Electrochemistry of platinum(II) porphyrins: effect of substituents and π-extension on redox potentials and site of electron transfer

Excited-State Charge Transfer in Push-Pull Platinum(II) π-Extended Porphyrins Fused with Pentacenequinone

Platinum(II) π-extended porphyrins fused with pentacenequinone and dihydropentacene have been successfully synthesized. These porphyrins were investigated using various techniques including absorption, steady-state, and time-resolved phosphorescence spectroscopy and differential pulse voltammetry. UV-vis absorption spectra of pentacenequinone-fused porphyrins (SW-Pt1 and SW-Pt2) showed unusually broad and nontypical absorption patterns. Phosphorescence spectra of SW-Pt1, SW-Pt2, and SW-Pt3 displayed similar emissions in the 704-706 nm region indicating electronic transitions of similar origin; however, the triplet lifetimes were found to be quenched in the case of both SW-Pt1 and SW-Pt2, suggesting the occurrence of excited-state events. Facile reductions were obtained for both the pentacene-quinone-fused monomer (SW-Pt2) and dimer (SW-Pt1) and were identified to be located at the pentacenequinone components. The observed orbital segregations for SW-Pt2 and SW-Pt1 from DFT calculations supported the possibility of charge transfer in these push-pull systems. Interestingly, the established energy level diagram revealed that the charge transfer from the triplet excited Pt porphyrin is thermodynamically an uphill process. Systematic studies involving both femtosecond and nanosecond transient absorption techniques revealed that the singlet excited Pt porphyrins undergo an intermediate charge transfer state prior to populating the triplet state, providing a plausible explanation for phosphorescence quenching. The lifetime of the intermediate charge transfer states was found to be 25.9 and 5.68 ps, respectively, for SW-Pt1 and SW-Pt2.

Molecular Engineering of Corrole Radicals by Polycyclic Aromatic Fusion: Towards Open-Shell Near-Infrared Materials for Efficient Photothermal Therapy

Open-shell radicals are promising near-infrared (NIR) photothermal agents (PTAs) owing to their easily accessible narrow band gaps, but their stabilization and functionalization remain challenging. Herein, highly stable π-extended nickel corrole radicals with [4n+1] π systems are synthesized and used to prepare NIR-absorbing PTAs for efficient phototheranostics. The light-harvesting ability of corrole radicals gradually improves as the number of fused benzene rings on β-pyrrolic locations increases radially, with naphthalene- and anthracene-fused radicals and their one-electron oxidized [4n] π cations exhibiting panchromatic visible-to-NIR absorption. The extremely low doublet excited states of corrole radicals promote heat generation via nonradiative decay. By encapsulating naphthocorrole radicals with amphiphilic polymer, water-soluble nanoparticles Na-NPs are produced, which exhibit outstanding photostability and high photothermal conversion efficiency of 71.8 %. In vivo anti-tumor therapy results indicate that Na-NPs enable photoacoustic imaging of tumors and act as biocompatible PTAs for tumor ablation when triggered by 808 nm laser light. The "aromatic-ring fusion" strategy for energy-gap tuning of corrole radicals opens a new platform for developing robust NIR-absorbing photothermal materials.

Metalation of Tellurophene: Reactivity of 21,23-Ditelluraporphodimethene toward Palladium(II), Platinum(II), and Rhodium(I)

Ditelluraporphodimethene, a nonaromatic porphyrinoid containing two tellurophene rings, reacted with palladium(II), platinum(II), and rhodium(I) following two different paths. Palladium(II) formed bonds to two tellurium donors of the macrocycle, yielding a side-on coordination compound, with a square planar (Te₂Cl₂) metal ion environment. An alternative reaction path has been observed for ditelluraporphodimethene with platinum(II) or rhodium(I) in high boiling solvents. These conditions led to the profound transformation, that is, one tellurium atom to a metal atom exchange, resulting in the formation of organometallic species containing metallacyclopentadiene rings, that is, 21-platina-23-telluraporphodimethene and 21-rhoda-23-telluraporphodimethene. The substitution reaction proceeded selectively at the tellurophene ring within the conjugated part of the molecule, that is, the tellurophene ring bound to two sp² meso-carbon atoms. In the case of platinum, the exchange was accompanied by one meso-aryl ring fusion with the formed platinacyclopentadiene ring, and the platinum(II) macrocycle underwent reversible oxidation with chlorine. The products are stable and represent first nonaromatic examples of metalloporphyrinoids, with a metallacyclopentadiene ring incorporated into a porphodimethene skeleton.

