Showing papers on "Porphyrin published in 2018"

Direct evidence of charge separation in a metal–organic framework: efficient and selective photocatalytic oxidative coupling of amines via charge and energy transfer

Abstract: The selective aerobic oxidative coupling of amines under mild conditions is an important laboratory and commercial procedure yet a great challenge. In this work, a porphyrinic metal–organic framework, PCN-222, was employed to catalyze the reaction. Upon visible light irradiation, the semiconductor-like behavior of PCN-222 initiates charge separation, evidently generating oxygen-centered active sites in Zr-oxo clusters indicated by enhanced porphyrin π-cation radical signals. The photogenerated electrons and holes further activate oxygen and amines, respectively, to give the corresponding redox products, both of which have been detected for the first time. The porphyrin motifs generate singlet oxygen based on energy transfer to further promote the reaction. As a result, PCN-222 exhibits excellent photocatalytic activity, selectivity and recyclability, far superior to its organic counterpart, for the reaction under ambient conditions via combined energy and charge transfer.

Synthesis of Self-Assembled Porphyrin Nanoparticle Photosensitizers.

Abstract: The use of nanoparticles as a potential building block for photosensitizers has recently become a focus of interest in the field of photocatalysis and photodynamic therapy. Porphyrins and their derivatives are effective photosensitizers due to extended π-conjugated electronic structure, high molar absorption from visible to near-infrared spectrum, and high singlet oxygen quantum yields as well as chemical versatility. In this paper, we report a synthesis of self-assembled porphyrin nanoparticle photosensitizers using zinc meso-tetra(4-pyridyl)porphyrin (ZnTPyP) through a confined noncovalent self-assembly process. Scanning electron microscopy reveals formation of monodisperse cubic nanoparticles. UV–vis characterizations reveal that optical absorption of the nanoparticles exhibits a red shift due to noncovalent self-assembly of porphyrins, which not only effectively increase intensity of light absorption but also extend light absorption broadly covering visible light for enhanced photodynamic therapy. Ele...

Acid and Base Resistant Zirconium Polyphenolate-Metalloporphyrin Scaffolds for Efficient CO2 Photoreduction.

Abstract: A series of zirconium polyphenolate-decorated-(metallo)porphyrin metal-organic frameworks (MOFs), ZrPP-n (n = 1, 2), featuring infinite ZrIV -oxo chains linked via polyphenolate groups on four peripheries of eclipse-arranged porphyrin macrocycles, are successfully constructed through a top-down process from simulation to synthesis. These are the unusual examples of Zr-MOFs (or MOFs in general) based on phenolic porphyrins, instead of commonly known carboxylate-based types. Representative ZrPP-1 not only exhibits strong acid resistance (pH = 1, HCl) but also remains intact even when immersed in saturated NaOH solution (≈20 m), an exceptionally large range of pH resistance among MOFs. The metallation at the porphyrin core gives rise to materials with enhanced sorption and catalytic properties. In particular, ZrPP-1-Co, with precise and uniform distribution of active centers, exhibits not only high CO2 trapping capability (≈90 cm3 g-1 at 1 atm, 273 K, among the highest in Zr-MOFs) but also high photocatalytic activity for reduction of CO2 into CO (≈14 mmol g-1 h-1 ) and high selectivity over CH4 (>96.4%) without any cocatalyst under visible-light irradiation (λ > 420 nm). Given the strong chemical resistance under extreme alkali conditions, these catalysts can be recycled without appreciable loss of activity. The possible mechanism for photocatalytic reduction of CO2 -to-CO over ZrPP-1-Co is also proposed.

Highly efficient visible-light driven photocatalytic reduction of CO2 over g-C3N4 nanosheets/tetra(4-carboxyphenyl)porphyrin iron(III) chloride heterogeneous catalysts

