Porphyrin Dimers Research Articles

Soluble meso and deuteroporphyrin analogs of the malaria pigment hematin anhydride

Two soluble heme analogs of the insoluble malaria pigment hematin anhydride (HA, or β-hematin), [Fe(III)(protoporphyrin)]2, with either mesoporphyrin (MHA) or deuteroporphyrin (DHA) are characterized by elemental analysis, SEM, IR spectroscopy, electronic spectroscopy, paramagnetic 1H NMR spectroscopy and solution magnetic susceptibility. While prior single crystal and X-ray powder diffraction results indicate all three have a common propionate linked dimer motif, there is considerable solid state variation in the conformation. This is associated with enhanced solubility of MHA and DHA. As with HA, DHA undergoes thermally promoted reversible hydration/dehydration in the solid state. Solution 1H NMR studies of DHA suggest a high spin dimeric structure with the porphyrin methyls distributed between two isomers which are also present in the solid state. These soluble iron(III)porphyrin dimers allow for the first direct solution studies by NMR and UV–Vis spectroscopies of these key species. Taken together the results illustrate the importance and utility of varying the substituents on the periphery of the porphyrin for studying heme aggregation and malaria pigment formation.

Controlling the light-induced structural isomerism of lipophilic azo-bridged porphyrin dimer via steric hindrance modulated functional linkers

Herein, two azo-bridged porphyrin dimers were synthesized via Sonogashira and Suzuki coupling reactions. The relationship between molecular structures and electronic structures was investigated by spectroscopic and electrochemical characterizations. In addition, the light-induced structural isomerism of lipophilic azo-Bridged porphyrin dimer could be controlled via steric hindrance modulated functional linkers, and it can only be succeeded in the case of expanded azo-bridged porphyrin dimer.

A Heterometallic Porphyrin Dimer as a Potential Quantum Gate: Magneto‐Structural Correlations and Spin Coherence Properties

AbstractIn the development of two‐qubit quantum gates, precise control over the intramolecular spin‐spin interaction between molecular spin units plays a pivotal role. A weak but measurable exchange coupling is especially important for achieving selective spin addressability that allows controlled manipulation of the computational basis states |00⟩ |01⟩ |10⟩ |11⟩ by microwave pulses. Here, we report the synthesis and Electron Paramagnetic Resonance (EPR) study of a heterometallic meso‐meso (m‐m) singly‐linked VIVO−CuII porphyrin dimer. X‐band continuous wave EPR measurements in frozen solutions suggest a ferromagnetic exchange coupling of ca. 8 ⋅ 10−3 cm−1. This estimation is supported by Density Functional Theory calculations, which also allow disentangling the ferro‐ and antiferromagnetic contributions to the exchange. Pulsed EPR experiments show that the dimer maintains relaxation times similar to the monometallic CuII porphyrins. The addressability of the two individual spins is made possible by the different g‐tensors of VIV and CuII‐ions, in contrast to homometallic dimers where tilting of the porphyrin planes plays a key role. Therefore, single‐spin addressability in the heterometallic dimer can be maintained even with small tilting angles, as expected when deposited on surface, unlocking the full potential of molecular quantum gates for practical applications.

A Heterometallic Porphyrin Dimer as a Potential Quantum Gate: Magneto-Structural Correlations and Spin Coherence Properties.

In the development of two-qubit quantum gates, precise control over the intramolecular spin-spin interaction between molecular spin units plays a pivotal role. A weak but measurable exchange coupling is especially important for achieving selective spin addressability that allows controlled manipulation of the computational basis states |00⟩ |01⟩ |10⟩ |11⟩ by microwave pulses. Here, we report the synthesis and Electron Paramagnetic Resonance (EPR) study of a heterometallic meso-meso (m-m) singly-linked VIV O-CuII porphyrin dimer. X-band continuous wave EPR measurements in frozen solutions suggest a ferromagnetic exchange coupling of ca. 8 ⋅ 10-3 cm-1 . This estimation is supported by Density Functional Theory calculations, which also allow disentangling the ferro- and antiferromagnetic contributions to the exchange. Pulsed EPR experiments show that the dimer maintains relaxation times similar to the monometallic CuII porphyrins. The addressability of the two individual spins is made possible by the different g-tensors of VIV and CuII -ions, in contrast to homometallic dimers where tilting of the porphyrin planes plays a key role. Therefore, single-spin addressability in the heterometallic dimer can be maintained even with small tilting angles, as expected when deposited on surface, unlocking the full potential of molecular quantum gates for practical applications.