Hydrogen Evolution Reaction, Electrochemical CO2 Reduction, and Oxidative Photodegradation of Organic Dyes Catalyzed by Co(II) Trimethoxy-Meso-Arylporphyrin

In search of robust catalysts for redox transformations such as the hydrogen evolution reaction (HER) or CO2 to CO reduction, we stepped on the previously reported meso-tetrakis(3,4,5-trimethoxyphenyl)porphyrinato cobalt(II) complex [Co(TTMPP)]. We prepared [Co(TTMPP)] in good yields and characterized it by IR, UV-vis absorption, photoluminescence spectroscopy, and cyclic voltammetry (CV). The [Co(TTMPP)] was used as a homogeneous catalyst for the electrochemical formation of H2 (HER) in DMF (N,N’-dimethylformamide)/TFA (trifluoroacetic acid) and DMF/EtN3BF4 solutions, with high faradic efficiencies (FE). Additionally, the reduction of CO2 to CO in DMF under a CO2 atmosphere was catalyzed in DMF/TFE (TFE = 2,2,2-trifluoroethanol) and DMF/PhOH with high FE and only traces of H2 as a by-product. Turnover frequencies of 15.80 or 9.33 s−1, respectively were determined from CV experiments or controlled potential electrolysis in the presence of 1eq. TFE. They were lower with PhOH as proton source with 13.85 or 8.31 s−1, respectively. Further, [Co(TTMPP)] as a solid catalyst (suspension) allowed the photodecomposition of the organic dyes methylene blue (MB) and rhodamine B (RhB) using H2O2 under visible light irradiation. The photocatalyst was photostable over five cycles. A photocatalytic mechanism was proposed based on trapping experiments of reactive oxygen species.

Carbazole appended trans-dicationic pyridinium porphyrin finds supremacy in DNA binding/photocleavage over a non-carbazolyl analogue

A carbazolyl appended trans-pyridyl porphyrin (1) was synthesized and its dicationic form 2 was obtained by methylation of the pyridyl group. Copper and zinc complexes of porphyrin 2 (Cu(II), 3; Zn(II), 4) were isolated and characterized by various modern spectroscopic techniques. The DNA binding properties of 2, 3, and 4 have been explored against calf thymus-DNA (CT-DNA). DNA binding was quantized using the intrinsic binding constant (K_b) that was calculated by UV-visible absorption spectroscopy, and the value K_b = 1.6 × 10⁶ M^-1 for compound 2 reveals a better interaction of 2 towards CT-DNA than those of 3 (3.1 × 10⁵ M^-1) and 4 (3.4 × 10⁵ M^-1), which follows the order 2 > 4 > 3. The fluorescence quenching efficiency and ethidium bromide quenching assay also indicated a good binding affinity of all the compounds towards CT-DNA. Furthermore, the spectroscopic data suggest that the possible mode of interaction is intercalation. The docking studies were in accordance with the experimental results. Notably, DNA cleavage studies reveal that 2 shows better damage than 3 and 4 which is in accordance with the binding affinity order 2 > 4 > 3. The observed quantum yield (2: 0.65, 3: 0.33, and 4: 0.97) and no change in DNA cleavage in the presence of NaN₃ reveal the involvement of singlet oxygen. The singlet excited state lifetimes were in the range of 6.3-1.2 ns. Furthermore, these porphyrins can be investigated as interesting photosensitizers in photodynamic therapy and photochemotherapy.

Fluorescence of CoTPP Mediated by the Plasmon-Exciton Coupling Effect in the Tunneling Junction

CoTPP, as a common hypsoporphyrin, is usually not a luminescent molecule because of the open-shell Co ion. In this paper, well-defined multilayer CoTPP molecules self-assembled on Au(111) surface are characterized layer by layer with scanning tunneling microscope (STM) induced luminescence. By using the highly localized STM tunneling current, we not only investigate the influence of bias polarity on the amplitude of distinct plasmonic emission resulted from the interaction between the metal substrate and the metal ions but also first obtain the light emission from the hypsoporphyrins in the tunneling junction. The density-matrix method and the combined approach of classical electrodynamics and first-principles calculation are used to explain the mechanism of the light emission. These findings may expand the underlying physics of plasmon-exciton coupling in STM nanocavity and reveal a new possible path to overcome the fluorescent potential of hypsoporphyrins by the intense localized electric fields.

