Redox and photochemical behaviour of a porphyrin monolayer on an indium-tin oxide electrode

In order to investigate photoluminescence behaviour of an ordered molecular porphyrin monolayer and its quenching properties by oxygen gas, a porphyrin with long alkyl chains, 5,10,15,20-tetrakis[4-(11-carboxylundecane-1-oxy)phenyl]porphyrin (4), was synthesized and adsorbed onto an indium-tin oxide (ITO) substrate by a chemical dipping method. Cyclic voltammetry was used to analyze the ITO electrode coated with 4. The peak current of the first oxidation was proportional to the sweep rate, and the surface coverage was estimated to be 2.3-2.5 × 10⁻¹⁰ mol cm⁻². The UV-vis spectrum of the monolayer showed a broadened Soret band, which shifted to longer wavelength. These features suggest that the porphyrin moieties of 4 are packed to form a J-type structure. The oxygen quenching ratio of the porphyrin 4 monolayer on the ITO electrode, I₀/I₁₀₀, was estimated to be 1.25, where I₀ and I₁₀₀ are, respectively, luminescence intensity values in 100% argon and 100% oxygen. On repeated step cycling between 100% argon and 100% oxygen atmospheres, the response times of luminescence quenching were 10 s (argon to oxygen) and 23 s (oxygen to argon). These findings suggest that a monolayer of sensing dye is applicable for oxygen sensing system without deterioration of size-accuracy of models.     

Novel D-π-A system based on zinc porphyrin dyes for dye-sensitized solar cells: Synthesis, electrochemical, and photovoltaic properties

We have designed and synthesized novel zinc porphyrin dyes which have a D-π-A system based on porphyrin derivatives containing a triphenylamine (TPA) electron-donating group and a phenyl carboxyl anchoring group substituted at the meso position of the porphyrin ring, yielding the push-pull porphyrins as the most efficient green dye for dye-sensitized solar cell (DSSC) applications. The synthesis and characterization of a novel D-π-A system based on zinc-porphyrin derivatives have been investigated through their photophysical and photoelectrochemical studies. A large red-shift of the absorption maxima due to introduction of the TPA moiety at the meso position of the porphyrin ring was expected in the D-π-A porphyrins, but the absorption maxima of HKK-Por dyes were a little red-shifted in contrast to Zn[5,-10,15-triphenyl-20-(4-carboxylphenyl)-porphyrin], due to the tilted structure between TPA and the porphyrin unit. Under the photovoltaic performance measurement, the maximum incident photon-to-current conversion efficiency (IPCE) value of the DSSC based on HKK-Por 5 was slightly higher than the efficiencies of the DSSCs based on other HKK-Por dyes due to the introduction of the alkoxy group into the TPA moiety at the meso position of the porphyrin ring. A maximum photon-to-electron conversion efficiency of 3.36% was achieved with the DSSC based on HKK-Por 5 dye (J_SC = 9.04 mA/cm², V_OC = 0.57 V, FF = 0.66) under AM1.5 irradiation (100 m Wcm⁻²).     

Synthesis,structures and properties of a meso-substituted pyrazolyl porphyrin and its Co(II) porphyrin complex

In this work, one new porphyrin, 5, 10, 15, 20-tetrakis(4-N-pyrazolyl)phenyl porphyrin (H₂Pp) was synthesized and characterized. The single crystal structures of H₂Pp and its cobalt(II) porphyrin (Co(II)Pp) were obtained with a space group of P₁⁻ and I2/c, respectively. The porphyrin macrocycle is close to a perfect plane in H₂Pp, while Co(II)Pp exhibits a saddle-type distortion due to the formation of shorter Co–N coordination bonds. In H₂Pp, the molecules are interconnected through π⋯π and C–H⋯π interactions to form 3D architecture, while in Co(II)Pp the porphyrin molecules are interlinked only by C–H⋯π interactions to yield 3D structure. We examined the UV–vis spectra and fluorescent spectra of H₂Pp and Co(II)Pp in CH₂Cl₂ and solid state at room temperature. In addition, the catalytic activities of Co(II)Pp to the ethylbenzene oxidation was examined, the results indicate that Co(II)Pp exhibits a high selectivity to acetophenone (> 99%) with the conversion of 83%.     

