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.     

Cyclic porphyrin dimers as hosts for coordinating ligands

Bicovalently linked tetraphenylporphyrins bearing dioxypentane groups at the opposite (transoid, H₄A) and adjacent (cisoid, H₄B) aryl groups have been synthesised. Protonation of the free-base porphyrins leads to fully protonated species H₈A⁴⁺/H₈A⁴⁺ accompanied by expansion of cavity size of the bisporphyrins. The electrochemical redox studies of these porphyrins and their Zinc(II) derivatives revealed that the first ring oxidation proceeds through a two-electron process while the second ring oxidation occurs at two distinct one-electron steps indicating unsymmetrical charge distribution in the oxidized intermediate. The axial ligation properties of the Zinc(Il) derivatives of H₄A/H₄B with DABCO and PMDA investigated by spectroscopic and single crystal X-ray diffraction studies showed predominant existence of 1: I complex. The Zn₂A.DABCO complex assumes an interesting eclipsed structure wherein DABCO is located inside the cavity between the two porphyrin planes with Zn-N distances at 2.08 and 2.22 ?. The Zn atoms are pulled into the cavity due to coordination towards nitrogen atoms of DABCO and deviate from the mean porphyrin plane by 0.35 ?. The electrochemical redox potentials of the axially ligated metal derivatives are found to be sensitive function of the relative coordinating ability of the ligands and the conformation of the hosts.     

π-Electronic Charge-Transfer Interactions in Inclusion Complexes of Fullerenens with Cyclic Dimers of Metalloporphyrins

Spectroscopic and voltammetric analyses on inclusion complexes of a fullerene such as C₆₀ with a cyclic dimer of a free-base porphyrin (1-M; M = 2H) and its metal complexes (M = Co, Ag, and Zn) showed that a charge-transfer interaction is partly responsible for the complexation.     

Tuning Selectivity and Sensitivity of Mixed‐polymeric Tetraruthenated Metalloporphyrins Modified Electrodes as Voltammetric Sensors of Chloramphenicol

Mixed Ni?Co tetraruthenated porphyrin films were successfully electropolymerized on glassy carbon electrodes in alkaline solutions (pH=13) of NiTRP and CoTRP, giving excellent electrocatalytic responses for determination of the antibiotic drug chloramphenicol. Electrodes with four different compositions were obtained by varying the ratio of NiTRP and CoTRP in the deposition solution. For the characterization of these materials, SEM, ICP‐MS, EIS and CV were explored. The porphyrin modified glassy carbon electrodes presented two oxidation peaks for chloramphenicol (except for Ni‐25). The potential shifted to lower values as the percentage of CoTRP increased decreasing its oxidation potential in more than 200 mV for Ni‐50 as compared to Ni‐100. Interestingly, the materials with cobalt content larger than 50 % did not show the typical catalytic response of the Ni^IIIOOH species, but rather showed an increase in current at potentials larger than 0.4 V, demonstrating the key role played by nickel in this type of materials. The composition of polymeric mixed porphyrin materials influenced the oxidation current response of both redox waves, resulting in different sensitivities on the calibration curves.     

Photoinduced Electron vs. Concerted Proton Electron Transfer Pathways in SnIV (l-Tryptophanato)2 Porphyrin Conjugates

Aromatic amino acids such as l -tyrosine and l -tryptophan are deployed in natural systems to mediate electron transfer (ET) reactions. While tyrosine oxidation is always coupled to deprotonation (proton-coupled electron-transfer, PCET), both ET-only and PCET pathways can occur in the case of the tryptophan residue. In the present work, two novel conjugates 1 and 2 , based on a Sn^IV tetraphenylporphyrin and Sn^IV octaethylporphyrin, respectively, as the chromophore/electron acceptor and l -tryptophan as electron/proton donor, have been prepared and thoroughly characterized by a combination of different techniques including single crystal X-ray analysis. The photophysical investigation of 1 and 2 in CH₂Cl₂ in the presence of pyrrolidine as a base shows that different quenching mechanisms are operating upon visible-light excitation of the porphyrin component, namely photoinduced electron transfer and concerted proton electron transfer (CPET), depending on the chromophore identity and spin multiplicity of the excited state. The results are compared with those previously described for metal-mediated analogues featuring Sn^IV porphyrin chromophores and l -tyrosine as the redox active amino acid and well illustrate the peculiar role of l -tryptophan with respect to PCET.     