Synthesis and Redox Properties of Superbenzene Porphyrin Conjugates

Superbenzene porphyrin conjugates find wide range of applications from nonlinear optical materials to semiconductors. Herein, we report the synthesis and characterization of 5,15-bis(3,5-di-tert-butylphenyl)-10,20-bis(pentaphenylphenyl)phenylporphyrin and its Zinc-metallated complex. Oxidative planarization of 5,15-bis(3,5-di-tert-butylphenyl)-10,20-bis(pentaphenylphenyl)phenylporphyrin and its metallated complex was carried out by using NOBF₄ as an oxidizing agent. The formation of superbenzene porphyrin conjugates validates its Scholl type reactions. The laboratory-synthesized porphyrin conjugates were characterized experimentally using spectroscopic techniques such as ¹H NMR, ¹³C NMR, electron spin resonance, and ultraviolet-visible spectroscopy for structural conformation. In addition, density functional theory calculations were carried out to validate the experimental results. The theoretical and experimental results show that the 4-(pentaphenylphenyl)phenyl ligand increases the stability, optical properties, and rate of planarization of synthesized porphyrins. The conjugates exhibited intense and distant electronic communication between two hexabenzocoronene sites, taking advantage of porphyrin as a π-spacer. The π-radical cation has also been found to be an intermediate in oxidative C-C bond formation. NICS calculations support such a conclusion.

Examining the influence of bilayer structure on energy transfer and molecular photon upconversion in metal ion linked multilayers

Metal ion linked multilayers is a unique motif to spatially control and geometrically restrict molecules on a metal oxide surface and is of interest in a number of promising applications. Here we use a bilayer composed of a metal oxide surface, an anthracene annihilator molecule, Zn(II) linking ion, and porphyrin sensitizers to probe the influence of the position of the metal ion binding site on energy transfer, photon upconversion, and photocurrent generation. Despite being energetically similar, varying the position of the carboxy metal ion binding group (i.e. ortho, meta, para) of the Pt(II) tetraphenyl porphyrin sensitizer had a large impact on energy transfer rates and upconverted photocurrent that can be attributed to differences in their geometries. From polarized attenuated total reflectance measurements of the bilayers on ITO, we found that the orientation of the first layer (anthracene) was largely unperturbed by subsequent layers. However, the tilt angle of the porphyrin plane varies dramatically from 41° to 64° to 57° for the para-, meta-, and ortho-COOH substituted porphyrin molecules, which is likely responsible for the variation in energy transfer rates. We go on to show using molecular dynamics simulations that there is considerable flexibility in porphyrin orientation, indicating that an average structure is insufficient to predict the ensemble behavior. Instead, even a small subset of the population with highly favorable energy transfer rates can be the primary driver in increasing the likelihood of energy transfer. Gaining control of the orientation and its distribution will be a critical step in maximizing the potential of the metal ion linked structures.

Meso-Tetrapyrenylporphyrins: Synthesis, structural, spectral, electrochemical properties and Förster energy transfer (FRET) studies

Meso-tetrapyrenylporphyrin and its metal (Co[Formula: see text], Cu[Formula: see text], Ni[Formula: see text] and Zn[Formula: see text]) complexes were synthesized, characterized and studied for their spectral, electrochemical and energy transfer properties. DFT optimization was carried out to gain an insight into the interactions between the porphyrin [Formula: see text]-system and the pyrenyl substituents. The pyrenyl substituents and the porphyrin core remain essentially orthogonal to each other in both the free base and the metallated porphyrins. Redox potentials of the pyrenylporphyrins are marginally shifted as compared to their corresponding phenyl derivatives. Förster resonance energy transfer (FRET) studies were carried out in toluene for free-base pyrenylporphyrin and its Zn(II) complex. Since pyrene is a good donor, an efficient energy transfer from pyrene (D) to the porphyrin core (A) on the order of 80–85% was observed for these two compounds. It was observed that energy transfer occurs mainly via ”through-bond” (TB) interaction rather than ”through-space” (TS) interaction.

A Comprehensive Study on Tetraaryltetrabenzoporphyrins

Tetraaryltetrabenzoporphyrins (TATBPs) show, due to their optoelectronic properties, rising potential as dyes in various fields of physical and biomedical sciences. However, unlike in the case of porphyrins, the potential structural diversity of TATBPs has been explored only to little extent, owed mainly to synthetic hurdles. Herein, we prepared a comprehensive library of 30 TATBPs and investigated their fundamental properties. We elucidated structural properties by X-ray crystallography and found explanations for physical properties such as solubility. Fundamental electronic aspects were studied by optical spectroscopy as well as by electrochemistry and brought in context to the stability of the molecules. Finally, we were able to develop a universal synthetic protocol, utilizing a readily established isoindole synthon, which gives TATBPs in high yields, regardless of the nature of the used arylaldehyde and without meticulous chromatographic purifications steps. This work serves as point of orientation for scientists, that aim to utilize these molecules in materials, nanotechnological, and biomedical applications.

