Donor-Acceptor-Donor Dyads with Electron-Rich π-Extended Azahelicenes to Panchromatic Absorbing Dyes.

Panchromatic dyes have been highly useful in the realm of optical devices. Here, we report that panchromatic dyes with heterohelicenes have been successfully synthesized using a donor-acceptor strategy. Our synthesis resulted in the creation of π-extended aza[5]helicene oligomers with butadiyne linkages, which displayed bathochromically shifted absorption and emission spectra.

A Strategy for Polar Crystals with Dipolar Heterohelicenes.

Polar crystals have attracted interest for the applications to polar materials with piezo- and pyroelectricity, and second harmonic generation. Despite their potential utility for flexible polar materials, a strategy for ordering polar helicenes has remained elusive. Here, we demonstrate the creation of polar crystals with unsymmetrically substituted aza[5]helicenes tuned by substituents.

π-Conjugated Compounds for Molecular Materials.

Depth of a conjugated system! The chemistry of π-conjugated compounds is discussed by Guest Editors Satoru Hiroto and Jishan Wu in their Editorial for this special issue.

Synthesis of π-Functional Molecules through Oxidation of Aromatic Amines.

In this review, we focus on the synthesis of π-conjugated functional molecules by the oxidation of aromatic amines, which is one of the most effective methods for the construction of C-C, C-N, and N-N bonds between two π-conjugated molecular units, and consider their characteristics and applications. Polyanilines are the most common products of the oxidation of aromatic amines; however, azobenzenes, phenazines, and 1,1'-binaphthyl-2,2'-diamines may be produced in this manner also, depending on the reaction conditions. Recent advances in the methodology of aniline oxidation have led to the development of high-regioselectivity industrial-scale syntheses of optically or electroactive π-functional dyes containing nitrogen atoms.

Ni(II) 10-Phosphacorrole: A Porphyrin Analogue Containing Phosphorus at the Meso Position.

Ni(II) 10-Phosphacorrole, a porphyrinoid containing phosphorus at the meso position, was synthesized from a bis(α,α'-dibromodipyrrin) Ni(II) complex and a phosphine anion via the palladium-catalyzed formation of a C-C and two C-P bonds. The optoelectronic properties of Ni(II) 10-phosphacorrole can be modulated effectively by oxidation or coordination of a metal to the phosphorus center. While Ni(II) 10-phosphacorrole exhibits a distinctly aromatic character due to the cyclic conjugation of 18 π-electrons, its oxide exhibited weak antiaromaticity, which was confirmed experimentally and theoretically.

X-Shaped Cyclobutane-Linked Tetraporphyrins through a Thermal [2+2] Cycloaddition of Etheno-Fused Diporphyrins.

A nickel-mediated tandem double cyclization of ethynylene-linked dibromodiporphyrins afforded highly reactive etheno-fused diporphyrins, which undergo a thermal [2+2] cycloaddition at the fused C-C double bond to afford the cyclobutane moiety in X-shaped cyclobutane-linked tetraporphyrins. During the reaction of a Zn(II) complex precursor, the initial double cyclization product was converted into the diketodiporphyrin, which exhibits red chemiluminescence under ambient conditions.

Azabuckybowl-Based Molecular Tweezers as C and C Receptors.

We designed and synthesized molecular tweezers consisting of nitrogen-embedded buckybowl subunits. The judicious choice of the covalent linkers modulated their binding strength with C or C in solution. Titration studies by optical and H NMR analyses revealed a 1:1 composition of the resulting complexes.

Supramolecular assemblies of a nitrogen-embedded buckybowl dimer with C.

A directly connected azabuckybowl dimer was synthesized a palladium-catalysed C-H/C-Br coupling. The electron-donating nature of the pyrrolic nitrogen atoms of the azabuckybowl enabled a strong complexation with pristine C. In the presence of two equivalents of C, the azabuckybowl dimer formed crystals with a 1 : 2 stoichiometry.

Reversible σ-Bond Formation in Bowl-Shaped π-Radical Cations: The Effects of Curved and Planar Structures.

