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.     

Monodisperse Giant Porphyrin Arrays

Our synthetic attempts for the preparation oligo‐ and polyporphyrin arrays were reviewed in comparison with recent accomplishment in the related field. Especially, the synthesis and structural characteristics of huge monodisperse meso‐meso linked porphyrin arrays with multidimensional architectures were focused. The Ag^I‐promoted meso‐meso coupling reaction of 5,15‐diaryl and 5,10,15‐triaryl Zn^II‐porphyrins is advantageous in light of its high regioselectivity, as well as its easy extension to large porphyrin arrays. When applied to 1,4‐phenylene‐bridged linear porphyrin substrates, the coupling reaction gave three‐dimensionally arranged windmill‐shaped and grid‐shaped porphyrin arrays. The meso‐meso coupling doubling reaction was repeated up to the synthesis of a discrete 128‐mer. During these attempts, many porphyrin arrays were isolated in a discrete form by repetitive gel‐permeation chromatography and, interestingly, all the arrays exhibited high solubility in common organic solvents in spite of their giant molecular size. Furthermore, the Ag^I‐promoted coupling reaction was extended to the preparation of long polyporphyrinylenes under slightly modified conditions by either adding N,N‐dimethylacetamide (DMA) or heating slightly.     

Synthesis of Extremely π‐Extended Porphyrin Tapes from Hybrid meso‐meso Linked Porphyrin Arrays: An Approach Towards the Conjugation Length

Directly meso‐meso, β‐β, β‐β triply linked porphyrin arrays are exceptional π‐conjugated molecules exhibiting remarkably red‐shifted absorption bands extending deeply in the IR region. In order to determine the effective conjugated length (ECL), we embarked on the synthesis of the porphyrin tapes far beyond the 12‐mer, which is the longest we have prepared so far. In this study, to find the compromise between the feasibility of the meso‐meso coupling reaction up to longer arrays and the sufficient solubility and chemical stability of the resultant porphyrin tapes, we prepared hybrid meso‐meso linked porphyrin arrays BOn up to 24‐mer, which have two different aryl groups, a 2,4,6‐tris(3,5‐di‐tert‐butylphenoxy) phenyl group (Ar¹) and a 3,5‐dioctyloxy phenyl group (Ar²). All these arrays were effectively converted into the corresponding triply linked porphyrin tapes TBOn by oxidation with DDQ‐Sc(OTf)₃. Importantly, the low energy Q‐band‐like absorption bands of TBOn are progressively red‐shifted with an increase in the number of porphyrins n until 16 but the red‐shift is saturated at n=16, indicating the ECL of the porphyrin tape to be around 14–16. The regularly introduced meso‐aryl bulky substituents impose facial encumbrance, hence leading to the effective suppression of π–π interactions as well as improvement of the chemical stabilities of TBOn .     

β to β Terpyridylene-bridged porphyrin nanorings

β β to Terpyridine bridged cyclic porphyrin dimer, trimer, tetramer and pentamer were obtained through one-pot Suzuki-Miyaura crossing coupling reaction in good yields with template free. These porphyrin nanorings possess high fluorescence quantum yields and large extinction coefficients.     

Photochemistry of covalently-linked multi-porphyrinic systems

Synthesis, structural characteristics, and optical and electrochemical properties of various covalently-linked porphyrin arrays are described. First, aromatic-spacer bridged diporphyrins were prepared in which the diporphyrin geometries were conformationally-restricted and thus suitable for detailed studies on the exciton coupling and the intramolecular energy and/or electron transfer reactions. Secondly, the Ag(I)-salt oxidation of 5,15-diaryl Zn(II) porphyrins provided meso–meso-linked Zn(II)-diporphyrins. This reaction is advantageous in light of its high regioselectivity and easy extension to longer porphyrin arrays. The doubling reaction was repeated up to the synthesis of a discrete 128-mer, which is, to the best of our knowledge, the longest man-made molecule. Finally, the oxidation of meso–meso-linked Zn(II) porphyrin arrays with a combination of 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) and Sc(III)(OTf)₃ produced fused porphyrin arrays with full π-conjugation, which displayed extremely small HOMO–LUMO gaps that reach into the infrared region.     

