Showing papers on "Porphyrin published in 2008"

Zeolite-like Metal−Organic Frameworks as Platforms for Applications: On Metalloporphyrin-Based Catalysts

Abstract: The extra-large cavities of zeolite-like metal−organic frameworks (ZMOFs) offer great potential for their exploration in applications pertinent to larger molecules, like porphyrins. The anionic nature of the framework allowed for facile in situ encapsulation of a cationic free-base porphyrin, and the α-cage of our (In-imidazoledicarboxylate)-based rho-ZMOF is ideally suited to the isolation of one porphyrin molecule per cage, which prevents the oxidative self-degradation associated with self-dimerization common in homogeneous catalysis and upon aggregation in solid supports like mesoporous silicates or polymers. The encapsulation of a free-base porphyrin [5,10,15,20-tetrakis(1-methyl-4- pyridinio)porphyrin] and the stability of the rho-ZMOF to metalation conditions, allows for the preparation of a variety of metalloporphyrins (i.e., Mn, Cu, Co, Zn ions) with the ZMOF serving as a platform. The Mn-metallated porphyrin encapsulated in rho-ZMOF shows catalytic activity toward the oxidation of cyclohexane, wi...

Nature of the Catalytic Centers of Porphyrin-Based Electrocatalysts for the ORR: A Correlation of Kinetic Current Density with the Site Density of Fe−N4 Centers

Abstract: In this work, it has been shown that structural changes of an as-prepared catalyst enable the assignment of the catalytic centers responsible for the direct and indirect oxygen reduction reaction, respectively, of porphyrin-based electrocatalysts. An iron porphyrin (FeTMPPCl)-based catalyst as well as a catalyst based on H2TMPP were prepared using the so-called foaming agent technique (FAT). The obtained iron catalyst was used as a generic material for the post-treatments. Structural changes were analyzed by 57Fe Mossbauer spectroscopy. The catalytic activity toward the oxygen reduction reaction (ORR) was determined using rotating (ring) disc electrode (R(R)DE) experiments. The catalysts exhibit a variation in the iron content between 2.9 and 4.5 wt % caused by the post-treatments. It has been found that the Mossbauer spectra of all catalysts can be fitted assuming two different ferrous Fe−N4 centers, a CFeN2 center (Fe2+, S = 2) and an Fe3C center (Fe0). After the intensities found in the Mossbauer spect...

Catalysis by microporous phthalocyanine and porphyrin network polymers

Abstract: Cobalt phthalocyanine and iron porphyrin network polymers of intrinsic microporosity (network-PIMs) were prepared and their performance as heterogeneous catalysts compared with that of low molar mass analogues. Spiro-linked Co phthalocyanine network-PIMs prepared from preformed chlorinated phthalocyanines showed lower surface areas and lower catalytic activity than those prepared by a phthalocyanine-forming reaction from a rigid precursor incorporating a spiro-centre. However, all the phthalocyanine network-PIMs were much more effective catalysts than low molar mass Co phthalocyanine for the decomposition of hydrogen peroxide, the oxidation of cyclohexene and the oxidation of hydroquinone. An Fe porphyrin network-PIM showed a higher surface area than any of the phthalocyanine polymers and showed higher activity for the oxidation of hydroquinone, also outperforming a low molar mass FeCl porphyrin.

Single molecule conductance of porphyrin wires with ultralow attenuation.

Abstract: A series of thioacetate-terminated butadiyne-linked porphyrin oligomers have been synthesized with one to three porphyrin repeat units. Single molecule electrical scanning tunneling microscopy measurements using the I(s) and I(t) methods were used to determine the molecule conductances for this series of oligomers. The molecular conductance shows an exponential falloff with sulfur−sulfur distance with a remarkably low attenuation factor of β = (0.04 ± 0.006) A−1.

Ruthenium porphyrin compounds for photodynamic therapy of cancer.

