Porphyrin Monomers Research Articles

Quantification of Active Apohemoglobin Heme-Binding Sites via Dicyanohemin Incorporation.

Apohemoglobin (apoHb) is produced by removing heme from hemoglobin (Hb). However, preparations of apoHb may contain damaged globins, which render total protein assays inaccurate for active apoHb quantification. Fortunately, apoHb heme-binding sites react with heme via the proximal histidine-F8 (His-F8) residue, which can be monitored spectrophotometrically. The bond between the His-F8 residue of apoHb and heme is vital for maintenance of fully functional and cooperative Hb. Additionally, most apoHb drug delivery applications facilitate hydrophobic drug incorporation inside the apoHb hydrophobic heme-binding pocket in which the His-F8 residue resides. This makes the His-F8 residue a proper target for apoHb activity quantification. In this work, dicyanohemin (DCNh), a stable monomeric porphyrin species, was used as a probe molecule to quantify active apoHb through monocyanohemin-His-F8 bond formation. ApoHb activity was quantified via the analysis of the 420 nm equilibrium absorbance of DCNh and apoHb mixtures. His-F8 saturation was determined by the presence of an inflection point from a plot of the 420 nm absorbance of a fixed concentration of apoHb against an increasing DCNh concentration. Various concentrations of a stock apoHb solution were tested to demonstrate the precision of the assay. The accuracy of the assay was assessed via spectral deconvolution, confirming His-F8 saturation at the inflection point. The effect of the heme-binding protein bovine serum albumin and precipitated apoHb on assay sensitivity was not significant. An analysis of the biophysical properties of reconstituted Hb confirmed heme-binding pocket activity. Taken together, this assay provides a simple and reliable method for determination of apoHb activity.

Alkyne-Bridged Multi[Copper(II) Porphyrin] Structures: Nuances of Orbital Symmetry in Long-Range, Through-Bond Mediated, Isotropic Spin Exchange Interactions.

Spin and conformational dynamics in symmetric alkyne-bridged multi[copper(II) porphyrin] structures have been studied in toluene solution at variable temperature using steady-state electron paramagnetic resonance (EPR) spectroscopy. Comparison of the dimer EPR spectra to those of Cu porphyrin monomers shows evidence of an isotropic exchange interaction (Javg) in these biradicaloid structures, manifested by a significant line broadening in the dimer spectra. The extent line broadening depends on molecular structure and temperature, suggesting Javg is modulated by conformational dynamics that impact the torsional angle distribution between the porphyrin-porphyrin least-squares planes. Computational simulation of the experimental EPR spectra, using a developed algorithm for J modulation in flexible organic biradicals, supports this hypothesis. Comparison of ethyne and butadiyne alkyne bridges reveals remarkable sensitivity to orbital interactions between the spacer and the metal, reflected in measurements of Javg as a function of temperature. The results suggest orbital symmetry relationships may be more important than recognized in design of optimized molecular spintronic devices.

Design and Synthesis of Porphyrin Oligomers and Porphyrinoids Via Suzuki-Miyaura Reaction