Synthesis, Photophysical Properties, and Toxicity of o-Xylene-Bridged Porphyrin Dimers

In this work, a number of new porphyrin dimers coupled with spacers based on α,α’-dibromo-o-xylene were synthesized and characterized by 1H, 13C NMR, 1H-1H COSY NMR, UV-vis-spectroscopy, and MALDI-TOF mass spectrometry. The initial A3B-type hydroxy-substituted porphyrins form dimer structures with high yields of 80–85%, while the use of amino-substituted porphyrins as starting compounds leads to the heterocyclization and formation of N-heterocycle fused porphyrins. For porphyrin dimers, photophysical properties and quantum yields of singlet oxygen were investigated. The peripheral alkoxy-substituents increase fluorescence quantum yield in comparison with the unsubstituted compounds. Also, it was found that dimers are characterized by lower singlet oxygen quantum yields compared to the corresponding monomers. Model aggregation experiments in micellar systems demonstrate stabilization of the photoactive monomolecular form of all the porphyrins, using nonionic surfactant Triton X-100. Cytotoxicity of received dimers shows high inhibition against HEK293T cells in the absence of light.

Enhanced coherence by coupling spins through a delocalized π-system: Vanadyl porphyrin dimers

Enhanced coherence by coupling spins through a delocalized π-system: Vanadyl porphyrin dimers

Anthracene‐Porphyrin Nanoribbons

Abstractπ‐Conjugated nanoribbons attract interest because of their unusual electronic structures and charge‐transport behavior. Here, we report the synthesis of a series of fully edge‐fused porphyrin‐anthracene oligomeric ribbons (dimer and trimer), together with a computational study of the corresponding infinite polymer. The porphyrin dimer and trimer were synthesized in high yield, via oxidative cyclodehydrogenation of singly linked precursors, using 2,3‐dichloro‐5,6‐dicyano‐1,4‐benzoquinone (DDQ) and trifluoromethanesulfonic acid (TfOH). The crystal structure of the dimer shows that the central π‐system is flat, with a slight S‐shaped wave distortion at each porphyrin terminal. The extended π‐conjugation causes a dramatic red‐shift in the absorption spectra: the absorption maxima of the fused dimer and trimer appear at 1188 nm and 1642 nm, respectively (for the nickel complexes dissolved in toluene). The coordinated metal in the dimer was changed from Ni to Mg, using p‐tolylmagnesium bromide, providing access to free‐base and Zn complexes. These results open a versatile avenue to longer π‐conjugated nanoribbons with integrated metalloporphyrin units.

Anthracene-Porphyrin Nanoribbons.

π-Conjugated nanoribbons attract interest because of their unusual electronic structures and charge-transport behavior. Here, we report the synthesis of a series of fully edge-fused porphyrin-anthracene oligomeric ribbons (dimer and trimer), together with a computational study of the corresponding infinite polymer. The porphyrin dimer and trimer were synthesized in high yield, via oxidative cyclodehydrogenation of singly linked precursors, using 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) and trifluoromethanesulfonic acid (TfOH). The crystal structure of the dimer shows that the central π-system is flat, with a slight S-shaped wave distortion at each porphyrin terminal. The extended π-conjugation causes a dramatic red-shift in the absorption spectra: the absorption maxima of the fused dimer and trimer appear at 1188 nm and 1642 nm, respectively (for the nickel complexes dissolved in toluene). The coordinated metal in the dimer was changed from Ni to Mg, using p-tolylmagnesium bromide, providing access to free-base and Zn complexes. These results open a versatile avenue to longer π-conjugated nanoribbons with integrated metalloporphyrin units.

