Porphyrin Anion Research Articles

Photochemical Properties of Propargylamine-based Polymers

Propargylamines are a promising but quite poorly studied category of organic compounds. This work aimed to study the photochemical properties of propargylamines polymers containing porphyrin fragments with electron transfer reactions. The study was carried out in 2019 at the Institute of Organic Chemistry (RAS, Moscow, Russia). The obtained polymer was irradiated with a luminous source. The absorption spectra were studied by electron paramagnetic resonance using a radio spectrometer. The presence of porphyrin and propargylamine in the polymer solution has been established to promote the reaction of complexation. This is due to the presence of double bonds in the amino groups, whereas also porphyrin and bromanil, which is an electron acceptor. The resulting data allow explaining the processes involved in photochemical reactions during the irradiation of the porphyrin complex in the presence of bromanil. In the long-wavelength part of the spectrum (above 540 nm), electron phototransfer inside the polymer molecule to the porphyrin side and between molecules from the porphyrin anion radical to the neutral polymer molecule take place.

Postsynthesis Ligand Exchange Induced Porphyrin Hybrid Crystalloid Reconstruction for Self-Enhanced Electrochemiluminescence.

In traditional coreactant electrochemiluminescence (ECL), the efficiency of the coreactant catalyzed into an active intermediate is one of the dominant factors restricting the luminous intensity. In this work, Co-2-MI-ZnTCPP is designed as a composite material integrating coreaction accelerator (Co-N) and luminophore. Through the catalytic effect of Co-N structures on hydrogen peroxide, the in situ generation and accumulation of active intermediates are achieved, which will react with porphyrin anion radical, thereby bringing out self-enhanced ECL. By adjusting the scanning potential range, the ECL mechanism is thoroughly studied and the contribution of each potential window to the luminescence is obtained. This work provides inspiration for the design of integrated ECL emitters with a coreaction accelerator and luminophore, providing a new way for the construction of a self-enhanced ECL emitter.

Synthesis and Characterization of Supramolecules of Li + @C60 and Fluorinated Porphyrins

Metal endohedral [60]fullerenes (M@C60) have a unique structure encapsulating a metal atom (M) inside the π−conjugated spherical C60 cage. Lithium cation endohedral fullerene (Li + @C60) is a commercially available M@C60 and has a potential for application in nano material fields. The cationic Li+@C60 crystallizes with weakly coordinated anions such as SbCl6 − [1], PF6 − [2], Tetrakis[3,5-bis(trifluoromethyl)phenyl]borate anion (TFPB−) [3], and bis(trifluoromethanesulfonyl)imide anion (TFSI−) [3]. Due to the inside Li+ cation, the first reduction potential of Li+@C60 is shifted to positive direction by 0.7 eV than that of pristine C60. As a result, Li+@C60 has larger electron acceptability than C60 [1]. Li+@C60 also forms a guest–host type supramolecule with [10]cycloparaphenylene ([10]CPP) [4] and π−π stacking supramolecules with porphyrins or phthalocyanines [5][6]. A supramolecule of Li+@C60 and 5,10,15,20-tetrakis(4–sulfonatophenyl) zinc porphyrin anion (ZnTPPS4 –), [Li+@C60 – ZnTPPS4 –] with the binding constant of ca. 105 M– 1 shows a long−lived electron charge separation state by photoinduced electron transfer and can be used in photovoltaic cells [5]. The [Li+@C60 – ZnTPPS4 –] based photovoltaic cell shows maximum incident photon-to-photocurrent efficiency (IPCE) value of 78% under the certain condition [7]. The performance of the photovoltaic cells would be changed by the chemical modification of porphyrins.Here, we synthesized two kinds of porphyrins to obtain new supramolecules of Li+@C60. The first one is neutral 5,10,15,20-Tetrakis(1,2,4,5-tetrafluorophenyl) porphyrin (H2TTFPP). H2TTFPP was synthesized by Lindsey method and characterized by 1H NMR, 19F NMR, UV-vis, CV, DPV, and XRD. The second one is anionic 5,10,15,20-Tetrakis(4-carboxymethylthio-2,3,5,6-tetrafluorophenyl) zinc porphyrin tetrabutylammonium (ZnTFPP4TC4 −4TBA+). ZnTFPP4TC4 −4TBA+ was synthesized according to the modified Lourenço method [8] and characterized by 1H NMR, 19F NMR, UV-vis, CV, and DPV.H2TTFPP was confirmed to form supramolecular structure with Li+@C60 in the co-crystal by X-ray structure analysis. ZnTFPP4TC4 − was confirmed to form a supramolecule with Li+@C60 in solution by UV-vis titration experiment. The binding constant of [ZnTFPP4TC4 − − Li+@C60] is significantly larger than that of [H2TTFPP − Li+@C60] because of strong coulomb interactions between anionic ZnTFPP4TC4 − and cationic Li+@C60.