Abstract: Photocatalytic reduction of CO 2 into value-added chemicals is particularly attractive as it could produce renewable energy and capture greenhouse gas. Photoreduction of CO 2 can be realized over molecular and inorganic catalysts. The former usually exhibit high activity, but low stability and often inactive under visible-light irradiation; the latter has low activity, but good stability. Here we use g-C 3 N 4 nanosheets as the photosensitizer to integrate with Fe tetra(4-carboxylphenyl)porphyrin chloride (FeTCPP) molecular catalyst. Besides π-π stacking between tri- s -triazine unit and porphyrin, the carboxyl group modified Fe porphyrin is used for the first time in CO 2 photoreduction so as to form hydrogen bonding with the rich amino groups in g-C 3 N 4 nanosheets. g-C 3 N 4 /FeTCPP heterogeneous catalysts are prepared via a facile self-assembly approach, in which light harvest is separated from catalysis spatially and temporally. The obtained g-C 3 N 4 /FeTCPP heterogeneous catalysts exhibit high activity for CO 2 reduction under visible-light irradiation, with CO yield of 6.52 mmol g −1 in 6 h and selectivity up to 98%. Fluorescence data indicate that the electrons can efficiently transfer from the g-C 3 N 4 nanosheets to FeTCPP. The mechanism for CO 2 reduction over the g-C 3 N 4 /FeTCPP heterogeneous catalysts is proposed based on the results of quasi in-situ ESR and UV–vis measurements. This work may pave a facile approach for fabricating the high-efficient photocatalysts for CO 2 reduction, as well as better understanding the related mechanism.

Boosting Photocatalytic Hydrogen Production of Porphyrinic MOFs: The Metal Location in Metalloporphyrin Matters

Abstract: Metal–organic frameworks (MOFs) have demonstrated great potentials toward catalysis, particularly in the establishment of structure–property relationships. Herein, an unusual OOP (out-of-plane) porphyrin-based MOF, synthesized by controlling the metal ion release with an unprecedented In(OH)3 precursor, possesses high stability and exhibits unexpectedly high photocatalytic hydrogen production activity, far surpassing the isostructural in-plane porphyrin-based MOF counterparts. In the MOF structure, indium ions not only form indium–oxo chains but also metalate the porphyrin rings in situ, locating above the porphyrin plane instead of fitting in a coplanar fashion into the cavity and affording an unusual OOP porphyrin. Control experiments demonstrate that the OOP In(III) ions readily detach from the porphyrin rings under light excitation, avoiding the fast back electron transfer and thus greatly improving electron–hole separation efficiency and photocatalytic performance. To our knowledge, this is an unprec...

Self-Assembled One-Dimensional Porphyrin Nanostructures with Enhanced Photocatalytic Hydrogen Generation

Abstract: There has been a widespread interest in the preparation of self-assembled porphyrin nanostructures and their ordered arrays, aiming to emulate natural light harvesting processes and energy storage and to develop new nanostructured materials for photocatalytic process. Here, we report controlled synthesis of one-dimensional porphyrin nanostructures such as nanorods and nanowires with well-defined self-assembled porphyrin networks that enable efficient energy transfer for enhanced photocatalytic activity in hydrogen generation. Preparation of these one-dimensional nanostructures is conducted through noncovalent self-assembly of porphyrins confined within surfactant micelles. X-ray diffraction and transmission electron microscopy results reveal that these one-dimensional nanostructures contain stable single crystalline structures with controlled interplanar separation distance. Optical absorption characterizations show that the self-assembly enables effective optical coupling of porphyrins, resulting in much...

Covalent Organic Polymers Based on Fluorinated Porphyrin as Oxygen Nanoshuttles for Tumor Hypoxia Relief and Enhanced Photodynamic Therapy

Abstract: Effective and sustained tumor oxygenation has found practical significance in benefiting the treatment of solid tumors. In this study, fluorinated covalent organic polymers (COPs) are prepared by crosslinking the photosensitizer meso-5, 10, 15, 20-tetra (4-hydroxylphenyl) porphyrin (THPP) with perfluorosebacic acid (PFSEA) and poly(ethylene glycol) (PEG) via a one-pot esterification, to enable simultaneous tumor oxygenation and photodynamic treatment. Due to the presence of PFSEA, the obtained THPPpf–PEG shows efficient loading of perfluoro-15-crown5-ether (PFCE), a type of perfluocarbon, and thereby molecular oxygen, both of which would significantly enhance the photodynamic effect of THPP. After chelating THPP with a radio-isotope, 99mTc, both THPPpf– PEG and PFCE-loaded THPPpf–PEG (PFCE@THPPpf–PEG) can be vividly visualized under the single-photon emission computed tomography (SPECT) imaging, which uncovers efficient tumor accumulation of those COPs’ post intravenous injection. Owing to the oxygen delivery ability of PFCE, efficient tumor oxygenation is observed for mice post injection of PFCE@THPPpf–PEG, which further leads to greatly enhanced photodynamic treatment of tumors. This study presents a unique type of multifunctional fluorinated COPs with well-defined composition, long blood circulation time, and sustained tumor oxygenation ability, showing great promises for potential clinical translation in photodynamic treatment of tumors.

