Porphyrin Trimer Research Articles

ChemInform Abstract: Effect of the Exciton Coupling on the Optical and Photophysical Properties of Face-to-Face Porphyrin Dimer and Trimer. A Treatment Including the Solvent Stabilization Effect.

A treatment of the exciton coupling interaction including the solvent stabilization effect is given. The method is successfully applied to porphyrin dimer and trimer. the maxima of the Soret bands can be predicted with a high accuracy. The effect of exiton coupling on the photophysical properties of basket handle cofacial, doubly linked porphyrin dimer and trimer is investigated and compared to that in the singly linked dimer

ChemInform Abstract: Synthesis of Dimeric and Trimeric Porphyrins Based on Intramolecular Macrocyclization Reactions.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Directly Pd(II)-Bridged Porphyrin Belts with Remarkable Curvatures

A beta,beta'-doubly 2,6-pyridylene-bridged porphyrin dimer and trimer were prepared by Suzuki-Miyaura coupling reactions and confirmed to have largely bent structures. These oligoporphyrins were readily metalated via meso-C-H bond activation with the assistance of the pyridyl nitrogen atoms to produce the corresponding Pd(II) complexes, which display even larger bent structures and larger TPA values at 800 nm.

Strategic Synthesis of 2,6‐Pyridylene‐Bridged β‐to‐β Porphyrin Nanorings through Cross‐Coupling

Since the crystal structure of LH2 was elucidated to be circularly arranged chromophoric assemblies, [1–3] much effort has been devoted towards the synthesis of cyclic porphyrin arrays to study the excitation energy transfer (EET) and electronic coupling along the wheel. [4] These cyclic porphyrin arrays are also interesting in host–guest chemistry, [5] single-molecule photochemistry, [6] nonlinear optical (NLO) materials [7] and so on. [8–12] Cyclic porphyrin arrays are constructed by means of covalent bonds, noncovalent bonds, or metal coordination bonds. [8–12] Although the last two are beneficial to construct cyclic porphyrin arrays, those are often unstable toward solvent change or addition of other competing species. The covalently bonded arrays are structurally robust, but often difficult to synthesize. In addition, the final macrocyclization steps are the most tedious and generally need assistance from a suitable template. [5] Although there are some reports on covalently bonded cyclic porphyrin arrays, most of them were constructed through meso-to-meso bridging methods. As rare examples, we recently reported two b,b’-bridged cyclic porphyrin arrays with a 1,3-butadiyne or a 2,5-thienyl spacer. [13] Herein, we wish to report the efficient synthesis of 2,6-pyridylene-bridged b-tob porphyrin nanorings by Suzuki–Miyaura coupling, which is particularly effective for medium to large porphyrin rings. We have achieved the synthesis of 2,5-thienylene-bridged cyclic porphyrin dimers and trimers, but it was difficult to expand the size of the macrocycle beyond trimers. We then examined the Suzuki–Miyaura coupling of b,b’-diborylated Ni II porphyrin 1 with 2,6-dibromopyridine, which provided linear oligomers as the main products. However, we noticed that bromopyridyl-terminated oligomers were selectively obtained with the use of an excess amount of 2,6-dibromopyridine. For instance, b,b’-diborylporphyrin 1–Ni II[14] was crosscoupled with 2,6-dibromopyridine (5 equiv) under standard conditions to give 1–Br in 80 % yield, along with 2–Br (10 %) and 3–Br (2 %) (Scheme 1). It is worth noting that deborylated products were hardly detected in this reaction. Compound 2–Br was also obtained in 42 % yield through the three-component coupling of 1 (1 equiv), 1–Br (2.5 equiv), and 2,6-dibromopyridine (2.5 equiv). Further cross-coupling of 1 (1 equiv) with 1–Br (5 equiv) or 2–Br (5 equiv) afforded 3–Br or 5–Br in 50 or 45 % yields, respectively. Compound 7–Br was prepared in 50 % yield from 1 and 3–Br. With the linear precursors 2–Br, 3–Br, 5–Br, and 7–Br in hand, we examined the cyclization with 1 through a 1:1 Suzuki–Miyaura coupling reaction, which worked very effectively to give porphyrin rings 3–Ni, 4–Ni, 6–Ni, and 8–Ni in 60, 58, 55, and 55 % yields, respectively, even without any template. Treatment of 3–Ni, 4–Ni, 6–Ni, and 8–Ni with sulfuric acid in chloroform at room temperature induced Ni II demetalation to provide 3–H, 4–H, 6–H, and 8–H quantitatively, which were all converted into 3–Zn, 4–Zn, 6–Zn, and 8–Zn upon treatment with ZnA2 in quantitative yields. These newly synthesized porphyrin rings were fully characterized by high-resolution mass spectrometry and

