Protic Processes in an Extended Pyrazinacene: The Case of Dihydrotetradecaazaheptacene.

Pyrazinacenes are linearly fused heteroaromatic rings, with N atoms replacing all apical CH moieties. Component rings may exist in a reduced state, having NH groups instead of N, causing cross-conjugation. These compounds have interesting optical and electronic properties, including strong fluorescence in the near-infrared region and photocatalytic properties, leading to diverse possible applications in bio-imaging and organic synthesis, as well as obvious molecular electronic uses.

Regio- and Stereoselective α-Allylation with Enolates Prepared from N-C Axially Chiral Thiolactam and Lactam.

The reaction of allyl bromide derivatives with the enolate prepared from enantioenriched N-C axially chiral -(2,5-di--butylphenyl)-3,4-dihydroquinolin-2-one (lactam) and -thione (thiolactam) proceeded in a completely regio- and stereoselective manner to afford S2 and S2'-like products, respectively. Furthermore, through the conversion of thiolactam to lactam, the regiodivergent and stereoselective synthesis of N-C axially chiral lactams bearing a chiral tertiary α-carbon was achieved.

Catalytic Enantioselective Synthesis of N-C Axially Chiral -(2,6-Disubstituted-phenyl)sulfonamides through Chiral Pd-Catalyzed -Allylation.

Recently, catalytic enantioselective syntheses of N-C axially chiral compounds have been reported by many groups. Most N-C axially chiral compounds prepared through a catalytic asymmetric reaction possess carboxamide or nitrogen-containing aromatic heterocycle skeletons. On the other hand, although N-C axially chiral sulfonamide derivatives are known, their catalytic enantioselective synthesis is relatively underexplored.

The Pyrazinacenes.

Pyrazinacenes are a class of nitrogen-containing heteroacene molecules composed of linearly fused pyrazine units, which might also include dihydropyrazine groups leading to different reduced states of the compounds. While they are structurally similar to hydrocarbon acenes (e.g.

Pyrazinacenes exhibit on-surface oxidation-state-dependent conformational and self-assembly behaviours.

Acenes and azaacenes lie at the core of molecular materials' applications due to their important optical and electronic features. A critical aspect is provided by their heteroatom multiplicity, which can strongly affect their properties. Here we report pyrazinacenes containing the dihydro-decaazapentacene and dihydro-octaazatetracene chromophores and compare their properties/functions as a model case at an oxidizing metal substrate.

Amphiprotism-Coupled Near-Infrared Emission in Extended Pyrazinacenes Containing Seven Linearly Fused Pyrazine Units.

Peripherally substituted tetradecaazaheptacene (NHp) compounds, exhibiting amphiprotism-coupled emission, have been synthesized. X-ray crystallography reveals a planar acene-like chromophore, and electronic absorption and emission occur in the near-infrared biological transparency window (650-900 nm). The compounds exhibit long-wavelength emission with photoluminescence quantum yields Φ up to ∼0.

Design of Low Pt Concentration Electrocatalyst Surfaces with High Oxygen Reduction Reaction Activity Promoted by Formation of a Heterogeneous Interface between Pt and CeO(x) Nanowire.

Pt-CeO(x) nanowire (NW)/C electrocatalysts for the improvement of oxygen reduction reaction (ORR) activity on Pt were prepared by a combined process involving precipitation and coimpregnation. A low, 5 wt % Pt-loaded CeO(x) NW/C electrocatalyst, pretreated by an optimized electrochemical conditioning process, exhibited high ORR activity over a commercially available 20 wt % Pt/C electrocatalyst although the ORR activity observed for a 5 wt % Pt-loaded CeO(x) nanoparticle (NP)/C was similar to that of 20 wt % Pt/C. To investigate the role of a CeO(x) NW promotor on the enhancement of ORR activity on Pt, the Pt-CeO(x) NW interface was characterized by using hard X-ray photoelectron spectroscopy (HXPS), transmission electron microscopy (TEM), and electron energy loss spectroscopy (EELS).

Alkyl imidazolium ionic-liquid-mediated formation of gold particle superstructures.