Novel hybrids of graphitic carbon nitride sensitized with free-base meso-tetrakis(carboxyphenyl) porphyrins for efficient visible light photocatalytic hydrogen production

Abstract: Novel hybrid photocatalysts of graphitic carbon nitride (g-C 3 N 4 , CN) sensitized with free-base porphyrins were prepared by impregnation through non-covalent interactions. Their photocatalytic activity was evaluated towards the generation of hydrogen (H 2 ) from water splitting. For this purpose, and in order to ascertain the influence of the carboxy substituents groups and their position on the porphyrin periphery on H 2 production, the porphyrins meso -tetraphenylporphyrin (TPP), meso -tetrakis( meta -carboxyphenyl)porphyrin ( m TCPP) and meso -tetrakis( para -carboxyphenyl)porphyrin ( p TCPP) were used. All the hybrids (TPP-CN, m TCPP-CN and p TCPP-CN) show higher performance for photocatalytic H 2 production than that of pure CN. Among all the hybrids, m TCPP-CN presents the highest amount of H 2 evolved, being of 326 and 48.4 μmol under 6 h of UV–vis and visible light (λ > 400 nm) irradiation, respectively. This photocatalyst was fully characterized by UV-vis, FTIR, XRD, XPS, SEM, TEM, N 2 isotherms and steady-state and time-resolved fluorescence measurements. The fluorescence emission of the m TCPP porphyrin was remarkably quenched by CN semiconductor for the various hybrids m TCPP-CN containing different amounts of m TCPP, consistent with electron injection from the porphyrin excited state into the conduction band of the semiconductor. This works demonstrates that the sensitization of CN with dye porphyrins enhances the photocatalytic H 2 evolution under UV–vis and visible light irradiation, making it a potential material for solar conversion to produce hydrogen from water.

Visible-Light-Driven Conversion of CO2 to CH4 with an Organic Sensitizer and an Iron Porphyrin Catalyst.

Abstract: Using a phenoxazine-based organic photosensitizer and an iron porphyrin molecular catalyst, we demonstrated photochemical reduction of CO2 to CO and CH4 with turnover numbers (TONs) of 149 and 29, respectively, under visible-light irradiation (λ > 435 nm) with a tertiary amine as sacrificial electron donor. This work is the first example of a molecular system using an earth-abundant metal catalyst and an organic dye to effect complete 8e–/8H+ reduction of CO2 to CH4, as opposed to typical 2e–/2H+ products of CO or formic acid. The catalytic system continuously produced methane even after prolonged irradiation up to 4 days. Using CO as the feedstock, the same reactive system was able to produce CH4 with 85% selectivity, 80 TON and a quantum yield of 0.47%. The redox properties of the organic photosensitizer and acidity of the proton source were shown to play a key role in driving the 8e–/8H+ processes.

Photocatalytically Active Superstructures of Quantum Dots and Iron Porphyrins for Reduction of CO2 to CO in Water

Abstract: This paper describes the use of electrostatic assemblies of negatively charged colloidal CuInS2/ZnS quantum dot (QD) sensitizers and positively charged, trimethylamino-functionalized iron tetraphenylporphyrin catalysts (FeTMA) to photoreduce CO2 to CO in water upon illumination with 450 nm light. This system achieves a turnover number (TON) of CO (per FeTMA) of 450 after 30 h of illumination, with a selectivity of 99%. Its sensitization efficiency (TON per Joule of photons absorbed) is a factor of 11 larger than the previous record for photosensitization of an iron porphyrin catalyst for this reaction, held by a system in which both QDs and metal porphyrin were uncharged. Steady-state and time-resolved optical spectroscopy provides evidence for electrostatic assembly of QDs and FeTMA. Control of the size of the assemblies with addition of a screening counterion, K+, and a correlation between their measured size and their catalytic activity, indicates that the enhancement in performance of this system over the analogous uncharged system is due to the proximity of the FeTMA catalyst to multiple light-absorbing QDs and the selective formation of QD-FeTMA contacts (rather than QD-QD or FeTMA-FeTMA contacts). This system therefore shows the ability to funnel photoinduced electrons to a reaction center, which is crucial for carrying out reactions that require multistep redox processes under low photon flux, and thus is an important advance in developing artificial photocatalytic systems that function in natural light.