Electrochemical and spectroelectrochemical characterization of Cu(II) and Mn(III) tetrabutano- and tetrabenzoporphyrins containing sterically hindered meso -(2,6-difluorophenyl) substituents in nonaqueous media

Four tetrabutano and tetrabenzoporphyrins containing sterically hindered meso-(2,6-difluorophenyl) substituents and copper(II) or manganese(III) central metal ions were synthesized and characterized as to their electrochemical and spectroelectrochemical properties in nonaqueous media. The copper(II) derivatives exhibit the expected two one-electron reductions to give [Formula: see text]-anion radicals and dianions in CH2Cl2. Electrochemical and spectroelectrochemical data suggest that a Cu(II) phlorin anion is generated from the doubly reduced Cu(II) butanoporphyrin and it is this species which undergoes the third reduction in pyridine. The first one-electron reduction of the Mn(III) porphyrins is metal-centered to give a Mn(II) compound, while the second and third reductions are macrocycle-centered to give Mn(II) porphyrin [Formula: see text]-anion radicals and dianions in both CH2Cl2 and pyridine. A Mn(II) phlorin anion is also generated from the Mn(II) dianion on the spectroelectrochemical timescale under the given solution conditions. The [Formula: see text],[Formula: see text]-butano and benzo groups have a significant effect on the measured redox potentials. Steric hindrance of the meso-(2,6-difluorophenyl) substituents also has an effect on the potential separation between the first two oxidations of the benzoporphyrins.

Spectral, Electrochemical, and ESR Characterization of Manganese Tetraarylporphyrins Containing Four β,β'-Pyrrole Fused Butano and Benzo Groups in Nonaqueous Media

Two series of β,β'-pyrrole butano- and benzo-substituted mangenese(III) tetraarylporphyrins were synthesized and characterized with regard to their spectral and electrochemical properties. The investigated compounds have the general formula butano(Ar)₄PorMnCl and benzo(Ar)₄PorMnCl, where Por is the dianion of the porphyrin and Ar is a p-CH₃Ph, Ph or p-ClPh group on each of the four meso-positions of the macrocycle. Each manganese(III) butano- or benzoporphyrin was examined in CH₂Cl₂ and/or pyridine containing 0.1 M tetra- n-butylammonium perchlorate and the data then were compared to that of the parent tetraarylporphyrins having the same meso-substituents. Up to four reductions are observed for each compound, the first being metal-centered to generate a Mn(II) porphyrin, and the second and third being porphyrin ring-centered to give a Mn(II) porphyrin π-anion radical and dianion, respectively. The one-electron reduced manganese porphyrins have an ESR spectrum with signals at g_⊥= 5.6-5.8 and g_// = 2.0, indicating a mixture of the four- and five-coordinated Mn(II) complexes in a high-spin state (3d⁵, S = 5/2, I = 5/2). Data from cyclic voltammetry and spectroelectrochemistry both suggest that formation of the porphyrin dianion is followed by a chemical reaction at the electrode surface to give an electroactive phlorin anion. The effects of solvent and porphyrin substituents on ultraviolet-visible light (UV-vis) spectra, redox potentials, and electron transfer mechanisms are discussed.

Electrochemistry of zinc tetraarylporphyrins containing fused butano and benzo groups. Effect of solvent and substituents on spectra, potentials and mechanism in nonaqueous media

Two series of zinc tetraarylporphyrins containing four [Formula: see text],[Formula: see text]′-pyrrole fused butano or benzo groups were synthesized and characterized as to their electrochemical and spectroelectrochemical properties in nonaqueous media. The examined compounds are represented as butano(Ar)4PorZn and benzo(Ar)4PorZn, where Por is the porphyrin dianion and Ar is a [Formula: see text]-CH3Ph, Ph or [Formula: see text]-ClPh substitutent on [Formula: see text]-positions of the macrocycle. Each Zn(II) butano- and benzoporphyrin undergoes two one-electron reductions to give a [Formula: see text]-anion radical and dianion in CH2Cl2. In contrast, three reductions were observed for the benzoporphyrin derivatives in pyridine, the third of which is assigned as electron addition to a benzophlorin anion generated from the doubly reduced benzoporphyrin. Two overlapped one-electron oxidations were observed for the butanoporphyrins in CH2Cl2, a result not previously observed for any other zinc porphyrin. The electrochemically measured HOMO-LUMO gap of the benzoporphyrins ranges from 1.89 to 1.90 V in CH2Cl2 and from 1.93 to 1.95 V in pyridine. Both values are smaller than the gaps of butanoporphyrins at 2.11-2.13 V in CH2Cl2 and 2.07.2.09 V in pyridine.

