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International audience; The preparation of several covalently linked [6]-heliceneporphyrins is reported. A fused [6]-helicene-porphyrin p-extended aromatic system was isolated, the enantiomers separated and the chiroptical properties determined. The oxidative cyclodehydrogenation proved to be very effective for six-membered fused helical systems, but not suited for the formation of five-membered fused systems.

The syntheses of nickel(II)porphyrins bearing palladium(II) or platinum(II) complexes at their periphery were performed. These new compounds were characterized by standard spectroscopic techniques and studied by electrochemistry. The electrochemical data were then compared with previously published data of porphyrin dimers linked by metal ions like palladium(II) or platinum(II). An X-ray structure of one of these species was obtained and confirmed the structure of this series of compounds.

Polyoxometalates (POMs) can act as unique reservoirs for multiple electron transfers. As POMs display only weak absorption in the visible spectrum, they can be associated with chromophores such as porphyrins and porphyrin antennae. In this Minireview, the research dedicated to the combination of porphyrins and polyoxometalates is put in context and the state of the art identifying the challenges addressed in the optimization of hybrid materials for applications is detailed.

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The synthesis of porphyrin dimers linked by metal ions is described and the X-ray structure of two new dimers is presented. As previously shown for diamagnetic metal ions, strong electronic interactions between the individual subunits were observed. Antiferromagnetic coupling between copper(II)porphyrins linked by palladium(II) or copper(II) ions was studied by EPR and SQUID measurements. For the palladium(II)-linked dimer, the very small antiferromagnetic coupling was estimated by EPR measurements ([Formula: see text]

Porphyrins are conjugated, stable chromophores with a central core that binds a variety of metal ions and an easily functionalized peripheral framework. By combining the catalytic, electronic or cytotoxic properties of selected transition metal complexes with the binding and electronic properties of porphyrins, enhanced characteristics of the ensemble are generated. This review article focuses on porphyrins bearing one or more peripheral transition metal complexes and discusses their potential applications in catalysis or biomedicine. Modulation of the electronic properties and intramolecular communication through coordination bond linkages in bis-porphyrin scaffolds is also presented.

Porphyrin derivatives are highly relevant to biological processes such as light harvesting and charge separation. Their aromatic electronic structure and their accessible HOMO−LUMO gap render porphyrins highly attractive for the development of opto- and electro-active materials. Due to the often difficult covalent synthesis of multiporphyrins, self-assembly using metal complexation as the driving force can lead to well defined objects exhibiting a controlled morphology, which will be required to analyse and understand the electronic properties of porphyrin wires. This article presents two assembly approaches, namely by peripheral coordination or by binding to a metal ion in the porphyrin core, that are efficient and well designed for future developments requiring interactions with a surface.

The reactivity of porphyrin radical cationic species derived from octaethyl porphyrin (OEP) or meso-aryl porphyrins with nucleophiles, envisioned as an access route to elaborate porphyrin dimers, has been studied and optimized in the case of OEP. Standardized conditions have been applied to various spacers to show that the success of the reaction is mostly nucleophile dependent and that the method has little chances to yield non-linear bis-porphyrins.

Nanostructures were built at the solid/liquid interface by self-assembly and/or coordination bonds. Metalloporphyrins bearing two external coordination sites and long alkyl chains allowed the self-assembly of the compounds on highly oriented pyrolitic graphite. After addition of a metal ion, long transition-metal linked porphyrin nanoribbons were obtained and visualized by scanning tunneling microscopy. In these porphyrin ribbons electronic delocalization is possible through the d orbitals of the connecting metal ions.

The synthesis of new metalated diporphyrinylamines is described. The electronic ≪communication≫ through the amino function linking the two porphyrins was clearly demonstrated by electronic spectroscopy. In addition, intramolecular magnetic interactions were measured between two copper(II) ions located in the two linked porphyrins. Compared to the reported value ([Formula: see text] -2 K) for Osuka’s triply fused bis-copper(II) porphyrin dimer, a relatively high antiferromagnetic coupling constant was determined in our compound ([Formula: see text] = -11 K).

The synthesis of new porphyrins bearing external coordination sites and long alkyl chains is described. In particular, the possibility to use the Sonogashira coupling to introduce long alkynyl chains and the synthetic pathway to obtain these compounds is detailed. Two crystal structures of these new porphyrin derivatives were obtained. The synthesis of porphyrin dimers linked by a palladium(II) ion is also reported and some electronic consequences presented.