Abstract: Five 5,10,15,20-tetra(4-pyridyl)porphyrin (TPP) areneruthenium(II) derivs., a p-cymeneosmium, a pentamethylcyclopentadienyliridium and a pentamethylcyclopentadienylrhodium analog were prepd. and characterized as potential photosensitizing chemotherapeutic agents. The dinuclear areneruthenium complexes [Ru(h6-arene)(m-Cl)Cl]2 (arene = C6H6, C6H5CH3, p-iPrC6H4Me, C6Me6, and 1,4-C6H4(COOEt)2) react with TPP in MeOH to give the corresponding tetranuclear complexes [Ru4(h6-arene)4(TPP)Cl8] (arene = C6H6 (1, 56% yield), C6H5CH3 (2, 70%), p-iPrC6H4Me (3, 70%), C6Me6 (4, 79%), 1,4-C6H4(COOEt)2 (5, 73%)). The dinuclear p-cymeneosmium complex [Os(h6-p-iPrC6H4Me)(m-Cl)Cl]2 reacts with TPP to form the tetranuclear areneosmium complex [Os4(h6-p-iPrC6H4Me)4(TPP)Cl8] (6) in 47% yield. The isoelectronic Rh and Ir pentamethylcyclopentadienyl derivs. [Rh4(h5-C3Me5)4(TPP)Cl8] (7, 73%) and [Ir4(h5-C3Me5)4(TPP)Cl8] (8, 83%) were obtained in MeOH from the reaction of [M(h5-C5Me5)(m-Cl)Cl]2 (M = Rh, Ir) with TPP. The mol. structures of 4 and 7 were detd. by x-ray crystallog. The biol. effects of all these derivs. were assessed on human melanoma tumor cells, and their cellular uptake and intracellular localization were detd. All mols., except the Rh complex which was not cytotoxic, demonstrated comparable cytotoxicity in the absence of laser irradn. The Ru complexes exhibited excellent phototoxicities toward melanoma cells when exposed to laser light at 652 nm. Cellular uptake and localization microscopy studies of [Ru4(h6-C6H5CH3)4(TPP)Cl8] and [Rh4(h5-C5Me5)4(TPP)Cl8] revealed that they accumulated in the melanoma cell cytoplasm in granular structures different from lysosomes. The fluorescent porphyrin moiety and the metal component were localized in similar structures within the cells. Thus, the porphyrin areneruthenium(II) derivs. represent a promising new class of organometallic photosensitizers able to combine chemotherapeutic activity with photodynamic therapeutic treatment of cancer.

Structural diversity in expanded porphyrins.

Abstract: Inspired by the chemistry of porphyrins, in the last decade, a new research area where porphyrin analogues such as expanded, isomeric, and contracted porphyrins have been synthesized, and their chemistry has been exploited extensively. Expanded porphyrins are macrocyclic compounds where pyrrole or heterocyclic rings are connected to each other through meso carbon bridges. Depending on the number of pyrrole rings in conjugation or the number of double bonds linking the four pyrrole rings expanded porphyrins containing up to 64 π electrons are reported in the literature. The interest in these systems lies in their potential applications as anion binding agents, as photosensitizers for photodynamic therapy (PDT), in antisensing applications, as MRI contrasting agents, and more recently, as material for nonlinear optical application. Expanded porphyrins containing more than four pyrrole or heterocyclic rings, such as sapphyrin (five pyrrole), rubyrin (six pyrrole), heptaphyrin (seven pyrrole), and octaphyrin ...

Quinoxaline-fused porphyrins for dye-sensitized solar cells

Abstract: 5,10,15,20-Tetrakis(2,4,6-trimethylphenyl)-6‘-carboxyquinoxalino[2,3-β]porphyrinatozinc (II) (ZnQMA) and 5,10,15,20-tetrakis(2,4,6-trimethylphenyl)-6‘,7‘-dicarboxyquinoxalino[2,3-β]porphyrinatozinc (II) (ZnQDA) have been synthesized to evaluate the effects of β,β‘-carboxyquinoxalino moieties on the structure and optical, electrochemical, and photovoltaic properties of the porphyrins. Both ZnQMA and ZnQDA exhibited broadened and red-shifted light absorption in UV−visible absorption spectra compared with 5,10,15,20-tetrakis(2,4,6-trimethylphenyl)porphyrinatozinc (II) (ZnP). ZnQMA and ZnQDA also showed decrease in the highest occupied molecular orbital−lowest unoccupied molecular orbital (HOMO−LUMO) gap due to the extension of the porphyrin π-system. From the results of 1H NMR spectroscopy and DFT calculations, ZnQMA and ZnQDA were found to adopt saddle and planar structures, respectively. ZnQMA-sensitized TiO2 solar cell with TiO2 nanoparticles (P25) revealed the power conversion efficiency (η) of 5.2%, whe...