Synthesis of poly[2]catenane having rigid linkage by 1,3-dipolar cycloaddition of diazido[2]catenane with 4,4′-diethynylbiphenyl

A novel poly[2]catenane having rigid triazole rings between [2]catenane moieties was synthesized by the 1,3-dipolar cycloaddition of diazido[2]catenane with 4,4′-diethynylbiphenyl. The reaction proceeded effectively under mild conditions and gave a polymer in high yield. The number average molecular weight (M_n) of the polymers was 1.5 × 10⁴-2.5 × 10⁴. A cyclic dimer consisting of two [2]catenane moieties and two biphenylene units was formed along with the polymer. The cyclodimerization was suppressed by performing the reaction at a low temperature without lowering the yield or molecular weight of the polymer. The novel poly[2]catenane had higher solubility in some solvents than the corresponding non-catenated polymer having a similar primary structure.     

Role of Cobalt(III) Cationic Complexes in the Self-Assembling Process of a Water Soluble Porphyrin

Under moderate acidic conditions, the cationic (+3) complexes ions tris(1,10-phenanthroline)cobalt(III), [Co(phen)₃]³⁺, and hexamminecobalt(III), [Co(NH₃)₆]³⁺, efficiently promote the self-assembling process of the diacid 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin (H₂TPPS₄) into J-aggregates. The growth kinetics have been analyzed according to a well-established autocatalytic model, in which the rate determining step is the initial formation of a nucleus containing m porphyrin units (in the range 2–3), followed by a stage whose rate constant k_c evolves as a power of time. The observed catalytic rate constants and the extent of J-aggregation increase on increasing the metal complex concentration, with the phen complex being the less active. The UV/Vis extinction spectra display quite broad envelops at the J-band, especially for the amino-complex, suggesting that electronic dipolar coupling between chromophores is operative in these species. The occurrence of spontaneous symmetry breaking has been revealed by circular dichroism and the measured dissymmetry g-factor decreases on increasing the aggregation rates. The role of these metal complexes on the growth and stabilization of porphyrin nano-assemblies is discussed in terms of the different degree of hydrophilicity and hydrogen bonding ability of the ligands present in the coordination sphere around the metal center.     

The interaction of water-soluble iron porphyrins with DNA films and the electrocatalytic properties for inorganic and organic nitro compounds

The electrochemistry of water-soluble iron porphyrins (Fe(n-TMPyP)) (where n=2 and 4) was studied as an electrochemically active film on DNA modified glassy carbon, gold, platinum, and transparent semiconductor tin oxide electrodes in solutions of various pH values. The two layers of the modified electrode containing the iron porphyrin and the DNA film were prepared by depositing the iron porphyrin on a DNA film modified electrode. The Fe(4-TMPyP)/DNA film was electrocatalytic reductive for p-nitrobenzoic acid in a weak acidic, or neutral aqueous solution through an Fe^II species, and the electrocatalytic reduction peak potential became more negative than the cathodic peak of the Fe^III/II redox couple. The electrocatalytic reduction properties by the Fe(2-TMPyP)/DNA film as catalysts for nitrite reduction have also been determined, and shown to be active through an Fe^I species and to be pH-dependent. The electrocatalytic oxidation properties of nitrite by Fe(n-TMPyP)/DNA (for n=2 and 4) film have also been determined and shown to be active through an Fe^IV species with the electrocatalytic oxidation efficiency of NO₂⁻ with Fe^IV(O)(n-TMPyP) being higher than with (HO)Fe^IV(O)(n-TMPyP). The electrocatalytic oxidation efficiency of NO₂⁻ by iron porphyrin is pH-dependent. The electrocatalytic reduction of p-nitrophenol by Fe(2-TMPyP)/DNA film are also discussed.     