A bromonium oxidizing agent was used to produce a ring-oxidized zinc phthalocyanine (PcZn), [PcZn(solvent)]•2[BArF4]2 (1·solvent), in good yield. This material is dimeric in the solid state with one axially coordinated solvent [tetrahydrofuran (THF) or 1,2-dimethoxyethane (DME)] and close intradimer ring–ring distances of 3.18 and 3.136 A (THF and DME respectively); this proximity facilitates strong antiferromagnetic coupling to yield diamagnetic dimers. 1·THF is present in solution as a monomer and a dimer. In CH2Cl2, the dimer is favored above 0.1 mM, and it is almost exclusively present in solvents with a high dielectric constant such as acetonitrile. The material 1·THF/DME decomposes in DME to a meso-nitrogen-protonated species, [HPcZn(DME)2][BArF4] (2), which was isolated and represents the first example of such a structurally characterized, protonated, unsubstituted PcM complex. A partially oxidized dimer or “pimer” [(PcZn(DME))2]•[BArF4] (3) was also structurally characterized and has a intradimer ...

Several porphyrin dimers linked by metal ions were prepared. One trimeric compound was also isolated and one porphyrin dimer linked by palladium(II) could be structurally characterized. In solution, the size of the new compounds was estimated by DOSY NMR techniques. These compounds all contained long aliphatic chains (O-C12H25), which were used to assemble them at a highly oriented pyrolytic graphite (HOPG)/liquid interface. The highly ordered arrays were visualized by scanning tunneling microscopy (STM).

International audience; A dyad built up of a zinc(II) porphyrin and the corresponding free base, [Zn-Fb], fused to N-heterocyclic carbene (NHCs) ligands, respectively acting as singlet energy donor and acceptor, and a bridging trans-PdI2 unit, along with the corresponding [Zn-Zn] and [Fb-Fb] dimers were prepared and investigated by absorption and emission spectroscopy and density functional computations. Despite favorable structural and spectroscopic parameters, unexpectedly slow singlet energy transfer rates are measured in comparison with the predicted values by the Förster theory and those observed for other structurally related dyads. This observation is rationalized by the lack of large molecular orbital (MO) overlaps between the frontier MOs of the donor and acceptor, thus preventing a double electron exchange through the trans-PdI2 bridge, and by an electronic shielding induced by the presence of this same linker preventing the two chromophores to fully interact via their transition dipoles.

The synthesis of new diporphyrinylamines is described. In particular, the possibility to use the Buchwald or Ullmann amination reactions to obtain these compounds is detailed. Attempts to obtain symmetrical diporphyrinylamines linked by a tertiary amine are exposed and the obtention as side-product of an unexpected unsymmetrical porphyrin dimer with a meso–β linkage is described.

Photophysical and structural properties of a Cu(I) diimine complex with very strong steric hindrance, [Cu(I)(dppS)2](+) (dppS = 2,9-diphenyl-1,10-phenanthroline disulfonic acid disodium salt), are investigated by optical and X-ray transient absorption (OTA and XTA) spectroscopy. The bulky phenylsulfonic acid groups at 2,9 positions of phenanthroline ligands force the ground state and the metal-to-ligand charge-transfer (MLCT) excited state to adopt a flattened pseudo-tetrahedral coordination geometry in which the solvent access to the copper center is completely blocked. We analyzed the MLCT state dynamics and structures as well as those of the charge separated state resulting from the interfacial electron injection from the MLCT state to TiO2 nanoparticles (NPs). The OTA results show the absence of the sub-picosecond component previously assigned as the time constant for flattening, while the two observed time constants are assigned to a relatively slow intersystem crossing (ISC) rate (∼13.8 ps) and a decay rate (100 ns) of the [Cu(I)(dppS)2](+) MLCT state in water. These results correlate well with the XTA studies that resolved a flattened tetrahedral Cu(i) coordination geometry in the ground state. Probing the (3)MLCT state structure with XTA establishes that the (3)MLCT state has the same oxidation state as the copper center in [Cu(II)(dppS)2](2+) and the Cu-N distance is reduced by 0.06 Å compared to that of the ground state, accompanied by a rotation of phenyl rings located at 2,9 positions of phenanthroline. The structural dynamics of the photoinduced charge transfer process in the [Cu(I)(dppS)2](+)/TiO2 hybrid is also investigated, which suggests a more restricted environment for the complex upon binding to TiO2 NPs. Moreover, the Cu-N bond length of the oxidized state of [Cu(I)(dppS)2](+) after electron injection to TiO2 NPs shortens by 0.05 Å compared to that in the ground state. The interpretation of these observed structural changes associated with excited and charge separated states will be discussed. These results not only set an example for applying XTA in capturing the intermediate structure of metal complex/semiconductor NP hybrids but also provide guidance for designing efficient Cu(I) diimine complexes with optimized structures for application in solar-to-electricity conversion.