Enhanced pi conjugation around a porphyrin[6] nanoring

Abstract: (Figure Presented) Strong cycle: The cyclic hexamer-template complex 3 obtained through template-directed trimerization of a porphyrin dimer 2, using a hexapyridyl template 1, is extremely stable (K f =7×10 38 m -1 ), but the free macrocycle 4 can be liberated using amine ligands. Spectroscopic data and DFT calculations show that the cyclic hexamer is more conjugated than its linear analogue. © 2008 Wiley-VCH Verlag GmbH & Co. KGaA.

Coordination of Iron Atoms by Tetraphenylporphyrin Monolayers and Multilayers on Ag(111) and Formation of Iron-Tetraphenylporphyrin

Abstract: The in situ metalation of monolayers and multilayers of 2H-tetraphenylporphyrin (2HTPP) with Fe atoms on Ag(111) was studied with scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS). This surface-confined coordination reaction results in the formation of adsorbed iron(II)-tetraphenylporphyrin (FeTPP). It is demonstrated that metalation of 2HTPP is achieved either by depositing iron atoms onto a monolayer of 2HTPP at room temperature or, alternatively, by depositing 2HTPP onto a Ag(111) surface with predeposited iron. The latter route requires elevated temperatures, indicating that this reaction includes at least one step with an activation barrier. In addition, it is demonstrated that vapor deposited Fe atoms also react with multilayers of the porphyrin at room temperature under the formation of FeTPP.

Protoporphyrin IX Nanoparticle Carrier: Preparation, Optical Properties, and Singlet Oxygen Generation

Abstract: The present study is focused on developing a nanoparticle carrier for the photosensitizer protoporphyrin IX for use in photodynamic therapy. The entrapment of protoporphyrin IX (Pp IX) in silica spheres was achieved by modification of Pp IX molecules with an organosilane reagent. The immobilized drug preserved its optical properties and the capacity to generate singlet oxygen, which was detected by a direct method from its characteristic phosphorescence decay curve at near-infrared and by a chemical method using 1,3-diphenylisobenzofuran to trap singlet oxygen. The lifetime of singlet oxygen when a suspension of Pp IX-loaded particles in acetonitrile was excited at 532 nm was determined as 52 micros, which is in good agreement with the value determined for methylene blue in acetonitrile solution under the same conditions. The Pp IX-loaded silica particles have an efficiency of singlet oxygen generation (eta Delta) higher than the quantum yield of free porphyrins. This high efficiency of singlet oxygen generation was attributed to changes on the monomer-dimer equilibrium after photosentisizer immobilization.

Morphology-Controlled Self-Assembled Nanostructures of 5,15-Di[4-(5-acetylsulfanylpentyloxy)phenyl]porphyrin Derivatives. Effect of Metal−Ligand Coordination Bonding on Tuning the Intermolecular Interaction

Abstract: Novel metal-free 5,15-di[4-(5-acetylsulfanylpentyloxy)phenyl]porphyrin H2[DP(CH3COSC5H10O)2P] (1) and its zinc congener Zn[DP(CH3COSC5H10O)2P] (2) were designed and synthesized. Single-crystal X-ray diffraction (XRD) analysis confirmed the tetrapyrrole nature of these two compounds, revealing the existence of metal−ligand coordination bond between the carbonyl oxygen in the aryloxy side chain of meso-attached phenyl group in the porphyrin molecule with the zinc center of neighboring porphyrin molecule in the crystal structure of 2. This intermolecular Zn−O coordination bond induces the formation of a supramolecular chain structure in which the porphyrinato zinc moieties are arranged in a “head-to-tail” mode (J-aggregate), which is in contrast to a “face-to-face” stacking mode (H-aggregate) in the supramolecular structure formed depending on the C−H···π interaction in the crystal of 1. Their self-assembling properties in MeOH and n-hexane were comparatively investigated by scanning electronic microscopy an...