Ionic self-assembly reactions of a porphyrin octacation

To determine if ionic self-assembly can be used to produce nanomaterials from unusual porphyrin ions we have investigated the reactions of a novel octacationic porphyrin. A range of nanomaterials are obtained depending upon the tetra(4-sulfonatophenyl)porphyrin (TPPS) anion(s) used in the reaction: binary ionic solids (from reactions with metal TPPS complexes), ternary ionic solids (from reactions with two different metal TPPS complexes) and binary solids with variable compositions (from reactions with diprotonated TPPS).

Metalloporphyrin-Nitroxyl Interactions: The Low-Energy States of Reduced Manganese, Iron, and Cobalt Porphyrin Nitrosyls.

DFT calculations employing the OLYP and B3LYP functionals have been used to map out the low energy states of the metalloporphyrin-nitroxyl adducts "M(Por) + NO(-)" and "M(Por) + HNO", where M = Fe, Co, and Mn and Por(2-) is the dianion of unsubstituted porphyrin. For [Fe(Por)(NO)](-), the calculations yield two low-energy solutions, with MS = 0 and 1. The MS = 0 solution is thought to represent the experimentally observed diamagnetic ground states of {FeNO}(8) porphyrins, and both functionals yield FeNO geometrical parameters in excellent agreement with a recent crystal structure. For [Co(Por)(NO)](-), the lowest-energy solution for both OLYP and B3LYP is a true {CoNO}(9) state that appears to be best described as a high-spin Co(II) center with a dxy(2)dxz(1)dyz(1)dz2(2)dx2-y2(1) configuration antiferromagnetically coupled to a NO(-) diradical. Such an electronic configuration is expected to lead to diagnostic structural features, including long equatorial Co-N distances (∼2.1 Å), a strong displacement (∼0.4 Å) of the metal from the mean plane of the equatorial nitrogens, and a relatively short Co-N(O) distance (1.8 Å), which should all be experimentally observable. The dx2-y2(1) electronic configuration should also lead to characteristic EPR hyperfine parameters. The calculations also indicate a number of other low-energy states for [Co(Por)(NO)](-), including multiple {CoNO}(8) porphyrin anion radical states. For [Mn(Por)(NO)](-), both functionals indicate a rather complex electronic state landscape, including multiple {MnNO}(6) porphyrin anion radical states as well as a high-spin S = 3/2 {MnNO}(7) state. Both functionals clearly indicate a low-spin Fe(II) state for [Fe(Por)(HNO)]. On the other hand, two comparably low-energy states are predicted for both [Co(Por)(HNO)] and [Mn(Por)(HNO)]. For [Co(Por)(HNO)], the two states are a low-spin Co(II) state with a dxy(2)dxz(2)dyz(2)dz2(1) configuration and a low-spin Co(III)(HNO)(•-) state. For [Mn(Por)(HNO)], the two states may be described as low- (S = 1/2) and intermediate-spin (S = 3/2) Mn(II). The latter state has a relatively long Mn-N(O) distance of about 2.07 Å, which may be indicative of facile HNO dissociation.

Consecutive Aromatic Carbon–Fluorine Bond and Carbon–Hydrogen Bond Activations by Iridium Porphyrins

Consecutive aromatic C–F bond and C–H bond activations of aryl fluorides were achieved by iridium porphyrins to initially give aryl and finally fluoroaryl iridium porphyrins. The C–F bond activation product is generated first, which is the precursor for the C–H bond activation. Both experimental and theoretical results support that the C–F bond is cleaved by iridium porphyrin anion through nucleophilic aromatic substitution, and the C–H bond cleavage is through homolytic aromatic substitution by iridium porphyrin radical followed by hydrogen atom abstraction. Moreover, the meta-fluorophenyl iridium porphyrin is the most thermodynamic stable regioisomers.