The development of new methodologies for controlling the organization of quantum materials in multiple dimensions is crucial to the advancement of device fabrication. By using a self-assembly route using selected imidazolium ionic liquids bearing long alkyl chains (C(n)Imida, n = 8, 10, 12) as ligands, we have achieved a tunable assembly of quantum-sized gold nanoparticles. The initial stabilizer of the gold nanoparticles was partially or wholly substituted depending on the concentration and alkyl chain length.

Antioxidant-substituted tetrapyrazinoporphyrazine as a fluorescent sensor for basic anions.

Tetrapyrazinoporphyrazine substituted at its periphery with eight antioxidant 3,5-di-t-butyl-4-hydroxyphenyl groups behaves as a turn-on fluorescent sensor for fluoride anions. Conversely, the precursor antioxidant-substituted 1,2-phthalonitrile was found to act in turn-off mode suggesting that the origin of the phenomenon lies at the phenolate-substituted 1,4-pyrazinyl moiety.

Crystallographic phase induced electro-optic properties of nanorod blend nematic liquid crystal.

Ultrasmall ZnS or PbS nanorods encapsulated in fluid-like soft organic surfactants show excellent miscibility in the nematic liquid crystal (LC ZLI-4792) host resulting in a novel soft matter type blend with enhanced electro-optic properties. The ultranarrow ZnS rods are of wurtzite phase and possess a chemical bipolarity and a net dipole moment. The centrosymmetric ultranarrow PbS rods possess a finite size and shape dependent inherent dipole moment despite their cubic rock-salt structure.

Reversible photoredox switching of porphyrin-bridged bis-2,6-di-tert-butylphenols.

Porphyrin derivatives bearing 2,6-di-tert-butylphenol substituents at their 5,15-positions undergo reversible photoredox switching between porphyrin and porphodimethene states as revealed by UV-vis spectroscopy, fluorescence spectroscopy, and X-ray single-crystal analyses. Photoredox interconversion is accompanied by substantial variations in electronic absorption and fluorescence emission spectra and a change of conformation of the tetrapyrrole macrocycle from planar to roof-shaped. Oxidation proceeds only under photoillumination of a dianionic state prepared through deprotonation using fluoride anions.

Putting the 'N' in ACENE: pyrazinacenes and their structural relatives.

Acenes have emerged as an important class of organic electronic material. Related heteroatom-substituted compounds, or heteroacenes, introduce an important means for modulating properties and improving materials' stability. In this perspective, we will review the historical origins of the heteroacenes and discuss recent progress in the field of acene and related compounds containing fused 1,4-diazabenzene units, i.

Nanoarchitectonics: a conceptual paradigm for design and synthesis of dimension-controlled functional nanomaterials.

Nanomaterials have been prepared over a wide range of length scales from nanoscopic objects to bulk structural materials. Recent investigations have been focused on the regulation and control of nanoscopic structures for the modulation of the properties of even macroscopic objects. As an emerging concept, nanoarchitectonics has been proposed as a technology system to be used for arranging nanoscale structural units--i.

Self-assembled pyrazinacene nanotubes.

Nanotubes of a pentacene derivative, 6,13-bis(1-n-dodecyl)-[a,c,l,n]-tetrabenzo-5,6,7,12,13,14-hexaazapentacene, have been prepared by a hierarchical self-assembly mechanism. The oligoazaacenes 1-3, referred to as pyrazinacenes due to their structures of linearly fused pyrazine heterocycles, can also be considered as two azatriphenylenes fused through a reduced pyrazine ring. Dissolution of 6,13-bis(1-n-dodecyl)-[a,c,l,n]-tetrabenzo-5,6,7,12,13,14-hexaaza pentacene in nearly boiling toluene followed by standing of the solution at room temperature yields self-assembled (sa) pyrazinacene (Pa) nanotubes (NT's), or sa-PaNTs.

Tautomers of extended reduced pyrazinacenes: a density-functional-theory based study.