In view of multi-porphyrin arrays and new porphyrinoids, whih has potential applications in optoelectronic devices, sensors, photovoltaic devices, non-linear optical(NLO) materials, photodynamic therapy (PDT) pigments, light-harvesting models, and host-guest chemistry. Both the manipulation of interporphyrinic interaction and design of new structural porphyrinods are often essential to achieve desirable electronic and photophysical properties. Recently, the Osuka group developed a transition metal-catalyzed coupling reaction that has been proven to be very useful to construct multiporphyrinic systems. Till now we have adopted this strategy and prepared many heterocycles bridged β-to-β porphyrin arrays, including direct-bridged β-to-β porphyrin nanorings[ 1 ], earring porphyrins[ 3 ]. The experiment results indicated that the building blocks will remarkably affect the target molecules. As the bridge is thienylene, the main products is cyclic dimer, trimer, when the bridge is pyridylene, there are trace cyclic products are obtained. when the bridge is free base or Zn(II) porphyrin, bigger loop are formed, while Ni(II)porphyrin is used, the products is much simple. As to synthesis of porphyrin nanobarrel, if the porphyrin monomer is free base or Zn(II) porphyrin, no porphyrin barrel is obtained, which means that only ruffled Ni(II)porphyrin monomers can be used to synthesis porphyrin barrels. Synthesis of direct linked porphyrin nanorings is affected by the meso-substituent on porphyrin, when the substituent is aryl, only trimer and twinned pentamer can be prepared, when the substituent is alkyl, tetramer and twinned heptamer can be obtained.The photophysical study revealed that these porphyrin arrays and porphyrinoids exhibit either longer fluorescent lifetime, larger two photon absorption values or Near-infrared absorptions. Some new porphyrin arrays or porphyrinnoids recently have been constructed through Pd-catalyzed cross-coupling reactions (Figure 1), further study on their properties is underway in our lab. Figure 1. Crystals of earring porphyrins and multi-porphyrin arrays

Synthesis of Oligomeric Benzoporphyrins Via Imidation

In recent years, it is known that the porphyrin electronic system is susceptible to conjugative perturbation at the periphery. [1] So, the electronic and optical properties of porphyrin can be rationally tuned. Because of this, a variety of conjugated porphyrin arrays have been constructed over the last two decades. It is one strategy to link electron donors and electron acceptors together using π-conjugated molecular spacers to investigate photoinduced electron transfer processes on a molecular level. [2] The electronic properties of these molecules make them potentially useful in molecular photonics, optoelectronics, nanoscale application and in solar energy conversion. [1] In this work, we report the synthesis and electronic properties of conjugated porphyrin dimer and monomers. All the porphyrins were synthesized using bromination, palladium catalyzed domino heck reaction followed by electrocyclization/dehydration strategy [3]and then imidation with coupling reagents. Reference [1] S. V. Kirner, D. Arteaga, C. Henkel, J. T. Margraf, N. Alegret, K. Ohkubo, B. Insuasty, A. Ortiz, N. Martı´n, L. Echegoyen, S. Fukuzumi, T. Clark and D. M. Guldi, Chem. Sci., 2015, 6, 5994–6007 [2] S. Fukuzumi, K. Ohkubo and T. Suenobu, Acc. Chem. Res., 2014, 47, 1455. [3] Jinadasa, R. G. W.; Fang, Y.; Kumar, S.; Osinski, A. J.; Jiang, X.; Ziegler, C. J.; Kadish, K. M.; Wang, H. J. Org. Chem., 2015, 80 (24), 12076–12087 Figure 1

Demetallatation of electrochemically polymerised Mn porphyrin anion / PEDOT composites under light-illumination

This work reports photo-demetallation studies of thin-layer, electropolymerized poly(3,4-ethylenedioxythiophene) (PEDOT) loaded with low levels of: (i) an anionic Mn porphyrin monomer (5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrinato manganese(III) chloride (MnTPPS)), and (ii) an anionic Mn porphyrin polymer (poly(5-(4-vinylphenyl)-10,15,20-tris(4-sulfonatophenyl)) porphyrinato manganese(III) chloride (MnPVTPPS)). UV–vis and other measurements confirm that, like previously-studied cationic Mn(III) porphyrins embedded within vapour-phase polymerized PEDOT in low loadings, de-metallation under light illumination also occurs in these systems. However, it occurs to a significantly lesser degree. It can be concluded that demetallation appears to be an inherent feature of PEDOT coatings containing low levels of Mn porphyrins when they are illuminated with light. The demetallation process does not depend on the mode of polymerisation or the nature of the Mn porphyrin dopant. These findings have potentially important implications in water-splitting photocatalysis by Mn porphyrin-doped conducting polymers.