Rearrangements of Internally‐bridged Octaphyrin(1.1.1.1.1.1.1.1)s to Porphyrin Dimers

AbstractInternally‐bridged octaphyrin(1.1.1.1.1.1.1.1) underwent a rearrangement to meso‐meso linked porphyrin dimer as a new metamorphosis. Extensive examination suggests that hydride‐addition is a key step for the rearrangements to afford thermodynamically more stable porphyrin framework. Further, β‐tetrabromo[36]octaphyrin was transformed to meso‐meso, β‐β, β‐β triply linked porphyrin dimer via a similar mechanism combined with Pd‐mediated reductive homocoupling.

Rearrangements of Internally-bridged Octaphyrin(1.1.1.1.1.1.1.1)s to Porphyrin Dimers.

Internally-bridged octaphyrin(1.1.1.1.1.1.1.1) underwent a rearrangement to meso-meso linked porphyrin dimer as a new metamorphosis. Extensive examination suggests that hydride-addition is a key step for the rearrangements to afford thermodynamically more stable porphyrin framework. Further, β-tetrabromo[36]octaphyrin was transformed to meso-meso, β-β, β-β triply linked porphyrin dimer via a similar mechanism combined with Pd-mediated reductive homocoupling.

Redox properties of bis-cobalt(III) complex of 3,3′-linked N-confused porphyrin dimer with axial pyridine ligands

Novel cobalt(III) complexes of N-confused porphyrin (5,10,15,20-tetrakis(penta-fluorophenyl)-2-aza-21-carbaporphyrin) and its 3,3[Formula: see text]-linked dimer, Co1 and Co2, were synthesized and their structures were elucidated by X-ray crystallographic analysis and NMR spectroscopy. The redox properties of the complexes were examined by electrochemical approaches, and the corresponding oxidized/reduced species were analyzed by spectroelectrochemistry and DFT calculations. Notably, due to the facile redox feature of the N-confused porphyrins, ligand-centered oxidative/reductive processes were assumed for Co1 and Co2 presumably as inferred from the spectral analyses. These results indicate the unique multi-electron reservoir capability of the metal complexes of the N-confused porphyrin dimer.

Synthetic Model for FRET Constructed from Covalently Linked Porphyrin Dimers through a Pyrene Bridge.

We report the synthesis and characterization of two porphyrin arrays C6F5-PyZnDP and Mes-PyZnDP covalently linked by a pyrene moiety which differs from their substituents at their meso-positions. The key precursor bis-dipyrromethane linked with a pyrene bridge was prepared by the acid-catalyzed condensation of pyrene-1,6-dialdehyde with excess pyrrole. The synthesis of C6F5-PyZnDP was carried out via two different synthetic routes, with one being efficient over the other. Therefore, the superior route was employed for the synthesis of C6F5-PyZnDP and Mes-PyZnDP. Both the free base and metalated diporphyrins show bathochromically shifted absorption and intense red emission due to the extended π-conjugation through pyrene and porphyrins. The single-crystal X-ray structure reveals an orthogonal orientation of pyrene in between the two planar porphyrins and a slipped stacked packing arrangement in the crystal structure with large meso-meso distances. DFT analysis of both the ground state and the excited S1 state of the macrocycles indicates the difference in the HOMO and LUMO contribution in both the states arising from slight twisting from the mean orthogonal position in the excited state. Further, the Förster energy transfer (FRET) efficiencies from pyrene (donor) to the covalently linked Zn-porphyrins (acceptor) are estimated to be 85 and 91% for Mes-PyZnDP and C6F5-PyZnDP, respectively.