The reversible formation of σ-bonds between organic radicals has been widely investigated. However, reports on the formation of σ-dimers from delocalized π-radical cations are scarce. Herein, we report the reversible σ-dimerization behavior of a bowl-shaped π-radical cation generated from a nitrogen-embedded buckybowl, both in the crystalline state and in solution.

Acid-Mediated Migration of Bromide in an Antiaromatic Porphyrinoid: Preparation of Two Regioisomeric Ni(II) Bromonorcorroles.

The regioselective halogenation of porphyrinoids is critical for their selective functionalization, which enables the fine tuning of their electronic and optical properties. Here we report the synthesis of two regioisomeric Ni(II) bromonorcorroles on the basis of the acid-induced migration of the bromo substituent. Treatment of Ni(II) dimesitylnorcorrole with N-bromosuccinimide (NBS) selectively afforded Ni(II) 3-bromonorcorrole, which was further converted into Ni(II) 2-bromonorcorrole upon treatment with hydrogen bromide.

Shaping Antiaromatic π-Systems by Metalation: Synthesis of a Bowl-Shaped Antiaromatic Palladium Norcorrole.

The synthesis of a bowl-shaped antiaromatic molecule was achieved through the deformation of a planar antiaromatic porphyrinic π-conjugation system by insertion of palladium into the small cavity of a metal-free norcorrole. The bowl-to-bowl inversion dynamics of the antiaromatic Pd-coordinated norcorrole was determined by variable-temperature H NMR spectroscopy. The metal-free norcorrole was prepared from acid-induced demetalation of a copper norcorrole, which was obtained from the intramolecular coupling of a bis(diiododipyrrin) copper complex with copper thiophenecarboxylate.

π-Extended Dihydrophenazines with Three-State NIR Electrochromism Involving Large Conformational Changes.

π-Extended dihydrophenazines were successfully prepared by oxidation of 2-(N-arylamino)anthracenes. Their roof-type conformations were revealed by X-ray diffraction analysis, and the analysis of the optical properties indicated the presence of intramolecular charge-transfer processes. Upon chemical oxidation, the electronic absorption dramatically changed in a two-step fashion.

10-Silacorroles Exhibiting Near-Infrared Absorption and Emission.

10-Silacorroles were obtained from the Pd-catalyzed silylative cyclization of a bis(α,α'-dibromodipyrrin) Ni precursor with dihydrosilanes. These 10-silacorroles show substantially red-shifted absorption bands relative to those of normal porphyrins and isocorroles. Notably, the corresponding free base and Zn  10-silacorroles exhibit emissions in the NIR region.

Synthesis of bright red-emissive dicyanoetheno-bridged hexa-peri-hexabenzocoronene dimers.

The introduction of a dicyanomethyl anion group to hexa-peri-hexabenzocoronene (HBC) substantially enhanced the emission properties of HBC due to a large perturbation of its electronic structure. In addition, dicyanoetheno-bridged HBC dimers obtained from oxidation of a dicyanomethyl HBC anion exhibited bright red emission in solution and solid states. Intramolecular charge transfer interactions between the HBC units and the dicyanoethene bridge induced solvatochromic behaviour in their emission spectra.

Synthesis and Functionalization of Porphyrins through Organometallic Methodologies.

This review focuses on the postfunctionalization of porphyrins and related compounds through catalytic and stoichiometric organometallic methodologies. The employment of organometallic reactions has become common in porphyrin synthesis. Palladium-catalyzed cross-coupling reactions are now standard techniques for constructing carbon-carbon bonds in porphyrin synthesis.

Synthesis of Free-Base 10-Azacorroles.

A novel synthetic protocol has been developed for free-base 10-azacorroles. Ni(0)-mediated homocoupling of nitrogen-bridged bisdipyrrin Zn(II) complexes afforded a series of free-base 5,15-diaryl-10-azacorroles in good yields. Pd(II) and Cu(II) complexes have been prepared through metalation of free-base 10-azacorroles.

Control of Conformation and Chirality of Nonplanar π-Conjugated Diporphyrins Using Substituents and Axial Ligands.