A Bioinspired Construct That Mimics the Proton Coupled Electron Transfer between P680•+ and the TyrZ-His190 Pair of Photosystem II

Abstract: A bioinspired hybrid system, composed of colloidal TiO2 nanoparticles surface modified with a photochemically active mimic of the PSII chlorophyll-Tyr-His complex, undergoes photoinduced stepwise electron transfer coupled to proton motion at the phenolic site. Low temperature electron paramagnetic resonance studies reveal that injected electrons are localized on TiO2 nanoparticles following photoexcitation. At 80 K, 95% of the resulting holes are localized on the phenol moiety and 5% are localized on the porphyrin. At 4.2 K, 52% of the holes remain trapped on the porphyrin. The anisotropic coupling tensors of the phenoxyl radical are resolved in the photoinduced D-band EPR spectra and are in good agreement with previously reported g-tensors of tyrosine radicals in photosystem II. The observed temperature dependence of the charge shift is attributed to restricted nuclear motion at low temperature and is reminiscent of the observation of a trapped high-energy state in the natural system. Electrochemical stu...

Naphthyl-Fused π-Elongated Porphyrins for Dye-Sensitized TiO2 Cells

Abstract: Novel unsymmetrically π-elongated porphyrins, in which the naphthyl moiety is fused to the porphyrin core at the naphthyl bridge with a carboxyl group (fused-Zn-1) or at the opposite side of the phenyl bridge with a carboxyl group (fused-Zn-2), have been synthesized to improve the light-harvesting abilities in porphyrin-sensitized solar cells. As the results of π-elongation with low symmetry, Soret and Q bands of fused-Zn-1 and fused-Zn-2 were red-shifted and broadened, and the intensity of Q-band relative to that of Soret band was enhanced. The fused-Zn-1 and fused-Zn-2-sensitized TiO2 solar cells showed the power conversion efficiencies (η) of 4.1% and 1.1%, respectively, under standard AM 1.5 conditions. The η value of the fused-Zn-1 cell was improved by 50% compared to the reference cell using unfused porphyrin (Zn-1). The fused-Zn-1-sensitized cell revealed high IPCE (incident photon-to-current efficiency) values of up to 55%, extending the response of photocurrent generation close to 800 nm. Thus, t...

Immobilization of metalloporphyrins into nanotubes of natural halloysite toward selective catalysts for oxidation reactions

Abstract: This paper describes the immobilization of anionic and cationic metalloporphyrins into the nanotubes/nanoscrolls of natural halloysite and investigates the catalytic activity of these novel materials in the oxidation of organic substrates. Two methods for metalloporphyrin immobilization were tested: immobilization under pressure and immobilization under stirring/reflux conditions. The best immobilization rate (100%) was obtained with the anionic iron(III) porphyrin immobilized via the pressurized system. A cationic iron(III) porphyrin was also immobilized into the support with relatively good yields, but no encouraging results were obtained for the immobilization of a neutral iron(III) porphyrin. The obtained materials were characterized by UV–vis and infrared spectroscopies, X-ray diffraction, and transmission electron microscopy. The catalytic activity of a fully immobilized iron(III) porphyrin was evaluated in the oxidation of cyclo-octene, cyclohexane and n -heptane, using iodosylbenzene as the oxygen donor. It has been shown that these novel immobilized catalysts are a promising system for selective oxidation reactions.

Noncovalent Assembly of a Metalloporphyrin and an Iron Hydrogenase Active-Site Model: Photo-Induced Electron Transfer and Hydrogen Generation

Abstract: A noncovalent assembly of a pyridyl-functionalized hydrogenase active-site model complex and zinc tetraphenylporphyrin has been obtained and characterized. Upon light irradiation, fluorescence quenching by electron transfer was observed from the singlet excited state of the porphyrin to the diiron center, and the mechanism was verified by fluorescence lifetime and transient absorption spectroscopic measurements. In contrast to molecular dyads linked by covalent bonds, the assembled system was designed to avoid charge recombination via complex dissociation after photo-induced electron transfer. Visible light-driven hydrogen generation was observed from this self-assembled system. The assembling strategy employed in this study has the potential to be used for any other hydrogenase models in the future.