We present a structural and electronic inspection of reduced pyrazinacenes within the DFT framework. Our analysis provides a clear indication that compounds in which reduced pyrazine rings are well separated from each other are rather stable. Conversely, if the reduced pyrazine rings approach each other or cluster together, the compounds become increasingly unstable.

Tautomerism in Reduced Pyrazinacenes.

Monoprotic and diprotic NH tautomerism in reduced oligoazaacenes, the pyrazinacenes, was studied by using first principles simulations. Stepwise reductions in the metadynamics-sampled free energy profile were observed during consecutive monoprotic tautomerizations, with energy barriers gradually reducing with increasing proton separation during monoprotic processes. This is accompanied by an increasing contribution from the quinoidal electronic structure, as evidenced by the computed highest occupied molecular orbital (HOMO) structure.

Intelligent chiral sensing based on supramolecular and interfacial concepts.

Of the known intelligently-operating systems, the majority can undoubtedly be classed as being of biological origin. One of the notable differences between biological and artificial systems is the important fact that biological materials consist mostly of chiral molecules. While most biochemical processes routinely discriminate chiral molecules, differentiation between chiral molecules in artificial systems is currently one of the challenging subjects in the field of molecular recognition.

Pyrazinacenes: aza analogues of acenes.

A series of edge-sharing condensed oligopyrazine analogues of acenes, the pyrazinacenes, were synthesized and characterized. X-ray crystallographic determinations revealed intermolecular interactions that affect the propensity of the molecules to undergo pi-pi stacking. Increasing heteroatom substitution of the acene framework induces shorter intermolecular pi-pi stacking distances (shorter than for graphite) probably due to lower van der Waals radius of nitrogen atoms.

Self-assembly of optical molecules with supramolecular concepts.

Fabrication of nano-sized objects is one of the most important issues in nanoscience and nanotechnology. Soft nanomaterials with flexible properties have been given much attention and can be obtained through bottom-up processing from functional molecules, where self-assembly based on supramolecular chemistry and designed assembly have become crucial processes and techniques. Among the various functional molecules, dyes have become important materials in certain areas of nanotechnology and their self-assembling behaviors have been actively researched.

Diverse self-assembly in soluble oligoazaacenes: a microscopy study.

The synthesis and morphologies of self-assembled aggregates of novel oligoazapentacene 2 and oligoazaheptacene 3 derivatives are reported. Double nucleophilic substitution on 2,3-dicyano-[h,j]-dibenzo-1,4,5,10-tetrazaanthracene 4 gives the corresponding dihydro-oligoacene derivatives, which were then N-alkylated using n-dodecyl bromide to yield self-assembling acene molecules. 2 and 3 self-assemble in solution, leading to a variety of aggregated structures including rolled-up sheets, foams, and fibrous structures reminiscent of organogels.

Stokes parameter studies of spontaneous emission from chiral nematic liquid crystals as a one-dimensional photonic stopband crystal: experiment and theory.

The helical structure of uniformly aligned chiral nematic liquid crystals results in a photonic stopband for only one sense of circular polarization. The spectroscopic Stokes polarimeter is used to analyze spontaneous emission in the stopband. Highly polarized photoluminescence is found and the polarization properties vary with the excitation wavelength.

Stokes-parameter analysis of the polarization of light transmitted through a chiral nematic liquid-crystal cell.

A spectroscopic Stokes polarimeter is used to directly measure the linearly, circularly, and randomly polarized components of light obtained on transmission of unpolarized light through thick chiral nematic liquid-crystal cells in the stop band. The Stokes parameters are simulated to fit the experimental data by use of the Berreman 4 x 4 transfer matrix by means of the Jones and Stokes vectors and taking into account multiple reflections at the interfaces of the cell. Excellent agreement is obtained.

Optical amplification in a first-generation dendritic organic semiconductor.

We report a study of a new class of organic semiconductor as an optical gain medium. We demonstrate amplification of violet light by use of stimulated emission in a solution of a first-generation bis-fluorene-cored semiconducting dendrimer. Amplification is also observed in the solid state by means of amplified spontaneous emission in an optically pumped dendrimer planar waveguide.