meso–meso‐Linked Diarylamine‐Fused Porphyrin Dimers

A meso–meso‐linked diphenylamine‐fused porphyrin dimer and its methoxy‐substituted analogue were synthesized from a meso–meso‐linked porphyrin dimer by a reaction sequence involving Ir‐catalyzed β‐selective borylation, iodination, meso‐chlorination, and S_NAr reactions with diarylamines followed by electron‐transfer‐mediated intramolecular double C?H/C?I coupling. While these dimers commonly display characteristic split Soret bands and small oxidation potentials, they produced different products upon oxidation with tris(4‐bromophenyl)aminium hexachloroantimonate. Namely, the diphenylamine‐fused porphyrin dimer was converted into a dicationic closed‐shell quinonoidal dimer, while the methoxy‐substituted dimer gave a meso–meso, β‐β doubly linked porphyrin dimer.     

Chiroporphyrines froncées à distorsion adjustable

We have synthesized a series of chiroporphyrins in which the ester functions on adjacent meso substituents are linked by a bridle of adjustable length. The ruffled distortion induced by the α, β, α, β alternation of the porphyrin meso substituents can be controlled by the length of the bridles. X-ray structure determinations show that intermolecular constraints within the crystalline network can stabilize conformers that considerably differ from the mean conformation observed in solution by ¹H–NMR. To cite this article: S. Gazeau et al., C. R. Chimie 5 (2002) 27–31     

Excitonic Coupling Strength and Coherence Length in the Singlet and Triplet Excited States of meso–meso Directly Linked Zn(II)porphyrin Arrays

Excitation‐energy transport (EET) phenomena in meso–meso directly linked Zn(II )porphyrin arrays in the singlet and triplet excited states were investigated with a view to electronic coupling strength and coherence length by steady‐state and time‐resolved spectroscopic measurements. To investigate energy transfer in the triplet states, we modified the Zn(II )porphyrin arrays with bromo substituents at both ends. The coupling strength of the Soret bands of the arrays was estimated to be about 2200 cm^?1, and that of the Q bands is about 570 cm^?1. The coherence length in the S₁ state of the Zn(II )porphyrin arrays was determined to be 4–5 porphyrin units, which is comparable to that of the well‐ordered two‐dimensional circular structure B850 in the peripheral light‐harvesting antenna (LH2) in photosynthetic purple bacteria. This indicates that the Zn(II )porphyrin arrays are well suited for mimicking natural light‐harvesting antenna complexes. On the other hand, the rate of energy transfer in the triplet state is estimated to be on the order of 100 μs^?1, and the very weak coupling between the triplet states (ca. 0.003 cm^?1), indicates that the triplet excitation energy is essentially localized on a single porphyrin moiety.     

Oligoporphyrin Arrays Conjugated to [60]Fullerene: Preparation,NMR Analysis,and Photophysical and Electrochemical Properties