New luminescent extended linear dimer based on meso-tetrafluorenylporphyrins

Abstract A series of porphyrin monomers bearing four n -butyl substituted fluorenyl donor groups is presented; successively, intermediate compounds 1 (TMS protected), 2 (possessing an acetylene group) and corresponding zinc complex 3 have been synthesized. Starting from these building blocks, new extended Dimer, with in totally 9 fluorenyl groups, has been obtained and fully characterized. For the first time two highly luminescent tetrafluorenylporphyrin units ( TFP ) are connected to form a linear geometry and in addition, a rigid 2,7-fluorenyl linker was selected to connect these building blocks. The luminescence properties were compared with TFP monomer, dimer and trimer described earlier by our group.

Fabrication of a TiO2@porphyrin nanofiber hybrid material: a highly efficient photocatalyst under simulated sunlight irradiation

The solar spectrum consists of 8% UV radiation, while 45% of solar energy is from visible light. It is therefore desirable to fabricate a hybrid material which is able to harvest energy from a wide range of photons from the sun for applications such as solar cells, photovoltaics, and photocatalysis. In this study we report on the fabrication of a TiO2@porphyrin hybrid material by surfactant-assisted co-assembly of monomeric porphyrin molecules with TiO2 nanoparticles. The obtained TiO2@porphyrin composite shows excellent integration of TiO2 particles with diameters of 15–30 nm into aggregated porphyrin nanofibers, which have a width of 70–90 nm and are several µm long. SEM, XPS, XRD, FTIR, UV–Vis and fluorescence spectroscopy were employed to characterize the TiO2@TCPP hybrid material. This material exhibits efficient photocatalytic performance under simulated sunlight, due to synergistic photocatalytic activities of the porphyrin aggregates in visible light and TiO2 particles in the UV region. A plausible mechanism for photocatalytic degradation is also proposed and discussed.

Spectroscopic investigation on porphyrins nano-assemblies onto gold nanorods

The interaction between gold nanorods (Au NRs), synthesized by a conventional seeded growth protocol, and the anionic tetrakis-(4-sulfonatophenyl)porphyrin (TPPS4) has been investigated through various spectroscopic techniques. At neutral pH, the formation of H-aggregates and the inclusion of porphyrin monomers in CTAB micelles covering the nanorods have been evidenced. Under mild acidic conditions (pH=3) a nano-hybrid assembly of porphyrin J-aggregates and Au NRs has been revealed. For the sake of comparison, Cu(II) and Zn(II) metal porphyrin derivatives as well as a cationic porphyrin have been studied in the same experimental conditions, showing that: i) CuTPPS4 forms porphyrin H-dimers onto the Au NRs; ii) ZnTPPS4 undergoes to demetallation, followed by acidification of the central core and eventually aggregation onto Au NRs; iii) cationic porphyrin does not interact with Au NRs.

Tuning the Electronic Structure and Properties of Perylene-Porphyrin-Perylene Panchromatic Absorbers.

Light-harvesting architectures that afford strong absorption across the near-ultraviolet to near-infrared region, namely, panchromatic absorptivity, are potentially valuable for capturing the broad spectral distribution of sunlight. One previously reported triad consisting of two perylene monoimides strongly coupled to a free base porphyrin via ethyne linkers (FbT) shows panchromatic absorption together with a porphyrin-like S1 excited state albeit at lower energy than that of a typical monomeric porphyrin. Here, two new porphyrin-bis(perylene) triads have been prepared wherein the porphyrin bears two pentafluorophenyl substituents. The porphyrin is in the free base (FbT-F) or zinc chelate (ZnT-F) forms. The zinc chelate (ZnT) of the original triad bearing nonfluorinated aryl rings also was prepared. The triads were characterized using static and time-resolved optical spectroscopy. The results were analyzed with the aid of molecular-orbital characteristics obtained using density functional theory calculations. Of the four triads, FbT is the most panchromatic in affording the most even distribution of absorption spectral intensity as well as exhibiting the largest wavelength span (380-750 nm). The triads exhibit fluorescence yields (0.35 for FbT-F in toluene) that are substantially greater than for the porphyrin benchmarks (0.049 for FbP-F). The singlet excited-state lifetimes (τS) for the triads in toluene decrease in the order FbT-F (2.7 ns) > FbT (2.0 ns) > ZnT (1.2 ns) ∼ ZnT-F (1.1 ns). The τS values in benzonitrile are FbT (1.3 ns) > FbT-F (1.2 ns) > ZnT-F (0.6 ns) > ZnT (0.2 ns). Thus, the free base triads exhibit relatively long (1.2-2.7 ns) excited-state lifetimes in both polar and nonpolar media. The combined photophysical characteristics indicate that FbT and FbT-F are the best choices for panchromatic light-harvesting systems. Collectively, the findings afford insights into the effects of electronic structure on the panchromatic behavior of ethynyl-linked porphyrin-perylene architectures that can help guide next-generation designs and utilization of these systems.