Selective Stepwise Suzuki Cross-Coupling Reaction for the Modelling of Photosynthetic Donor−Acceptor Systems

A Suzuki reaction performed as a selective stepwise substitution of two boryl groups on a diarylporphyrin precursor is reported for straightforward construction of a porphyrin trimer, modeling photosynthetic donor-acceptor systems.

Synthesis and Stereochemistry of Highly Unsymmetric β,Meso-Linked Porphyrin Arrays

Porphyrin arrays with tailor-made photophysical properties and well-defined three-dimensional geometries constitute attractive synthetic targets in porphyrin chemistry. The paper describes a variable, straightforward synthetic procedure for the construction of beta,meso-linked porphyrin multichromophores in good to excellent yields. In a Suzuki-type coupling reaction beta-borylated 5,10,15,20-tetraarylporphyrins (TAPs) served as versatile building blocks for the preparation of a plethora of directly linked, unsymmetrically substituted di- and triporphyrins. Besides their interesting photophysical properties, especially the trimeric porphyrin arrays show exciting stereochemical features. The established protocols thus open a convenient entry into the synthesis of achiral and chiral, unsymmetrically substituted beta,meso-linked oligoporphyrins, e.g., for applications in biomedicine or nonlinear optics.

Correlation studies on structurally diverse porphyrin monomers, dimers and trimers and their nonlinear optical responses

An investigation of the nonlinear absorption of a wide range of structurally diverse porphyrin monomers, bisporphyrins and trisporphyrins, using open Z-scan technique with 6 ns pulsed laser operating at 532 nm was carried out. Using the theory of reverse saturable absorption, the intensity dependent nonlinear absorption coefficient β eff was deduced from the experiments. Monomers which Soret band maximum was situated closer to the experimental wavelength had higher β eff . The β eff of dimers and trimers were in the same range as for monomers. The highest β eff = 5.3 × 10 −8 cm W −1 was found for a zinc complex of 5,15-A 2B 2 type porphyrins with 3-methoxyphenyl and trimethylsilyl-ethynyl groups in the meso positions.

Triptycene as a rigid, 120° orienting, three-pronged, covalent scaffold for porphyrin arrays

The synthesis of novel porphyrin trimers covalently linked by one central, rigid triptycene unit is described. Reaction of 2,6,14-triiodotriptycene, generated in a three-step synthesis from triptycene, with borylated porphyrins under Suzuki cross-coupling conditions afforded porphyrin trimers. In addition, Sonogashira cross-coupling conditions could be successfully applied for the synthesis of trimeric porphyrin arrays as well.

Influence of the Central Metal Ion on Nonlinear Optical and Two-Photon Absorption Properties of Push−Pull Transition Metal Porphyrins

We present a quantum-chemical analysis of the central metal ion's effect on first hyperpolarizabilities and two-photon absorption (TPA) cross sections at the infrared region of a series of push-pull porphyrins whose synthesis and NLO properties have been reported earlier (J. Am. Chem. Soc. 2005, 127, 9710). The molecular geometries are obtained via the B3LYP/6-31G(d,p) level optimization including SCRF/PCM approach, and the NLO and TPA properties are calculated with the ZINDO/CV method including solvent effects. It is found that the CT transition between the metal ion's d orbital and the macrocycle pi orbitals plays an important role on NLO and TPA properties of metal porphyrins. Our data suggest a new approach to enhance TPA properties of porphyrin materials. We also present a quantum-chemical analysis on porphyrin dimers and trimers to understand the relationship between structural and collective NLO properties. It has been observed that beta values can be improved about an order of magnitude and TPA properties can be enhanced by 2 orders of magnitude by the formation of a trimer. The importance of our results with respect to the design of photonic and photodynamic therapy materials have been discussed.

Synthetic strategies and porphyrin building blocks for unsymmetrical multichromophores

A sequential use of halogenation, S NAr, Sonogashira and/or Suzuki couplings together with the use of either mono-5-, 5,15- or 5,10-di- meso-substituted porphyrins allows the facile construction of unsymmetrical porphyrin dimers and trimers with different spatial orientation. The protocols established allow a convenient entry into multichromophores suitable for application in nonlinear optics and biomedicine.