The Effect of Miscibility and Morphology of Porphyrin Donors and Non‐Fullerene Acceptors on Exciton Dissociation Processes: A Quantum Chemical and Molecular Dynamics Study

AbstractPorphyrins and their derivatives have been employed extensively in organic solar cells (OSCs) in recent years. However, a deeper understanding of the exciton dissociation process for the porphyrin donor/non‐fullerene acceptor (NFA) interface is still lacking. Herein, we have combined quantum chemistry and molecular dynamics simulations to explore the combination of mono and dimer porphyrin donors with various types of NFAs. The work reveals that the key issue lies in the exciton dissociation process of porphyrin materials, which have strong crystallinity to increase spacing (more than 5.0 Å), resulting in lesser miscibility and weaker intermolecular π‐π stacking. The pathway for exciton dissociation will be limited by the small number of high‐energy charge transfer (CT) states. To solve the above‐mentioned issues, we implement an improved strategy for modifying the side chain of the terminal unit, reducing the stacking distance to 4.4 Å, while the number of CT states reaches up to 40 % (3/A3 style 1). Additionally, the results also indicate the development potential for all porphyrin OSCs, particularly, the charge recombination (kCR) rate of the 1/Rf‐Iso system is lowered by nearly nine orders of magnitude. This research may offer fresh perspectives for extending the application range of porphyrin materials in OSCs.

Covalent Template‐Directed Synthesis of a Spoked 18‐Porphyrin Nanoring**

AbstractRings of porphyrins mimic natural light‐harvesting chlorophyll arrays and offer insights into electronic delocalization, providing a motivation for creating larger nanorings with closely spaced porphyrin units. Here, we demonstrate the first synthesis of a macrocycle consisting entirely of 5,15‐linked porphyrins. This porphyrin octadecamer was constructed using a covalent six‐armed template, made by cobalt‐catalyzed cyclotrimerization of an H‐shaped tolan with porphyrin trimer ends. The porphyrins around the circumference of the nanoring were linked together by intramolecular oxidative meso‐meso coupling and partial β‐β fusion, to give a nanoring consisting of six edge‐fused zinc(II) porphyrin dimer units and six un‐fused nickel(II) porphyrins. STM imaging on a gold surface confirms the size and shape of the spoked 18‐porphyrin nanoring (calculated diameter: 4.7 nm).

Covalent Template-Directed Synthesis of a Spoked 18-Porphyrin Nanoring.

Rings of porphyrins mimic natural light-harvesting chlorophyll arrays and offer insights into electronic delocalization, providing a motivation for creating larger nanorings with closely spaced porphyrin units. Here, we demonstrate the first synthesis of a macrocycle consisting entirely of 5,15-linked porphyrins. This porphyrin octadecamer was constructed using a covalent six-armed template, made by cobalt-catalyzed cyclotrimerization of an H-shaped tolan with porphyrin trimer ends. The porphyrins around the circumference of the nanoring were linked together by intramolecular oxidative meso-meso coupling and partial β-β fusion, to give a nanoring consisting of six edge-fused zinc(II) porphyrin dimer units and six un-fused nickel(II) porphyrins. STM imaging on a gold surface confirms the size and shape of the spoked 18-porphyrin nanoring (calculated diameter: 4.7 nm).

Highly Coupled Heterobicycle-Fused Porphyrin Dimers: Excitonic Coupling and Charge Separation with Coordinated Fullerene, C60.

Porphyrin dimers have been widely explored and studied owing to their importance in photosynthetic systems. A vast variety of dimers linked by different groups and at different angles have been synthesized and studied; however, the means by which to synthesize rigidly fused porphyrins with direct conjugation of the chromophores remains limited. Such a class of porphyrins may possess interesting properties that unconjugated or stacked dimers may not exhibit. In this study, bisbenzimidazole-fused porphyrin dimers and their mono- and bis-zinc derivatives are synthesized and characterized. As a consequence of excitonic coupling, these dimers exhibit a split Soret band irrespective of the metal ion in the porphyrin cavity. Steady-state fluorescence and excitation spectra followed by femtosecond transient absorption spectral studies of the heterometallated dimer, (free-base and zinc porphyrin) reveals the occurrence of efficient singlet-singlet energy transfer (>95 % efficiency and rate constant >1012 s-1 ) within the dyad. Further, donor-acceptor conjugates were formed by metal-ligand axial coordination of phenyl imidazole functionalized C60 and were characterized by a variety of physicochemical techniques. Excited state charge separation from both singlet and triplet excited states of ZnP in the conjugates has been established. The lifetime of the final charge-separated state was in the 30-40 μs range revealing charge stabilization. Interestingly, no charge separation in the conjugate derived from the heterometallated dimer was observed wherein excitation transfer dominated the process. The present study brings out the importance of the rigid π-spacer connecting porphyrin dimers in governing the energy and electron transfer events when coupled with an electron acceptor.