Luminescent ruffled iridium(iii) porphyrin complexes containing N-heterocyclic carbene ligands: structures, spectroscopies and potent antitumor activities under dark and light irradiation conditions

A panel of iridium(iii) porphyrin complexes containing axial N-heterocyclic carbene (NHC) ligand(s) were synthesized and characterized. X-ray crystal structures of the bis-NHC complexes [Ir^III(ttp)(IMe)₂]⁺ (2a), [Ir^III(oep)(BIMe)₂]⁺ (2d), [Ir^III(oep)(I ⁱ Pr)₂]⁺ (2e) and [Ir^III(F₂₀tpp)(IMe)₂]⁺ (2f) display ruffled porphyrin rings with mesocarbon displacements of 0.483-0.594 Å and long Ir-C_NHC bonds of 2.100-2.152 Å. Variable-temperature ¹H NMR analysis of 2a reveals that the macrocycle porphyrin ring inversion takes place in solution with an activation barrier of 40 ± 1 kJ mol^-1. The UV-vis absorption spectra of Ir^III(por)-NHC complexes display split Soret bands. TD-DFT calculations and resonance Raman experiments show that the higher-energy Soret band is derived from the ¹MLCT dπ(Ir) → π*(por) transition. The near-infrared phosphorescence of Ir^III(por)-NHC complexes from the porphyrin-based ³(π, π*) state features broad emission bands at 701-754 nm with low emission quantum yields and short lifetimes (Φ _em < 0.01; τ < 4 μs). [Ir^III(por)(IMe)₂]⁺ complexes (por = ttp and oep) are efficient photosensitizers for ¹O₂ generation (Φ _so = 0.64 and 0.88) and are catalytically active in the light-induced aerobic oxidation of secondary amines and arylboronic acid. The bis-NHC complexes exhibit potent dark cytotoxicity towards a panel of cancer cells with IC₅₀ values at submicromolar levels. The cytotoxicity of these complexes could be further enhanced upon light irradiation with IC₅₀ values as low as nanomolar levels in association with the light-induced generation of reactive oxygen species (ROS). Bioimaging of [Ir^III(oep)(IMe)₂]⁺ (2c) treated cells indicates that this Ir complex mainly targets the endoplasmic reticulum. [Ir^III(oep)(IMe)₂]⁺ catalyzes the photoinduced generation of singlet oxygen and triggers protein oxidation, cell cycle arrest, apoptosis and the inhibition of angiogenesis. It also causes pronounced photoinduced inhibition of tumor growth in a mouse model of human cancer.

Potentiometric Sensors for Iodide and Bromide Based on Pt(II)-Porphyrin

Pt(II) 5,10,15,20-tetra(4-methoxy-phenyl)-porphyrin (PtTMeOPP) was used in the construction of new ion-selective sensors. The potentiometric response characteristics (slope and selectivity) of iodide and bromide-selective electrodes based on (PtTMeOPP) metalloporphyrin in o-nitrophenyloctylether (NPOE), dioctylphtalate (DOP) and dioctylsebacate (DOS) plasticized poly(vinyl chloride) membranes are compared. The best results were obtained for the membranes plasticized with DOP and NPOE. The sensors have linear responses with near-Nernstian slopes toward bromide and iodide ions and good selectivity. The membrane plasticized with NPOE was electrochemically characterized using the EIS method to determine its water absorption and the diffusion coefficient into the membrane.

Synthesis, electrochemical and spectroelectrochemical characterization of iron(III) tetraarylporphyrins containing four β,β′-butano and β,β′-benzo fused rings

Six iron(III) tetraarylporphyrins containing four [Formula: see text]-butano or [Formula: see text]-benzo fused rings were synthesized and characterized by electrochemistry and spectroelectrochemistry in nonaqueous media. The examined compounds are represented as butano(TpYPP)FeCl and benzo(TpYPP)FeCl, where TpYPP is a dianion of the meso-substituted porphyrin, Y is a CH[Formula: see text], H or Cl substituent on the para-position of the four meso-phenyl rings and butano and benzo are the [Formula: see text]-substituents on each of the four pyrrole rings of the compound. Up to three reductions are observed for each Fe(III) butano- and benzoporphyrin in CH[Formula: see text]Cl[Formula: see text] or pyridine containing 0.1 M TBAP, the first of which is assigned in each case to a metal-centered electron transfer. The second reduction is also metal-centered in CH[Formula: see text]Cl[Formula: see text] and leads to formation of an Fe(I) porphyrin, but it is porphyrin ring-centered and gives an Fe(II) porphyrin [Formula: see text]-anion radical reduction product when pyridine is used as the solvent. The effects of the solvent and type of fused ring system (butano or benzo) on the UV-vis spectra and electrochemical properties of the Fe(III) porphyrins are discussed and comparisons are made to both the structurally related non-[Formula: see text]-substituted iron porphyrins and earlier described butano- or benzotetraarylporphyrins containing Cu(II) or Co(II) central metal ions.