The preparation of porphyrins functionalized with one or two carbazoles (or phenoxazines) is described. The electron donors were introduced into one or two porphyrin meso positions by using the inexpensive Ullmann coupling procedure. Very good yields were obtained, and for two new compounds, the X-ray structures were solved. Preliminary electrochemical data coupled with electronic spectroscopy are also reported.

A weakly fluorescent Pt-bridged dyad composed of zinc(II) porphyrin (Zn; donor) and free base (Fb; acceptor) has been designed and exhibits an ultrafast singlet energy transfer between porphyrins. The use of larger atoms within the central linker significantly increases the MO coupling between the two chromophores and inherently the electronic communication.

We report the preparation of several new porphyrin homodimers bridged by a platinum(II) ion in which very intense electronic communication through the coordination link occurs. Moreover, the synthesis of a new porphyrin dyad and its photophysical properties are reported. This dyad exhibits the fastest singlet energy transfer ever reported for synthetic systems between a zinc(II) porphyrin and a porphyrin free base. This extremely fast transfer (∼100 femtoseconds) is in the same range as the fastest one measured in natural systems. This feature is due to the platinum(II) linker, which allows for strong MO couplings between the two porphyrin units as experimentally supported by electrochemistry and corroborated by DFT computations.

A new route to N-phenylquinolino[2,3,4-at]porphyrins is described and the electrochemical and photochemical properties of the synthesized derivatives were investigated. The electrochemical studies (cyclic voltammetry and rotating disk voltammetry) of the free-base and the corresponding Ni , Cu and Pd complexes have shown that the presence of the phenyl group is responsible for the formation of stable radical cations. The capacity of the N-phenylquinolino[2,3,4-at]porphyrins to generate singlet oxygen was evaluated and some of them have promising features as photosensitizers.

A highly symmetrical doubly fused porphyrin was obtained after two successive intramolecular cyclizations.1 The first supplementary ring was closed by using the Cadogan reaction, involving the generation of an intermediate nitrene from the starting nitro function. By trying to use the same methodology for the second ring closure, we found that the Cadogan reaction could be used but that cyclization yields remained low. We showed, by taking into account unusual mass spectroscopy results, that the cyclization of the nitro functionality with the neighboring meso-phenyl took place in the absence of the oxygen abstracting phosphite used by Cadogan. The bis-biquinolino-fused porphyrin, bearing an internal and an external coordination site, was obtained in very good yield and showed strong absorbance between 700 and 800 nm.

A doubly fused porphyrin has been synthesized by two successive cyclization reactions. The first meso-phenyl group was fused by an intramolecular Cadogan reaction leading to an enamine-functionalized porphyrin. After Vilsmeier–Haack formylation of the nickel enaminoporphyrin, an intramolecular Friedel–Crafts reaction followed by dehydration of the intermediate alcohol afforded the doubly fused aromatic nickel porphyrin, which could be demetalated. The free base and the copper and palladium porphyrins show extremely high absorbances in the 700–800 nm range. The palladium complex was a good catalyst for the oxidation of cholesterol with singlet oxygen, which makes this chromophore a potential candidate for photodynamic therapy.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

International audience; A symmetrical bis-nickelporphyrin was prepared in very good yield by oxidative coupling of a nickel(II) enaminoporphyrin. This dimer was obtained by the intermolecular reaction of the starting enamine (acting as nucleophile) with the porphyrin radical cation (acting as electrophile) generated in situ. Alternatively, by using different reaction conditions, an N-N linked porphyrin dimer was obtained in moderate yield. The monomeric extended porphyrin leading to the N-N linked dimer was obtained by the intramolecular reaction of the same radical cation with the neighbouring meso-aryl group (acting as nucleophile).

Friedel-Crafts acylation of nickel meso-tetraarylporphyrins with aryl anhydrides, followed by air oxidation in the presence of pyridine, DMAP, and excess anhydride, produced corroles in 8-21% yields. Other products include a porphyrinic ketone, an additional corrole whose bridge has been retained as an acyl group attached to a pyrrole, and a lactone resulting from the insertion of an oxygen atom into an alpha,beta-pyrrole bond. The ring contraction is best explained by a pinacolic rearrangement reminiscent of the one taking place in the formation of corrinoids, a benzoyloxy group replacing the acetic side chain found in the natural products.

