Synthesis of zigzag- and fjord-edged nanographene with dual amplified spontaneous emission

We report the synthesis of a dibenzodinaphthocoronene (DBDNC) derivative as a novel nanographene with armchair, zigzag, and fjord edges, which was characterized by NMR and X-ray crystallography as well as infrared (IR) and Raman spectroscopies. Ultrafast transient absorption (TA) spectroscopy revealed the presence of stimulated emission signals at 655 nm and 710 nm with a relatively long lifetime, which resulted in dual amplified spontaneous emission (ASE) bands under ns-pulsed excitation, indicating the promise of DBNDC as a near-infrared (NIR) fluorophore for photonics. Our results provide new insight into the design of nanographene with intriguing optical properties by incorporating fjord edges.

Dibenzo[a,m]dinaphtho[ef,hi]coronene with zigzag and fjord edges was synthesized and characterized, demonstrating a nonplanar structure with near-infrared stimulated emission with a relatively long lifetime and dual-amplified spontaneous emission.     

X-ray study of molecular oxygen adsorbed on graphite

We have performed a detailed X-ray diffraction study of O₂ adsorbed on UCAR-ZYX and Le Carbon Lorraine vermicular exfoliated graphite between 15 and 50 K. At least four phases of physisorbed oxygen are found. The monolayer δ phase consists of a centered parallelogram lattice, with the molecular axes parallel to the graphite surface. The data are consistent with a triple point at 26 K. The melting transition at a coverage of one monolayer appears to be first order. At higher coverages the molecules undergo a lying-down to standing-up transition; the higher coverage ζ phase froms an approximately triangular lattice with the molecular axes perpendicular to the graphite surface. Satellite peaks around the (1, 0) Bragg peak indicate, however, that this cannot be a simple triangular lattice; possible explanations include successively incommensurate layers or a sinusoidal density modulation. For coverages in the two-layer region the ζ phase modulation peaks disappear at 37 K, and at 40 K the adsorbed oxygen appears to undergo a first order melting transition into a fluid phase. With increasing coverage, the 2D X-ray diffraction profiles and phase boundaries do not connect smoothly onto those of the 3D α and β phases. At low temperatures (T < 30 K) the ζ phase always coexists with bulk crystallites; for temperatures near the 2D melting transition the 3D peaks are not observable. These data, taken together with the heat capacity results, suggest a wetting transition with only the bilayer lamellar phase or bulk O₂ being stable at low temperatures.     

The magnetic field dependence of the low temperature (0.1K to 3K) residual specific heat of Pr<Subscript>2−<Emphasis Type="Italic">x</Emphasis></Subscript>Ce<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>CuO<Subscript>4−δ</Subscript>

Measurements are presented of the low temperature specific heat of three polycrystalline samples of Pr_2?x Ce _x CuO₄ in magnetic fields of 0, 2 and 4 Tesla. The residual specific heat contribution in zero field seems to have a form αT ⁿ (n<1) for all of the samples, whether superconducting or non-superconducting. The behaviour in magnetic fields is similar to that reported for other high Tc superconductors where a change in exponent of the residual term occurs at some crossover temperature in magnetic fields.     

Base-discriminating fluorescent (BDF) nucleoside: distinction of thymine by fluorescence quenching

A novel fluorescence BDF probe containing pyrene-labeled 7-deaza-2[prime or minute]-deoxyadenosine has been developed for the detection of thymine base on a target DNA.     

Synthesis and properties of a novel fluorescent nucleobase, naphthopyridopyrimidine

A new base-discriminating fluorescent nucleoside, NPP, that can sharply distinguish between A and G bases opposite NPP is described. The hybridization of an ODN probe containing NPP with a target DNA facilitates the judgment of the type of purine base located at a specific site on the target DNA.     

Ligand-protected gold/silver superatoms: current status and emerging trends

Monolayer-protected gold/silver clusters have attracted much interest as nano-scale building units for novel functional materials owing to their nonbulk-like structures and size-specific properties. They can be viewed as ligand-protected superatoms because their magic stabilities and fundamental properties are well explained in the framework of the jellium model. In the last decade, the number of ligand-protected superatoms with atomically-defined structures has been increasing rapidly thanks to the well-established synthesis and structural determination by X-ray crystallography. This perspective summarizes the current status and emerging trends in synthesis and characterization of superatoms. The topics related to synthesis include (1) development of targeted synthesis based on transformation, (2) enhancement of robustness and synthetic yield for practical applications, and (3) development of controlled fusion and assembly of well-defined superatoms to create new properties. New characterization approaches are also introduced such as (1) mass spectrometry and laser spectroscopies in the gas phase, (2) determination of static and dynamic structures, and (3) computational analysis by machine learning. Finally, future challenges and prospects are discussed for further promotion and development of materials science of superatoms.

This perspective summarizes the current status and emerging trends in synthesis and characterization of ligand-protected gold/silver superatoms.     

Preparation of micron-size monodisperse polymer particles by seeded polymerization utilizing the dynamic monomer swelling method

Utilizing a new type of monomer swelling method, 6.1 m-size monodisperse polymer particles were prepared by seeded polymerization. 1.8 m-size monodisperse polystyrene (PS) seed particles (1.8 m in size) were prepared by dispersion polymerization in ethanol-water (80/20, v/v) medium in the presence of poly(acrylic acid) as stabilizer with 2,2-azobisisobutyronitrile as initiator. The PS seed dispersion was mixed with ethanol-water (60/40, v/v) solution dissolving styrene (S) monomer, benzoyl peroxide as initiator, and poly(vinyl alcohol) as stabilizer. By slow, continuous, dropwise addition of water with a micro feeder into the mixture, the PS particles absorbed the many S monomers, which were separated from the medium and swelled from 1.8 m to 8.4 m while keeping the monodispersity high. We named this procedure the dynamic swelling method. Then, the seeded polymerization of the absorbed S monomer was carried out in the presence of NaNO₂ as water-solube inhibitor.Part CXXII of the series Studies on Suspension and Emulsion.     

One-pot preparation of subnanometer-sized gold clusters via reduction and stabilization by meso-2,3-dimercaptosuccinic acid

We report herein a simple method to prepare subnanometer-sized gold clusters by the reactions between hydrogen tetrachloroaurate (HAuCl4) and meso-2,3-dimercaptosuccinic acid (DMSA; HO2CCH(SH)CH(SH)CO2H) in water. It is demonstrated that DMSA molecules efficiently reduce the Au(III) species and stabilize the resultant gold clusters. The Au:DMSA clusters, which tend to aggregate into assemblages in water, can be well-isolated from each other by ion-pair formation between the carboxyl groups of DMSA and tetraoctylammonium (TOA) cations. This surface modification enables us to examine the core size distributions of the individual clusters by mass spectrometry and TEM. It is revealed that the gold clusters comprised of 10-13 atoms (ca. 0.8 nm) are the main products of the reactions.