We report the synthesis and physical properties of novel fullerene–oligoporphyrin dyads. In these systems, the C‐spheres are singly linked to the terminal tetrapyrrolic macrocycles of rod‐like meso,meso‐linked or triply‐linked oligoporphyrin arrays. Monofullerene–mono(Zn^II porphyrin) conjugate 3 was synthesized to establish a general protocol for the preparation of the target molecules (Scheme 1). The synthesis of the meso,meso‐linked oligopophyrin–bisfullerene conjugates 4 – 6 , extending in size up to 4.1 nm ( 6 ), was accomplished by functionalization (iodination followed by Suzuki cross‐coupling) of the two free meso‐positions in oligomers 21 – 23 (Schemes 2 and 3). The attractive interactions between a fullerene and a Zn^II porphyrin chromophore in these dyads was quantified as ΔG=−3.3 kcal mol⁻¹ by variable‐temperature (VT) ¹H‐NMR spectroscopy (Table 1). As a result of this interaction, the C‐spheres adopt a close tangential orientation relative to the plane of the adjacent porphyrin nucleus, as was unambiguously established by ¹H‐ and ¹³C‐NMR (Figs. 9 and 10), and UV/VIS spectroscopy (Figs. 13–15). The synthesis of triply‐linked diporphyrin–bis[60]fullerene conjugate 8 was accomplished by Bingel cyclopropanation of bis‐malonate 45 with two C₆₀ molecules (Scheme 5). Contrary to the meso,meso‐linked systems 4 – 6 , only a weak chromophoric interaction was observed for 8 by UV/VIS spectroscopy (Fig. 16 and Table 2), and the ¹H‐NMR spectra did not provide any evidence for distinct orientational preferences of the C‐spheres. Comprehensive steady‐state and time‐resolved UV/VIS absorption and emission studies demonstrated that the photophysical properties of 8 differ completely from those of 4 – 6 and the many other known porphyrin–fullerene dyads: photoexcitation of the methano[60]fullerene moieties results in quantitative sensitization of the lowest singlet level of the porphyrin tape, which is low‐lying and very short lived. The meso,meso‐linked oligoporphyrins exhibit ¹O₂ sensitization capability, whereas the triply‐fused systems are unable to sensitize the formation of ¹O₂ because of the low energy content of their lowest excited states (Fig. 18). Electrochemical investigations (Table 3, and Figs. 19 and 20) revealed that all oligoporphyrin arrays, with or without appended methano[60]fullerene moieties, have an exceptional multicharge storage capacity due to the large number of electrons that can be reversibly exchanged. Some of the Zn^II porphyrins prepared in this study form infinite, one‐dimensional supramolecular networks in the solid state, in which the macrocycles interact with each other either through H‐bonding or metal ion coordination (Figs. 6 and 7).     

Synthesis and characterization of meso-ferrocenylethynyl 5,15-diphenylporphyrins

A series of four meso-ferrocenylethynyl (5,15-diphenylporphyrinato)nickel(II) derivatives have been synthesized by Sonogashira coupling reactions. Three of these compounds contain the electron-withdrawing groups including -CHO, -CHC(CN)₂, and -CCC₆H₄NO₂ at the remaining meso position, with a view to preparing push-pull chromophores, in which ferrocene serves as the electron donor. All the new compounds have been characterized spectroscopically and the molecular structure of one of these porphyrins (compound 11) has also been determined. The studies show that although the ferrocenylethynyl group can extend the π system of the central porphyrin core, the cyclopentadienyl rings of ferrocene are almost orthogonal to the porphyrin ring. This hinders ferrocene serving as a good electron donor in these systems.     

Synthesis of functionalized core-modified sapphyrins and covalently linked porphyrin–sapphyrin dyads

We adopted simple synthetic strategy to synthesize mono-functionalized thiasapphyrins containing functionalized aryl group in the meso-position at thiophene side. The thiasapphyrin building block containing iodophenyl functional group was coupled with three different porphyrin building blocks with N₄, N₃S and N₂S₂ cores containing meso-ethynylphenyl functional group under mild Pd(0) coupling conditions to synthesize three covalently linked diphenyl ethyne bridged porphyrin–thiasapphyrin dyads. The porphyrin–thiasapphyrin dyads were characterized by mass, NMR, absorption, electrochemical and fluorescence techniques. The NMR, absorption and electrochemical studies indicated that the two components in dyads interact weakly and retain their individual identities. The steady state fluorescence studies indicated that the porphyrin fluorescence is reduced to a significant extent because of energy and/or electron transfer to the thiasapphyrin unit. The protonation studies indicated that N₄ porphyrin unit is more basic, whereas N₃S and N₂S₂ porphyrin units are less basic compared to thiasapphyrin unit in respective dyads. We explored the potential of dyads as fluorescent anion sensors and showed that two out of three dyads can be used as fluorescent anion sensors.     

An efficient route to biscardanol derivatives and cardanol-based porphyrins via olefin metathesis

Ru-catalyzed olefin metathesis has been successfully applied to the synthesis of biscardanol derivatives and cardanol-based porphyrins. Using Hoveyda–Grubbs catalyst (C627), the reactions were performed with various cardanol derivatives (2, 5, 7, and 9) to make novel biscardanol derivatives. With the use of the second-generation Grubbs catalyst (C848) and Ti(OⁱPr)₄, the ring-closing metathesis of cardanol-based porphyrin 11 was carried out to afford cyclic cardanol-based porphyrin derivative 12.     