Co (II) porphyrin adsorbed on SiO2/SnO2/phosphate prepared by the sol-gel method: Application in electroreduction of dissolved dioxygen

This paper describes the immobilization procedure of 5,10,15,20-tetrakis(1-methyl-4-pyridyl)-21-H,23-H-porphyrin ion on SiO₂/SnO₂/phosphate, obtained by the sol-gel processing method. P 2p X-ray photoelectron and the ³¹P MAS NMR spectra revealed that dihydrogen phosphate is the species present on the surface. The porphyrin was adsorbed on the surface of the modified material and furthermore metallized in situ with Co (II) ion. The porphyrin metallation process was followed with UV-vis spectroscopy by inspecting the Q bands of the free and metallated porphyrin. The free porphyrin presented four Q bands associated to a D_2h local symmetry and the metallated one, two bands related to a D_4h local symmetry. The amount of electroactive species adsorbed on the material was estimated by integrating the area under the peak of Co (II) → Co (I) reduction by using the pulse differential voltammetric technique. The amount of the metallated porphyrin was 2.3 × 10⁻¹⁰ mol cm⁻². A carbon paste electrode of the modified material containing metallated porphyrin was used to study the electrocatalytic reduction of dissolved dioxygen by means of cyclic voltammetry, chronoamperometry and linear sweeping voltammetry. The modified electrode was very stable and exhibited the electrocatalytic reduction of dissolved dioxygen at −180 mV versus SCE by a two-electron mechanism, producing hydrogen peroxide at pH 5.4. The electroactive species was strongly retained on the material surface, presumably inside the pores of the material, since in a test of various oxidation-reduction cycles no significant decrease of the current densities was detected, indicating that it was not leached off during the experiment.     

Characterization of Polyglycerol Polyricinoleate Formulations Using NMR Spectroscopy, Mass Spectrometry and Dynamic Light Scattering

Three different analytical techniques, namely NMR spectroscopy, mass spectrometry and dynamic light scattering, were used to unravel the structure and morphology of polyglycerol polyricinoleate (PGPR). This material is used as an emulsifier in the preparation of chocolate and other confectionary products. The use of 1D and 2D NMR techniques led to the distinction of two separate entities in commercial ricinoleic acid (RA) and PGPR samples, namely the monomeric and oligomeric RA (estolides). ¹H and ¹³C spectra of PGPR confirmed the presence of polyglycerol moieties of various lengths being esterified by RA and estolides and to a lesser extent by oleic and linoleic acids. ¹³C-NMR DOSY experiments demonstrated the occurrence of several species in PGPR. Electrospray Ionization and tandem Mass Spectrometry succeeded in identifying the presence of over 30 glycerol/polyglycerol species containing n glycerol moieties with n = 1–6 esterified by monomeric and oligomeric RA molecules. Dynamic light scattering contributed to the characterization of PGPR morphology. The PGPR mixture contains relatively small-sized entities (monomers, dimmers, trimmers) and larger aggregates resulted from chain association. The percentage of larger aggregates is minimal compared to small-sized species.     

Efficient Electron Transfer Processes and Enhanced Electrocatalytic Activity of Cobalt(II) Porphyrin Anchored on Graphene Oxide

We investigated the electronic perturbation between graphene oxide and cobalt porphyrin to reveal the origin of the enhanced electrocatalytic activity of a hybrid complex using time-resolved spectroscopic measurements and theoretical calculations. The impulsively generated charge-separated state, GO⁻-(Co^IIAPFP)⁺, undergoes fast charge recombination (<10 ps) between GO⁻ and (Co^IIAPFP)⁺ moieties. This fast charge recombination is directly related to the quick neutralization of (Co^IIAPFP)⁺, which shortens the dead time of inactive Co^IIIAPFP after the electrocatalytic reduction reaction. The fast transformation of inactive Co^IIIAPFP to active Co^IIAPFP is an important factor in the enhanced electrocatalytic activity of the hybrid complex.     