Prolonged Lifetime of Near-IR Emission due to a Reservoir State in a Phenylene-linked Copper(II) Porphyrin–Zinc(II) Porphyrin Dimer

A phenylene-linked copper(II) porphyrin–zinc(II) porphyrin dimer exhibits near-IR emission, the lifetime of which is 310 ns at 300 K in toluene. Based on transient absorption measurements and emission temperature dependence, the observed emission was ascribed to phosphorescence from the trip-doublet state of copper porphyrin, which is thermally activated with an energy gap of 430 cm−1 from the zinc(II) porphyrin triplet state. The zinc–porphyrin triplet state acts as a reservoir and emission lifetime of the dimer is prolonged by ten times compared to the copper–porphyrin monomer, of which the lifetime is 30 ns.

Morphologically Determined Excitonic Properties of Porphyrin Aggregates in Alcohols with Variable Acidity

Self-assembled, excitonically coupled aggregates of 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin (TSPP) in acidified alcohols were studied by absorption, resonance light scattering (RLS), and resonance Raman (RR) spectroscopy along with scanning probe microscopy. In ethanol, the major absorption bands of aggregates in 0.5 mM HCl (sample E1) were narrower, with smaller total RLS intensity, compared to those of aggregates in 50 mM HCl (sample E2). RR scattering cross sections were smaller, and depolarization ratio dispersion greater, for E2 than E1. Two distinct types of aggregates at differing acidity in 1-propanol, analogous to the ethanolic samples, but only one type in methanol, were also identified. Atomic force microscopy (AFM) images for E1 showed small, single layered structures (∼5–20 nm diameter, ∼1.5–2 nm thickness). Variable morphologies for E2 included double-layered, elongated structures consistent with collapsed nanotubes (∼25 nm width, ∼3.5–4 nm thickness, ∼100–200 nm length) and single molecule thick sheets (∼50–200 nm in characteristic diameter). The former were also observed in ultrahigh vacuum scanning tunneling microscopy (UHV-STM) images. Aggregate morphology appears to depend on protonation and deprotonation kinetics of porphyrin monomers. Spectroscopic observations suggest that a larger subset of J-band excitonic transitions are significantly active in E2 than in E1. These variations in excitonic properties are attributed to the differing aggregate sizes, shapes, and possibly molecular packing. Formation of long nanotubes appears to require a solvent able to donate two hydrogen bonds, such as water. An open sheet structure is favored otherwise, as in ethanol.

