Porphyrin-based Metal-organic Frameworks Research Articles

Porphyrin-based metal–organic framework thin films for electrochemical nitrite detection

Uniform zirconium-based porphyrin metal–organic framework (MOF-525) thin films are grown on conducting glass substrates by using a solvothermal approach. The obtained MOF-525 thin film is electrochemically addressable in aqueous solution and shows electrocatalytic activity for nitrite oxidation. The mechanism for the electrocatalytic oxidation of nitrite at the MOF-525 thin film is investigated by cyclic voltammetry. The redox mechanism of the MOF-525 thin film in the KCl aqueous solution is studied by amperometry. The MOF-525 thin film is deployed as an amperometric nitrite sensor. The linear range, sensitivity, and limit of detection are 20–800 μM, 95 μA/mM-cm2, and 2.1 μM, respectively.

Rapid and Specific Aqueous-Phase Detection of Nitroaromatic Explosives with Inherent Porphyrin Recognition Sites in Metal-Organic Frameworks.

Development of a rapid and effective method for the detection of 2,4,6-trinitrotoluene (TNT) in aqueous phase has attracted great attention. In this work, the fluorescent porphyrin-based metal-organic frameworks (MOFs) of PCN-224 were successfully exploited as a fluorescent probe for the rapid and selective TNT detection in water media. This strategy combined the advantages of fluorescent porphyrin molecules and porous MOFs, which not only overcame the aggregation of hydrophobic tetrakis(4-carboxyphenyl)porphyrin (TCPP) recognition sites but also promoted TNT to interact with recognition sites in virtue of the high surface and intrinsic open structure of MOFs. As a result, a rapid response time of as short as 30 s was obtained for the elaborated fluorescent probe. Meanwhile, the bright red emission of porphyrin units in PCN-224 could be proportionally quenched in correlation with the applied TNT level through the formation of TNT-TCPP complex in the ground state. The specificity of the employed sensory platform for TNT recognition was scarcely affected by other possible coexistent interfering species. Furthermore, this fluorescent PCN-224 probe presented a much higher quenching efficiency for TNT than other structurally similar nitroaromatic compounds and was successfully applied for the quantitative detection of TNT in the mixed nitroaromatic explosive samples. This prefigured their great potentials of practical TNT detection in water media for public safety and security.

Acid loaded porphyrin-based metal-organic framework for ammonia uptake.

A porphyrin-based metal-organic framework is shown to be structurally stable towards acid loading using either hydrochloric or formic acid. The capacity of this material as an ammonia sorbent was analysed using micro-breakthrough experiments in both dry and humid ammonia flows. The acid loaded material exhibited excellent uptake in comparison with the parent MOF.

Electronic structure of porphyrin-based metal–organic frameworks and their suitability for solar fuel production photocatalysis

Density functional theory calculations reveal that the electronic structure of a family of porphyrin-based metal–organic frameworks is suitable for the photocatalysis of water splitting and carbon dioxide reduction reactions.

Epoxidation of alkenes with molecular oxygen catalyzed by a manganese porphyrin-based metal–organic framework

The flexible nature of reticular assemblies and high specific surfaces of metal–organic frameworks (MOFs) offers new opportunities for the design of heterogeneous catalysts capable of industrially relevant reactions. We demonstrate the first instance of alkene epoxidation at mild conditions using molecular oxygen by a manganese porphyrin containing MOF, MOF-525-Mn [Zr6O4(OH)4(MgC48H24O8N4Cl)3]. This zirconium MOF with a manganese porphyrin catalyst shows minimal deactivation over long periods and maintains its structure and high activity after multiple catalytic cycles. Kinetic studies of styrene epoxidation are in agreement with theoretical and experimental studies of homogeneous reactions with the same porphyrin unit, suggesting that the heterogeneous catalyst operates according to a similar mechanism as its homogeneous counterpart.

Porphyrin-Based Metal Organic Frameworks: Unusual examples of Mn(II) carboxylate frameworks containing free-base porphyrins.

The structures of two porphyrin-based metal-organic frameworks are reported. The reaction of a carbäoxylic acid functionalised porphyrin with Mn(NO3)2 gives rise to either a one-dimensional or a two-dimensional framework structure depending on the reaction solvent employed. 1 (a = 8.3080(5) Å, b = 14.4466(10) Å, c = 21.8737(14) Å, α = 99.182(6)°, β = 94.118(5)°, γ = 92.562(5)°, P-1, R1 = 0.0894, wR2 = 0.2850) consists of one-dimensional coordination polymers linked through hydrogen-bonded porphyrin molecules leading to a two-dimensional array. In contrast 2 (a = 13.6852(6) Å, b = 41.1655(15) Å, c = 15.4535(6) Å, β = 109.954(5)°, P21/c, R1 = 0.1218, wR2 = 0.3806) consists of two-dimensional sheets, constructed from dinuclear Mn(II) clusters and bridging porphyrin ligands, which, as in 1, are linked through hydrogen-bonded porphyrin molecules but in this case leading to a three-dimensional array. In both structures it is notable that the porphyrin molecules do not bind the Mn(II) cations through the macrocyclic carity, rather both structures.

