Porphyrin Trimer Research Articles

Synthesis of direct β-to-β linked porphyrin arrays with large electronic interactions: branched and cyclic oligomers.

Direct β-to-β linked branched and cyclic porphyrin trimers and pentamers have been synthesized by the Suzuki-Miyaura coupling of β-borylporphyrins and β-bromoporphyrins. The cyclic porphyrin trimer, the smallest directly linked cyclic porphyrin wheel to date, and its twined pentamer, exhibit small electrochemical HOMO-LUMO gaps, broad nonsplit Soret bands, and red-shifted Q-bands, thus indicating large electronic interactions between the constituent porphyrin units.

Dye-sensitized Solar Cells Using Ethynyl-linked Porphyrin Trimers with an Anchoring Group at Long-axis End or Short-axis End

An ethynyl-linked porphyrin trimer with a carboxyphenyl anchoring group at its long-axis end can be adsorbed more densely on a TiO2 surface and exhibited better performance in dye-sensitized solar cells than did the trimer with short-axis anchoring, with photoelectric conversion in the near-IR region.

New luminescent fluorenyl-armed linear porphyrin trimers with diphenylacetylene bridges

Abstract First a series of porphyrins bearing various fluorenyl donor groups is presented; an intermediate porphyrin bearing three fluorenyl arms (zinc complex 12 ) and compound 13 , bearing only two fluorenyl groups. Then starting from these building blocks, synthesis of new porphyrin trimers 7 and 8 , with in totally eight peripheral fluorenyl arms is performed by using a palladium catalyst. Photophysical properties; absorption and luminescence, of new trimers 7 and 8 are presented. We can then compare these properties to those of reference porphyrin monomer TFP ( 2 ), as well as to those of porphyrin dendrimers bearing various numbers of fluorenyl arms ( 3 and 4 ) and finally to those of the corresponding dimers 5 and 6 , which are the precursor models of this work.

Synthesis of Porphyrin Arrays and Investigation of Their Optical and Electrochemical Properties

Porphyrin arrays have attracted much attention in a wide range of scientific applications such as in artificial photosynthetic antenna1, electronic devices, and single-molecule devices2. Although various synthetic methods have been reported, they are applicable only to the homologous porphyrin arrays; in addition, it is difficult to synthesize the elaborate porphyrin arrays with programmable order of each unit. Thus, we synthesized porphyrin dimers and trimers that have varying sequences of the porphyrin units via the consecutive Suzuki coupling reactions using the same key porphyrin compound. The use of the consecutive Suzuki coupling reactions for the effective syntheses of elaborate oligoarenes by repetition of the same reaction at each elongation step3, has been reported. In this work, the consecutive Suzuki coupling was applied for the synthesis of porphyrin arrays of various orders.We synthesized two porhpyrins as the starting monomers: porhyrin 2 bearing a triflate group, and the key porphyrin 3 bearing a boronic ester and a hydroxyl group. Porphyrins 2 and 3 were synthesized in three and four steps, respectively. The Suzuki coupling reaction between 2 and 3 in various combinations afforded four different dimers, as denoted by 4 in Scheme 1. After triflation of the hydroxyl group of 4, a further coupling of 4 with 3 afforded five different trimers, as denoted by 6 in Scheme 1. The porphyrin monomers were synthesized in gram scale in one batch, and the coupling reactions afforded moderate to good yields. The optical and electrochemical properties of these dimers and trimers were investigated.The absorption and emission spectra of the dimers and trimers, possessing the same molecular formula, were different (Fig. 1) when the order of the units was different. The emission profiles of the arrays, 4-HZn and 6-HZnH, were attributed to that from the free-base porphyrin unit; however, the wavelengths and intensities of their emission were different. (Fig. 1.(b)). The differential pulse voltammograms of the monomers, 1-H and 1-Zn, and the dimer 4-HZn are demonstrated in Fig. 2. Certain redox peaks of the dimer 4-HZn were almost identical to those of the component monomers (1-H and 1-Zn); however, a few new redox peaks were observed, which indicated the emergence of new electronic states via interaction of each unit component.(1) Nakamura, Y.; Aratani, N.; Osuka, A. Chem. Soc. Rev. 2007, 36, 831.(2) Sedghi, G.; Garcia-Suarez, V. M.; Esdaile, L. J.; Anderson, H. L.; Lambert, C. J.; Martin, S.; Bethell, D.; Higgins, S. J.; Elliott, M.; Bennett, N.; Macdonald, J. E.; Nichols, R. J. Nat Nano 2011, 6, 517.(3) Noguchi, H.; Hojo, K.; Suginome, M. J. Am. Chem. Soc. 2007, 129, 758.