Novel 5-benzazolyl-10,15,20-triphenylporphyrins and β,meso-benzoxazolyl-bridged porphyrin dyads: Synthesis, characterization and photophysical properties

Novel 5-benzazolyl-10,15,20-triphenylporphyrins and β,meso-benzoxazole-linked diporphyrins were synthesized through La(OTf)₃ catalyzed reaction of newly prepared 5-(3,4-diaminophenyl)-10,15,20-triphenylporphyrin or 5-(3-amino-4-hydroxyphenyl)-10,15,20-triphenylporphyrin with aromatic aldehydes in 1,2-dichlorobenzene. On metalation with zinc acetate, freebase β,meso-benzoxazole-linked diporphyrin was successfully converted to the Zn-Zn diporphyrin complex in good yield. The synthesized porphyrin analogues were characterized using electronic absorption, IR and ¹H NMR spectroscopy in addition to mass and elemental analyses. The fluorescence studies of 5-benzazolyl-10,15,20-triphenylporphyrins showed efficient intramolecular energy transfer from the pyrene and fluorene subunits to the porphyrin core. In addition, the fluorescence quenching observed in β,meso-benzoxazolyl-bridged porphyrin dyads was attributed to the possible nonplanarity of a component of the diporphyrins. The freebase-Ni diporphyrin complex underwent strong emission quenching in comparison to that of freebase diporphyrin and dizinc diporphyrin analogues.     

Preparation and Characterization of a Chloroperoxidase-like Catalytic Antibody

The small molecule, meso-tetra(α,α,α,α-o-phenylacetamidophenyl) porphyrin (Mr1147.0) was used as complete antigen to elicit MAb through the immunization and cell fusion techniques. The MAb 1F2 obtained was demonstrated to be very pure by MALDI/TOFMS. The subtype of MAb 1F2 is IgG2a, which has a relative molecular weight of 156,678.8 Da.No significant change in the intensity of absorption peaks in UV and CD spectra was observed over a pH range between 6 and 12. The high stability of the abzyme and the tight binding between Fe porphyrin and antibody were also demonstrated. V_max, K_m, κcat, κcat/K_m for abzyme are 5.18 × 10⁻⁸ Ms⁻¹, 1.50 × 10⁻⁸ M, 0.518 s⁻¹, 3.45 × 10⁷ M⁻¹s⁻¹, respectively. The data obtained indicate that catalytic antibody has high catalytic activity. The chloroperoxidase activity of MAb 1F2-Fe porphyrin complex is stable from 10 °C to 60 °C.     

Binaphthol-strapped chiral bis(porphyrinato) cerium double-decker complexes

(R)-(+)- or (S)-(−)-1,1′-bi-2-naphthol (BINOL) was applied as a remote chiral auxiliary to connect the two facing porphyrin rings, resulting in the BINOL-strapped chiral bis(porphyrinato) cerium double-decker complexes (R)-/(S)-1 and (R)-/(S)-2, which were carefully characterized by a range of spectroscopic and electrochemical methods. Perfect mirror images were observed in their circular dichroism (CD) spectra with a negative sign in the Soret band for (R)-enantiomers and a positive sign for (S)-enantiomers, which suggests the C₂-chirality of a BINOL strap is transcribed to the double-decker core as a defined chiral twist in the inter-porphyrin arrangement. Furthermore, the CD intensities of (R)-/(S)-1 are always larger than those of (R)-/(S)-2, indicating that the intramolecular chirality transfer efficiency can be finely tuned by changing the length of interlocking moieties.     

A novel polymeric Hg[(CN)2N2] central core four-coordinate complex: Synthesis,X-ray structure and 199Hg, 13C and 15N CP MAS NMR characterization of catena((μ2-1,4-diaminobutane-N,N′)dicyanomercury(II))

Mercury(II) cyanide reacts with 1,4-diaminobutane (bn) at a 1:1 ratio forming a polymeric complex [(bn)Hg(CN)₂]_∞ in which (bn) acts as a bridge between the Lewis acid Hg(CN)₂ moieties. The metal complex coordination sphere Hg[(CN)₂N₂] is best described as distorted trigonal pyramidal. The ¹³C and ¹⁵N CP MAS NMR data show two chemically different CN groups consistent with the hydrogen bonding scheme involving only one of the cyano ligands.     

