Photocatalytic CO2 Reductions Catalyzed by meso-(1,10-Phenanthrolin-2-yl)-Porphyrins Having a Rhenium(I) Tricarbonyl Complex

We have prepared Zn and free-base porphyrins appended with a fac-Re(phen)(CO)₃Br (where phen is 1,10-phenanthroline) at the meso position of the porphyrin, and performed photocatalytic CO₂ reduction using porphyrin–Re dyads in the presence of either triethylamine (TEA) or 1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzo[d]imidazole (BIH) as an electron donor. The Zn porphyrin dyad showed a high turnover number for CO production compared with the free-base porphyrin dyad, suggesting that the central Zn ion of porphyrin plays an important role in suppressing electron accumulation on the porphyrin part and achieving high durability of the photocatalytic CO₂ reduction using both TEA and BIH. The effect of acids on the CO₂ reduction was investigated using the Zn porphyrin–Re dyad and BIH. Acetic acid, a relatively strong Brønsted acid, rapidly causes the porphyrin's color to fade upon irradiation and dramatically decreases CO production, whereas proper weak Brønsted acids such as 2,2,2-trifluoroethanol and phenol enhance the CO₂ reduction.     

Mono- meso- tert-butylporphyrin

Treatment of meso-tetra(tert-butyl)porphyrin with sulfuric acid/n-butanol affords a mixture of porphyrin and mono-tert-butylporphyrin in relatively high yield.     

Mono-<Emphasis Type="Italic">meso</Emphasis>-<Emphasis Type="Italic">tert</Emphasis>-butylporphyrin

Summary. Treatment of meso-tetra(tert-butyl)porphyrin with sulfuric acid/n-butanol affords a mixture of porphyrin and mono-tert-butylporphyrin in relatively high yield.     

Synthesis and Characterization of Donor–π‐Acceptor‐Based Porphyrin Sensitizers: Potential Application of Dye‐Sensitized Solar Cells

New porphyrin sensitizers based on donor–π‐acceptor (D‐π‐A) approach have been designed, synthesized, characterized by various spectroscopic techniques and their photovoltaic properties explored. N,N′‐Diphenylamine acts as donor, the porphyrin is the π‐spacer, and either carboxylic acid or cyanoacryclic acid acts as acceptor. All compounds were characterized by using ¹H NMR spectroscopy, ESI‐MS, UV–visible emission spectroscopies as well as electrochemical methods. The presence of aromatic groups between porphyrin π‐plane and acceptor group push the absorption of both Soret and Q‐bands of porphyrin towards the red region. The electrochemical properties suggests that LUMO of these sensitizers above the TiO₂ conduction band. Finally, the device was fabricated using liquid redox electrolyte (I^?/I₃^?) and its efficiency was compared with that of a leading sensitizer.     

Fluorescent Arylphosphonic Acids: Synergic Interactions between Bone and the Fluorescent Core

Herein, we report the third generation of fluorescent probes (arylphosphonic acids) to target calcifications, particularly hydroxyapatite (HAP). In this study, we use highly conjugated porphyrin-based arylphosphonic acids and their diesters, namely 5,10,15,20-tetrakis[m-(diethoxyphosphoryl)phenyl]porphyrin ( m -H₈TPPA-OEt₈ ) and 5,10,15,20-tetrakis [m-phenylphosphonic acid]porphyrin ( m -H₈TPPA ), in comparison with their positional isomers 5,10,15,20-tetrakis[p-(diisopropoxyphosphoryl)phenyl]porphyrin ( p -H₈TPPA-iPr₈ ) and 5,10,15,20-tetrakis [p-phenylphosphonic acid]porphyrin ( p -H₈TPPA ), which have phosphonic acid units bonded to sp² carbon atoms of the fluorescent core. The conjugation of the fluorescent core is thus extended to the (HAP) through sp²-bonded −PO₃H₂ units, which generates increased fluorescence upon HAP binding. The resulting fluorescent probes are highly sensitive towards the HAP in rat bone sections. The designed probes are readily taken up by cells. Due to the lower reported toxicity of ( p -H₈TPPA ), these probes could find applications in monitoring bone resorption or adsorption, or imaging vascular or soft tissue calcifications for breast cancer diagnosis etc.     