Controlling the Rotation of Porphyrin Units in Ethynyl-linked Porphyrin Trimers for Dye-sensitized Solar Cells by Anchoring onto TiO2 Surface

Abstract An ethynyl-linked porphyrin trimer bearing carboxyphenyl anchoring groups at all the porphyrin units becomes planar upon adsorption onto TiO2, showing the Q band absorption and IPCE maximum at longer wavelengths.

Clawlike Tripodal Porphyrin Trimer: Ion-Controlled On–Off Fullerene Binding

A practical method for the preparation of novel tripodal tris(porphyrinato-urea) TP3 1 was readily achieved. Because of its appreciable preorganized triangular cone-shaped cavity resulting from the intramolecular hydrogen bonds of the tripodal tris-urea backbone, this porphyrin trimer host was found to have a high affinity toward fullerenes to form stable inclusion complexes in solution. A 120-fold binding selectivity toward C70 (Kassoc = 1.81 × 10(7) M(–1)) over C60 (Kassoc = 1.51 × 10(5) M(–1)) was further achieved in toluene. Moreover, the dissociation of such inclusion complexes can be easily realized by introducing H2PO4(–), and recapturing of the fullerene can be achieved after withdrawing H2PO4(–) by Ca(2+). A recyclable process for the inclusion and release of fullerene was therefore built by alternately feeding H2PO4(–) and Ca(2+). Benefiting from this approach, TP3 1 was sequentially applied to isolate C70 from the C60-enriched fullerene mixture successfully.

Dye-sensitized solar cells using ethynyl-linked porphyrin trimers

Toward the extension of the light-harvesting region of sensitizers in dye-sensitized solar cells (DSSCs), two ethynyl-linked porphyrin trimers were synthesized and investigated. The zinc–freebase–zinc trimer (Zn–FbA–Zn) showed an absorption maximum at a longer wavelength than the all-zinc trimer (Zn–ZnA–Zn), although the energy level of Zn–FbA–Zn was lower than that of Zn–ZnA–Zn. The DSSCs using these trimers showed spectral sensitivities up to 900 nm. Reflecting the energy levels of these trimers, the DSSC using Zn–ZnA–Zn showed better performance than that using Zn–FbA–Zn. After the optimization of cell fabrication conditions, the photoelectric conversion efficiency η of the DSSC using Zn–ZnA–Zn reached 3.17%. The larger TiO2 nanoparticles (ca. 37 nm) than the conventional cases (ca. 13 nm) were found to be preferable in this case, due to high molar extinction coefficients of the porphyrin trimers.

Linear conjuncted porphyrin trimer synthesis via "click" reaction

Two isomers of porphyrin trimer with 1,4-diaryltriazole linkers have been synthesized using "click" methodology and characterized by MS, NMR and UV-vis spectroscopy. The porphyrin compounds were shown to exhibit photostability and high solubility. Photophysical data were compared with corresponding ones of synthesized triazole-bridged dimer with the same electronic surrounding and known linear dimer and trimer with diarylethyne linkers. Obtained data revealed weak inter-chromophore electronic communication in the ground state but significant exciton coupling whereas the properties of the individual chromophores are mainly retained for triazole-bridged dimer and trimers.

Solution scattering studies of the hierarchical assembly of porphyrin trimers based on benzene triscarboxamide.

The self-assembly of achiral and chiral porphyrin trimers based on benzene triscarboxamide in solution is studied with the help of NMR, FT-IR, UV-vis, and CD spectroscopy. These studies revealed that in apolar solvents the porphyrin trimers self-assembled in columnar stacks via a combination of hydrogen bonding and π-π stacking interactions. While the critical aggregation constant is about 0.2 mM in chloroform, aggregation already occurs at micromolar concentrations in n-hexane. Small angle neutron scattering (SANS) studies in chloroform, toluene, and n-hexane confirmed aggregation of the trimers into columnar stacks. In chloroform and n-hexane, but not in toluene, the trimers gelated the solvent. In chloroform the stacks of the achiral trimer were found to contain on average about 70 molecules, while in toluene the stacks were much smaller and contained on average 7-9 molecules. In n-hexane the SANS studies revealed that the chiral trimer formed a gel with an average mesh size of the transient network of chains of approximately 90 nm, with chains being built up from effective cylindrical aggregates with an average length of 20 nm.

