Two-step access to bis-meso-perfluoroalkyl-corroles towards meso-perfluoroacyl-ABC-corroles.

A solventless and acid-catalyzed condensation of meso-perfluoroalkyl-dipyrromethanes with selected benzaldehydes was used to prepare ten different bilanes that were isolated before their oxidation into trans-A2B-corroles bearing two meso-perfluoroalkyl groups. Macrocycles bearing long chains (C3F7 or C7F15) are key precursors to afford ABC-corroles having a meso-acyl substituent when subjected to a mild and basic hydrolysis affecting one of the alkyl substituents.

Deciphering Electronic and Structural Effects in Copper Corrole/Graphene Hybrids.

Non-covalent hybrid materials based on graphene and A3 -type copper corrole complexes were computationally investigated. The corroles complexes contain strong electron-withdrawing fluorinated substituents at the meso positions. Our results show that the non-innocent character of corrole moiety modulates the structural, electronic, and magnetic properties once the hybrid systems are held. The graphene-corrole hybrids displayed outstanding stability via the interplay of dispersion and electrostatic driving forces, while graphene act as an electron reservoir. The hybrid structures exposed an intriguing magneto-chemical performance, compared to the isolated counterparts, that evidenced how structural and electronic effects contributed to the magnetic response for both ferromagnetic and antiferromagnetic cases. Directional spin polarization and spin transfer from the corrole to the graphene surface participate in the amplification. Finally, there are relations between the spin transfer, the magnetic response, and the copper distorted ligand field, offering exciting hints about modulating the magnetic response. Therefore, this work shows that copper corroles emerged as versatile building blocks for graphene hybrid materials, especially in applications requiring a magnetic response.

Breaking Azacalix[4]arenes into Induline Derivatives.

Tetraamino-tetranitro-azacalixarene 5 is at the crossroad of two different families of compounds depending on the conditions and the agent used to reduce the NO2 groups: (1) azacalixphyrin 7 in neutral medium, or (2) phenazinium of type 8 in acidic medium. The key role of the N-substituted amino functions at the periphery is highlighted by investigating octaaminoazacalixarene as a model compound, and by using the corresponding tetrahydroxy-tetranitro-azacalixarene 15 as a precursor, which behaves differently.

Synthesis and Electron Accepting Properties of Two Di(benz[f]indenone)-Fused Tetraazaanthracene Isomers.

We designed and synthesized a novel di(benz[f]indenone)-fused tetraazaanthracene derivative and isolated its two isomers, 1a and 1s, having anti and syn configurations, respectively. Their structure and that of the condensation reaction intermediates, anti-2a and syn-2s, were fully characterized using one- and two-dimensional nuclear magnetic resonance spectroscopy and single-crystal X-ray diffraction. The optical and electronic properties of 1a and 1s were investigated using ultraviolet-visible absorption and fluorescence spectroscopies, cyclic voltammetry, and time-dependent density functional theory calculations. The presence of the carbonyl and ethynyltris(isopropyl)silane groups endows the di(benzoindenone)-fused azaacene derivatives with a strong electron accepting character. With an electron affinity of approximately -3.7 eV, the two isomers represent attractive electron-deficient molecular systems for the generation of n-channel semiconducting materials. Organic field effect transistors of 1a and 1s showed electron transport, and organic solar cells gave a proof of concept of the potential of the two compounds as electron acceptor materials when they are paired with an electron donor polymer.

Switching from Single to Simultaneous Free-Radical and Anionic Polymerization with Enamine-Based Organic Electron Donors.

Although most monomers can polymerize through different propagation pathways, polymerization-initiating systems that can switch from one mode to another are rare. In this study, we demonstrate that enamine-based organic electron donors (OEDs) constitute the first systems able to initiate either free-radical or anionic polymerization under simple, mild, and safe conditions. While direct electron-transfer reduction of monomers by OEDs results in the initiation of anionic chain-growth polymerization, introduction of a competing oxidant with a higher reduction potential than the monomer switches the former anionic propagation to a clean radical-propagation process. The benefit of this dual-mode activator is highlighted in the synthesis of an interpenetrating polymer network through simultaneous initiation of radical and anionic propagation processes.

Exciton Interactions, Excimer Formation, and [2π+2π] Photodimerization in Nonconjugated Curcuminoid-BF2 Dimers.