Planar and Nonplanar Free‐Base Tetraarylporphyrins: β‐Pyrrole Substituents and Geometric Effects on Electrochemistry,Spectroelectrochemistry, and Protonation/Deprotonation Reactions in Nonaqueous Media

A series of planar and nonplanar free‐base β‐pyrrole substituted meso‐tetraarylporphyrins were characterized by electrochemistry, spectroelectrochemistry, and protonation or deprotonation reactions in neutral, acidic, and basic solutions of CH₂Cl₂. The neutral compounds are represented as H₂(P), in which P represents a porphyrin dianion with one of several different sets of electron‐withdrawing or ‐donating substituents at the messo and/or β‐pyrrole positions of the macrocycle. The conversion of H₂(P) to [H₄(P)]²⁺ in CH₂Cl₂ was accomplished by titration of the neutral porphyrin with trifluoroacetic acid (TFA) while the progress of the protonation was monitored by UV/Vis spectroscopy, which was also used to calculate logβ₂ for proton addition to the core nitrogen atoms of the macrocycle. Cyclic voltammetry was performed after each addition of TFA or TBAOH to CH₂Cl₂ solutions of the porphyrin and half‐wave potentials for reduction were evaluated as a function of the added acid or base concentration. Thin‐layer spectroelectrochemistry was used to obtain UV/Vis spectra of the neutral and protonated or deprotonated porphyrins under the application of an applied reducing potential. The magnitude of the protonation constants, the positions of λ_max in the UV/Vis spectra and the half‐wave or peak potentials for reduction are then related to the electronic properties of the porphyrin and the data evaluated as a function of the planarity or nonplanarity of the porphyrin macrocycle. Surprisingly, the electroreduction of the diprotonated nonplanar porphyrins in acid media leads to H₂(P), whereas the nonplanar H₂(P) derivatives are reduced to [(P)]^2? in CH₂Cl₂ containing 0.1 M tetra‐n‐butylammonium perchlorate (TBAP). Thus, in both cases an electrochemically initiated deprotonation is observed.     

Novel Zinc Porphyrin Sensitizers for Dye‐Sensitized Solar Cells: Synthesis and Spectral,Electrochemical, and Photovoltaic Properties

Novel meso‐ or β‐derivatized porphyrins with a carboxyl group have been designed and synthesized for use as sensitizers in dye‐sensitized solar cells (DSSCs). The position and nature of a bridge connecting the porphyrin ring and carboxylic acid group show significant influences on the spectral, electrochemical, and photovoltaic properties of these sensitizers. Absorption spectra of porphyrins with a phenylethynyl bridge show that both Soret and Q bands are red‐shifted with respect to those of porphyrin 6 . This phenomenon is more pronounced for porphyrins 3 and 4 , which have a π‐conjugated electron‐donating group at the meso position opposite the anchoring group. Upon introduction of an ethynylene group at the meso position, the potential at the first oxidation alters only slightly whereas that for the first reduction is significantly shifted to the positive, thus indicating a decreased HOMO–LUMO gap. Quantum‐chemical (DFT) results support the spectroelectrochemical data for a delocalization of charge between the porphyrin ring and the amino group in the first oxidative state of diarylamino‐substituted porphyrin 5 , which exhibits the best photovoltaic performance among all the porphyrins under investigation. From a comparison of the cell performance based on the same TiO₂ films, the devices made of porphyrin 5 coadsorbed with chenodeoxycholic acid (CDCA) on TiO₂ in ratios [ 5 ]/[CDCA]=1:1 and 1:2 have efficiencies of power conversion similar to that of an N3 ‐based DSSC, which makes this green dye a promising candidate for colorful DSSC applications.     

Kinetics of the formation and dissociation of complexes of cobalt(II) with <Emphasis Type="Italic">meso</Emphasis>-Phenylocta(methyl)porphyrin derivatives in organic solvents

The influence of the deformation of the tetrapyrrole aromatic macrocycle and the electronic effects of substituents on the kinetic parameters in the formation and dissociation reactions of cobalt complexes of porphyrins are discussed on the basis of a study of the kinetics of the formation and dissociation of cobalt complexes with meso-phenyl octa(methyl)porphyrin derivatives: 5,10,15-triphehyl octa(methyl) porphyrin; 5,15-bis-(3′,5′-di-tert-butyl phenyl) octa(methyl)porphyrin; 5,10,15-tris-(3′,5′-di-tert-butyl phenyl) octa(methyl)porphyrin; and 5,10,15,20-tetrakis-(3′,5′-di-tert-butyl phenyl) octa(methyl)porphyrin in acetic acid and pyridine.     