The Synthesis of a Heptacationic Porphyrin Trimer Connected with a Bipyridyl Linker on Axial Ligands

Abstract Tetracationic porphyrin dimers and heptacationic trimers were prepared by the connection of a bipyridyl linker with axial ligands of antimony(V) porphyrin and/or phosphorus(V) porphyrin complexes. The measurement of cyclic voltammetry and absorption spectra showed that the electrochemically reduced species was a long-lived species of antimony(IV) porphyrin chromophore.

Synthesis and Functionalization of Triply Fused Porphyrin Dimers

AbstractCurrent applications of porphyrins in medicine and optics, such as photodynamic therapy or nonlinear absorption, increasingly require the use of far‐red absorbing dyes. Modification of the porphyrin structure to accommodate these conditions can be achieved by extending the conjugation of the porphyrin π system, which causes a bathochromic shift in the absorption spectrum. Thus, conjugated porphyrin oligomers have found widespread use. However, past synthetic strategies have mainly targeted symmetric porphyrin dimers, trimers, and oligomers which limit the practical use of such chromophores. To further extend the absorption profile, a series of symmetric and unsymmetric dimeric and oligomeric porphyrin β–β, meso–meso, β′–β′ triply fused systems were synthesized by oxidative coupling methods. This required an analysis and optimization of the various synthetic strategies. These arrays exhibit a dramatic bathochromic shift into the near‐infrared region and many display absorption at wavelengths greater than 1050 nm. Additionally, post‐fusing chemical transformations, namely, organolithium, cycloaddition, and transition‐metal‐catalyzed reactions, at the meso and β positions enable the fine‐tuning of such arrays to enhance the bathochromic shift and their potential optical applications.

On the potential of porphyrin-spiked triarylamine stars for bulk heterojunction solar cells

A novel porphyrin–triarylamine compound was synthesized to serve as a photosensitizer in bulk heterojunction solar cells (BHJ-OSCs). Based on cyclic voltammetric analysis, the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels of the target porphyrin trimer were determined to be at −5.4 and −3.5 eV versus vacuum, respectively, and compared with those of other materials used for the construction of the BHJ-OSCs. Absorption and emission spectra of the film of the target porphyrin trimer were in good agreement with those of its solution. The charge transfer in a blended film of the porphyrin–triarylamine compound with phenyl-C61-butyric acid methyl ester (PCBM) was proven possible by photoluminescence measurements. The energy conversion efficiency of the BHJ-OSCs based on the target compound depended strongly on the donor : acceptor weight ratio and the thickness of the organic layer. Surface nanomorphologies of the films with different donor : acceptor ratios and thickness were investigated by atomic force microscopy (AFM). The short circuit current density (JSC) up to 2.06 mA cm−2 was obtained from the BHJ-OSC fabricated herein.

Trimer Porphyrin Star

A novel tripod star-shaped porphyrin trimer has been synthesized using “click” methodology (Huisgen’s 1,3-diploar cycloaddition reaction) from zinc(II) 5-(4-azidophenyl)-10,15,20-trimesitylporphyrin and 1,3,5-triethynylbenzene. The porphyrin tripod star was shown to exhibit coordination with DABCO and Bipy forming cofacial dimer aggregates and characterized by MS, NMR and UV-vis spectroscopy.

Solvent-dependent amplification of chirality in assemblies of porphyrin trimers based on benzene tricarboxamide

Self-assembling achiral and chiral porphyrin trimers based on benzene tricarboxamide exhibit amplification of chirality only in solvents in which the assemblies are dynamic enough to rearrange their constituting components.

Abstract B115: Pharmacokinetics and biodistribution analysis using near-infrared emissive polymersomes.