ABC–ABC-Type Directly meso–meso Linked Porphyrin Dimers

Covalently linked porphyrin oligomers are attractive because of their extended π-conjugated systems. Among various porphyrin oligomers, directly meso–meso linked porphyrin oligomers exhibit unique photophysical properties due to their strong exciton couplings derived from the alternative orthogonal geometry of the porphyrins. Although their structural and electronic properties can be greatly altered by substituents at meso positions, it is still difficult to introduce different substituents at the meso positions. Thus, it is a challenge to develop general synthetic methodologies for functional porphyrin dimers and oligomers with different substituents at the meso positions. Herein, a general synthetic strategy for ABC–ABC-type directly meso–meso linked porphyrin dimers by stepwise functionalization starting from 10,15,20-meso-free 5-substituted porphyrin as building block is established. A meso-ABC–ABC-type meso–meso-linked donor–π-acceptor-type porphyrin dimer was prepared and exhibited the highest power conversion efficiency (7.91 %) ever reported for dye-sensitized solar cells based on dimeric orthogonal donor–π-acceptor-type organic sensitizers. This synthetic strategy will provide useful guidance for the rational design of functional porphyrin dimers and oligomers for diverse applications.     

Synthesis of new azido porphyrins and their reactivity in copper(I)-catalyzed Huisgen 1,3-dipolar cycloaddition reaction with alkynes

We report herein the preparation of two novel porphyrins substituted with an azido group born either on the para-position of one phenyl meso-susbtituent of a tetraaryl zinc porphyrin (1) or directly on the meso-position of a trisaryl nickel porphyrin (2). We studied the scope and the limitation the Huisgen cycloaddition reaction of these two porphyrins using different catalytic conditions. We observed that the carbene (SIMes)CuBr in THF/H₂O 3:1 at 45 °C for 60 h gives almost quantitative yields for the reaction between 1 and different alkynes, but significantly lower yields with 2 probably due to its thermal instability.     

Synthesis and fluorescence properties of covalently linked homo- and hetero-porphyrin dyads containing meso-tolyl porphyrin and meso-furyl porphyrin sub-units

Three porphyrin building blocks with N₄, N₃S and N₂S₂ cores having three meso-furyl groups and one meso-iodophenyl group were synthesized and characterized. The porphyrin building blocks were used to synthesize six porphyrin dyads such as N₄-N₄, N₃S-N₃S, N₂S₂-N₂S₂, N₄-N₃S, N₄-N₂S₂ and N₃S-N₂S₂ containing meso-tolyl and meso-furyl porphyrin sub-units under mild Pd(0) mediated coupling conditions. Steady state fluorescence studies indicated an efficient energy transfer from the meso-tolyl porphyrin sub-unit to the meso-furyl porphyrin sub-unit in all six dyads. This study supported the argument that the meso-furyl porphyrins can be used as good energy acceptors when meso-aryl porphyrins act as energy donors in their metal free form.     

Synthesis and Aggregation Behavior of meso‐Sulfinylporphyrins: Evaluation of S‐Chirality Effects on the Self‐Organization to S–Oxo‐Tethered Cofacial Porphyrin Dimers

The synthesis and aggregation behavior of meso‐sulfinylporphyrins are described. The copper‐catalyzed C–S cross‐coupling reaction of a meso‐iodoporphyrin with benzenethiol and n‐octanethiol has proved to be an efficient method for the synthesis of meso‐sulfanylporphyrins, which are oxygenated by m‐chloroperbenzoic acid to produce the corresponding meso‐sulfinylporphyrins. Optically active zinc meso‐sulfinylporphyrins were successfully isolated by means of optical resolution of the racemates on a chiral HPLC column. Zinc sulfinylporphyrins readily undergo self‐organization through S–oxo–zinc coordination to form cofacial porphyrin dimers in solution, in which the hetero‐ and homodimers are present as a diastereomeric mixture. The aggregation modes of the S–oxo‐tethered porphyrin dimers were fully characterized by ¹H NMR, IR, and UV/Vis spectroscopy as well as DFT calculations on their model compounds, thus revealing that the self‐aggregation behavior depends on the combination of S chirality. The absolute configurations at the sulfur center can be determined by the exciton‐coupled CD method. The observed self‐association constant for the S–oxo‐tethered dimerization of (S)‐phenylsulfinylporphyrin in toluene is larger than that in dichloromethane, which reflects the difference in dipole moments between the homodimer and the monomer. In cyclic and differential pulse voltammetry, the first oxidation process of the cofacial dimers is split into two reversible steps, which indicates that the initially produced π radical cations are delocalized efficiently between the two porphyrin rings. The present findings demonstrate the potential utility of meso‐sulfinyl groups as promising ligands for investigating the effects of peripheral chirality on the structures and optical and electrochemical properties of metal‐assisted porphyrin self‐assemblies.     