Highly Soluble Porphyrin (TPP)-Perylene Diimide (PDI) Dyad and Triad:Synthesis and Spectroscopic Studies

Novel porphyrin‐perylene diimide dyad (TPP‐PDI) and porphyrin‐perylene diimide‐porphyrin triad (TPP‐PDI‐TPP) were synthesized and characterized. Their structure and properties were studied by UV, FL, ¹H NMR, MS, elemental analysis, etc. The variation of fluorescence feature and UV spectra of TPP‐PDI‐TPP triad were investigated at different concentration of CF₃COOH in THF. The incorporation of CF₃COOH leads to the closure of the efficient charge transfer decay. After protonation of porphyrin units, the fluorescence intensity of TPP‐PDI‐TPP triad increased greatly. The fluorescence intensity of TPP‐PDI‐TPP triad restored after addition of triethylamine into the solution. Thus, TPP‐PDI‐TPP triad was a proton‐type fluorescence switch based on acid‐base control. Moreover, different from porphyrin‐perylene type molecular switches reported before, this TPP‐PDI‐TPP triad has wonderful solubility in organic solvents.     

Synthesis and aggregation of cationic porphyrins

Tetra(N-R-pyridinium-4-yl)porphyrin and tetra(N-R-pyridinium-3-yl)porphyrin derivatives were synthesized with R = 3, 6, and 8 carbon alkene, alcohol and carboxylic acid chains. Self-aggregation of these systems was studied at I = 0.1 using visible spectroscopy. N-Alkyl chain length and functionality were determined to play the dominant role in aggregation of the cationic porphyrins. Position of peripheral charge (meta vs. para) also influenced spectral changes and the nature of the aggregate.     

Synthesis and Properties of Porphyrin Nanotubes

Discrete π‐conjugated zinc porphyrin nanotubes are investigated as molecular analogues of carbon nanotubes. These porphyrin nanotubes have a diameter of 2.4 nm (Zn–Zn distance) and lengths of up to 3.6 nm, measured to the van der Waals surfaces of the outer β‐pyrrole hydrogen atoms, or 4.5 nm measured to the para hydrogen atoms of the aryl groups. We explore three different strategies for synthesizing these nanotubes. The first two strategies use a template to achieve direct or sequential stave‐joining, respectively, and proceed via linear oligomers that pre‐define the length of the nanotube. These strategies are applied to synthesize porphyrin nanotubes containing 12‐ or 18‐porphyrin subunits, with ethynylene (C₂) or butadiynylene (C₄) links between the 6‐porphyrin nanorings. The third strategy involves the covalent stacking of pre‐formed 6‐porphyrin nanorings to form a 12‐porphyrin nanotube, without using a template to guide this coupling reaction. The nanotubes show strongly red‐shifted absorption spectra and low fluorescence quantum yields, indicating structural rigidity and extensive π‐conjugation.     

Hydrogen‐bonded assemblies of 20‐(4‐pyridyl)porphyrin‐54,104,154‐tribenzoic acid with dimethyl sulfoxide and 4‐acetylpyridine in their dimethyl sulfoxide and tetrahydrofuran solvates

Crystals of the title compounds, 20‐(4‐pyridyl)porphyrin‐5⁴,10⁴,15⁴‐tribenzoic acid–dimethyl sulfoxide (2/5), C₄₆H₂₉N₅O₆·2.5C₂H₆OS, (I), and 20‐(4‐pyridyl)porphyrin‐5⁴,10⁴,15⁴‐tribenzoic acid–4‐acetylpyridine–tetrahydrofuran (1/2/10), C₄₆H₂₉N₅O₆·2C₇H₇NO·10C₄H₈O, (II), consist of hydrogen‐bonded supramolecular chains of porphyrin units solvated by molecules of dimethyl sulfoxide [in (I)] and 4‐acetylpyridine [in (II)]. In (I), these chains consist of heterogeneous arrays with alternating porphyrin and dimethyl sulfoxide species, being sustained by COOH...O=S hydrogen bonds. They adopt a zigzag geometry and link on both sides to additional molecules of dimethyl sulfoxide. In (II), the chains consist of homogeneous linear supramolecular arrays of porphyrin units, which are directly connected to one another via COOH...N(pyridyl) hydrogen bonds. As in the previous case, these arrays are solvated on both sides by molecules of the 4‐acetylpyridine ligand via similar COOH(porphyrin)...N(ligand) hydrogen bonds. The two crystal structures contain wide interporphyrin voids, which accommodate disordered/diffused solvent molecules, viz. dimethyl sulfoxide in (I) and tetrahydrofuran in (II).     