Coordinative Self-Assembly and Solution-Phase X-ray Structural Characterization of Cavity-Tailored Porphyrin Boxes

Combining linear Zn porphyrin trimers with orthogonally derivatized porphyrin dimers leads rapidly and spontaneously to the formation of monodisperse, torsionally constrained boxes comprising six components and a total of 16 metalloporphyrins. In situ X-ray scattering measurements confirm the formation of monodisperse assemblies of precisely the size expected from model box structures. While simple subunits yield highly symmetrical boxes, we find that sterically demanding subunits produce unusual twisted boxes. Previous studies of porphyrin-based box-like assemblies (squares) for selective catalysis and molecular sieving revealed two function-inhibiting structural problems: torsional motion along the metal-porphyrin-metal axis and ambiguous outside versus inside functionalization (via axial ligation of available Zn(II) sites). The new 16-porphyrin box assemblies eliminate both problems.

Supramolecular Porphyrin Polymers in Solution and at the Solid−Liquid Interface

We have investigated in detail the self-assembly of a chiral porphyrin trimer in different solvents and correlated this behavior to the aggregation of the molecule at a solid-liquid interface. In n-hexane and cyclohexane, CD spectroscopy and dynamic and static light scattering studies showed that the porphyrin trimer self-assembles already at micromolar concentrations into long, chiral supramolecular polymers, which precipitate as fibers when the solution is drop-cast onto a mica surface. In contrast, in chloroform, the compound is molecularly dissolved up to concentrations of 0.2 mM and when micromolar solutions are drop-cast onto mica, no precipitation of large assemblies occurs. Instead, at the moment that the chloroform film becomes subject to spinodal dewetting and the porphyrin trimers within this film start to self-assemble, extended patterns of equidistant lines of single molecule thick columnar stacks are formed.

Synthesis of three-dimensionally arranged porphyrin arrays via intramolecular meso– meso coupling

The synthesis and photophysical properties of three-dimensionally arranged porphyrin arrays with through-space electronic communication are reported. 1,3,5-Trioxamethylphenylene bridged Zn(II) porphyrin trimer 3 was coupled by Ag(I)-promoted oxidative coupling reaction to give porphyrin cage 5 comprising three meso– meso linked diporphyrins, which was then transformed by oxidation with DDQ and Sc(OTf) 3 into porphyrin cage 7 comprising three fused diporphyrins. Intramolecular meso– meso coupling reaction was applied to porphyrin pentamer 11 to provide porphyrin array 12 consisting of a porphyrin core flanked by two meso– meso linked diporphyrins. Further oxidation of 12 with DDQ and Sc(OTf) 3 afforded triply stacked porphyrin array 13 that is comprised of a porphyrin core flanked by two porphyrin tapes. UV–vis–NIR absorption and fluorescence spectra of 5, 7, 12, and 13 showed their distorted conformations and electronic interaction within the stacked porphyrin arrays.

Synthesis of C 1- and C 3ν-Symmetric Porphyrin Trimers Based on Triphenylmethane Cores

This work describes the synthesis of a new class of tripodaphyrin derivatives with a triphenylmethane core. Both C 1- and C 3ν-symmetric tetrahedral large molecules with covalently linked rigid elements were obtained.

The development of self-assembled liquid crystal display alignment layers

From simple pocket calculators to mobile telephones and liquid crystal display (LCD)-TV, over the past few decades, devices based on LCD technology have proliferated and can now be found in all conceivable aspects of everyday life. Although used in cutting-edge technology, it is surprising that a vital part in the construction of such displays, namely the alignment layer, relies essentially on a mechanical rubbing process, invented almost 100 years ago. In this paper efforts to develop alignment layers (also called command layers) by processes other than rubbing, namely self-assembly of molecular and macromolecular components will be discussed. Two topics will be presented: (i) tuneable command layers formed by stepwise assembling of siloxane oligomers and phthalocyanine dyes on indium tin oxide surfaces and (ii) command layers formed by self-assembly of porphyrin trimers. The potential use of these layers in sensor devices will also be mentioned.