Synthesis of Functionalized trans‐A2B2‐Porphyrins Using Donor–Acceptor Cyclopropane‐Derived Dipyrromethanes

meso‐Substituted trans‐A₂B₂‐porphyrins bearing specific patterns of substituents are crucial building blocks in porphyrin‐based biomimetic systems and molecular materials and can be used for the construction of well‐defined porphyrin‐based architectures. A new stepwise and rational synthesis of functionalized trans‐A₂B₂‐porphyrins is reported in which for the first time donor–acceptor‐substituted cyclopropane precursors (d–a cyclopropanes) are exploited. The three presented d–a cyclopropanes are readily accessible in a multi‐gram scale and serve as aldehyde equivalents in the reaction with an excess of pyrrole to afford the corresponding dipyrromethanes (DPMs). The three DPMs were synthesized in yields of 60–74%. They are stable in purified form in the absence of light and air and were subsequently condensed with a wide range of aliphatic and aromatic aldehydes bearing electron‐donating or electron‐withdrawing substituents followed by oxidation to form the corresponding trans‐A₂B₂‐porphyrins. Fourteen functionalized porphyrins were synthesized in yields of 14–31%, indicating the broad scope of the synthetic procedure. The possibility to introduce key functional groups is emphasized, which enables subsequent modification of these porphyrins with moieties inducing biological activity. Modification of the tetrapyrroles may occur by addition to one of the porphyrin peripheral double bonds, the use of substituents of the aryl groups or via the methoxycarbonyl group at two of the meso‐substituents. Three examples of porphyrins were converted into the corresponding 7,8‐dihydroxychlorins by osmium‐mediated dihydroxylation and one of the resulting chlorins was subjected to saponification to give a highly polar chlorin dicarboxylic acid. A 4‐bromophenyl‐substituted d–a cyclopropane was prepared by rhodium‐catalyzed cyclopropanation and then transformed into a DPM which was subsequently condensed to a porphyrin. Its Zn complex allowed a Heck reaction to afford the functionalized bis(alkenyl)‐substituted trans‐A₂B₂‐Zn‐porphyrin.     

Monomeric Au(II) complex with hematoporphyrin IX

A stable monomeric Au(II) complex has been synthesized in the course of the Au(III)–hematoporphyrin IX (Hp, I) interaction in aqueous alkaline solution. Distorted octahedral structure with (d_xy)¹ ground state and general formula Au(II)Hp_-2H·2H₂O are suggested for the complex. Gold is located in the hole of the porphyrin macrocycle and the water molecules are in axial position. The +2 oxidation state of gold was proven by the corresponding EPR signal and the μ_eff value of 2.20 BM obtained. The α² value of 0.56 indicated a high degree of covalency of the gold–nitrogen bonds.     

Synthesis and characterization of [Ga(TPP)H] (TPP=tetraphenylporphyrinato)

The synthesis, spectroscopic and structural characterization of the stable gallium hydride compound [Ga(TPP)H] (TPP=5,10,15,20-tetraphenylporphyrinato) have been reported. The hydride compound was synthesized in high yield (85%) by reducing [Ga(TPP)Cl] with sodium borohydride in N,N-dimethylformamide. The title compound was fully characterized by spectroscopic methods (IR, UV–Vis, and ¹H NMR spectroscopy) and its molecular structure was established by X-ray crystallography. The Ga–H IR stretch occurs at 1864 cm⁻¹, and the hydride ¹H NMR resonance locates at −6.47 ppm. The gallium–hydrogen distance is 1.48(4) Å, whereas the gallium atom lies 0.46(1) Å from the perfect porphyrin plane.     