Cobalt Tetrabutano- and Tetrabenzotetraarylporphyrin Complexes: Effect of Substituents on the Electrochemical Properties and Catalytic Activity of Oxygen Reduction Reactions

Three series of cobalt tetraarylporphyrins were synthesized and characterized by electrochemistry and spectroelectrochemistry. The investigated compounds have the general formula (TpYPP)Co, butano(TpYPP)Co^II, and benzo(TpYPP)Co^II, where TpYPP represents the dianion of the meso-substituted porphyrin, Y is a CH₃, H, or Cl substituent on the para position of the four phenyl rings, and butano and benzo are respectively the β- and β'-substituted groups on the four pyrrole rings of the compound. Each porphyrin undergoes one or two reductions depending upon the meso substituent and solvent utilized. Two irreversible reductions are observed for (TpYPP)Co^II and butano(TpYPP)Co^II in CH₂Cl₂ containing 0.1 M tetra-n-butylammonium perchlorate; the first leads to the formation of a highly reactive cobalt(I) porphyrin, which can then rapidly react with a solvent to give a Co^IIICH₂Cl as the product. Only one reversible reduction is seen for benzo(TpYPP)Co^II under the same solution conditions, and the one-electron-reduction product is assigned as a cobalt(II) porphyrin π-anion radical. Three oxidations can be observed for each examined compound in CH₂Cl₂. The first oxidation is metal-centered for the (TpYPP)Co and benzo(TpYPP)Co^II derivatives, leading to generation of a cobalt(III) porphyrin with an intact π-ring system, but this redox process is ring-centered in the case of butano(TpYPP)Co^II and gives a Co^II π-cation radical product. Each porphyrin was also examined as a catalyst for oxygen reduction reactions (ORRs) when adsorbed on a graphite electrode in 1.0 M HClO₄. The number of electrons transferred (n) during ORRs is 2.0 for the butano(TpYPP)Co^II derivatives, consistent with only H₂O₂ being produced as a product for the reaction with O₂. However, the reduction of O₂ using the cobalt benzoporphyrins as catalysts gave n values between 2.6 and 3.1 under the same solution conditions, thus producing a mixture of H₂O and H₂O₂ as the reduction product. This result indicates that the β and β' substituents have a significant effect on the catalytic properties of the cobalt porphyrins for ORRs in acid media.

Donor–acceptor type A2B2porphyrins: synthesis, energy transfer, computational and electrochemical studies

Synthesis, photophysical, electrochemical and DFT studies of donor–acceptor type A₂B₂porphyrins and their Zn(ii) and Pd(ii) complexes have been described.

A platinum porphyrin modified TiO2 electrode for photoelectrochemical hydrogen production from neutral water driven by the conduction band edge potential of TiO2

A TiO₂ electrode modified with a platinum(ii) porphyrin catalyst, prepared by using our “pyridyl anchoring technique”, catalyzes H₂ production from neutral water with excellent long-term durability.

The Influence of Peripheral Substituent Modification on P(V), Mn(III), and Mn(V)(O) Corrolazines: X-ray Crystallography, Electrochemical and Spectroscopic Properties, and HAT and OAT Reactivities

The influence of remote peripheral substitution on the physicochemical properties and reactivity of phosphorus and manganese corrolazine (Cz) complexes was examined. The substitution of p-MeO for p-t-Bu groups on the eight phenyl substituents of the β-carbon atoms of the Cz ring led to changes in UV-vis transitions and redox potentials for each of the complexes. The oxygen atom transfer (OAT) and hydrogen atom transfer (HAT) reactivity of the Mn(V)(O) complexes was also influenced by p-MeO substitution. The OAT reactivity of Mn(V)(O)(MeOP8Cz) (MeOP8Cz = octakis(p-methoxyphenyl)corrolazinato(3-)) with triarylphosphine (PAr3) substrates led to second-order rate constants from 10.2(5) to 3.1(2) × 10(4) M(-1) s(-1). These rates of OAT are slower than those seen for Mn(V)(O)(TBP8Cz) (TBP8Cz = octakis(p-tert-butylphenyl)corrolazinato(3-)). A Hammett study involving para-substituted PAr3 substrates reveals a Hammett ρ-value for Mn(V)(O)(MeOP8Cz) that is more negative than that observed for Mn(V)(O)(TBP8Cz), consistent with a less electrophilic Mn center. The HAT reactivity of Mn(V)(O)(MeOP8Cz) with C-H substrates was examined and revealed second-order rate constants from 6.8(5) × 10(-5) to 1.70(2) × 10(-1) M(-1) s(-1). The rate constants varied with the C-H bond strength of the substrate. Slightly faster HAT rates with C-H substrates were observed with Mn(V)(O)(MeOP8Cz) compared to Mn(V)(O)(TBP8Cz), indicating that the basicity of the putative [Mn(IV)(O)](-) intermediate likely compensates for the more negative redox potential in the driving force for HAT. In addition, the complete, large-scale synthesis of the para-phenyl-substituted porphyrazines RP8PzH2 (R = p-tert-butylphenyl (TB), p-methoxyphenyl (MeO), and p-isopropylphenyl) and corrolazines RP8CzH3 (TBP8CzH3 and MeOP8CzH3) is presented. The crystal structures of the monoprotonated, metal-free corrolazine [(TBP8CzH3)(H)](+)[BArF](-), P(V)(OMe)2(MeOP8Cz), and Mn(III)(MeOP8Cz)(MeOH) are presented. This work provides the first insights into the influence of electronic substituent effects on the corrolazine periphery.