A porous rhodium(III)-porphyrin metal-organic framework as an efficient and selective photocatalyst for CO2 reduction

Abstract: A rhodium(III)-porphyrin zirconium metal-organic framework (Rh-PMOF-1(Zr)) has been prepared from the self-assembly of a Rh-based metalloporphyrin tetracarboxylic ligand Rh(TCPP)Cl (TCPP = tetrakis(4-carboxyphenyl)porphyrin) with ZrCl4. The framework of Rh-PMOF-1 is stable up to 270 °C as disclosed by the variable-temperature powder X-ray diffraction (VT-PXRD) measurements, and possesses good chemical stability over a wide range of solvents including water. The single-crystal structural analysis reveals that Rh-PMOF-1 contains 3-D channels (1.9 × 1.9 nm2), and the Rh-porphyrin units are exposed to the cavities. The calculation based on the N2 adsorption at 77 K shows Rh-PMOF-1(Zr) has a high BET surface area (3015 m2g−1). The luminescence decay of Rh-PMOF-1 is well fitted to a tri-exponential curve featuring a long average lifetime of 207 μs at 298 K under vacuum, which represents a rare example of room-temperature phosphorescence of Rh-porphyrin complexes. Under 1 atm, it displays CO2 uptake up to 42, 53 and 98 cm3g−1 at 308, 298 and 273 K, respectively. Catalytic results show that, under the visible light (≥400 nm) irradiation without any additional photosensitizer, Rh-PMOF-1 is powerful to catalyze CO2 reduction to the formate ion with up to 99% selectivity, and can be recycled and reused for 3 runs. Theoretical study was further carried out to reveal the energy levels of the frontier orbitals of Rh-PMOF-1 and the preferred binding sites of CO2 in the framework.

Porphyrin-Implanted Carbon Nanodots for Photoacoustic Imaging and in Vivo Breast Cancer Ablation

Abstract: The incorporation of intensive light absorbing porphyrins macrocycles with biocompatible nanoparticles would lead to new nanomaterials with multiple imaging and therapeutic modalities. Herein, a facile synthetic strategy has been applied to prepare porphyrin-implanted carbon nanodots (PNDs) by partial and selective pyrolysis of 5,10,15,20-tetrakis(4-aminophenyl)porphyrin (TAPP) and citric acid (CA) at an appropriate temperature. As-prepared PNDs exhibit not only the excellent stability and biocompatibility characteristic of carbon nanodots but also the unique properties of porphyrin macrocycle such as strong UV–visible and near-infrared absorption, specifically, high photodynamic therapy efficiency. More importantly, the PNDs with near-infrared absorption could act as a contrast agent for photoacoustic molecular imaging with deep tissue penetration and fine spatial resolution. The Cetuximab-conjugated porphyrin-based carbon nanodots (C225-PNDs) have been further prepared to precisely target the cancer cel...

Synthesis of porphyrin-based two-dimensional metal–organic framework nanodisk with small size and few layers

Abstract: A novel porphyrin-based two-dimensional metal–organic framework (MOF) nanodisk with small size and few layers was prepared by coordination chelation between meso-tetra(4-carboxyphenyl)porphine ligand and Zn(II) paddlewheel metal nodes. With 4,4′-biphenyldicarboxylic acid (BPDC) as nucleation modulator, the anisotropic growth of MOF was impeded by the increased steric hindrance, yielding small Zn–TCPP(BP) MOF crystals. The as-prepared MOF nanodisk exhibited good electrocatalytic activity and selectivity towards nitrite due to the independent distribution of the porphyrin molecules in the framework and the sandwich structure of the prepared Zn–TCPP(BP) nanodisk, which increased the accessible active sites.