We describe the synthesis of a series of covalently linked dimers of quadrupolar curcuminoid-BF2 dyes and the detailed investigation of their solvent-dependent spectroscopic and photophysical properties. In solvents of low polarity, intramolecular folding induces the formation of aggregated chromophores, the UV/Vis absorption spectra of which display the optical signature characteristic of weakly-coupled H-aggregates. The extent of folding and, in turn, of ground-state aggregation is strongly dependent on the nature of the flexible linker. Steady-state and time-resolved fluorescence emission spectroscopies show that the Frenkel exciton relaxes into a fluorescent symmetrical excimer state with a long lifetime. Furthermore, our in-depth studies show that a weakly emitting excimer lies on the pathway toward a photocyclomer. Two-dimensional 1 H NMR spectroscopy and density functional theory (DFT) allowed the structure of the photoproduct to be established. To our knowledge, this represents the first example of a [2π+2π] photodimerization of the curcuminoid chromophore.

Azacalixquinarenes: From Canonical to (Poly-)Zwitterionic Macrocycles.

Azacalixquinarenes, a new family of macrocycles composed of diaminobenzoquinone diimine units linked by dinitrobenzene rings, are synthesized by selective oxidation of the parent azacalixarenes. Crystallographic analyses of two compounds demonstrated the presence of canonical (uncharged) and zwitterionic quinones within a single structure. The electron-withdrawing nature of the dinitrobenzene moieties can trigger the intramolecular H-transfer that generates zwitterionic ground-state quinones. The nature of the N-substituents and the polarity of the solvent have a crucial impact on the equilibrium between the canonical and zwitterionic forms that present distinct optical and electrochemical properties. Thus, within [4]- and [6]-membered macrocycles, poly-zwitterionic structures can be reached, as demonstrated experimentally and theoretically using first-principle approaches.

Hetero-Bimetallic Effect as a Route to Access Multinuclear Complexes.

We report the synthesis of a key mononuclear intermediate complex based on a quinoid ligand and its further metalation to afford the corresponding hetero-bimetallic compound that revealed unique properties. An unprecedented hetero-bimetallic effect in coordination chemistry could be indeed observed and exploited to prepare, through selective ligand exchange, a tetranuclear complex (Pd-Ni-Ni-Pd) absorbing light up to the far-red region. Most importantly, we describe here to the best of our knowledge the first use of bischelating ligand for ligand exchange, and this approach can be considered as a new route for incorporating planar units to access multi-heteronuclear complexes. The origin of this specific ligand exchange as well as of the nature of the electronic excited states of the relevant structures were investigated by first-principle calculations.

1,3-Alternate Tetraamido-Azacalix[4]arenes as Selective Anion Receptors.

Six tetraaza[1.1.1.1]cyclophane derivatives bearing peripheral amide groups were prepared according to two distinct synthetic strategies that depend on the connection pattern between the aryl units. NMR experiments combined with the X-ray structures of two tetraamide derivatives 4 b and 10 show that these cavitands adopt a 1,3-alternate conformation both in solution and in the solid state. Consequently, the four amide groups of the aza[1.1.1.1]-m,m,m,m-cyclophane isomer 10 can contribute to the same recognition process towards neutral water molecules or anion guests. NMR experiments, mass spectrometry analyses and single-crystal X-ray structures confirm the anion-binding ability of this receptor. Absorption spectrophotometric titrations in nonpolar solvents provided evidence for the selectivity of 10 to chloride anions in the halide series, with a corresponding association constant Ka reaching 2.5 × 10(6) m(-1).

N-Substituted Azacalixphyrins: Synthesis, Properties, and Self-Assembly.

Pre- and postintroduction of substituents with respect to the macrocyclization step leads to previously unknown N-substituted azacalixphyrins. The stepwise synthetic approach has been studied in detail to highlight the key role of the N-substituents of the precursors and/or intermediates in terms of reactivity. Based on a combined experimental and theoretical investigation, the relationship between the properties of the macrocycles and their degree of substitution is rationalized. Depending on the nature of the N-substituents, the formation of supramolecular ribbon-like structures could also be observed, as demonstrated by combined TEM, SEM, AFM, and FTIR experiments.

Polymerization Initiated by Organic Electron Donors.

Polymerization reactions with organic electron donors (OED) as initiators are presented herein. The metal-free polymerization of various activated alkene and cyclic ester monomers was performed in short reaction times, under mild conditions, with small amounts of organic reducing agents, and without the need for co-initiators or activation by photochemical, electrochemical, or other methods. Hence, OED initiators enabled the development of an efficient, rapid, room-temperature process that meets the technical standards expected for industrial processes, such as energy savings, cost-effectiveness and safety. Mechanistic investigations support an electron-transfer initiation pathway that leads to the reduction of the monomer.

meso-Ester Corroles.