DFT Study on Structural Distortion and Vibronic Coupling of Vanadyl Porphyrin Anion and Cation

The geometries of one‐electron reduced/oxidized species ([TOP]−/[VOP]+) of vanadyl porphyrin (VOP) have been calculated with PBE1PBE method. The results show that for both [VOP]− and [VOP]+ the ground states are triplet, in which one of the two unpaired electron occupies the dxy orbital of the V atom while the other occupies the π‐orbital of porphyrin ring. Thus both [VOP]− and [VOP]+ can be considered as π‐radicals. The ground state of neutral VOP molecule is doublet with the unpaired electron occupying dxy orbital of V atom. In contract to the C4v symmetry of neutral VOP molecule, [VOP]− anion has a “rectangular” distorted C2v structure due to Jahn‐Teller effect. The linear vibronic coupling constants for the Jahn‐Teller active modes of [TOP]− were evaluated and the node patterns of frontier KS orbitals are used to explain the reason why the distortion occurs along specific modes. The ground state [VOP]+ has a porphyrin ring with pronounced bond length alternation due to pseudo‐Jahn‐Teller effect, causi...

Charge Effects on the Structure and Composition of Porphyrin Binary Ionic Solids: ZnTPPS/SnTMePyP Nanomaterials

The pH of the solution from which a cooperative binary ionic material is formed can alter the charges of the organic anions and cations and thus the composition, crystal structure, and properties of the materials obtained by ionic self-assembly. In particular, this pH/charge effect provides a means of synthetic control over the properties and morphologies of ionic solids formed from cationic and anionic porphyrins. In the case of titration of an axial hydroxide ligand of the metal of the porphyrin to water, the charge increases by +1 with little perturbation of the molecular structure of the constituent porphyrin anion or cation. The structure of the material is thus altered without significantly altering the electronic structure of the porphyrin tecton. These novel porphyrin-based ionic materials have potential applications as catalysts, photocatalysts, and optoelectronic and sensing materials.

Equilibrium, photophysical and photochemical examination of anionic lanthanum(iii) mono- and bisporphyrins: the effects of the out-of-plane structure

Lanthanum(III) ions form kinetically labile complexes with the 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin anion (H(2)TSPP(4-)), the compositions and formation constants of which significantly depend on the presence of potential axial ligands (at 0.01 M). Deviating from the chloride ion, acetate coordinating to the metal center hinders the formation of a bisporphyrin complex. In these lanthanum(III) complexes, the metal center, due to its large ionic radius (103.2 pm), is located out of the ligand plane, distorting it. Accordingly, the absorption and fluorescence spectra of these coordination compounds display special properties characteristic of the so-called sitting-atop (SAT) or out-of-plane (OOP) porphyrin complexes. Metalation significantly decreases the quantum yield of the fluorescence from the S(1) excited state. Quantum chemical calculations (DFT) confirm the considerable OOP displacement of the La(III) center (about 120 pm in the monoporphyrin complexes). The monoporphyrins display efficient fluorescence (Φ ≈ 0.03), while the bisporphyrin does not emit. Differing from the normal (in-plane) metalloporphyrins, the excitation of these lanthanum(III) porphyrins leads to an irreversible ligand-to-metal charge transfer (LMCT) followed by the opening of the porphyrin ring, which is also typical of OOP complexes. Dissociation releasing free-base porphyrin can also be observed upon irradiation of the monoporphyrin in acetate solution, while in the presence of chloride ions interconversions of the mono- and bisporphyrins may also take place beside the irreversible photoredox reaction.