Electron-Transfer Kinetics within Supramolecular Assemblies of Donor Tetrapyrrolytic Dyes and an Acceptor Palladium Cluster

9,18,27,36-Tetrakis[meso-(4-carboxyphenyl)]tetrabenzoporphyrinatozinc(II) (TCPBP, as a sodium salt) was prepared in order to compare its photoinduced electron-transfer behavior toward unsaturated cluster Pd3(dppm)3(CO)(2+) ([Pd3(2+)]; dppm = Ph2PCH2PPh2 as a PF6(-) salt) with that of 5,10,15,20-tetrakis[meso-(4-carboxyphenyl)]porphyrinatozinc(II) (TCPP) in nonluminescent assemblies of the type dye···[Pd3(2+)]x (x = 0-4; dye = TCPP and TCPBP) using femtosecond transient absorption spectroscopy. Binding constants extracted from UV-vis titration methods are the same as those extracted from fluorescence quenching measurements (static model), and both indicate that the TCPBP···[Pd3(2+)]x assemblies (K14 = 36000 M(-1)) are slightly more stable than those for TCPP···[Pd3(2+)]x (K14 = 27000 M(-1)). Density functional theory computations (B3LYP) corroborate this finding because the average ionic Pd···O distance is shorter in the TCPBP···[Pd3(2+)] assembly compared to that for TCPP···[Pd3(2+)]. Despite the difference in the binding constants and excited-state driving forces for the photoinduced electron transfer in dye*···[Pd3(2+)] → dye(•+)···[Pd3(•+)], the time scale for this process is ultrafast in both cases (<85 fs). The time scales for the back electron transfers (dye(•+)···[Pd3(•+)] → dye···[Pd3(2+)]) occurring in the various observed species (dye···[Pd3(2+)]x; x = 0-4) are the same for both series of assemblies. It is concluded that the structural modification on going from porphyrin to tetrabenzoporphyrin does not greatly affect the kinetic behavior in these processes.

Highly selective and efficient oxidation of sulfide to sulfoxide catalyzed by platinum porphyrins

Two platinum porphyrins, meso-tetramesitylporphyrinatoplatinum and meso-tetrakis(pentaflourophenyl) porphyrinatoplatinum, are explored for catalytic application in the selective oxidation of sulfide to sulfoxide by iodosylbenzene. The obtained overall turnover number of 90,000 in the oxidation of thioanisole in the presence of meso-tetrakis(pentaflourophenyl) porphyrinatoplatinum indicates the pronounced catalytic activity of the platinum porphyrins. Perfect selectivity toward sulfoxide or sulfone also was achieved via stoichiometric control of reactants.

Cunning metal core: efficiency/stability dilemma in metallated porphyrin based light-emitting electrochemical cells

The syntheses, the photophysical/electrochemical characterization, and the first application in LECs of different metallated porphyrins are provided.

Electrochemistry of nonplanar copper(ii) tetrabutano- and tetrabenzotetraarylporphyrins in nonaqueous media

Copper tetrabutano and tetrabenzoporphyrins were synthesized and electrochemically characterized and the substituent effect on spectra, potentials and the HOMO–LUMO gap is discussed.