Hybrid Organic–Inorganic Porphyrin–Polyoxometalate Complexes

Abstract: Two Anderson-type polyoxomolybdates [FeMo6O18{(OCH2)3CNHCO(4-C5H4N)}2]3– and [MnMo6O18{(OCH2)3CNHCO(4-C5H4N)}2]3– and two Lindqvist-type polyoxovanadates [V6O13{(OCH2)3CCH2OC(O)(4-C5H4N)}2]2– and [V6O13{(OCH2)3CNHCO(4-C5H4N)}2]2– were functionalized with pendant pyridyl groups. The electrochemical analysis revealed reversible redox processes at the heteroatom of the Anderson-type compounds and at the vanadium atoms in the Lindqvist series. Axial coordination of the polyoxometalate-grafted pyridyl groups to the metal ion in [Ru(CO)TPP] (TPP = tetraphenylporphyrin) and [ZnTPP] yielded polyoxometalate–porphyrin assemblies in solution. Evidence for electronic communication between the polyoxometalate and the porphyrin was established by fluorescence spectroscopy. Cyclic voltammetry showed the influence of the porphyrin on the redox process of the polyoxometalate and also nucleophilic attack at the porphyrin skeleton by the pendant pyridyl groups. Implications for the construction of supramolecular functional devices based on these components are discussed.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

Zinc(II) tetraarylporphyrins anchored to TiO2, ZnO, and ZrO2 nanoparticle films through rigid-rod linkers.

Abstract: A series of six Zn(II) tetraphenylporphyrins (ZnTPP), with a phenyl (P) or oligophenyleneethynylene (OPE = (PE)n) rigid-rod bridge varying in length (9−30 A) and terminated with an isophthalic acid (Ipa) anchoring unit, were prepared as model dyes for the study of sensitization processes on metal oxide semiconductor nanoparticle surfaces (MOn = TiO2, ZnO, and insulating ZrO2). The dyes were designed such that the electronic properties of the central porphyrin chromophore remained consistent throughout the series, with the rigid-rod anchoring unit allowing each porphyrin unit to be located at a fixed distance from the metal oxide nanoparticle surface. Electronic communication between the porphyrin and the rigid-rod unit was not desired. Rigid-rod porphyrins ZnTPP−Ipa, ZnTPP−P−Ipa, ZnTPP−PE−Ipa, ZnTPP−(PE)2−Ipa, ZnTPP−(PE)3−Ipa, and ZnTMP−Ipa (with mesityl substituents on the porphyrin ring) were synthesized using combinations of mixed aldehyde condensations and Pd-catalyzed cross-coupling reactions. Their ...

Merging porphyrins with organometallics: synthesis and applications.

Abstract: The coordination chemistry of porphyrins has traditionally involved the ability of the porphyrin's tetrapyrrolic core to accommodate metal ions of varying charges and sizes, and on the organometallic chemistry of the resulting metalloporphyrins. However, the organometallic chemistry of porphyrins is not necessarily restricted to the metal bound in the porphyrin core, but can also be extended to the porphyrin periphery, be it through direct metalation of the porphyrin macrocycle at the meso or position, or by attachment to or merger of the porphyrin skeleton with ligands, followed by metalation. This Review focuses on the synthetic strategies used for porphyrins with peripheral metal-carbon bonds. The exciting results that have been produced underscore the importance and future potential of this field.