Formation, photophysical and photochemical properties of water-soluble bismuth(III) porphyrins: The role of the charge and structure

Bismuth(III) ion forms kinetically labile complexes with the 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin anion (H2TSPP4−) and the 5,10,15,20-tetrakis(1-methyl-4-pyridinium)porphyrin cation (H2TMPyP4+), the formation constants of which are 3.54 × 104 M−1 and 1.62 × 103 M−1, respectively (at pH = 6). In these complexes, the metal center, due to its large ionic radius (103 pm), is located out of the ligand plane, distorting it. Accordingly, the absorption and fluorescence spectra of these coordination compounds display special properties characteristic of the so-called sitting-atop (SAT) or out-of-plane (OOP) porphyrin complexes. The shifts of the absorption bands upon metalation indicate that the structural distortion results in stronger perturbation on the S2- than on the S1-states of the porphyrin ligand. Metalation significantly decreases the lifetime and the quantum yield of the fluorescence from the S1 excited state. The relatively rare S2-fluorescence can also be detected for these metalloporphyrins. Quantum chemical calculations (DFT and TDDFT) confirm the considerable OOP displacement of the Bi(III) center (88 pm) and the typical tendencies of the band-shifts. Differing from the normal (in-plane) metalloporphyrins, excitation of these bismuth(III) porphyrins leads to an irreversible ligand-to-metal charge transfer (LMCT) followed by the opening of the porphyrin ring, which is also typical of SAT complexes. The quantum yields of this photoinduced redox reaction are significantly higher for the anionic than for the cationic complex, due to the stronger Lewis-basicity of H2TSPP4−. In the mechanism of the reaction between these free-base porphyrins and bismuth(III) ions formation of a longer-lived intermediate was observed. In the case of the cationic porphyrin also the photochemistry of this intermediate could be studied; deviating from the photoinduced behavior of the final product metalloporphyrins, excitation of this intermediate results in predominantly the dissociation to the initial porphyrin ligand and metal ion, indicating a relatively weak coordination bond and significantly distorted structure.

Reductive Fluorescence Quenching of the Photoexcited Free Base meso-Tetrakis (Pentafluorophenyl) Porphyrin by Amines

Steady state and time resolved fluorescence quenching behaviors of meso-Tetrakis (pentafluorophenyl) porphyrin (H(2)F(20)TPP) in presence of different aliphatic and aromatic amines have been executed in homogeneous dichloromethane (DCM) solution. At room temperature in DCM, free base (H(2)F(20)TPP) shows fluorescence with two distinct peaks at 640 and 711 nm and natural lifetime tauf=9.8 ns which are very similar to that of meso-tetraphenyl porphyrin (TPP). Unlike TPP, addition of both aliphatic and aromatic amines to a solution containing H(2)F(20)TPP results in an efficient decrease in fluorescence intensity without altering the shape and peak position of fluorescence emission. Upon addition of amines there was no change in optical absorption spectra of H(2)F(20)TPP. The fluorescence quenching rate constants ranged from 1 x 10(9) to 4 x 10(9) s(-1), which are one order below to the diffusion control limit, and temperature dependent quenching rate constants yield the activation energies which are found to be order of 0.1 eV. Femto second transient absorption studies reveal the existence of amine cation radical and porphyrin anion radicals with very short decay time (15 ps). The fluorescence quenching reaction follows Stern-Volmer kinetics. Steady state and time-resolved data are interpreted within general kinetic scheme of Marcus semi-classical model which attributes bimolecular electron transfer process between amines and the lowest excited singlet state of H(2)F(20)TPP. Calculated internal reorganization energies are found to be in between 0.04 and 0.22 ev. Variation of electron transfer rate as function of free energy change (DeltaG(0)) points the ET reactions in the present systems are in Marcus normal region. This is the first example of reductive fluorescence quenching of free base neutral porphyrins in homogeneous organic solvent ever known.

Equilibrium, photophysical, photochemical and quantum chemical examination of anionic mercury(I) porphyrins

Hg22+ion and 5,10,15,20-tetrakis(parasulphonato-phenyl)porphyrin anion can form 2:1 (2 clusters:1 porphyrin) and 2:2 complexes, while the formation of the 1:1 species is not observable: it is only an intermediate, similarly to the cases of other large metal ions of small charge-density. The differences between mercury(I) and mercury(II) porphyrins in the composition of monoporphyrins (2:1 vs. 1:1), in the stability and the Soret absorption based on the arrangement of 2:2 complexes (asymmetric vs. probably symmetric sandwich-structure), in the kinetic behavior (molecularities and the special dimerization of HgIIP4-), in the product of the photoinduced dissociations of 2:2 bisporphyrins (free-base ligand vs. 1:1 complex) can prove that no mercury(II) porphyrins can form due to the possible disproportion of dimercury(I) ions. However, the similarities in the absorption, photophysical and photochemical features (also to other out-of-plane metalloporphyrins) suggest that the out-of-plane position of metal center and the distorted structure of complexes may be responsible for these common properties, the so-called sitting-atop characteristics. Moreover, the calculated structural data of the theoretically studied 1:1 mercury(I) porphyrin are very similar to those of HgIIP as a consequence of the charge separation in the cluster based on the strength of metal-nitrogen bonds. In the case of the 2:2 species, neither the increased distance (because of the Hg-Hg bond), nor the absence of 45° rotation of the two ligands can significantly modify the π-π interaction because its both measured and calculated absorption spectra are similar to those of HgII2P2.