Supramolecular command surfaces for liquid crystal alignment

AbstractDevices based on liquid crystal display technology, ranging from watches to flat panel displays, have proliferated over the past few decades and can now be found in all conceivable aspects of everyday life. It is surprising that a crucial part in the construction of such displays, namely the alignment layer, which dictates the surface alignment of mesogenic molecules, relies essentially on a mechanical rubbing process which was invented 100 years ago. In this paper, recent developments in the construction of alignment layers (also called command layers) based on the self‐assembly of molecular and macromolecular components are discussed. Two topics are highlighted: (i) tuneable layers formed by hierarchical assembly of siloxane oligomers and phthalocyanine dyes on indium‐tin‐oxide surfaces and (ii) command layers formed by self‐assembly of porphyrin trimers. Copyright © 2007 Society of Chemical Industry

Macroscopic Hierarchical Surface Patterning of Porphyrin Trimers via Self-Assembly and Dewetting

The use of bottom-up approaches to construct patterned surfaces for technological applications is appealing, but to date is applicable to only relatively small areas (approximately 10 square micrometers). We constructed highly periodic patterns at macroscopic length scales, in the range of square millimeters, by combining self-assembly of disk-like porphyrin dyes with physical dewetting phenomena. The patterns consisted of equidistant 5-nanometer-wide lines spaced 0.5 to 1 micrometers apart, forming single porphyrin stacks containing millions of molecules, and were formed spontaneously upon drop-casting a solution of the molecules onto a mica surface. On glass, thicker lines are formed, which can be used to align liquid crystals in large domains of square millimeter size.

Triply Fused ZnII–Porphyrin Oligomers: Synthesis, Properties, and Supramolecular Interactions with Single‐Walled Carbon Nanotubes (SWNTs)

The photophysical, electrochemical, and self-assembly properties of a novel triply fused Zn(II)-porphyrin trimer were investigated and compared to the properties of a triply fused porphyrin dimer and the analogous monomer. The trimer exhibited significantly red-shifted absorption bands relative to the corresponding monomer and dimer. Electrochemical investigations indicated a clear trend in redox properties amongst the three porphyrin structures, with the lowest oxidation potential and the lowest HOMO-LUMO gap exhibited by the triply fused trimer. This electrochemical behavior is attributed to the extensive pi-electron delocalization in the trimeric structure relative to the monomer and dimer. Additionally, it was found that the trimer forms extremely strong and nearly irreversible supramolecular interactions with single-walled carbon nanotubes (SWNTs), resulting in stable solutions of porphyrin-nanotube complexes in THF. Formation of these complexes required the addition of trifluoroacetic acid (TFA) to the solvent. This allowed the oligomers to make close contact with the nanotubes, enabling the formation of stable supramolecular assemblies. Atomic force microscopy (AFM) was used to observe the supramolecular porphyrin-nanotube complexes and revealed that the porphyrin trimer formed a uniform coating on the SWNTs. Height profiles indicated that nanotube bundles could be exfoliated into either individual tubes or very small bundles by exposure to the porphyrin trimer during sonication.

Accurate Length Control of Supramolecular Oligomerization: Vernier Assemblies

Linear oligomeric supramolecular assemblies of defined length have been generated using the Vernier principle. Two molecules, containing a different number (n and m) of mutually complementary binding sites, separated by the same distance, interact with each other to form an assembly of length (n x m). The assembly grows in the same way as simple supramolecular polymers, but at a molecular stop signal, when the binding sites come into register, the assembly terminates giving an oligomer of defined length. This strategy has been realized using tin and zinc porphyrin oligomers as the molecular building blocks. In the presence of isonicotinic acid, a zinc porphyrin trimer and a tin porphyrin dimer form a 3:4 triple stranded Vernier assembly six porphyrins long. The triple strand Vernier architecture introduced here adds an additional level of cooperativity, yielding a stability and selectivity that cannot be achieved via a simple Vernier approach. The assembly properties of the system were characterized using fluorescence titrations and size-exclusion chromatography (SEC). Assembly of the Vernier complex is efficient at micromolar concentrations in nonpolar solvents, and under more competitive conditions, a variety of fragmentation assemblies can be detected, allowing determination of the stability constants for this system and detailed speciation profiles to be constructed.

Construction of Multiporphyrin Arrays via Selective Cross-Metathesis

Selective cross-metathesis of type I and type II meso-functionalized porphyrin olefins afforded alkenyl-coupled dimeric and trimeric porphyrin systems in good yield with excellent E/Z selectivity. The synthetic utility of the method is demonstrated through the preparation of mixed metalated (M = 2H, Zn) porphyrin dimer and trimer. [reaction: see text]