Interwoven hydrogen‐bonded network assembly and supramolecular isomerism of meso‐5,10,15,20‐tetrakis(4‐carboxyphenyl)porphyrin as its dimethylformamide solvate

Molecules of the title compound, porphyrin‐5⁴,10⁴,15⁴,20⁴‐tetrabenzoic acid, C₄₈H₃₀N₄O₈, lie on sites of 2/m symmetry in the space group Cmca. The crystals consist of doubly interwoven two‐dimensional supramolecular arrays sustained by multiple (COOH)₂ cyclic dimeric hydrogen bonds, each molecule of the porphyrintetrabenzoic acid coordinating to four neighbouring species. This structure, which encloses substantial spaces occupied by disordered dimethylformamide solvent molecules, represents yet another supramolecular isomer of this porphyrin.     

Electronic and steric effects of substituents on the coordinating properties of porphyrins

Kinetics of the formation of zinc complexes of porphyrin with various substituents was studied in acetic acid and pyridine. The introduction of strong electron-withdrawing substituents (nitro groups) to the meso-positions of the porphyrin macrocycle was shown to change the reaction rate by an order of magnitude or less compared to the phenyl-substituted analogs. However, the introduction of a large number of bulky substituents leads to the deformation of the porphyrin ligand and thus affects much stronger the coordination properties of porphyrins, decreasing or increasing the rate of the complexation reaction by several orders of magnitude.     

THE EFFECTS OF PERIPHERAL SUBSTITUENTS ON THE KINETICS OF ZINC ION INCORPORATION AND ACID CATALYZED REMOVAL FROM WATER SOLUBLE SULFONATED PORPHYRINS

Abstract

The kinetics of Zn²⁺ and Zn(OH)⁺ incorporation into and the kinetics of the acid catalyzed removal of Zn(II) from twelve water-soluble, sulfonated derivatives of tetraphenylporphyrin with alkyl or halogen groups in the para, ortho or di-ortho positions were investigated. While the incorporation reactions showed little dependence on porphyrin basicity, the Zn-P (P = porphyrin derivative) acid solvolysis reactions were faster the higher the basicity of the free base (H₂-P) compound. Equilibrium constants for the formation of cadmium porphyrins decreased with an increase in porphyrin basicity. The predeformed tetrakis(4-sulfonatophenyl)-β-octabromo-porphyrin reacted with Zn²⁺ about 10³ times faster than porphyrins of similar basicity. These results indicate how substituents on the phenyl and beta-pyrrole rings influence the solution chemistry of water soluble porphyrins.     

Effect of Solvent and Protonation/Deprotonation on Electrochemistry,Spectroelectrochemistry and Electron‐Transfer Mechanisms of N‐Confused Tetraarylporphyrins in Nonaqueous Media

A series of N‐confused free‐base meso‐substituted tetraarylporphyrins was investigated by electrochemistry and spectroelectrochemistry in nonaqueous media containing 0.1 M tetra‐n‐butylammonium perchlorate (TBAP) and added acid or base. The investigated compounds are represented as (XPh)₄NcpH₂, in which “Ncp” is the N‐confused porphyrin macrocycle and X is a OCH₃, CH₃, H, or Cl substituent on the para position of each meso‐phenyl ring of the macrocycle. Two distinct types of UV/Vis spectra are initially observed depending upon solvent, one corresponding to an inner‐2H form and the other to an inner‐3H form of the porphyrin. Both forms have an inverted pyrrole with a carbon inside the cavity and a nitrogen on the periphery of the π‐system. Each porphyrin undergoes multiple irreversible reductions and oxidations. The first one‐electron addition and first one‐electron abstraction are located on the porphyrin π‐ring system to give π‐anion and π‐cation radicals with a potential separation of 1.52 to 1.65 V between the two processes, but both electrogenerated products are unstable and undergo a rapid chemical reaction to give new electroactive species, which were characterized in the present study. The effect of the solvent and protonation/deprotonation reactions on the UV/Vis spectra, redox potentials and reduction/oxidation mechanisms is discussed with comparisons made to data and mechanisms for the structurally related free‐base corroles and porphyrins.     