Construction of reduction-responsive photosensitizers based on amphiphilic block copolymers and their application for photodynamic therapy

A novel reduction-responsive porphyrin monomer bearing a disulfide bond (TPPC6SAM) was synthesized, and then it was utilized to construct a series of POEGMA-b-PTPPC6SAM block copolymers via reversible addition–fragmentation transfer (RAFT) polymerization with water-soluble and biocompatible monomer, oligo(ethylene glycol) methyl ether methacrylate (OEGMA). POEGMA-b-PTPPC6SAM block copolymers could self-assemble into spherical micelles and vesicles by varying the mass ratio of hydrophilic block to hydrophobic block. Confocal laser scanning microscopy (CLSM) and flow cytometry showed that POEGMA-b-PTPPC6SAM micelles could effectively accumulate in A549 cells, compared to that of free porphyrin. In addition, minimal dark toxicity and efficacious photo-toxicity in vitro were also evaluated by MTT assay. According to the result of MTT assay, POEGMA-b-PTPPC6SAM block copolymers had a higher photo-toxicity with a lower IC50 (below 3 μg/mL). Thus, reduction-responsive POEGMA-b-PTPPC6SAM block copolymers could well improve the release of porphyrin photosensitizers and enhance the efficiency of PDT.

(Invited) Carbon Nanotube-Templated Synthesis of Covalent Porphyrin Network for Oxygen Reduction Reaction

The fabrication of functional hybrid materials that preserves and combines the properties of their building blocks is a central issue of nanosciences. Among the different classes of nanomaterials, carbon nanotubes are promising for electronics, catalysis and composite applications. Within the context of sustainable development and renewable energy, we and others envisioned the use of functionalized or doped carbon nanotubes in electrocatalytic systems.1 , 2 In such systems, the catalytic sites need to be supported on conducting materials. Carbon nanotubes, thanks to their electrical conductivity and their high surface area appear as the ideal material for that purpose. In actual proton exchange membrane fuel cell devices (PEMFC), the reactions at the electrodes and in particular the reduction of oxygen is performed by platinum nanoparticles. The cost of platinum encourages the development of new catalysts based on non-noble metals. In nature, the reduction of oxygen is performed by iron porphyrins in the active center of enzymes. Thus bio-inspired catalysts based on cobalt or iron macrocycles have been extensively studied for oxygen reduction reaction (ORR).3 , 4 Here, we describe the formation of a covalent network of porphyrins around MWNTs. Our approach is based on adsorption of ethynylporphyrins followed by the dimerization of the triple bonds. The nanotube acts as a template for the formation of the polymeric layer. The nanotube hybrids were characterized and tested for the ORR in a series of electrochemical measurements in acidic conditions. Compared to similar systems in which monomeric porphyrins are simply physisorbed, the nanotube hybrib showed a higher activity, a higher current density, a lower overpotential and a four electrons reaction pathway.5 References (1) Zhang, W.; Sherrell, P.; Minett, A. I.; Razal, J. M.; Chen, J. Energy Environ. Sci. 2010, 3, 1286-1293. (2) Morozan, A.; Jousselme, B.; Palacin, S. Energy Environ. Sci. 2011, 4, 1238-1254. (3) Zagal, J. H.; Griveau, S.; Silva, J. F.; Nyokong, T.; Bedioui, F. Coord. Chem. Rev. 2010, 254, 2755-2791. (4) Morozan, A.; Campidelli, S.; Filoramo, A.; Jousselme, B.; Palacin, S. Carbon 2011, 49, 4839-4847. (5) Hijazi, I.; Bourgeteau, T.; Cornut, R.; Morozan, A.; Filoramo, A.; Leroy, J.; Derycke, V.; Jousselme, B.; Campidelli, S. J. Am. Chem. Soc. 2014, 136, 6348-6354. Figure 1

(Invited) Porphyrin/Carbon Nanotube Supramolecular Self-Assembly : A Thermodynamical Approach