Porphyrinoids as a platform of stable radicals

Abstract: The non-innocent ligand nature of porphyrins was observed for compound I in enzymatic cycles of cytochrome P450. Such porphyrin radicals were first regarded as reactive intermediates in catabolism, but recent studies have revealed that porphyrinoids, including porphyrins, ring-contracted porphyrins, and ring-expanded porphyrins, display excellent radical-stabilizing abilities to the extent that radicals can be handled like usual closed-shell organic molecules. This review surveys four types of stable porphyrinoid radical and covers their synthetic methods and properties such as excellent redox properties, NIR absorption, and magnetic properties. The radical-stabilizing abilities of porphyrinoids stem from their unique macrocyclic conjugated systems with high electronic and structural flexibilities.

Mn Porphyrin-Based Redox-Active Drugs: Differential Effects as Cancer Therapeutics and Protectors of Normal Tissue Against Oxidative Injury.

Abstract: Significance: After approximatelty three decades of research, two Mn(III) porphyrins (MnPs), MnTE-2-PyP5+ (BMX-010, AEOL10113) and MnTnBuOE-2-PyP5+ (BMX-001), have progressed to five clini...

Enhancing the Efficacy of Photodynamic Therapy through a Porphyrin/POSS Alternating Copolymer

Abstract: Aggregation-induced quenching (AIQ) of photosensitizers greatly reduces the quantum yield of singlet oxygen generation and mitigates the efficacy of photodynamic therapy (PDT). We have prepared an alternating copolymer starting from 4-vinylbenzyl-terminated tetraphenylporphyrin (VBTPP) and maleimide isobutyl polyhedral oligomeric silsesquioxane (MIPOSS), via alternating reversible addition-fragmentation chain transfer (RAFT) polymerization. Porphyrin and POSS are installed on the amphiphilic block copolymers backbone in an alternating fashion and POSS completely inhibits the aggregation of porphyrin units via stacking. The amphiphilic block copolymer can self-assemble into nanoparticles and its application in PDT treatment was tested. These porphyrin-containing polymeric nanoparticles display high photochemical yield and phototoxicity in vitro and in vivo, providing a novel strategy to enhance the PDT efficacy.

A Supramolecular [10]CPP Junction Enables Efficient Electron Transfer in Modular Porphyrin-[10]CPP⊃Fullerene Complexes.

Abstract: Efficient photoinduced electron transfer was observed across a [10]cycloparaphenylene ([10]CPP) moiety that serves as a rigid non-covalent bridge between a zinc porphyrin and a range of fullerenes. The preparation of iodo-[10]CPP is the key to the synthesis of a porphyrin-[10]CPP conjugate, which binds C60 , C70 , (C60 )2 , and other fullerenes (KA >105 m-1 ). Fluorescence and pump-probe spectroscopy revealed intramolecular energy transfer between CPP and porphyrin and also efficient charge separation between porphyrin and fullerenes, affording up to 0.5 μs lifetime charge-separated states. The advantage of this approach towards electron donor-acceptor dyads is evident in the case of dumbbell-shaped (C60 )2 , which gave intricate charge-transfer behavior in 1:1 and 2:1 complexes. These results suggest that [10]CPP and its cross-coupled derivatives could act as supramolecular mediators of charge transport in organic electronic devices.

Cationic Zn–Porphyrin Polymer Coated onto CNTs as a Cooperative Catalyst for the Synthesis of Cyclic Carbonates

Abstract: The development of solid catalysts containing multiple active sites that work cooperatively is very attractive for biomimetic catalysis. Herein, we report the synthesis of bifunctional catalysts by supporting cationic porphyrin-based polymers on carbon nanotubes (CNTs) using the direct reaction of 5,10,15,20-tetrakis(4-pyridyl)porphyrin zinc(II), di(1H-imidazol-1-yl)methane, and 1,4-bis(bromomethyl)benzene in the presence of CNTs. The bifunctional catalysts could efficiently catalyze the cycloaddition reaction of epoxides and CO2 under solvent-free conditions with porphyrin zinc(II) as the Lewis acid site and a bromine anion as a nucleophilic agent working in a cooperative way. Furthermore, a relative amount of porphyrin zinc(II) and quaternary ammonium bromide could be facilely adjusted for facilitating cooperative behavior. The bifunctional catalyst with a TOF up to 2602 h–1 is much more active than the corresponding homogeneous counterpart and is one of the most active heterogeneous catalysts ever repo...