Double-stranded dinuclear complexes with either twisted or parallel arrangements were obtained by reaction between Schiff-base ligands and PdII ions. Linear ligands mainly afforded twisted arrangements, while macrocyclic ligands forced the complex to adopt parallel arrangements. In these dinuclear complexes, one isomer could not be converted into the other even upon prolonged heating. The NMR spectra showed that the chemical shifts of the diastereotopic protons can be used as an indicator to distinguish between the arrangements. The NOE cross-peak characteristics of the complexes with twisted arrangements are interpreted with reference to the crystal structure of a CuII complex as an isostructural model of the PdII complex. Variable-temperature measurements revealed the rotational interference between the ligands of the counterpart strands, the first time that this has been observed for helically arranged complexes. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

Aryl groups bound to the meso positions of porphyrins often react with neighboring groups, in particular ß-acyl groups to give highly diversified monomeric and dimeric new functionalized porphyrins. The products, whose meso-aryl ring approaches coplanarity with the porphyrin macrocycle, show large shifts of UV-visible absorption bands and various potentialities for building external chelating moieties and assembling oligoporphyrins.

Ultrafast structural dynamics of the metal to ligand charge transfer (MLCT) states of two copper bis-phenanthroline complexes were captured by using x-ray transient absorption (XTA) spectroscopy at the Linac Coherent Light Source and further described by theoretical calculations. These complexes have the general formula [Cu(I)(R)_2]+, where R = 2,9-dimethyl-1,10-phenanthroline (dmp) and 2,9-diphenyl-1,10-phenanthroline disulfonic acid disodium salt (dpps). [Cu(I)(dmp)_2]+ has methyl groups at the 2,9 positions of phenanthroline (phen) and adopts a pseudo-tetrahedral geometry. In contrast, [Cu(I)(dpps)_2]+ possesses two bulky phenyl-sulfonate groups attached to each phen ligand that force the molecule to adopt a flattened tetrahedral geometry in the ground state. Previously, optical transient absorption (OTA) and synchrotron based XTA experiments with 100 ps time resolution have been employed to study the relationship between structural distortions and excited state relaxation pathways in the two complexes. However, the dynamics of the MLCT transition during the first few picoseconds after excitation in these complexes remained unclear because of limitations in element specificity in OTA and in the time resolution of synchrotron sources in XTA. In this experiment, the local coordination geometry and oxidation state of copper were probed with a temporal resolution of ~300 fs. Unexpectedly, the depletion of the Cu(I) signal due to the MLCT transition was found to be non-impulsive in the case of [Cu(I)(dpps)_2]+ with a time constant of 0.6 ps, while the Cu(I) depletion in [Cu(I)(dmp)_2]+ was instantaneous within the 300 fs instrument response time. The slower Cu(I) depletion kinetics in [Cu(I)(dpps)_2]+, previously unobserved in femtosecond OTA experiments, is likely due to intramolecular motions on the sub-picosecond time scale that could alter the localization of the transferred electron in the phen ligands.

The preparation of porphyrins functionalized with one or two carbazoles (or phenoxazines) is described. The electron donors were introduced into one or two porphyrin meso positions by using the inexpensive Ullmann coupling procedure. Very good yields were obtained, and for two new compounds, the X-ray structures were solved. Preliminary electrochemical data coupled with electronic spectroscopy are also reported.

The photooxidation of a meso-gem-disubstituted phlorin gave two isomeric biladienones in an equilibrium involving a Z-E double bond photoisomerism. The structures of these bile pigments were elucidated using NMR techniques and show terminal benzoyl and pyrrolone moieties. Complexation with divalent cations (nickel(II), copper (II)) gave stable compounds whose crystal and molecular structure could be determined by X-ray diffraction. The metal is coordinated with three pyrrole nitrogen atoms and one oxygen atom of a terminal benzoyl group. In the crystal, the molecules are arranged in pairs through hydrogen bonds between the free terminal pyrrolones.

Oxonaphtoporphyrins show a 1,4 reactivity involving the conjugated pyrrole double bond, the addition being followed by oxidation or elimination leading to rearomatization. Addition of nitrogen or carbon nucleophiles gives amino and substituted aminoporphyrins, or alkyl and cyanoporphyrins, respectively.