Nonplanar conformations of pyrazine-fused Zn(II) diporphyrins could be controlled by the choice of the meso-aryl substituents and an axial ligand on the central metals. Zn(II) diporphyrins bearing sterically demanding meso-aryl groups with ortho-substituents led to a twisted chiral D2 conformation, while an achiral C2h form was preferred in the case of aryl groups without ortho-substituents. Helical chirality induction on Zn(II) diporphyrins in the twisted conformation was achieved by controlling their handedness of the molecular twist through coordination of optically active 1-phenethylamine.

The synthesis of Ni(II) and Al(III) 10-azacorroles through coordination-induced cyclisation involving 1,2-migration.

We have synthesized Ni(II) and Al(III) 10-azacorroles through coordination-induced cyclisation of nitrogen-bridged bisdipyrrins. Al(III) 10-azacorrole displayed contrasting optoelectronic behaviours from Ni(II) 10-azacorrole, underlining the different electronic effects of the azacorrole ligand from the porphyrin.

Nitrogen-embedded buckybowl and its assembly with C60.

Curved π-conjugated molecules have attracted considerable interest because of the unique properties originating from their curved π surface. However, the synthesis of such distorted molecules requires harsh conditions, which hamper easy access to heteroatom-containing curved π systems. Here we report the synthesis of a π-extended azacorannulene with nitrogen in its centre.

Regioselective Nucleophilic Functionalization of Antiaromatic Nickel(II) Norcorroles.

Treatment of antiaromatic nickel(II) norcorrole with potassium cyanide provided nickel(II) 3-cyanonorcorrole with perfect regioselectivity without the help of a catalyst. The reaction of the nickel(II) norcorrole with phenol or thiophenol in the presence of a base also yielded substitution products. The antiaromatic 16π conjugation system in the norcorrole core was preserved in the functionalized products.

Isolation of a 1,4-diketone intermediate in oxidative dimerization of 2-hydroxyanthracene and its conversion to oxahelicene.

Oxidation of 2-hydroxy-9,10-dialkynylanthracenes resulted in highly regioselective dimerization to furnish metastable dearomatized 1,4-diketones rather than stable aromatic diols. The 1,4-diketones were converted to oxahelicenes, which exhibited strong fluorescence both in solution and solid state as well as chiroptical properties.

Synthesis of highly twisted and fully π-conjugated porphyrinic oligomers.

Highly twisted π-conjugated molecules have been attractive but challenging targets. We report here an efficient synthesis of highly twisted diporphyrins with 126° and 136° twist angles that involves an oxidative fusion reaction of planar aminoporphyrin precursors at room temperature. Repeated amination-oxidative fusion sequences provide a unidirectionally twisted tetramer.

Synthesis of diazo-bridged BODIPY dimer and tetramer by oxidative coupling of β-amino-substituted BODIPYs.

A diazo-bridged BODIPY dimer and tetramer were prepared by the oxidative coupling reaction of β-amino-substituted BODIPYs. The structure of the dimer was elucidated by X-ray diffraction analysis, showing its coplanar orientation of two BODIPY units. Effective extension of π-conjugation was confirmed by optical and electrochemical investigations.

Silylethynyl substituents as porphyrin protecting groups for solubilization and selectivity control.

Silylethynyl substituents are proposed as protecting groups for porphyrin derivatives to enhance their solubility and enable regioselective functionalization. After usage as protecting groups, silylethynyl groups at the meso-positions can be efficiently removed upon heating with aqueous H2SO4 in the presence of a surfactant. This approach was applied to the preparation of unsymmetrically β-substituted porphyrins and porphin-porphyrin oligomers, which were inaccessible by conventional methods.

Near-IR absorbing nickel(II) porphyrinoids prepared by regioselective insertion of silylenes into antiaromatic nickel(II) norcorrole.

The treatment of an antiaromatic norcorrole Ni(II) complex with a kinetically stabilized silylene provided ring-expansion products in excellent yields through the highly regio- and stereoselective insertion into the β-β pyrrolic CC bonds. The resultant Ni(II) porphyrinoid monoinsertion product exhibited relatively strong near-IR absorption bands due to the small HOMO-LUMO gap in spite of the disrupted cyclic π-conjugation by the silicon atom.