Equilibrium, Photophysical, Photochemical, and Quantum Chemical Examination of Anionic Mercury(II) Mono- and Bisporphyrins

Mercury(II) ion and 5,10,15,20-tetrakis(parasulfonato-phenyl)porphyrin anion can form 1:1, 2:2, and 3:2 (metal ion/porphyrin) out-of-plane (OOP) complexes, from which Hg2P2(8-) has not been identified until now. Identification of this species significantly promoted the confirmation of the composition and the precise elucidation of the equilibrium of Hg3P2(6-). Since the formation of each complex is too fast, their kinetic behavior was studied from the side of dissociation. The rate-determining step in dissociations, as well as in the formation of the 2:2 complex, that is, the dimerization of 1:1 complex, proved to be virtually first-order under these conditions, while the consecutive formations of HgP(4-) and Hg3P2(6-) are second-order reactions. The equilibria can be spectrophotometrically investigated because the Soret- as well as the Q-absorption bands of the free-base ligand are more and more red-shifted in the series of 1:1, 2:2, and 3:2 complexes, and the split of Q-bands disappears as the singlet-1 excited states become degenerate; in the case of bisporphyrins, the bands broaden, especially in the longer-wavelength region of the spectra. The quantum yield and the lifetime of S1-fluorescence from the macrocycle is decreased by the insertion of a mercury(II) ion due to distortion, and in bisporphyrins the luminescence totally ceases because their more complicated structure promotes other ways of energy dissipation. The lifetime of the triplet excited-state is also reduced by metalation. The transient absorption measured upon excitation of Hg3P2(6-) probably originates from Hg2P2(8-) formed by efficient photodissocation during the laser pulse. This photoinduced dissociation is characteristic to out-of-plane complexes, but in metallo-monoporphyrins it needs the energetically higher Soret-excitation; in bisporphyrins, it can take place during irradiation at the longer Q-wavelengths. Investigation of the intramolecular photoredox reactions has proved that for the increased efficiency of the indirect photoinduced LMCT, not the redox potential, but the position of the metal center is responsible. The two orders of magnitude higher photoredux quantum yield for the 3:2 complex, compared to that of the 2:2 species, can be explained by the repulsive effect of the inner mercury(II) ion pushing the other two farther out of the ligand cavity. In bisporphyrins the second excited states are photochemically more reactive than the first ones, while most of the photochemical processes of HgP(4-) originate from the first excited state. According to our quantum chemical calculations, the mercury(II) ion causes the expansion of the porphyrin-cavity; therefore its out-of-plane position is smaller than the value expected based on its ionic radius. In the hitherto unknown 2:2 dimer two 1:1 saucer-shaped monomers are kept together by secondary forces, mostly by pi-pi interaction, but their relative arrangement was not unequivocally determined by the two DFT functionals used. The arrangements with a symmetry axis or plane perpendicular to both rings are not favored; instead, the two monomers are shifted along the porphyrin planes, either in a Hg-P-Hg-P or a Hg-P-P-Hg order. Our time-dependent density functional theory (TD-DFT) calculations indicate that the electronic spectra are not very sensitive to the structure of the dimer, even though the environment of the porphyrin rings is quite different if one of the metal ions is between or outside of both macrocycles. The calculated spectral shifts agree only partially with the experimental data. The TD-DFT calculations suggest that the chromophores are not fully independent in the bisporphyrins and that the observed spectral shift cannot be uniquely assigned to the geometrical distortion of the porphyrin macrocyle.