Photoelectrochemical Properties of Doubly β-Functionalized Porphyrin Sensitizers for Dye-Sensitized Nanocrystalline-TiO2 Solar Cells

Abstract: Functionalized porphyrins at meso- and β-positions with different carboxylic acid groups were prepared to investigate electronic and photovoltaic properties as dye-sensitized nanocrystalline-TiO2 solar cells. The electronic structures of the porphyrin macrocyclic core are strongly coupled with olefinic side chains so that the absorption spectrum exhibits largely broad and red-shifted Soret and Q-bands, especially up to 475 nm at the Soret band in a porphyrin doubly functionalized with malonic diacid groups. Among porphyrin derivatives prepared in this study, 2b-bdta-Zn exhibits the maximum overall conversion efficiency of 3.03% and the maximum incident photon to current efficiency of 60.1% in the Soret band region, superior to the others. From such photovoltaic performances, we can suggest that multiple pathways through olefinic side chains at two β-positions enhance the overall electron injection efficiency and the moderate distance between the porphyrin sensitizer and the TiO2 semiconductor layer is imp...

Fluorinated porphyrin tweezer: a powerful reporter of absolute configuration for erythro and threo diols, amino alcohols, and diamines.

Abstract: A general and sensitive nonempirical protocol to determine the absolute configurations of erythro and threo diols, amino alcohols, and diamines is reported. Binding of diols to the porphyrin tweezer system is greatly enhanced by increasing the Lewis acidity of the metalloporphyrin. Supramolecular complexes formed between the porphyrin tweezer host and chiral substrates exhibited exciton-coupled bisignate CD spectra with predictable signs based on the substituents on the chiral center. The working model suggests that the observed helicity of the porphyrin tweezer is dictated via steric differentiation experienced by the porphyrin ring bound to each chiral center. A variety of erythro and threo substrates were investigated to verify this chiroptical method. Their absolute configurations were unequivocally determined, and thus a general mnemonic is provided for the assignment of chirality.

Growth of Narrowly Dispersed Porphyrin Nanowires and Their Hierarchical Assembly into Macroscopic Columns

Abstract: The self-assembly of amphiphilic (porphyrin)Sn 1 in an aqueous Pluronic F127 media results in the formation of narrowly dispersed nanowires. Variation of aqueous Pluronic concentrations allows for a systematic variation of porphyrin nanowire lengths while keeping their widths constant. These nanowires can be further assembled into secondary macroscopic columns.

Observation of vanadyl porphyrins and sulfur-containing vanadyl porphyrins in a petroleum asphaltene by atmospheric pressure photonionization Fourier transform ion cyclotron resonance mass spectrometry.

Abstract: Vanadyl (VO) porphyrins and sulfur-containing vanadyl (VOS) porphyrins of a wide carbon number range (C(26) to C(52)) and Z-number range (-28 to -54) were detected and identified in a petroleum asphaltene by atmospheric pressure photonionization (APPI) and Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS). APPI provides soft ionization of asphaltene molecules (including VO and VOS porphyrins), generating primarily molecular ions (M(+.)). The ultra-high mass resolving power (m/Delta m(FWHM) approximately 500 K) of FTICR-MS enabled resolution and positive identification of elemental formulae for the entire family of VO and VOS porphyrins in a complicated asphaltene matrix. Deocophylerythro-etioporphyrin (DPEP) is found to be the most prevalent structure, followed by etioporphyrins (etio)- and rhodo (benzo)-DPEP. The characteristic Z-distribution of VO porphyrins suggests benzene and naphthene increment in the growth of porphyrin ring structures. Bimodal carbon number distributions of VO porphyrins suggest possible different origins of low and high molecular weight species. To our knowledge, the observation of VOS porphyrins in a petroleum product has not previously been reported. The work is also the first direct identification of the entire vanadyl porphyrin family by ultra-high resolution mass spectrometry without chromatographic separation or demetallation.

Complexation-induced transition of nanorod to network aggregates: alternate porphyrin and cyclodextrin arrays.

Abstract: Tetrakis(permethyl-β-cyclodextrin)-modified zinc(II) porphyrin (1) and tetra(β-cyclodextrin)-modified zinc(II) porphyrin (2) were synthesized via “click chemistry”. Intermolecular inclusion complexation of these structurally similar 1 and 2 with tetrasodium tetraphenylporphyrintetrasulfonate (3) led to formation of two distinctly different nanoarchitectures with alternate porphyrin and cyclodextrin arrays, which were proven to be network and nanorod aggregates, respectively, by using transmission electron microscopy, atomic force microscopy, and scanning electron microscopy. From the results of comparative studies in different solutions, we elucidated the mechanisms that result in nanorod to network aggregates transition, concluding that the complexation strength of porphyrin with cyclodextrin is a crucial factor to activate the potential binding sites of a molecular building block.