Survival of spin state in magnetic porphyrins contacted by graphene nanoribbons

Abstract: We report on the construction and magnetic characterization of a fully functional hybrid molecular system composed of a single magnetic porphyrin molecule bonded to graphene nanoribbons with atomically precise contacts. We use on-surface synthesis to direct the hybrid creation by combining two molecular precursors on a gold surface. High-resolution imaging with a scanning tunneling microscope finds that the porphyrin core fuses into the graphene nanoribbons through the formation of new carbon rings at chemically predefined positions. These ensure the stability of the hybrid and the extension of the conjugated character of the ribbon into the molecule. By means of inelastic tunneling spectroscopy, we prove the survival of the magnetic functionality of the contacted porphyrin. The molecular spin appears unaffected by the graphenoid electrodes, and we simply observe that the magnetic anisotropy appears modified depending on the precise structure of the contacts.

Rational Design of Mononuclear Iron Porphyrins for Facile and Selective 4e–/4H+ O2 Reduction: Activation of O–O Bond by 2nd Sphere Hydrogen Bonding

Abstract: Facile and selective 4e–/4H+ electrochemical reduction of O2 to H2O in aqueous medium has been a sought-after goal for several decades Elegant but synthetically demanding cytochrome c oxidase mimics have demonstrated selective 4e–/4H+ electrochemical O2 reduction to H2O is possible with rate constants as fast as 105 M–1 s–1 under heterogeneous conditions in aqueous media Over the past few years, in situ mechanistic investigations on iron porphyrin complexes adsorbed on electrodes have revealed that the rate and selectivity of this multielectron and multiproton process is governed by the reactivity of a ferric hydroperoxide intermediate The barrier of O—O bond cleavage determines the overall rate of O2 reduction and the site of protonation determines the selectivity In this report, a series of mononuclear iron porphyrin complexes are rationally designed to achieve efficient O—O bond activation and site-selective proton transfer to effect facile and selective electrochemical reduction of O2 to water In

Development of a Lower Energy Photosensitizer for Photocatalytic CO2 Reduction: Modification of Porphyrin Dye in Hybrid Catalyst System

Abstract: A series of Zn–porphyrin dyes was prepared and anchored onto a TiO2 surface to complete a dye-sensitized photocatalyst system, Zn–porphyrin-|TiO2|-Cat, and tested as lower energy photosensitizers for photocatalytic CO2 reduction. Three major synthetic modifications were performed on the Zn–porphyrin dye to obtain a lower energy sensitization and improve the catalyst lifetime. We found that incorporating acetylene and linear hexyl groups into the Zn–porphyrin core allowed facile lower energy sensitization, and the addition of the cyanophosphonic acid as an anchoring group gave the long-term dye stability on the TiO2 surface. Under irradiation with red light of >550 nm and a light intensity of 207 mW/cm2, the hybrid ZnPCNPA catalyst showed a TONRe of ∼800 over an extended time period of 90 h. The photocatalytic activities of porphyrin hybrids differ greatly with the binding strength of the anchoring groups of dye and spectral range of the irradiated light and its intensity.

Oxygen Reduction Reaction Promoted by Manganese Porphyrins

Abstract: The oxygen reduction reaction (ORR) is catalyzed by manganese(II) porphyrins in the presence of Bronsted acids (HAs). Analyses of the catalytic cyclic voltammetric profiles have permitted the ORR mechanism to be constructed and rate constants to be extracted for both the formation of the initial oxygen adduct and the O–O bond cleavage event for a series of HAs. The dependence of the formation rate constant of the oxygen adduct on reactant concentrations reveals a rate law that is first order in Mn porphyrin and oxygen substrate. A second order dependence in HA is observed for unadorned Mn porphyrin platforms whereas with Mn hangman porphyrin, a proton is provided intramolecular to the oxygen adduct and consequently the HA order is reduced to unity. The stabilization of the oxygen adduct with an additional hydrogen bond from HA engenders a rate-determining step involving O–O bond cleavage, resulting in the rare instance where the activation of the O–O bond is directly observed.

