral bis(hydroxyethylthio) moiety were synthesised by mixed condensation of bis(2-hydroxyethylthio)maleonitrile and phthalonitrile. Complexation of the thioether groups of metal-free porphyrazine with PdCl2 further lowered the intensity of the Q-band absorption of the porphyrazine core. The new compounds were characterised by elemental analyses, IR, 1H NMR, UV-Vis, and mass spectra.

Synthesis and electrochemical properties of porphyrazines with annulated 1,4-dithiaheterocycles

Porphyrazines (M=H, Mg, Zn or Cu) with 2,3-trimethyleneoxy-2,3-dihydro-1,4-dithiin or 2-ethoxy-2,3-dihydro-1,4-dithiin groups fused to each pyrrol unit have been synthesised starting with the corresponding unsaturated dicarbonitrile derivative. The elemental analysis and IR, 1H NMR, UV–Vis and mass spectral data have been used to characterise the new compounds. Electrochemical investigations have shown that metal insertion into the porphyrazine core and substituents having high electron donating ability shift the ring centred reduction processes towards negative potentials.

ChemInform Abstract: Diels—Alder Reaction of Tribenzo[b,g,l]thiopheno[3,4‐q]porphyrazine as a New Path for Porphyrazine Core Modification.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Optical, magnetic, and electronic properties of peripherally fused macrocycles: molybdocene porphyrazines.

Metal-free and copper porphyrazines, [H(2)pz] and [Cu pz], have been fused at the periphery with molybdocene dithiolene, [Cp(2)Mo]. The optical, magnetic, and electronic properties of the resulting neutral and cationic complexes are studied, using first-principles density functional theory implemented by the discrete variational method. Analysis of the charge and spin distribution shows that the porphyrazine core is strongly coupled with the peripheral complex. The calculated optical absorption is found to be in reasonable agreement with experimental spectra, lending support to our theoretical model. Under appropriate circumstances one observes interaction of unpaired spins localized in the vicinity of both metal sites. The calculated spin distribution shows that [Cp(2)Mo][Cu pz] and [Cp(2)Mo][H(2)pz](+) have a magnetic moment of 1 micro(B) while [Cp(2)Mo][Cu pz](+) and [Cp(2)Mo][H(2)pz] have no moment, in good agreement with the results of X-band EPR spectra. The Cu-Mo magnetic interaction is antiferromagnetic, being mediated by pyrrol nitrogens, meso nitrogens, carbons, and sulfurs.

Octakis(ferrocene)-substituted porphyrazines

Metal-free porphyrazine and metal porphyrazinates (M = Mg, Cu, Co or Zn) substituted with eight ferrocene moieties on the periphery through flexible alkylthio-bridges have been synthesised in a multi-step reaction sequence. The new compounds have been characterised by elemental analyses, i.r., 1H- and 13C-n.m.r., u.v.–vis. and mass spectra. The electrochemical investigation of porphyrazines indicates that all the ferrocene moieties are oxidised at the same potential, confirming the lack of any interaction among ferrocene groups or between ferrocenes and the porphyrazine core.