The introduction of ester groups on the 5- and 15-meso positions of corroles stabilizes them against oxidation and induces a redshift of their absorption and emission spectra. These effects are studied through the photophysical and electrochemical characterization of up to 16 different 5,15-diester corroles, in which the third meso position is free or occupied by an aryl group, a long alkyl chain, or an ester moiety. Single-crystal X-ray structure analysis of five 5,15-diestercorroles and DFT and time-dependent DFT calculations show that the strong electron-withdrawing character of the 5,15 ester substituents is reinforced by their π overlap with the macrocyclic aromatic system. The crystal packing of corroles 2, 4, 6, 9, and 15 features short distances between chromophores that are stacked into columns thanks to the low steric hindrance of meso-ester groups. This close packing is partially due to intermolecular interactions that involve inner hydrogen and nitrogen atoms, and thereby, stabilize a single, identical corrole tautomeric form.

An efficient synthesis of porphyrins with different meso substituents that avoids scrambling in aqueous media.

We have developed new conditions that afford regioisomerically pure trans-A2B2-, A3B-, and trans-AB2C-porphyrins bearing aryl and arylethynyl substituents. The porphyrins were prepared by the acid-catalyzed condensation of dipyrromethanes with aldehydes followed by oxidation with p-chloranil or 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ). Optimal conditions for the condensation were identified after examining various reaction parameters such as solvent composition, acid concentration, and reaction time. The conditions identified (for aromatic aldehydes: EtOH/H2O 4:1, [DPM] = 4 mM, [aldehyde] = 4 mM, [HCl] = 38 mM, 16 h; for arylethynyl aldehydes: THF/H2O 2:1, [DPM] = 13 mM, [aldehyde] = 13 mM, [HCl] = 150 mM, 3 h) resulted in the formation of porphyrins in yields of 9-38% without detectable scrambling. This synthesis is compatible with diverse functionalities such as ester or nitrile. In total, 20 new trans-A2B2-, A3B-, and trans-AB2C-porphyrins were prepared. The scope and limitations of the two sets of reaction conditions have been explored. The methodological advantage of this approach is its straightforward access to building blocks and the formation of the porphyrin core in higher yields than by any other methodology and by using environmentally benign and nonhazardous chemicals.

Post-functionalization of triamino-phenazinium dyes to reach near-infrared emission.

This study presents the synthesis and characterization of phenazinium dyes with absorption ranging from red to far-red, as well as emission extending into the far-red to near-infrared (NIR) region. The procedure involves the post-functionalization of a triamino-phenazinium that was recently reported as a theranostic agent. The introduction of electron-withdrawing moieties is accomplished through acylation or aromatic nucleophilic substitution. For one of the obtained products, a further substitution step could be achieved with primary amines to tune the electron density of the phenazinium core. The isolated dyes exhibit promising features that hold potential for future applications as biological markers or therapeutic agents.

A Strategy to Design Substituted Tetraamino-Phenazine Dyes and Access to an NIR-Absorbing Benzoquinonediimine-Fused Quinoxaline.

The straightforward access to N- or C-substituted dinitro-tetraamino-phenazines (P1-P5) is enabled in oxidative conditions via formation of two intermolecular C-N bonds from accessible 5-nitrobenzene-1,2,4-triamine precursors. The photophysical studies revealed green absorbing and orange-red emitting dyes, with enhanced fluorescence in the solid state. Further reduction of the nitro functions led to the isolation of a benzoquinonediimine-fused quinoxaline (P6), which undergoes diprotonation to form a dicationic coupled trimethine dye absorbing beyond 800 nm.

Anisotropic organization and microscopic manipulation of self-assembling synthetic porphyrin microrods that mimic chlorosomes: bacterial light-harvesting systems.