Abstract Introduction: Near-infrared (NIR) emissive polymersomes are bi-layered vesicles that contain membrane-incorporated multi-porphyrin fluorophores for in vivo imaging. The high emission dipole strength NIR fluorescence of these particles allows for deeper tissue imaging relative to conventional fluorophores, creating a noninvasive technique for analysis of biodistribution and pharmacokinetics (PK) of nano-scale systems - a significant improvement over current methodology. Due to controllable membrane properties, both hydrophilic and hydrophobic compounds can be incorporated into polymersomes, offering application in tumor imaging and drug delivery. Methods: Poly(ethylene oxide)-block-polycaprolactone (PEO-b-PCL) copolymers were used to form polymersomes through thin film hydration followed by sonication, freeze/thaw cycles, and membrane extrusion. An ethyne-bridged zinc porphyrin trimer (ex = 772; em = 806nm) was incorporated into these films prior to hydration. High MW PEO(2kDa)-b-PCL(14.6kDa) and low MW PEO(1kDa)-b-PCL(4kDa) formed vesicles of 250nm and 200nm diameters, respectively. Results: Epithelial, endothelial, and liver cells were treated with PEO-b-PCL polymersomes to study the effects on proliferation and viability. These vesicles were found to be non-toxic to all three cell types. In vivo studies were carried out on balb/c mice by i.v. injection of NIR emissive polymersomes. A LI-COR Pearl® Impulse was used for real-time imaging during and after treatment, demonstrating that polymersomes could be successfully imaged deep within the mouse, due to minimal NIR scattering and absorbance and strong emission of the multi-porphyrin within the polymersome membrane. Upon injection of the polymersomes, fluorescence was detected immediately within the vasculature of the mice. Over time, fluorescence localized within the spleen and liver, as expected due to the mononuclear phagocytic system. Ex vivo biodistribution results confirmed these in vivo imaging data, with all other organs having at least an order of magnitude lower intensity. Fluorescence intensities in the spleen, liver, and femoral artery were quantified for at least 50 time points over 6 or 24 hours. Mathematical modeling was used to evaluate the intensity changes in these tissues and to estimate circulation half-lives from the change in fluorescence of the femoral artery. PK analysis of PEO(2k)-b-PCL(14.6k) 250nm polymersomes unexpectedly demonstrated circulation half-lives varying from 0.5–10 hours, perhaps due to particle aggregation. PEO(1k)-b-PCL(4k) 200nm polymersomes, on the other hand, provided consistent, yet much lower than anticipated, half-lives of 0.25 hours. This short circulation time may be due to the smaller PEO length, reducing the “stealth” characteristic of the particles. Conclusions: NIR-emissive polymersomes were found to be non-toxic to various cell lines, and were successfully used to analyze vesicle biodistribution and PK in real-time in vivo. It is expected that once a tumor model is added, the polymersomes will accumulate within the tumor perivascular space due to the EPR effect. In addition to NIR imaging agents, both water soluble and insoluble compounds can be incorporated into these structures, thus providing a nano-scale technology for tumor imaging and drug delivery. This work was supported by NIH training grant 5T32GM008555-18. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2011 Nov 12-16; San Francisco, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2011;10(11 Suppl):Abstract nr B115.

Porphyrin Dimers and Arrays

AbstractCurrent applications of porphyrins in medicine and optics, such as photodynamic therapy or nonlinear absorbers, increasingly require the use of far‐red absorbing dyes. Modifications of the porphyrin structure to accommodate these conditions can be achieved by extending the conjugation of the porphyrin π‐system, which causes a bathochromic shift in the absorption spectrum. Thus, conjugated porphyrin oligomers have found widespread use. However, past synthetic strategies have mainly targeted symmetric porphyrin dimers, trimers, and oligomers, which limit the practical use of such chromophores. Here, a series of symmetric and unsymmetric dimeric and trimeric porphyrin systems, which are connected by conjugated linkers, namely alkyne and phenylacetylene, were synthesized by palladium‐catalyzed C–C coupling reactions. Adopting two approaches, firstly, a series of new unsymmetric dimers was synthesized by the incorporation of all substituents on the monomeric components prior to coupling. The second was the synthesis of new symmetric dimers and trimers with free meso positions enabling further chemistry to be carried out. The majority of these conjugated arrays exhibited a bathochromic shift in their UV/Vis absorption, in particular the alkyne‐linked arrays showed absorption greater than 720 nm. The mass spectra of phenylacetylene‐ and diphenylbutadiene‐linked zinc arrays exhibited detachment of zinc from the porphyrin core. These unusual results are both linker and metal dependent, usually only seen for more labile metals.