Energy Transfer from Quantum Dots to Metal–Organic Frameworks for Enhanced Light Harvesting

Because of their efficient energy-transport properties, porphyrin-based metal-organic frameworks (MOFs) are attractive compounds for solar photochemistry applications. However, their absorption bands provide limited coverage in the visible spectral range for light-harvesting applications. We report here the functionalization of porphyrin-based MOFs with CdSe/ZnS core/shell quantum dots (QDs) for the enhancement of light harvesting via energy transfer from the QDs to the MOFs. The broad absorption band of the QDs in the visible region offers greater coverage of the solar spectrum by QD-MOF hybrid structures. We show through time-resolved emission studies that photoexcitation of the QDs is followed by energy transfer to the MOFs with efficiencies of more than 80%. This sensitization approach can result in a >50% increase in the number of photons harvested by a single monolayer MOF structure with a monolayer of QDs on the surface of the MOF.

Light-Harvesting and Ultrafast Energy Migration in Porphyrin-Based Metal–Organic Frameworks

Given that energy (exciton) migration in natural photosynthesis primarily occurs in highly ordered porphyrin-like pigments (chlorophylls), equally highly ordered porphyrin-based metal-organic frameworks (MOFs) might be expected to exhibit similar behavior, thereby facilitating antenna-like light-harvesting and positioning such materials for use in solar energy conversion schemes. Herein, we report the first example of directional, long-distance energy migration within a MOF. Two MOFs, namely F-MOF and DA-MOF that are composed of two Zn(II) porphyrin struts [5,15-dipyridyl-10,20-bis(pentafluorophenyl)porphinato]zinc(II) and [5,15-bis[4-(pyridyl)ethynyl]-10,20-diphenylporphinato]zinc(II), respectively, were investigated. From fluorescence quenching experiments and theoretical calculations, we find that the photogenerated exciton migrates over a net distance of up to ~45 porphyrin struts within its lifetime in DA-MOF (but only ~3 in F-MOF), with a high anisotropy along a specific direction. The remarkably efficient exciton migration in DA-MOF is attributed to enhanced π-conjugation through the addition of two acetylene moieties in the porphyrin molecule, which leads to greater Q-band absorption intensity and much faster exciton-hopping (energy transfer between adjacent porphyrin struts). The long distance and directional energy migration in DA-MOF suggests promising applications of this compound or related compounds in solar energy conversion schemes as an efficient light-harvesting and energy-transport component.

Ultrafast Energy Migration in Porphyrin-based Metal Organic Frameworks (MOFs)

ABSTRACTIn this paper, we have studied the energy transport properties of two porphyrincontaining metal organic frameworks (MOFs) for light-harvesting applications. The photoinduced singlet exciton migration is investigated using fluorescence quenching experiments, whereas details on exciton transport anisotropy and net displacements are obtained using a Förster theory analysis. The striking difference in the energy-transport properties for the two MOFs, albeit for similar molecular organization, is attributed to dissimilar spatial expanse and difference in the electronic structure of their porphyrin struts. The observed exciton displacements, of up to 60 nm, provides motivation to explore new MOF materials. Several new linkers are considered, leading to predictions of MOF structures, which provide both broadwavelength harvesting and unidirectional energy transporting MOFs with selected examples.

Light-Harvesting Metal–Organic Frameworks (MOFs): Efficient Strut-to-Strut Energy Transfer in Bodipy and Porphyrin-Based MOFs

A pillared-paddlewheel type metal-organic framework material featuring bodipy- and porphyrin-based struts, and capable of harvesting light across the entire visible spectrum, has been synthesized. Efficient-essentially quantitative-strut-to-strut energy transfer (antenna behavior) was observed for the well-organized donor-acceptor assembly consituting the ordered MOF structure.

Active-Site-Accessible, Porphyrinic Metal−Organic Framework Materials

On account of their structural similarity to cofactors found in many metallo-enzymes, metalloporphyrins are obvious potential building blocks for catalytically active, metal-organic framework (MOF) materials. While numerous porphyrin-based MOFs have already been described, versions featuring highly accessible active sites and permanent microporosity are remarkably scarce. Indeed, of the more than 70 previously reported porphyrinic MOFs, only one has been shown to be both permanently microporous and contain internally accessible active sites for chemical catalysis. Attempts to generalize the design approach used in this single successful case have failed. Reported here, however, is the synthesis of an extended family of MOFs that directly incorporate a variety of metalloporphyrins (specifically Al(3+), Zn(2+), Pd(2+), Mn(3+), and Fe(3+) complexes). These robust porphyrinic materials (RPMs) feature large channels and readily accessible active sites. As an illustrative example, one of the manganese-containing RPMs is shown to be catalytically competent for the oxidation of alkenes and alkanes.