Being able to control in time and space the positioning, orientation, movement, and sense of rotation of nano- to microscale objects is currently an active research area in nanoscience, having diverse nanotechnological applications. In this paper, we demonstrate unprecedented control and maneuvering of rod-shaped or tubular nanostructures with high aspect ratios which are formed by self-assembling synthetic porphyrins. The self-assembly algorithm, encoded by appended chemical-recognition groups on the periphery of these porphyrins, is the same as the one operating for chlorosomal bacteriochlorophylls (BChl's). Chlorosomes, rod-shaped organelles with relatively long-range molecular order, are the most efficient naturally occurring light-harvesting systems. They are used by green photosynthetic bacteria to trap visible and infrared light of minute intensities even at great depths, e.g., 100 m below water surface or in volcanic vents in the absence of solar radiation. In contrast to most other natural light-harvesting systems, the chlorosomal antennae are devoid of a protein scaffold to orient the BChl's; thus, they are an attractive goal for mimicry by synthetic chemists, who are able to engineer more robust chromophores to self-assemble. Functional devices with environmentally friendly chromophores-which should be able to act as photosensitizers within hybrid solar cells, leading to high photon-to-current conversion efficiencies even under low illumination conditions-have yet to be fabricated. The orderly manner in which the BChl's and their synthetic counterparts self-assemble imparts strong diamagnetic and optical anisotropies and flow/shear characteristics to their nanostructured assemblies, allowing them to be manipulated by electrical, magnetic, or tribomechanical forces.

Allosteric effects in binuclear homo- and heterometallic triple-stranded lanthanide podates.

This work illustrates a simple approach for deciphering and exploiting the various free energy contributions to the global complexation process leading to the binuclear triple-stranded podates [Ln(2)(L9)](6+) (Ln is a trivalent lanthanide). Despite the larger microscopic affinities exhibited by the binding sites for small Ln(3+), the stability constants measured for [Ln(2)(L9)](6+) decrease along the lanthanide series; a phenomenon which can be ascribed to the severe enthalpic penalty accompanying the intramolecular cyclization around small Ln(III), combined with increasing anticooperative allosteric interligand interactions. Altogether, the microscopic thermodynamic characteristics predict ß(1,1,1)(La,Lu,L9)/ß(1,1,1)(Lu,La,L9) = 145 for the ratio of the formation constants of the target heterobimetallic [LaLu(L9)](6+) and [LuLa(L9)](6+) microspecies, a value in line with the quantitative preparation (>90%) of [LaLu(L9)](6+) at millimolar concentrations. Preliminary NMR titrations indeed confirm the rare thermodynamic programming of a pure heterometallic f-f' complex.

Stabilization of a 12-π electrons diamino-benzoquinonediimine tautomer.

The first example of diamino-benzoquinonediimine bearing both electron-donating and electron-withdrawing groups on the same 6-π electron subunit was synthesized using a straightforward one pot strategy. Photophysical analysis and theoretical calculations demonstrate that this unique substitution pattern is efficient to favour the establishment of a single tautomeric structure in solution.

Effect of the electron donating group on the excited-state electronic nature and epsilon-near-zero properties of curcuminoid-borondifluoride dyes.

Epsilon-near-zero (ENZ) properties have been reported in organic molecular films. In particular, cyanine and squaraine films have been shown to exhibit ENZ properties in the visible spectral region with a strong 3rd order nonlinear optical response near the ENZ spectral region. Noting both cyanine and squaraine belong to the polymethine family, a series of six curcuminoid borondifluoride (Curc) derivatives were developed to examine whether such a polymethine character is positively correlated with the ENZ property of the organic films. Those Curc derivatives possess a Donor-Acceptor-Donor (D-A-D) architecture with acceptor, AcacBF2, located at the molecular center. The backbone of Curc is designed such that the donor strength can be tuned to transit between charge transfer (CT) and polymethine character. This balance between CT and polymethine character of the Curc series is examined based on the Lippert-Mataga plot. As donor strength in the D-A-D structure increases, CT character is less marked resulting in a more dominant polymethine character. The structural and optical properties of the Curc films with a thickness in the order of 30 nm were examined to correlate the polymethine character with the ENZ response. The results obtained in isotropic Curc thin films demonstrate that an increase of polymethine character associated with a stronger donor strength leads to an appearance/enhancement of the ENZ property in the visible spectrum range from 500 to 670 nm. Overall, this study provides useful guidelines to engineer new organic materials showing ENZ properties in a desired spectral range.

Fused bis-azacalixphyrin that reaches NIR-II absorptions.

The fusion of two azacalixphyrin cycles absorbing in the NIR-I domain moves the absorption properties beyond 1000 nm, towards the second biological transparency window (NIR-II). This new type of NIR-II dye was synthesised through the intermediate preparation of a rare example of bis-tetra-azacalix[4]arene where the two macrocycles share a common aromatic unit.