Synthesis of oligo(p-phenylene)-linked dyads containing free base, zinc(II) or thallium(III) porphyrins for studies in artificial photosynthesis

A series of (p-phenylene)_n-linked meso-mesityl-substituted porphyrin dyads (n=2-4) was prepared via Suzuki coupling of zinc(II) and free base porphyrin building blocks. The resulting zinc(II)/free base porphyrin dyads were demetalated. The series of free base porphyrin dimers (n=1-4), four other porphyrin dimers (with p-phenylene, diphenylethyne or diphenylbutadiyne linkers; and aryl or tridec-7-yl meso substituents), and several benchmark monomers were converted to the thallium(III)chloride complexes under mild conditions. The collection of eight Tl(III)Cl/Tl(III)Cl dimers is designed for studies of ground-state hole-transfer processes and comparison with the excited-state energy- and hole-transfer processes of the corresponding Zn(II)/free base dyads. Altogether, 18 new porphyrin arrays and benchmark monomers have been prepared.     

Cationic porphyrins with inverted pyridinium groups and their fluorescence properties

One of the applications of cationic porphyrins is their use in microbial photodynamic inactivation (PDI). For this purpose there is a constant quest for new cationic photoactive derivatives. In this work, we synthesized and fully characterized a new porphyrin 3a and the corresponding cationic derivative 3b. The results presented here show that meso-tetrakis(pentafluorophenyl)porphyrin (TPPF₂₀, 1) can be used as scaffold to prepare different soluble compounds with interesting photophysical properties.     

First electrochemical evidence of existence of an oxomanganese(V) porphyrin intermediate in the reaction of manganese(III) porphyrin and hydrogen peroxide as a model of enzyme mimetics

We report in this study on the first electrochemical evidence of existence of an oxomanganese(V) porphyrin complex, formed upon the reaction of the manganese meso-tetrakis-(2,3,5,6-tetrafluoro-N,N,N-trimethyl-4-aniliniumyl) porphyrin (noted Mn(TF₄TMPA) with hydrogen peroxide in 50 mM borate buffer aqueous solution (pH 10.5) at 0 °C. The obtained results bring a clear insight into the previously reported and suggested formation of such an intermediate during the electroassisted reaction of manganese porphyrins or Schiff bases and molecular oxygen in various conditions, as enzyme mimetic.     

Reactivity of Nickel(II) Porphyrins in oCVD Processes—Polymerisation,Intramolecular Cyclisation and Chlorination

Oxidative chemical vapour deposition of (5,15-diphenylporphyrinato)nickel(II) (NiDPP) with iron(III) chloride as oxidant yielded a conjugated poly(metalloporphyrin) as a highly coloured thin film, which is potentially useful for optoelectronic applications. This study clarified the reactive sites of the porphyrin monomer NiDPP by HRMS, UV/Vis/NIR spectroscopy, cyclic voltammetry and EPR spectroscopy in combination with quantum chemical calculations. Unsubstituted meso positions are essential for successful polymerisation, as demonstrated by varying the porphyrin meso substituent pattern from di- to tri- and tetraphenyl substitution. DFT calculations support the proposed radical oxidative coupling mechanism and explain the regioselectivity of the C−C coupling processes. Depositing the conjugated polymer on glass slides and on thermoplastic transparent polyethylene naphthalate demonstrated the suitability of the porphyrin material for flexible optoelectronic devices.