Photoinduced electron transfer in nanostructures of ultrathin polyimide films containing porphyrin moieties

Photoinduced electron transfer between porphyrin moieties and pyromellitimide fragments has been investigated in multi-layered structures of ultrathin polyimide films prepared by the Langmuir-Blodgett (LB) technique. The LB films were composed of three kinds of polyimides, which contained zinc tetraphenylporphyrin (ZnTPP) unit as an electron donor (D-layer), no chromophoric groups (S-layer), and pyromellitimide fragments as an electron acceptor (A-layer). The layered structure and orientational distribution of porphyrin moieties in the LB films were evaluated by surface plasmon measurement and absorption dichroism measurement, respectively. The thickness of monolayer was estimated to be 0.9 nm for the polyamic acid films and 0.4 nm for the polyimide films. The molecular plane of porphyrin moieties was oriented in the direction parallel to the substrate plane. In the multi-layered structures of polyimide LB films, the efficiencies of photoinduced electron transfer from porphyrin moieties to pyromellitimide fragments varied sharply with the number of spacing layers, indicating that the short-range interactions such as electron transfer could be controlled by the fabric of ultrathin films. The rate of electron transfer observed by the fluorescence quenching measurements was numerically simulated for the nanostructure using the Monte Carlo method.     

Novel porphyrin‐grafted poly(phenylene vinylene) derivatives: Synthesis and photovoltaic properties

A series of novel porphyrin‐grafted poly (phenylene vinylene) derivatives, Porp‐RO‐PPV, were synthesized by a simple two‐step method. These copolymers contain conjugated poly(phenylene vinylene) derivatives as polymer backbone and covalently linked porphyrin units as side chain, which were confirmed by FTIR and ¹H NMR, and used for photovoltaic devices. The thermal, optical properties and sensitizing effect, and photovoltaic properties have been investigated. The emission spectra of Porp‐RO‐PPV copolymers revealed the existence of strong energy transfer from PPV backbone to porphyrin units. The energy conversion efficiency (η_e) of photovoltaic devices based on Porp‐RO‐PPV+PCBM reached 0.33% (78.2 mW/cm², AM1.5) and porphyrin units in the copolymers showed good sensitizing effect at low concentration. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Hydrothermal synthesis,crystal structure and properties of a thermally stable dysprosium porphyrin with a three-dimensional porous open framework

A thermally stable dysprosium porphyrin with a three-dimensional (3D) porous open framework, [Dy(H₂TPPS)]_n∙ nH₃O∙2nH₂O (1) (H₂TPPS = tetra(4-sulfonatophenyl)porphyrin), has been synthesized via hydrothermal reactions and structurally analyzed by an X-ray single-crystal diffraction method. The 24-membered macrocyclic ring of H₂TPPS is exactly coplanar and the center is free from metal. The dysprosium ion is coordinated by eight O_sulfonic atoms from eight H₂TPPS moieties, forming a distorted square anti-prism geometry. Complex 1 shows a void space of 210 Å³, occupying 9.06% of the unit-cell volume. The 3D porous open framework of 1 is thermally stable up to 380 °C. Complex 1 exhibits a red fluorescence emission with a quantum yield and lifetime of 2.7% and 136 μs, respectively. CV result reveals one reductive peak at − 0.33 V and one quasi-reversible wave with E_1/2 = − 0.81 V.     

Composition of triacylglycerols containing cyclopropene fatty acids in seed lipids of Munguba (Bombax munguba Mart.)

The seed lipids of Munguba (Bombax munguba Mart., Bombacaceae) were found to contain substantial proportions (ca. 30%) of cyclopropene acyl moieties (sterculoyl and malvaloyl). In a novel approach to the analysis of glycerolipids containing cyclopropene acyl moieties, the triacylglycerols of Munguba seed were first treated with silver nitrate in acetonitrile-acetone (1:1, v/v), in order to convert the cyclopropene groups to the correspondingα,β-unsaturated ketones. The resulting triacylglycerols were fractionated by thin layer chromatography into molecular species containing none, one and two keto (corresponding to none, one and two cyclopropene) acyl moieties per molecule. Each of these molecular species was further fractionated according to carbon numbers by gas chromatography, and the positional distribution of the acyl moieties in each species was determined. Both sterculoyl and malvaloyl moieties were found predominantly at thesn-2 position of the triacylglycerols. The major triacylglycerols of Munguba seed were found to be 1,3-dipalmitoyl-2-oleoylglycerol, 1,3-dipalmitoyl-2-linoleoylglycerol and 1,3-dipalmitoyl-2-sterculoylglycerol.