Titelbild: Multistate Structural Switching of [3]Catenanes with Cyclic Porphyrin Dimers by Complexation with Amine Ligands (Angew. Chem. 14/2023)

Structural switching of [3]catenane was induced by fitting the puzzle pieces. In their Research Article (202217002), Jun Terao et al. report a method for ligand-controlled structural switching of [3]catenane, which was realized by the complexation of metal ions on [3]catenane with added complementarily fitted organic ligands, like pieces in a jigsaw puzzle. The high tailorability of organic ligands offers multiple pieces with various sizes and numbers of coordination sites, enabling multistate structural switching of [3]catenane. Structural switching of [3]catenane was induced by fitting the puzzle pieces. In their Research Article (202217002), Jun Terao et al. report a method for ligand-controlled structural switching of [3]catenane, which was realized by the complexation of metal ions on [3]catenane with added complementarily fitted organic ligands, like pieces in a jigsaw puzzle. The high tailorability of organic ligands offers multiple pieces with various sizes and numbers of coordination sites, enabling multistate structural switching of [3]catenane. Organic Electronics Carboranes Batteries Enzyme Catalysis

Cover Picture: Multistate Structural Switching of [3]Catenanes with Cyclic Porphyrin Dimers by Complexation with Amine Ligands (Angew. Chem. Int. Ed. 14/2023)

Structural switching of [3]catenane was induced by fitting the puzzle pieces. In their Research Article (DOI: 10.1002/anie.202217002), Jun Terao et al. report a method for ligand-controlled structural switching of [3]catenane, which was realized by the complexation of metal ions on [3]catenane with added complementarily fitted organic ligands, like pieces in a jigsaw puzzle. The high tailorability of organic ligands offers multiple pieces with various sizes and numbers of coordination sites, enabling multistate structural switching of [3]catenane.

Circularly polarized luminescence from porphyrin-containing (supra)molecular systems

Functional dyes showing circularly polarized luminescence (CPL) have attracted considerable attention. Porphyrins and porphyrinoids have characteristic properties useful for the development of CPL materials, although the examples of CPL-active porphyrins and porphyrinoids are still limited. Here we have summarized recent progress in CPL-active systems containing porphyrins or phthalocyanines, which are classified into the following four categories: (i) porphyrins with chiral sources; (ii) axially chiral porphyrin dimers; (iii) self-assembled porphyrins; (iv) porphyrin-sensitized CPL dyes.

Indacenodithiophene Bridged Dimeric Porphyrin Donor and Absorption Complementary Indacenodithiophene Acceptor for Nonfullerene Organic Photovoltaics

Porphyrins are one of the most promising materials for organic photovoltaics (OPVs) because of their easily tunable functional groups. Herein, we present the design and synthesis of two porphyrin-based small molecule donors, IDT-2TPE and TPE, in which two porphyrin units are bridged by an indacenodithiophene (IDT) diethynylene unit for the former and a single porphyrin monomer for the latter, and 3-ethylrhodanine units are then end-capped symmetrically by phenylenethynylene π-linkers. The porphyrin dimer IDT-2TPE exhibits outstanding red-shifted absorptions with a valley in both solution (400–800 nm) and film (400–900 nm), low-lying energy levels, and excellent thermal stability compared to the porphyrin monomer TPE due to the extended π-conjugation and increased rigidity with the IDT unit. Impressively, the device based on the IDT-2TPE donor and IDTCR nonfullerene acceptor shows a broad photoelectron response up to 1000 nm and a power conversion efficiency (PCE) of 10.41% at AM 1.5G. For comparison, the device based on the TPE donor and IDTCR acceptor has a much lower PCE of 4.22%. The much better performance of the device IDT-2TPE/IDTCR is attributed to its higher photocurrent generation and more favorable surface morphology with elevated charge carrier mobilities.