Base-Promoted Silicon−Hydrogen Bond Activation of Silanes by Iridium(III) Porphyrin Complexes

Iridium(III) porphyrin silyls were synthesized in moderate to high yields conveniently from the reactions of iridium(III) porphyrin carbonyl chloride and methyl with silanes, via silicon−hydrogen bond activation (SiHA) in solvent-free conditions and nonpolar solvents. Base was found to promote the SiHA reactions. Specifically, K3PO4 accelerated the SiHA with iridium porphyrin carbonyl chloride, while KOAc promoted the SiHA by iridium porphyrin methyl. Mechanistic experiments suggested that iridium(III) porphyrin carbonyl chloride initially formed iridium porphyin cation, which then reacted with silanes likely via heterolysis to give iridium porphyrin hydride. Iridium porphyrin hydride further reacted with silanes to yield iridium porphyrin silyls. On the other hand, iridium(III) porphyrin methyl and silyls underwent either oxidative addition or σ-bond metathesis to form the products. In the presence of base, a pentacoordinated silicon hydride species likely formed and reacted with iridium porphyrin methyl to form iridium porphyrin anion, which could further react with silanes to yield iridium porphyrin hydride after protonation. Ir(ttp)H finally reacted with excess silanes to give iridium porphyrin silyl complexes.

EPR and ENDOR studies of Fe(II) hemoproteins reduced and oxidized at 77 K

gamma-irradiation of frozen solutions of Fe(II) hemoproteins at 77 K generates both electron paramagnetic resonance (EPR) active singly reduced and oxidized heme centers trapped in the conformation of the Fe(II) precursors. The reduction products of pentacoordinate (S = 2) Fe(II) globins, peroxidases and cytochrome P450cam show EPR and electron-nuclear double resonance (ENDOR) spectra characteristic of (3d 7) Fe(I) species. In addition, cryoreduced Fe(II) alpha-chains of hemoglobin and myoglobin exhibit an S = 3/2 spin state produced by antiferromagnetic coupling between a porphyrin anion radical and pentacoordinate (S = 2) Fe(II). The spectra of cryoreduced forms of Fe(II) hemoglobin alpha-chains and deoxymyoglobin reveal that the Fe(II) precursors adopt multiple conformational substates. Reduction of hexacoordinate Fe(II) cytochrome c and cytochrome b5 as well as carboxy complexes of deoxyglobins produces only Fe(II) porphyrin pi-anion radical species. The low-valent hemoprotein intermediates produced by cryoreduction convert to the Fe(II) states at T > 200 K. Cryogenerated Fe(III) cytochrome c and cytochrome b5 have spectra similar to these for the resting Fe(III) states, whereas the spectra of the products of cryooxidation of pentacoordinate Fe(II) globins and peroxidases are different. Cryooxidation of CO-Fe(II) globins generates Fe(III) hemes with quantum-mechanically admixed S = 3/2, 5/2 ground states. The trapped Fe(III) species relax to the equilibrium ferric states upon annealing at T > 190 K. Both cryooxidized and reduced centers provide very sensitive EPR/ENDOR structure probes of the EPR-silent Fe(II) state.

Synthesis of urea picket porphyrins and their use in the elucidation of the role buried solvent plays in the selectivity and stoichiometry of anion binding receptors.

The synthesis of alpha,alpha-5,10-diurea and alpha,alpha,alpha-5,10,15-triurea picket porphyrins are detailed in this report. In previous reports, these porphyrins, along with alpha,alpha,alpha,alpha-5,10,15,20-tetraurea picket porphyrin, were used to demonstrate the important role one buried solvent molecule plays in the selectivity and stoichiometry of binding inorganic anions. Building on prior work, this report discusses the results of acetate anion binding studies between tetra- and diurea picket porphyrins (the latter does not contain a buried solvent molecule in the anion-receptor complex), compares differences in thermodynamic data obtained from van't Hoff plots of a porphyrin anion receptor able to utilize buried solvent in its binding motif with one that does not, and compares the crystal structure of a tetraurea porphyrin 1-chloride anion complex that contains buried solvent with new X-ray crystal structures of tetraurea porphyrin 1-dichloride or bisdihydrogenphosphate anion complexes that contain no buried solvent. Data from our previous work, and the work described herein, demonstrates that one buried solvent molecule provides stability to the receptor-anion complex that is similar in energy to a moderately strong hydrogen bond.