Understanding the Mechanism Stabilizing Intermediate Spin States in Fe(II)-Porphyrin

Abstract: Spin fluctuations in Fe(II)-porphyrins are at the heart of heme-proteins functionality. Despite significant progress in porphyrin chemistry, the mechanisms that rule spin state stabilization remain elusive. Here, it is demonstrated by using multiconfigurational quantum chemical approaches, including the novel Stochastic-CASSCF method, that electron delocalization between the metal center and the π system of the macrocycle differentially stabilizes the triplet spin states over the quintet. This delocalization takes place via charge-transfer excitations, involving the π system of the macrocycle and the out-of-plane iron d orbitals, key linking orbitals between metal and macrocycle. Through a correlated breathing mechanism the 3d electrons can make transitions toward the π orbitals of the macrocycle. This guarantees a strong coupling between the on-site radial correlation on the metal and electron delocalization. Opposite-spin 3d electrons of the triplet can effectively reduce electron repulsion in this mann...

Porphyrins and flavins as endogenous acceptors of optical radiation of blue spectral region determining photoinactivation of microbial cells.

Abstract: It is shown that exposure of suspensions of gram-positive Staphylococcus aureus, gram-negative Escherichia coli and yeast-like fungi Candida albicans to laser radiation of blue spectral region with 405 and 445 nm causes their growth inhibition without prior addition of exogenous photosensitizers. It is experimentally confirmed that compounds of flavin type capable of sensitizing the formation of reactive oxygen species can act as acceptors of optical radiation of blue spectral region determining its antimicrobial effect along with endogenous metal-free porphyrins (the role of endogenous porphyrins has been confirmed earlier by a number of researchers). The participation of these compounds in the antimicrobial effect of laser radiation is supported by the registration of porphyrin and flavin fluorescence in extracts of microbial cells upon excitation by radiation used to inactivate the pathogens. In addition, the intensity of the porphyrin fluorescence in extracts of microbial cells in the transition from radiation with λ = 405 nm to radiation with λ = 445 nm decreases by 15–30 times, whereas the photosensitivity of the cells under study in this transition decreases only 3.7–6.2 times. The contribution of porphyrin photosensitizers is most pronounced upon exposure to radiation with λ = 405 nm (absorption maximum of the Soret band of porphyrins), and flavins – upon exposure to radiation with λ = 445 nm (maximum in the flavin absorption spectrum and minimum in the absorption spectrum of porphyrins). The ratio between the intensity of the porphyrin and flavin components in the fluorescence spectrum of extracts depends on the type of microbial cells.

Surface Decorated Porphyrinic Nanoscale Metal-Organic Framework for Photodynamic Therapy.

Abstract: Nanocrystallization of organic molecular photosensitizers (PSs) by means of NMOF platforms has been demonstrated to be a promising approach to build up highly efficient PDT therapeutics. We report herein a new UiO-66 type of NMOF-based PS (UiO-66-TPP-SH), which is generated from UiO-66 NMOF and S-ethylthiol ester monosubstituted metal free porphyrin (TPP-SH) via a facile postsynthetic approach under mild conditions. The obtained NMOF (size less than 150 nm) with surface-decorated porphyrinic PS can not only retain MOF crystallinity, structural feature, and size, but also exhibit highly efficient singlet oxygen generation. Compared to the interior-located porphyrinic NMOF, UiO-66-TPP-SH shows significantly higher photodynamic activity and more efficient PDT tumor treatment.

High Antimicrobial Activity of Metal-Organic Framework-Templated Porphyrin Polymer Thin Films.

Abstract: Development of surface coatings with high antimicrobial activity is urgently required to fight bacteria and other microorganisms on technical and hygiene relevant surfaces. Control over structure and topology of the surface coatings, combined with the ability to include functional molecules within the structure, is crucial for optimizing their performance. Herein, we describe a novel strategy to synthesize structurally well-defined porphyrin polymer thin films via a template approach. In this approach, bisazido-functionalized porphyrin molecules are preorganized within a metal–organic framework (MOF) structure. Afterward, porphyrin units within the MOF are covalently connected via a secondary linker. Removal of the metal ions of the MOF results in water-stable porphyrin polymer thin films that demonstrate high antibacterial activity against pathogens via visible-light-promoted generation of reactive oxygen species. In addition, this approach offers the inherent possibility to incorporate guest molecules w...