Crystal structure of meso‐substituted pyrazolyl porphyrin complexes and their highly active catalyst for oxidation of alkylbenzenes

During the past few years, a great deal of effort has been devoted to the anchoring of catalytic oxidation. In this work, three new catalysts CuPp, MnPp and ZnPp by solvothermal methods with 5, 10, 15, 20‐tetrakis(4‐N‐pyrazolyl)‐phenyl porphyrin (H₂Pp) and the corresponding metal salts have been synthesized and structurally characterized. The single crystal structures determined by X‐ray diffraction show the bond distances of M‐N in porphyrin cores determined the conformation of porphyrin rings. We explored the catalytic activity of CoPp, CuPp, MnPp and ZnPp for oxidation of alkylbenzenes. The experimental results display these products exhibit high catalytic activities and selectivities for oxidation of ethylbenzene to acetophenone, and can be reused by filtration without appreciable decrease in catalytic activity and selectivity.     

Synthesis of Zn-, Mn-, and Fe-Containing Mono- and Heterometallated Ethanediyl-Bridged Porphyrin Dimers

New ethanediyl-bridged unsymmetrical mono- and heterometallated dimers of 2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphyrin (H₂oep) containing transition-metal ions (Mn and Fe) were synthesized by a facile stepwise metallation/demetallation process under mild conditions. The novel metallation strategy initially involved the predominant insertion of Zn into one of the two porphyrin rings of the free-base dimer, followed by the incorporation of Mn or Fe into the other porphyrin ring under exceptionally mild conditions, giving corresponding heterometallic dimers; the subsequent removal of Zn yielded mono-transition-metal dimers. The emission spectrum of the monozinc dimer predominantly exhibited fluorescence bands of the free-base porphyrin component, indicating a very efficient energy-transfer process. Conversely, emission of the free-base or Zn porphyrin component of transition metal containing dimers was strongly quenched due to photoinduced electron transfer.     

A pentaporphyrin as a switching device activated by proton and redox stimuli.

A new pentaporphyrin array, constituted by a peptidic backbone and lateral chains with two free-base, one Mg(II), and two Zn(II) porphyrins, has been synthesized. The electrochemical and photophysical properties are not the mere superposition of those of its model compounds: slight shifts of the E(1/2) values and strong perturbation of both the Soret and Q-band absorption show substantial ground-state interactions among the component units, which take advantage of the rather flexible nature of the peptidic links. This multiporphyrin array, despite the flexible and nonconjugated nature of the peptidic spacers, plays the role of an antenna for visible light: an efficient photoinduced energy transfer takes place from the metalated porphyrin units to the free-base ones. Furthermore, the light emitted by the antenna can be: 1) tuned upon protonation of the free-base units, or 2) turned off by a redox input, since the formation of the Mg porphyrin radical cation, by either electrochemical or chemical methods, quenches the free-base porphyrin emission. Both quenching and tuning of the emission from the light-collecting center can be fully reverted by redox or chemical stimuli.     

Competition between energy transfer and interligand electron transfer in porphyrin-osmium(II) bis(2,2':6',2' '-terpyridine) dyads

Rapid intramolecular energy transfer occurs from a free-base porphyrin to an attached osmium(II) bis(2,2':6',2' '-terpyridine) complex, most likely by way of the F?rster dipole-dipole mechanism. The initially formed metal-to-ligand, charge-transfer (MLCT) excited-singlet state localized on the metal complex undergoes very fast intersystem crossing to form the corresponding triplet excited state ((3)MLCT). This latter species transfers excitation energy to the (3)pi,pi* triplet state associated with the porphyrin moiety, such that the overall effect is to catalyze intersystem crossing for the porphyrin. Interligand electron transfer (ILET) to the distal terpyridine ligand, for which there is no driving force, competes poorly with triplet energy transfer from the proximal (3)MLCT to the porphyrin. Equipping the distal ligand with an ethynylene residue provides the necessary driving force for ILET and this process now competes effectively with triplet energy transfer to the porphyrin. The rate constants for all the relevant processes have been derived from laser flash photolysis studies.     

Two self-assembled supramolecular solar cells sensitized via axial coordination with zinc porphyrin

In this work, two new self-assemblies based on zinc porphyrins substituted at the meso-positions with different donor units (denoted as ZnP1 and ZnP2) and anchor porphyrin (ZnPA) dyads formed by the coordination bonds of Zn-to-ligand have been prepared. Further, the assemblies were absorbed on semiconducting TiO₂ electrode surfaces by the carboxylic groups of anchor porphyrin (ZnPA), and their photovoltaic performances in solar cells were performed under 100 mW cm^?2 AM 1.5G sunlight. Photoelectrochemical studies reveal a significantly improved photovoltaic behavior for the dyad of triphenylamine-based zinc porphyrin (ZnP1) compared to the dyad with trimethylamine-based zinc porphyrin. The results were verified by electrochemical impedance spectroscopy, calculations, and optical performance. In addition, the modes of the assemblies immobilized on TiO₂ electrode surfaces were also verified by transmission electron microscopy.     

