Switching in molecular shapes: main chain length driven rod-circle transition of isolated helical polysilanes

Unique conformations such as rod, semicircle, and circle structures of isolated semi-flexible helical polysilanes were observed by atomic force microscopy (AFM); the chain topology was significantly related to the chain length (molecular weight) on the surfaces.     

The dimension of attractor of the 2D g-Navier-Stokes equations

The g-Navier-Stokes equations in spatial dimension 2 were introduced by Roh as

     

Suppression of Edge Localized Modes in High-Confinement KSTAR Plasmas by Nonaxisymmetric Magnetic Perturbations

Edge localized modes (ELMs) in high-confinement mode plasmas were completely suppressed in KSTAR by applying n=1 nonaxisymmetric magnetic perturbations. Initially, the ELMs were intensified with a reduction of frequency, but completely suppressed later. The electron density had an initial 10% decrease followed by a gradual increase as ELMs were suppressed. Interesting phenomena such as a saturated evolution of edge T_{e} and broadband changes of magnetic fluctuations were observed, suggesting the change of edge transport by the applied magnetic perturbations.     

A New Photoluminescent Conjugated Poly(1‐hexyl‐3,4‐dimethyl‐2,5‐pyrrolylene): Synthesis,Properties and Characterization

Oxidative coupling reaction of 1‐hexyl–3,4‐dimethylpyrrole affords a conjugated conducting poly(1‐hexyl‐3,4‐dimethyl‐2,5‐pyrrolylene) (PHDP), which is completely soluble in common organic solvents. The luminescence of PHDP is comparable to that of poly(N‐vinylcarbazole) (PVK), which has been widely used in electroluminescence devices. The quantum efficiency of PHDP is 2.5 times higher than that of PVK. A rationalization is presented relating the conductivity of PHDP to its polymer structure.     

Photoisomerization and Emission Properties of trans‐ and cis‐Poly(dimethylsilylenephenylenevinylene)s

The photoirradiation of trans‐ and cis‐poly(dimethylsilylenephenylenevinylene)s gave cis‐rich mixtures at equilibrium states. The degree of the photoisomerization could be exactly evaluated by comparing the UV spectra of the photoirradiated solutions with those of the trans and cis polymers. The geometric configuration of the trans and cis polymers was thermally stable and hardly changed even though they were heated. The trans and cis polymers exhibited different emission properties; e.g., trans polymer: λ_max = 400 nm, quantum yield = 3.4×10^–3; cis polymer: λ_max = 380 nm, quantum yield = 1.5×10^–3.     

High-Performance Near-Infrared Chlorinated Rylenecarboximide Fluorophores via Consecutive C−N and C−C Bond Formation

A new class of near-infrared (NIR) fluorophores, PAI , is obtained by consecutive C−N/C−C bond formation between diphenylamines and 9,10-dibromoperylenecarboximide. Owing to the rigid structure, extended π-conjugation and pronounced push-pull substitution, these fluorophores show emission maxima up to 804 nm and large Stokes shifts. The extraordinarily high fluorescence quantum yields from 47 % to 70 % are attributed to chloro substitution in the bay positions of the perylene core. These characteristics, together with high photostability, qualify them as useful NIR emitters for applications as biomarkers and security inks.     

Benzotrithiophene-based Covalent Organic Framework Photocatalysts with Controlled Conjugation of Building Blocks for Charge Stabilization

Covalent organic frameworks have recently shown high potential for photocatalytic hydrogen production. However, their structure-property-activity relationship has not been sufficiently explored to identify a research direction for structural design. Herein, we report the design and synthesis of four benzotrithiophene (BTT)-based covalent organic frameworks (COFs) with different conjugations of building units, and their photocatalytic activity for hydrogen production. All four BTT-COFs had slipped parallel stacking patterns with high crystallinity and specific surface areas. The change in the degree of conjugation was found to rationally tune the rate of photocatalytic hydrogen evolution. Based on the experimental and calculation results, the tunable photocatalytic performance could be mainly attributed to the electron affinity and charge trapping of the electron accepting units. This study provides important insights for designing covalent organic frameworks for efficient photocatalysts.