Non covalent interactions through pi-stacking between carbon aromatic cores appear as an essential building block to engender the structural stability and electronic coupling of organic and biologic supramolecular assemblies (DNA, proteins, photosynthetic reaction center...). Interestingly pi-stacking functionalization has emerged as a rich and powerful way to synthesize hybrid compounds made from carbon nanotubes with organic molecules adsorbed on their sidewall. This scheme opens avenues for various applications including photo-voltaics, photo-detection, bio-sensing or imaging. In this context, we recently demonstrated that the decoration of nanotubes with dye molecules (porphyrins) brings remarkable properties including an efficient and ultrafast photo-induced energy transfer as well as good stability [1-3]. In the present work, we unveil through a thermodynamics study an original diameter dependence of the interaction between nanotubes and porphyrin monomers, which favors the larger diameters. We extract parameters such as the reaction time constant and the Gibbs energy of the reaction, which can be described by the classical cooperative adsorption Hill model. Moreover, the evolution of the Gibbs energy as a function of the nanotube diameter is studied for 16 nanotube chiral species [4], and compared with DFT calculations [5]. Finally, we show how tiny changes in the molecules structure influence their self assembly around the nanotube.

(Invited) Efficient Electrocatalytic CO2 Reduction with Dinuclear Iron Complexes

Recently, reductive conversion of CO2 to useful carbon resources draws broad attentions from environmental and catalytic to biological sciences. Though many metal complexes as well as pure metals including mainly mononuclear rare metals such as Ru or Re have been proposed to date, they show rather high overpotentials and/or poor product selectivities. Thus, new catalyst design for efficient and robust CO2reduction is strongly demanded. In biological systems, anaerobic bacteria and archaea use oxygen-sensitive Ni-/Fe-containing carbon monoxide dehydrogenases (CODHases), which realize efficient mutual conversion between CO2 and CO at extremely low overpotentials (< 100 mV) (Fig. 1A).[1] The dinuclear active site motif with base metal ions is attractive as chemical models. According to this strategy, we designed iron porphyrin dimers linked by 1,2-phenylene group (Fig. 1B) as the catalysts and applied them for electrochemical CO2 reduction. The catalysts show extremely high catalytic TOF and high CO selectivity at relatively low overpotentials (η). When electron-withdrawing meso-aryl groups are used, η becomes as low as 0.4 V.[2] From the detailed CV analysis, Fe porphyrin monomer, e.g., FeTPP, shows the dischage current at its Fe0 state in CO2 atmosphere and FeII/III and FeI/II couples appear at the same potential as observed in Ar. The FeTPP dimer, however, shows a considerable positive shift of its FeI/II couple in CO2. This suggests that the FeII state of the dimer will make strong association with CO2 molecule and the resultant complex shows its reduction peak at more positve potential than its original FeI/II couple. Since FeII porphyrin monomesr are generally intact with CO2, this is the first example of the formation of the CO2-binding to FeII porphyrin by its dimerization. This is the reason of the considerable decrease of the CO2 reduction overpotential. This result also supports the two nucleus motif as observed in CODHase active site promote the CO2 reduction at low η. When two Fe ions are separated in a larger distance as observed in 1,3-phenylene linked Fe dimer, this cooperative effect of the two FeII ions is not work any longer and the m-dimer just work as two monomers. The present Fe porphyrin dimmr catalysts are quite robust and any current drop was not observed after 12 h at a constant potential electrolysis. High CO selectivity of these Fe catalysts is also advantage for their practical use on the aspect of easy product separation. Regerences [1] J.-H. Jeoung and H. Dobbek, Science, 318, 1461 (2007); J. Fesseler, J.-H. Jeoung, and H. Dobbek, Angew. Chem. Int. Ed., 54, 8560 (2015). [2] E. Mohamed, Z. Zaharan, and Y. Naruta, Chem. Commun, 51, 16900 (2015). (Cover article) Figure 1

Diameter-selective non-covalent functionalization of carbon nanotubes with porphyrin monomers.