Unimolecular and collision-induced reactions of doubly charged porphyrins

Results from a tandem mass spectrometry (MS/MS) study, obtained with a reverse-geometry mass spectrometer, of the unimolecular and collision-induced reactions of doubly charged free-base and metal containing alkyl-substituted porphyrins formed by electron ionization are reported. These doubly charged porphyrin ions dissociate to yield both singly and doubly charged product ions via a number of reactions. This article classifies the major reactions observed, illustrating each with the appropriate spectra. Supplementary data from the same porphyrins, acquired with a tandem quadrupole MS/MS instrument, are also presented. The potential utility of some of these reactions as new methods for porphyrin analysis is discussed.     

Effect of terminal substituents on self‐assembly behavior of porphyrin molecules on Ag(110)

Effect of terminal substituents on self‐assembly behavior of porphyrin molecules has been studied with three derivatives modified with distinctly different substituents, 5,15‐(di‐3,5‐di‐tert‐butylphenyl) porphyrin, 5,15‐(dimesityl) porphyrin, and 5,15‐(di‐4‐ethynylphenyl) porphyrin. Scanning tunneling microscopy and density functional calculations reveal that 5,15‐(di‐3,5‐di‐tert‐butylphenyl) porphyrin, 5,15‐(dimesityl) porphyrin, and 5,15‐(di‐4‐ethynylphenyl) porphyrin spontaneously give different ordered structures on Ag(110) surface both at room temperature and after annealing. It is clear that the tert‐butylphenyl substituent could increase the intermolecular van der Waals interactions to form stable network structure under condition of thermal activation, whereas the mesityl substituent plays an essential role in the formation of rigid chain structure as a result of the CH–π interactions between the mesityl groups of molecule enantiomers. Moreover, the ethynylphenyl substituent could induce metal atoms to coordinate with ethynyl to form organometallic chains. Copyright © 2016 John Wiley & Sons, Ltd.     

Intermacrocyclic Interactions upon Stepwise Oxidations in a Monometallic Porphyrin Dimer: Ring versus Metal-Center Oxidations and Effect of Counter Anions

The effect of intermacrocyclic interactions was studied by controlled and stepwise oxidations of a monometallic silver(II) porphyrin dimer that contains a highly flexible ethane bridge. Monometallic dimers are unique systems and behave differently from their dimetallic analogues on the basis of their available sites for storing oxidizing equivalents. UV-visible spectrometry, ¹H NMR spectroscopy, XPS and single crystal X-ray diffraction studies clearly suggest the removal of the first electron from the metal center. The removal of the second electron occurred from the ring center to form a π-cation radical and, thereby, form a very unique mixed-valent species. However, unlike in all other ethane-bridged metalloporphyrin dimers reported earlier, the 2e-oxidized species showed quite unusual structures depending on the nature of counter ions. Ions, such as SbF₆, SbCl₆ and PF₆, are engaged in strong interactions with the porphyrin π-cation radical and causes substantial structural changes, including large deformation of the ring. The solid-state structure remains intact in solution as well. The observations are further supported by DFT calculations.      

界面组装金属-多卟啉阵列结构及其纳米晶

金属-多卟啉阵列结构在模拟自然界的光合作用过程、太阳能的转换及研制配位聚合物纳米材料方面具有重要的理论意义和应用前景.本文综述了近年来在气液和固液界面上组装金属-多卟啉阵列结构,在液液界面上组装金属-多卟啉纳米晶和金属-卟啉/三嗪复合配位纳米管的方法;介绍了溶液相的金属离子的组成、卟啉环结构和成膜方式对多卟啉阵列结构中卟啉环的吸收和荧光光谱的影响规律,以及金属离子外层电子轨道的特征如何影响液液界面形成的纳米晶的形貌和结构.     