Perturbation of the charge density between two bridged Mo₂ centers: the remote substituent effects

A series of terephthalate-bridged dimolybdenum dimers with various formamidinate ancillary ligands, denoted as [Mo2(ArNCHNAr)3]2(μ-O2CC6H4CO2) (Ar = p-XC6H4, with X = OCH3 (1), CH3 (2), F (3), Cl (4), OCF3 (5), and CF3 (6)), has been synthesized and studied in terms of substituent effects on electron delocalization between the two dimetal sites. X-ray structural analyses show that these complexes share the same molecular scaffold with the para-substituents (X) being about 8 Å away from the Mo2 center. It is found that the remote substituents have the capability to tune the electronic properties of the complexes. For the series 1 to 6, the metal-metal bond distances (d(Mo-Mo)) decrease slightly and continuously; the potential separations (ΔE(1/2)) for the two successive one-electron oxidations decrease constantly, and the metal to ligand transition energies (λ(max)) increase in order. More interestingly, the two types of methine protons, H(∥) on the horizontal and H(⊥) on the vertical ligands with respect to the plane defined by the Mo-Mo bond vectors and bridging ligand, display separate resonant signals δ(∥) and δ(⊥) in the NMR spectra. The displacements of the chemical shifts, Δδ(∥-⊥) = δ(∥) - δ(⊥), are getting smaller as the substituents vary from electron-donating to -withdrawing. These results show that the peripheral groups on the [Mo2] units function to fine-tune the metal-metal interactions crossing the bridging ligand. The experimental parameters, ΔE(1/2), λ(max), and Δδ(∥-⊥), which are linearly related with the Hammett constants (σ(X)) of the X groups, can be used to probe the charge density on the two [Mo2] units and the electronic delocalization between them.

Two-photon antenna-core oxygen probe with enhanced performance

Recent development of two-photon phosphorescence lifetime microscopy (2PLM) of oxygen enabled first noninvasive high-resolution measurements of tissue oxygenation in vivo in 3D, providing valuable physiological information. The so far developed two-photon-enhanced phosphorescent probes comprise antenna-core constructs, in which two-photon absorbing chromophores (antenna) capture and channel excitation energy to a phosphorescent core (metalloporphyrin) via intramolecular excitation energy transfer (EET). These probes allowed demonstration of the methods' potential; however, they suffer from a number of limitations, such as partial loss of emissivity to competing triplet state deactivation pathways (e.g., electron transfer) and suboptimal sensitivity to oxygen, thereby limiting spatial and temporal resolution of the method. Here we present a new probe, PtTCHP-C307, designed to overcome these limitations. The key improvements include significant increase in the phosphorescence quantum yield, higher efficiency of the antenna-core energy transfer, minimized quenching of the phosphorescence by electron transfer and increased signal dynamic range. For the same excitation flux, the new probe is able to produce up to 6-fold higher signal output than previously reported molecules. Performance of PtTCHP-C307 was demonstrated in vivo in pO2 measurements through the intact mouse skull into the bone marrow, where all blood cells are made from hematopoietic stem cells.

Convenient synthesis of a highly soluble and stable phosphorescent platinum porphyrin dye

A new highly soluble platinum porphyrin derivative 10 with suppressed photobleaching is prepared on a multigram scale from inexpensive starting materials. 10 possesses intense absorption bands at λ = 463 nm (log ε = 5.39) and 633 nm (log ε = 5.20) with near-IR emission at 755 nm. Efficient NIR phosphorescence (PLQY = 0.45) and a large Stokes shift (eliminating self-absorption) make it an attractive and readily available material for a number of applications.

Electrochemical and spectroelectrochemical studies of β-phosphorylated Zn porphyrins

The electrochemical and spectroelectrochemical properties of two β-phosphorylated Zn porphyrins, [2-diethoxyphosphoryl-5,10,15,20-tetraphenylporphyrinato]zinc (1) and [2-diisopropoxyphosphoryl-5,10,15,20-tetraphenylporphyrinato]zinc (2), are reported in CH 2 Cl 2 and PhCN containing tetrabutylammonium perchlorate (TBAP) or tetrabutylammonium hexafluorophosphate (TBAPF6) as supporting electrolyte. Under certain solution conditions, three one-electron reductions are observed, with the last process being attributed to the product of a chemical reaction following formation of the porphyrin dianion. Two or three oxidations are observed for the same compounds, again depending upon the solution conditions. In some cases, two well-defined and well-separated one electron oxidations are observed but in others the first one-electron abstraction to give the porphyrin radical cation is split into two redox processes, separated from each other by 110–140 mV. This splitting of the first oxidation into two processes is attributed to linking of the two porphyrins which results when a P = O unit of the phosphoryl substituent on one porphyrin binds to the Zn ( II ) center of a second porphyrin, resulting in dimer formation. The interaction between the two macrocycles is discussed in terms of the difference in potentials between the two split redox processes (ΔE1/2) and the overall data is compared with that for other porphyrin dimers and bis-macrocycles reported in the literature.