We report on the spontaneous non-covalent functionalization of carbon nanotubes with hydrophobic porphyrin molecules in micellar aqueous solution. By monitoring the species concentrations with optical spectroscopies, we can follow the kinetics of the reaction and study its thermodynamical equilibrium as a function of the reagent concentrations. We show that the reaction is well accounted for by a cooperative Hill equation, reaching a molecular coverage close to a compact monolayer for a porphyrin concentration larger than a diameter-specific threshold concentration. The equilibrium constant is measured for 16 nanotube chiral species. The Gibbs energy of the reaction (of the order of -40 kJ mol(-1)) and its evolution with the nanotube diameter is consistent with theoretical calculations of the binding energy. This thermodynamical study shows a strong preferential binding of TPP molecules to larger diameter nanotubes. This original curvature selectivity can be used to induce diameter selective species enrichment.

Artificial hemes for DSSC and/or BHJ applications.

Lately solar to power energy conversion devices have attracted a lot of attention and there is an effort to synthesize novel light-harvesting organic materials. Inspired by nature and due to their remarkable role in photosynthesis, porphyrins have been extensively used for DSSC and BHJ applications. This review provides a summary of the developments and approaches that were used in our group in order to improve the power conversion efficiency of DSSCs and BHJs based on porphyrin hybrid derivatives. Aiming to extend the light absorption range of the sensitizing dyes and to achieve enhanced solar cell performances, functionalized porphyrins with carboxylic acid anchoring groups were synthesized. These include monomeric, dimeric and trimeric porphyrins with one or two anchoring groups and in the presence of an additional chromophore in some examples. Also, porphyrins with pyridyl anchoring groups were studied, in order to examine the influence on the power conversion efficiency of a different anchoring group. The photovoltaic properties improved after the reduction of dye-aggregation by means of chemical co-adsorbents, and by using co-sensitization, modified photoanodes and electrolyte additives. Finally, some of the above chromophores were used as electron donors for the preparation of solution processed BHJ organic solar cells in the presence of various electron acceptors.

Meso–meso Directly-linked trimeric and pentameric electron-deficient porphyrin–hexaphyrin hybrid arrays

meso–meso Directly-linked trimeric and pentameric porphyrin–hexaphyrin hybrid arrays 5 and 6 comprising of electron-deficient porphyrin units were prepared by cross-condensation of monomeric and dimeric electron-deficient meso-formyl porphyrins with a tripyrrane. The solid-state structures of 5 and 6 have been determined by single crystal X-ray diffraction analysis. The latter is the largest crystal structure of meso–meso linked multiporphyrinic array analogues reported to date.

Complete Double Epoxidation of Divinylbenzene Using Mn(porphyrin)-Based Porous Organic Polymers

A series of porphyrin-based porous organic polymers (PPOPs) were synthesized in excellent yields via the Yamamoto–Ullmann couplings of tetrabromo spirobifluorene with several brominated porphyrin monomers. After isolation and demetalation, the metal-free PPOP can be postsynthetically metalated to form a MnIII–PPOP that is catalytically active toward the selective double-epoxidation of divinylbenzene to divinylbenzene dioxide.

Covalent Cobalt Porphyrin Framework on Multiwalled Carbon Nanotubes for Efficient Water Oxidation at Low Overpotential

A noble-metal-free, efficient, and robust catalyst made of Earth-abundant elements for water oxidation is vital to achieve practical water splitting for future clean energy production. Herein, we report the synthesis of multilayer covalent cobalt porphyrin framework on multiwalled carbon nanotubes ((CoP)n-MWCNTs) to produce a highly active electrocatalyst for water oxidation. A linear sweep voltammetry curve showed that a catalytic current density of 1.0 mA/cm2 can be achieved under a potential of only 1.52 V (vs RHE, corresponding to an overpotential of only 0.29 V) in alkaline solution at pH 13.6. Such an onset potential is much lower than that of cobalt porphyrin monomer (CoP-TIPS) and pure MWCNTs. In addition, the chronopotentiometry data confirmed its excellent catalytic activity and suggested that the (CoP)n-MWCNTs catalyst has good durability for water oxidation catalysis. A Tafel slope of 60.8 mV per decade was obtained by bulk electrolysis measurement, and the Faradaic efficiency of oxygen production was >86%.