卟啉作为信号传递介质的紫外可见光谱研究

合成了6种氨基酸水杨醛席夫碱(Sal-AA)：Sal-Gly(甘氨酸)、Sal-Phe(苯丙氨酸)、Sal-Arg(精氨酸)、Sal-Tyr(酪氨酸)、Sal-Met(甲硫氨酸)、Sal-Glu(谷氨酸)及其金属铜配合物。并分别在2种不同介质(三氯甲烷和甲醇)中，与四苯基卟啉TPP进行反应，研究了其紫外可见光谱性质，讨论了卟啉作为人工信号转导体系的传递介质，与氨基酸水杨醛席夫碱铜配合物的反应中，实现信号分子铜离子进一步传递的可能性以及溶剂对该信号传递的影响。结果表明，在三氯甲烷为溶剂时，除了Sal-Met的铜配合物之外，其余均能被TPP夺取而形成Metal TPP。而在以甲醇为溶剂时，只有Sal-Gly的铜配合物能被TPP所夺取。     

由氢醌与2-硝基卟啉直接合成2-氢醌卟啉的反应研究

由氢醌与2-硝基-5,10,15,20-四苯基卟啉或其金属配合物(2-NO₂MTPP)直接反应合成2-氢醌卟啉I, 同时得到了另一产物II. 通过MS, IR, ¹H NMR及 2D NMR测定, 确定I与II中的2-取代基分别为氢醌与半醌, 两者为互变异构体, 且II是生成I的前体. 高温下, 水与空气介入反应体系能明显提高反应速率及产率, 此时氧气的介入是提高反应速率的关键, 而水介入反应体系将导致较强的酸性环境, 更有利于II异构为产物I. 整个反应可能为单电子转移(SET)的自由基反应.     

Sequence and linker dependent chiral dimerization of DNA–porphyrin conjugates

Circular dichroism (CD), UV–vis absorption, fluorescence, and resonance light scattering (RLS) spectroscopies were used to elucidate the role of the DNA sequence, linkers between DNA and porphyrin, and metal in the porphyrin coordination center on the self-assembly of DNA–porphyrin conjugates. A series of eight non-self-complementary DNA–porphyrin conjugates have been synthesized with zinc and free-base porphyrins covalently attached to the short ODNs (A₈ or T₈) via amide or phosphate linker. A small structural modification (e.g., amide linker replaced by the phosphate linker) showed a dramatic effect on the aggregation properties of DNA–porphyrin conjugates and greatly altered their spectroscopic properties. At low ionic strength, porphyrin aggregation was not observed for any conjugate. An increase in the ionic strength caused two out of eight conjugates to form chiral porphyrin dimers.     

Porphyrin Metalation at MgO Surfaces: A Spectroscopic and Quantum Mechanical Study on Complementary Model Systems

We show that both single‐crystalline and nanostructured MgO surfaces convert free‐base tetraphenyl porphyrin (2HTPP) into magnesium tetraphenyl porphyrin (MgTPP) at room temperature. The reaction can be viewed as an ion exchange between the two aminic protons of the 2HTPP molecule with a Mg²⁺ ion from the surface. The driving force for the reaction is the strong stability of the formed hydroxyl groups along the steps and at defects on the MgO surface. We have used an integrated characterization approach that includes UV/Vis diffuse reflectance measurements on nanostructured powders, X‐ray photoelectron spectroscopic investigation of atomically clean MgO(100) single‐crystalline thin films, and density functional theory (DFT) calculations on model systems. The DFT calculations demonstrate that MgTPP formation is strongly exothermic at the corners, edges and steps, but slightly endothermic on terrace sites. This agrees well with the UV/Vis diffuse reflectance, which upon adsorption of 2HTPP shows a decrease in the absorption band associated with corner and edge sites on MgO nanocube powders.     

Synthesis, excitation energy transfer and singlet oxygen photogeneration of covalently linked N-confused porphyrin-porphyrin and Zn(II) porphyrin dyads

Dyads of a N-confused porphyrin (NCP) moiety covalently linked to a porphyrin free-base (H₂P) or a zinc(II) porphyrinate (ZnP) moiety via a flexible alkyl chain of variable length have been synthesized. Photoluminescence study demonstrated an efficient excitation energy transfer from H₂P/ZnP moiety to the NCP moiety. Measurement of the near-IR emission of singlet oxygen produced by these dyads via photosensitization showed that the NCP-ZnP dyads (Ф_Δ = (0.61-0.65) ± 0.13) were better ¹O₂ generators than the NCP-P dyads (Ф_Δ = (0.36-0.41) ± 0.08).     

Sequential energy and electron transfer in aggregates of tetrakis[oligo(p-phenylene vinylene)] porphyrins and C60 in water

Chiral aggregation of oligo(p-phenylene vinylene)-functionalized Zn and free-base porphyrins is observed in water. The formation of mixed assemblies containing both porphyrins results in sequential energy transfer from OPV via zinc porphyrin to free-base porphyrin. Furthermore, the incorporation of C60 as electron acceptor yields a charge separated state by ultimate electron transfer.