A discrete supramolecular conglomerate composed of two saddle-distorted zinc(II)-phthalocyanine complexes and a doubly protonated porphyrin with saddle distortion undergoing efficient photoinduced electron transfer.

Abstract: Porphyrins (Por) and phthalocyanines (Pc) exhibit lightharvesting efficiency for producing charge-separated states as models of the reaction center in photosynthetic bacteria and photovoltaic cells for energy conversion. The use of supramolecular assemblies to model the functionality of the reaction center is an attractive and fruitful strategy to develop photofunctional materials and devices. Porphyrins exhibit strong Soret bands around 400 to 450 nm, whereas phthalocyanines show strong Q bands around 700 to 800 nm. Thus, the combination of those two p systems can cover nearly the whole range of the visible region and can be a useful strategy for development of photofunctional materials for efficient light-energy conversion. Attempts have so far been made to synthesize covalently linked Por–Pc heterodyad molecules and construct Por–Pc heterosupramolecules. Recently, ZnPor and ZnPc have been reported to form two-dimensional arrays on gold surfaces, and the formation of a cofacial ZnPor–ZnPc coordination tetrad has also been reported. However, a crystal structure determination of a discrete supramolecular assembly composed of both Por and Pc has yet to be reported. In addition, since the Q-band absorption of Pc usually overlaps the wavelength of fluorescence of Por, energy transfer is favored over electron transfer in most heterodyads. We have developed supramolecular assemblies based on a saddle-distorted nonplanar porphyrin, dodecaphenylporphyrin (H2DPP), and its metal complexes. [11–13] The saddle distortion facilitates protonation of pyrrole nitrogen atoms to allow access to a stable diprotonated porphyrin, which can act as an electron acceptor. In addition, the saddle distortion affords higher Lewis acidity at the metal center to maintain axial coordination of ligands, as a result of poor overlap of the pyrrole nitrogen lone pair orbitals with d orbitals of the metal center. In contrast, the Zn complex of the saddle-distorted phthalocyanine 1,4,8,11,15,18,22,25-octaphenylphthalocyanine (H2OPPc) exhibits a lower oxidation potential relative to the corresponding porphyrin complex. To construct supramolecular conglomerates composed of both porphyrin and phthalocyanine in a well-defined manner, we have taken advantage of saddle distortion of both components. Herein, we report formation of a discrete supramolecular assembly composed of H4DPP 2+ and [Zn(OPPc)] connected by 4-pyridinecarboxylate (4-PyCOO ) with coordination and hydrogen bonding (Figure 1). The supramolecular conglomerate [(H4DPP){Zn(OPPc)(k-N-4-PyCOO)}2] (1) was synthesized by reaction of [H4DPP](4-PyCOO)2 (2) and Zn(OPPc) (3) in toluene. We crystallized and isolated 1 in pure form by vapor diffusion of hexanes into solution of the mixture in toluene. X-ray crystallography of 1 unambiguously established its structure (Figure 2a).

The photochemical yield of singlet oxygen from porphyrins in different states of aggregation

Abstract: — Aqueous solutions of hematoporphyrin and hematoporphyrin derivatives were exposed to light. When present in such solutions tryptophan is degraded by a singlet oxygen mechanism. This is true for excitation at 396 nm, where porphyrin monomers have their absorption maximum, as well as for excitation at 360 nm, where porphyrin aggregates seem to absorb strongly. The quantum yield of singlet oxygen production is similar within 25% for excitation at 396 and 360 nm while the fluorescence quantum yield is more than a factor 2 lower for excitation at 360 nm than for excitation at 396 nm. Photoexcitation of the clinically used hematopotophyrin derivatives photofrin I and photofrin II produces singlet oxygen with significantly smaller yields than photoexcitation of hematoporphyrin. Thus, the aggregates present in solutions of photofrin I and photofrin II are of a different nature than those present in aqueous solutions of hematoporphyrin.