Surface electrochemistry and electrocatalytic activity of ion pairs formed from oppositely-charged phthalocyanine and porphyrin species

Self-assembled ion pairs are deposited onto a graphite electrode surface by dipping the electrode sequentially into phthalocyanine cations and anions, or a phthalocyanine cation and porphyrin anion. The electrochemical properties of these surface-bound ion pairs are compared with the properties of the individual surface-bound components. The order of deposition is shown to be crucial, implying that these species lie flat on the surface. A detailed study of the electrocatalytic oxidation of oxalate anion is used to explore their reactivity as a function of deposition order.

Electrochemical and resonance Raman studies of nitridomanganese(V) porphyrins in nonaqueous solution

The UV-vis spectral, electrochemical and resonance Raman data of [meso-tetrakis(4-pyridyl)porphyrinato]nitridomanganese(V), MnN(TPyP) , were investigated. MnN(TTP) (where ( TTP )2− = dianion of meso-tetrakis(p-tolyl)porphyrin) and MnN(OEP) (where ( OEP )2− = dianion of 2,3,7,8,12,13,17,18-octaethylporphyrin) were also examined in comparison. Cyclic voltammetry of MnN ( TPyP ) showed an irreversible oxidation wave at +1.22 V and two redox couples at −1.05 and −1.40 V vs. Ag / AgCl , respectively. According to spectroelectrochemical studies, the first and the second reductions involved formation of the porphyrin anion and dianion, respectively, the latter leading to a phlorin. The electron-withdrawing 4-pyridyl substituent shifted the redox potential of the porphyrin ring to a more positive value. However, the bond strength of the Mn - N triple bond was not affected. Resonance Raman studies indicated that the Mn≡N stretching frequencies (νMnN) occurring within 1050 ± 1 cm−1 in various solvents did not change significantly. The hydrogen-bonding between methanol and MnN ( TPyP ) lowered νMnN to 1040 cm−1. A further lowering of νMnN was found in the presence of nitrogeneous bases such as imidazole (ImH), piperidine (Pip) and pyridine (Py) and may be due to coordination to the manganese center. νMnN is correlated with the pKa's of a series of pyridines.

Osmium Complexes of the 5,10,15,20-Tetrakis(4-phosphonomethylphenyl)porphyrin Anion, A New Water-Soluble Tetraphenylporphyrinate System

The synthesis of a new class of water-soluble osmium tetraphenylporphyrinates, complexes of the tetrakis(4-phosphonomethylphenyl)porphyrin anion [H2(tP4O8{OH}4mpp)]4−(5), is described. Starting from OsCO(tmecpp)thf (1a) and OsO2(tmecpp) (1b), the new complexes 5a−c were synthesized by a four-step reaction with Os(t{OH}4mpp)LL′ (2a−b), Os(tBr4mpp)LL′ (3a−b), and Os(tP4O4{OEt}8mpp)LL′ (4a−c) as intermediates. The new complexes were characterized by UV/Vis, IR, 1H NMR, and 31P NMR spectroscopy, as well as by cyclic voltammetry and electrophoresis.

Synthesis and Excited State Raman Spectroscopy of Sterically Crowded Ruthenium(II) Octaethyltetraphenylporphyrin

Pyridine and CO adducts of RuIIOETPP (OETPP = 2,3,7,8,12,13,17,18-octaethyl-5,10,15,20-tetraphenylporphinato) have been prepared and characterized by absorption and resonance Raman (RR) spectroscopy. Ru → porphyrin back-bonding is evident from the ground state RR spectra. Skeletal mode frequency downshifts in RuIIOETPP(Py)2 relative to RuIIOETPP(CO)(Py) are comparable to those seen for the TPP (tetraphenylporphyrin) and OEP (octaethylporphyrin) analogs, indicating that distortion of the porphyrin ring from substituent crowding has little effect on the extent of back-bonding. Photoexcited RuIIOETPP(Py)2 has absorption and RR spectra which are similar to those of RuIITPP(Py)2 and are characteristic of a (dπ,π*) charge transfer state. As for RuIITPP(Py)2, the photoexcited RR spectrum has features indicating porphyrin anion formation and does not have pyridine anion features, as have been observed for photoexcited RuIIOEP(Py)2. The ethyl substituents raise the porphyrin eg* orbital above the lowest pyridine π...