Using both directional hydrogen bonding and electrostatic interactions, the self assembly of diprotonated 1,2-Bis(2′-tetrahydropyrimidyl)ethane 1-2H+ with dihydrogenopyrophosphate in the solid state leads to infinite discreet sheets composed of 1-2H+ and dihydrogenopyrophosphate ribbons interconnected through H2P2O72 anions by hydrogen bonds.

This review focuses on synthetic strategies leading to extended porphyrins, but is limited to examples in which at least one β-pyrrolic carbon is linked to a meso-aryl substituent. Friedel–Crafts reactions are covered first because historically they were the first reactions employed to link β-pyrrolic carbons with meso-aryl groups, thus creating new six-membered fused rings. Other reactions inserting heteroatoms follow. Direct cyclizations between an ortho-carbon and a β-pyrrolic position are presented next. Finally, new highly extended chromophores are described. These compounds are generally obtained in two consecutive reactions. First a Suzuki coupling is used to introduce an aryl group in one or two meso positions. Then the new fused rings are generated by oxidative cyclizations.

The properties of the ground and excited states of several porphyrins appended with external chelates coordinated to ruthenium-bisbipyridine units are reported. The important modification of the absorption spectrum upon coordination with the ruthenium complex showed that a significant electronic communication between the two subunits was present in the ground state. Experimental results were compared with quantum chemistry calculations performed at density functional theory and time-dependent density functional theory level. The influence of the exchange-correlation functional on the quality of the computed absorption spectrum is shown, and the better behavior of hybrid functionals over long-range corrected ones was rationalized. The excited states topology analysis, performed using natural transition orbitals, gave a more evident confirmation of the communication between the subunits and showed that these new compounds can be promising as dyes in dye-sensitized solar cells.

Porphyrins bearing enaminoketones at their periphery have been used as ancillary ligands in ruthenium complexes. Free base, nickel and zinc porphyrins were successfully coordinated to Ru(bpy)(2)Cl(2) under microwave irradiation. The positive contribution of the ruthenium complex was demonstrated by the complexes' wide absorption domains that covered the 500-600 nm region where the parent porphyrins did not absorb. Electrochemical as well as computational data revealed an efficient electronic communication between the porphyrins and the ruthenium cation in the dyads.

International audience; This review focuses on synthetic strategies leading to extended porphyrins, but is limited to examples in which at least one b-pyrrolic carbon is linked to a meso-aryl substituent. Friedel-Crafts reactions are covered first because historically they were the first reactions employed to link b-pyrrolic carbons with meso-aryl groups, thus creating new six-membered fused rings. Other reactions inserting heteroatoms follow. Direct cyclizations between an ortho-carbon and a b-pyrrolic position are presented next. Finally, new highly extended chromophores are described. These compounds are generally obtained in two consecutive reactions. First a Suzuki coupling is used to introduce an aryl group in one or two mesopositions. Then the new fused rings are generated by oxidative cyclizations.

The synthesis of a series of cyclic analogues of the naturally occurring polyamines putrescine, spermidine and spermine was achieved. The cyclic analogues of putrescine named cycloputrescine [4,n] were composed of cycloputrescine in which the two primary amines were connected with a polymethylene chain of variable length (n = 3, 4, 5). Cyclospermidines [4,n] and Cyclospermines [4,n] were composed of a cycloputrescine [4,n] moiety mono- or di-functionalized with an aminopropyl chain respectively.

The synthesis of diazatetraoxacyclooctadecane derivatives bearing two catechol groups was achieved in good yield. The binucleating ligands were designed to bind both soft and hard cations simultaneously.

The synthesis of a macrocyclic compound composed of two 2,2′-bipyridines interconnected at the 4 and 4′ positions by two CH 2 SiCH 2  fragments was achieved and its structure was established in the solid state by X-ray crystallography.

A general synthetic strategy for the preparation of polyazamacrocycles containing long aliphatic chains is reported. These compounds are 22- or 24-membered hexaazamacrocycles incorporating two diethylenetriamine subunits (H2NCH2CH2NHCH2CH2NH2) linked together either by two CH2CH2OCH2CH2 (see 4–6), two tetramethylene (see 7), or two pentamethylene (see 8) fragments. Whereas for compound 4, one of the centrally located amine functionalities of the triamine subunit bears a hexadecyl chain, for compound 5, two of such chains are centrally attached to both subunits. In macrocycles 6–8, all six amino functionalities bear hexadecyl chains. Compounds 4–8 are potential candidates for the construction of selective chemical sensors such as specific electrodes for adenosine mono-, di-, and tri-phosphate. They may also be used for nucleoside polyphosphates extraction and/or transport.