Crystallinity of bulk polyacetylene

The fine structure of bulk trans-polyacetylene (PA) was investigated by x-ray diffraction. The degree of crystallinity 0.81, determined by Ruland's method, was significantly higher than the value for linear polyethylene. The disorder parameter k was 5, which is much larger than the value for polyethylene. These results led us to propose that PA crystals are more disordered than PE crystals owing to the higher rigidity of PA chains. Small-angle x-ray diffraction indicated that the crystal morphology is of the extended-chain type rather than lamellar. All results obtained in this work showed that the fine structure of PA bulk is such as to facilitate electrical conduction of bulk PA.     

Control of a photoreaction by electron spin resonance (II): The effect of radical pair lifetime on the control efficiency

The magnetic-field and the microwave effects on the photoreactions of anthraquinone-2-sulfonate and anthraquinone-2-carboxylic acid with xanthene were observed in an SDS micellar solution. The reaction products were analyzed by high performance liquid chromatography. With increasing the magnetic-field strength from the residual value to 400 mT, the yield of dixanthenyl, which is an “escape product”, increased considerably. Upon irradiating the system with a microwave (9400 MHz, 1.0 kW), however, the yield decreased almost to the minimum value at around 334 mT, where the intermediate radical pair becomes resonant with the microwave field. Therefore, we can detect the ESR spectrum of the transient radical pair by the product yield (product-yield-detected ESR or PYESR). In the present study, we observed a clear reversed microwave effect at the center of the PYESR spectrum, whose cause was attributed to “spin locking” of the radical pair by an intense microwave field. The microwave effects for the two systems were, different from each other in several respects including the extent of this spin locking effect in the product yield. The PYESR spectra were calculated by using a quantum mechanical method to discuss the relation between the microwave effect and the radical pair dynamics, the latter of which was also observed in the present study by the “pulse-PYESR” method.     

Effects of alcohols on the aqueous solubility of disperse dyes

Summary The solubility of azobenzene in water and aqueous alcohol solutions was determined at 5 °C intervals from 0° to 40 °C. Prom the results the thermodynamic parameters for the transfer of one mole of azobenzene from water to aqueous alcohol solution were calculated. It was found that the process was endothermic: furthermore, it was invariably accompanied by a positive unitary entropy change. The solubilizing mechanism of alcohols was explained in terms of an adduct-formation with the compound to be dissolved by means of hydrophobic interaction.     

Navier-Stokes equations and nonlinear heat equations in modulation spaces with negative derivative indices

The Cauchy problems for Navier-Stokes equations and nonlinear heat equations are studied in modulation spaces . Though the case of the derivative index s=0 has been treated in our previous work, the case s≠0 is also treated in this paper. Our aim is to reveal the conditions of s, q and σ of for the existence of local and global solutions for initial data .     

Unusual Attractive Au–π Interactions in Small Diacetylene‐Modified Gold Clusters

It is well known that alkynes act as π‐acids in the formation of complexes with metals. We found unprecedented attractive Au–π interactions in diacetylene‐modified [core+exo]‐type [Au₈]⁴⁺ clusters. The 4‐phenyl‐1,3‐butadiynyl‐modified cluster has unusually short Au–C_α distances in the crystal structure, revealing the presence of attractive interactions between the coordinating C≡C moieties and the neighboring bitetrahedral Au₆ core, which is further supported by IR and NMR spectra. Such weak interactions are not found in mono‐acetylene‐modified clusters, which indicates that they are specific for diacetylenic ligands. The attractive Au–π interactions are likely associated with the low energy of the π* orbital in the diacetylenic moieties, into which the valence electrons of the gold core may be back donated. The [Au₈]⁴⁺ clusters show clear red‐shifts of >10 nm with respect to the corresponding mono‐acetylenic clusters in UV/Vis absorption bands, which indicates substantial electronic perturbation effects of the Au–π interactions.     

Significant Difference in Semiconducting Properties of Isomeric All‐Acceptor Polymers Synthesized via Direct Arylation Polycondensation

The direct arylation polycondensation (DArP) appeared as an efficient method for producing semiconducting polymers but often requires acceptor monomers with orienting or activating groups for the reactive carbon‐hydrogen (C‐H) bonds, which limits the choice of acceptor units. In this study, we describe a DArP for producing high‐molecular‐weight all‐acceptor polymers composed of the acceptor monomers without any orienting or activating groups via a modified method using Pd/Cu co‐catalysts. We thus obtained two isomeric all‐acceptor polymers, P1 and P2, which have the same backbone and side‐chains but different positions of the nitrogen atoms in the thiazole units. This subtle change significantly influences their optoelectronic, molecular packing, and charge‐transport properties. P2 with a greater backbone torsion has favorable edge‐on orientations and a high electron mobility μ_e of 2.55 cm² V^?1 s^?1. Moreover, P2‐based transistors show an excellent shelf‐storage stability in air even after the storage for 1 month.