Greatly Enhanced Intermolecular π-Dimer Formation of a Porphyrin Trimer Radical Trications through Multiple π Bonds

A trefoil-like porphyrin trimer linked by triphenylamine (TPA-TPZn(3)) was synthesized. A three-electron oxidation of TPA-TPZn(3) forms a radical trication (TPA-TPZn(3)(3+)), in which each porphyrin ring undergoes a one-electron oxidation. The radical trication TPA-TPZn(3)(3+) spontaneously dimerizes to afford (TPA-TPZn(3))(2)(6+) in CH(2)Cl(2) . The characteristic charge-resonance band due to the charge delocalization over the π system of (TPA-TPZn(3))(2)(6+) was observed in the NIR region. The initial oxidation potential of TPA-TPZn(3) is negatively shifted relative to that of the corresponding monomer porphyrin, which results from the stabilization of the oxidized state of TPA-TPZn(3) associated with the dimerization. The thermodynamic parameters (i.e., ΔH, ΔS, and ΔG) for the formation of (TPA-TPZn(3))(2)(6+) were determined by measuring Vis/NIR spectra at various temperatures. The formation constant of (TPA-TPZn(3))(2)(6+) is significantly larger than that of the radical cation dimer of the corresponding monomer porphyrin (e.g., over 2000-fold at 233 K). The electronic states were investigated using EPR spectroscopic analysis. The greatly enhanced dimerization of TPA-TPZn(3)(3+) results from multiple π-bond formation between the porphyrin radical cations.

Pd(II)-Mediated Assembly of Porphyrin Channels in Bilayer Membranes

A membrane-spanning bis(meso-3-pyridyl) porphyrin 1 has been synthesized, embedded in EYPC vesicles, and upon Pd(II) addition has been shown to form ionophores that allow the passage of anionic 5/6-carboxyfluorescein through membranes. The geometric matching of bis(meso-3-pyridyl) porphyrin 1 and trans-Pd(II) was designed to give a cyclic porphyrin trimer [PdCl(2)(1)](3). However, solution-phase studies showed that PdCl(2)(PhCN)(2) cross linked 1 into linear oligomers at porphyrin concentrations above 10 mM, although the formation of cyclic species was inferred from studies at concentrations below 2 μM. Fluorescence titrations showed that embedding porphyrin 1 in bilayers greatly reduced its affinity for Pd(II), but the combination of porphyrin 1 and Pd(II) gave an ionophoric species that increased the rate of 5/6-carboxyfluorescein (5/6-CF) transit through the phospholipid bilayer 12-fold. A maximum in the 5/6-CF release rate was observed at a Pd(II) concentration of 4 μM, and the application of a solution-phase binding model to the membrane phase showed that this peak in ionophoric activity corresponded to the greatest extent of porphyrin oligomerization. Further studies suggested these Pd(II)/porphyrin oligomers transported 5/6-CF via a channel mechanism.

Synthesis and ligand binding properties of triptycene-linked porphyrin arrays

Multiporphyrin arrays are a complex class of molecules with numerous potential applications in energy transfer, photomedicine, and light harvesting. We have developed a facile/versatile route to a class of triptycene-linked porphyrin arrays via both Suzuki and Sonogashira cross-coupling methods, which makes use of the rigid three-pronged orientation of triptycene to construct trimeric porphyrin arrays linked either in the meso or β-position with various linker groups. In order to understand the properties of these potential antenna systems and probe their potential applications, the coordination behavior of zinc(II) derivatives with mono- and bidentate N-donor ligands was investigated. Depending on ligand concentration, both one- and two-point binding was observed with a bidentate ligand. Also/in addition, different cavity sizes, obtained by the use of different linker groups, resulted in differences in the binding properties of each trimeric system.

ChemInform Abstract: The Synthesis of the Dimer and Trimer Ether-Linked Components of Hematoporphyrin Derivative

The preparation is described of all of the likely dimer and trimer ether-linked components of the anticancer material known as hematoporphyrin derivative. The hydroxyethyl side chain of one porphyrin, related to hematoporphyrin, reacts readily with a bromoethyl system derived from the same, or similar, hematoporphyrin -derived porphyrin to form a diporphyrin ether. The coupling reaction can be controlled to occur in situ, allowing the preparation of a symmetrical ether-linked dimer , or separately to provide an asymmetrically substituted porphyrin dimer . The bromoethyl groups can be formed from either the hydroxyethyl groups or, more slowly, from a vinyl side chain by using hydrogen bromide in dichloromethane. Ether-linked porphyrin trimers can be prepared by reacting a dibromoethyl system with 2 equiv. of a hydroxyethyl -containing porphyrin or by further reaction of an initially formed dimer. Hydroxyethyl side chains in the dimers and trimers are best obtained by reduction of an acetyl group. Some spectral properties of the products are described.