新型手性金属卟啉的合成及非线性光学性质研究

本文合成了一种新型Boc(叔丁氧羰基)保护手性苏氨酸修饰的自由卟啉及其锌配合物。通过元素分析、紫外-可见光谱、荧光光谱、核磁共振氢谱、CD光谱等多种谱图对结构进行了表征,并结合理论计算采用模拟退火的方法搜索了手性锌卟啉配合物的最低能量构象。此外,利用Z-扫描技术测定了手性卟啉化合物的三阶非线性折射率。     

Synthesis,and Optical and Electrochemical Properties of Cyclophane-Type Molecular Dyads Containing a Porphyrin in Close,Tangential Orientation Relative to the Surface of trans-1 Functionalized C60. Preliminary Communication

The synthesis of the cyclophane-type molecular dyads 1 and 1 . Zn was accomplished by Bingel macrocyclization of porphyrin-tethered bis-malonates 5 or 5 . Zn , respectively, with C₆₀ (Scheme). In these macrocycles, the doubly bridged porphyrin adopts a close, tangential orientation relative to the surface of the C-sphere. The porphyrin derivatives 6 and 6 . Zn with two appended, singly-linked C₆₀ moieties were also formed as side products in the Bingel macrocyclizations. The trans-1 addition pattern of the fullerene moiety in 1 and 1 . Zn was unambiguously established by ¹H- and ¹³C-NMR spectroscopy. Due to the close spatial relationship between the fullerene and porphyrin components in 1 and 6 and the corresponding Zn^II complexes, the porphyrin fluorescence is efficiently quenched as compared to the luminescence emitted by 5 and 5 . Zn , respectively (Fig. 2). Cyclic-voltammetry studies show that the mutual electronic effects exerted by the fullerene on the porphyrin and vice versa in 1 and 1 . Zn are relatively small despite the close proximity between the porphyrin donor and the fullerene acceptor (Fig. 3).     

Photodamage in a Mitochondrial Membrane Model Modulated by the Topology of Cationic and Anionic Meso‐Tetrakis Porphyrin Free Bases

The photodynamic effects of the cationic TMPyP (meso‐tetrakis [N‐methyl‐4‐pyridyl]porphyrin) and the anionic TPPS4 (meso‐tetrakis[4‐sulfonatophenyl]porphyrin) against PC/CL phosphatidylcholine/cardiolipin (85/15%) membranes were probed to address the influence of phorphyrin binding on lipid damage. Electronic absorption spectroscopy and zeta potential measurements demonstrated that only TMPyP binds to PC/CL large unilamellar vesicles (LUVs). The photodamage after irradiation with visible light was analyzed by dosages of lipid peroxides (LOOH) and thiobarbituric reactive substance and by a contrast phase image of the giant unilamellar vesicles (GUVs). Damage to LUVs and GUVs promoted by TMPyP and TPPS4 were qualitatively and quantitatively different. The cationic porphyrin promoted damage more extensive and faster. The increase in LOOH was higher in the presence of D₂O, and was impaired by sodium azide and sorbic acid. The effect of D₂O was higher for TPPS4 as the photosensitizer. The use of DCFH demonstrated that liposomes prevent the photobleaching of TMPyP. The results are consistent with a more stable TMPyP that generates long‐lived singlet oxygen preferentially partitioned in the bilayer. Conversely, TPPS4 generates singlet oxygen in the bulk whose lifetime is increased in D₂O. Therefore, the affinity of the porphyrin to the membrane modulates the rate, type and degree of lipid damage.     

Electrocatalytic Hydrogen Evolution by Water-Soluble Cobalt (II), Copper (II) and Iron (III) meso-Tetrakis(carboxyl)porphyrin

Three water-soluble carboxyl metalloporphyrins, cobalt (II), copper (II) and iron (III) meso-tetrakis (carboxyl) porphyrin were prepared and applied as homogeneous electrocatalysts for hydrogen evolution reaction (HER) with acetic acid, trifluoroacetic acid, p-toluene sulfonic acid and water as proton sources. Cyclic voltammetry (CV) results revealed the HER underwent different routes for these metalloporphyrins. Electrocatalysis tests in buffer solution of pH=7.0 showed the TOFs of cobalt (II), copper (II) and iron (III) meso-tetrakis (carboxyl) porphyrin were 184.78, 160.28 and 184.87 mol⁻¹ ⋅ h⁻¹ and the faradaic efficiency were 94.37 %, 93.01 % and 96.98 % at an overpotential of 788 mV, respectively. These results indicate the synthesized metal carboxyl porphyrins have good electrocatalytic activity for HER.