Determination of trace silica in highly purified water based on delayed quenching of Rhodamine B through nanoparticle formation with molybdosilicate

The development of a highly sensitive analytical method for trace silica is an urgent necessity for the real-time monitoring of highly purified water used in the semiconductor industry. However, there are no reports of a simple yet sensitive method for the determination of trace silica. Here we describe the delayed quenching phenomenon of Rhodamine B cation caused by nanoparticle formation with molybdosilicate ions in aqueous solution and its application to the one-step determination of trace silica at ppt to low ppb levels. We found that the quenching takes place over several minutes and the quenching time is dependent on the concentration of silica. The measurements made by a dynamic light scattering particle size analyzer indicated that the diameter of the particles were at nanometer levels. The detection limit was found to be 34 ng dm(-3) Si (1.2 x 10(-9) mol dm(-3)). The average quenching time for 1 microg dm(-3) was 239 s with an RSD of 2.2% (n= 7). The proposed method has been successfully applied to distilled and highly purified water samples. There was good agreement between the results obtained by the proposed method and those by ICP-three dimensions quadrupole MS/MS with 11-fold evaporation concentration. The main point of this method is that in the trace determination of silica, the signal is larger at lower concentrations. The advantages of the proposed method are that it can be used as real-time monitoring for trace silica in highly purified water, and will be a great aid to industries in which the quality control of water is crucial.     

Enhancement and band distortion of the IR absorption spectra of a methanol on silver evaporated thin films in UHV-ATR configuration

Enhanced infrared absorption spectra of methanol adsorbed on evaporated silver films were measured using Kretschmanns ATR configuration. Whereas the enhanced spectra were recordable using p-polarized radiation alone when the metal film was continuous, it was obtainable using both the p-polarized and s-polarized radiations from island films. Band distortion was also measured for changing incident angle and metal thickness. Furthermore, when film with silver of intermediate thickness was used, great distortion of the absorption band was observed. The relation between the anomalous absorption by the silver film and the band distortion was indicated.     

Intermolecular Arrangement of Fullerene Acceptors Proximal to Semiconducting Polymers in Mixed Bulk Heterojunctions

Precise control of the molecular arrangements at the interface between the electron donor and acceptor in mixed bulk heterojunctions (BHJs) remains challenging, despite the correlation between structural characteristics and efficiency in organic photovoltaics (OPVs). This study reveals that the substitution patterns of linear and branched alkyl side chains on electron‐donating/‐accepting alternating copolymers can control the positions of an acceptor molecule (C₆₀) around the π‐conjugated main chains in mixed BHJs. Two‐dimensional solid‐state NMR demonstrates a marked difference in the location of C₆₀ in the blend films. A copolymer with an electron‐accepting unit positioned in close proximity to C₆₀ demonstrated higher OPV performance in combination with various fullerene derivatives. This molecular design offers precise control over the interfacial molecular structure, thereby paving the way for overcoming the current limitations of OPVs comprising mixed BHJs.     

Sigmatropic Rearrangements of Hypervalent‐Iodine‐Tethered Intermediates for the Synthesis of Biaryls

Metal‐free dehydrogenative couplings of aryliodanes with phenols to afford 2‐hydroxy‐2′‐iodobiaryls have been developed. This reaction proceeds through ligand exchange on the hypervalent iodine atom followed by a [3,3] sigmatropic rearrangement and with complete regioselectivity. This coupling, in combination with in situ oxidation by mCPBA, enables the convenient conversion of iodoarenes into desirable biaryls. The obtained biaryls have convertible iodo and hydroxy groups in close proximity, and are thus synthetically useful, as exemplified by the controlled syntheses of π‐extended furans and a substituted [5]helicene. DFT calculations clearly revealed that the rearrangement is sigmatropic, with C?C bond formation and I?O bond cleavage proceeding in a concerted manner. Acetic acid, which was found to be the best solvent for this protocol, renders the iodine atom more cationic and thus accelerates the sigmatropic rearrangement.     

Palladium‐Catalyzed Insertion of Isocyanides into the C−S Bonds of Heteroaryl Sulfides

Insertion of tert‐butyl isocyanide into the C(sp²)?S bonds of heteroaryl sulfides is catalyzed by a palladium diphosphine complex. Thioimidates generated through this reaction could be readily hydrolyzed under acidic conditions to yield the corresponding thioesters, which are of synthetic use. This insertion is useful because starting heteroaryl sulfides were readily prepared by either conventional ways or through sulfur‐specific extended Pummerer reactions.     

Undoped Layered Perovskite Oxynitride Li2LaTa2O6N for Photocatalytic CO2 Reduction with Visible Light

Oxynitrides are promising visible‐light‐responsive photocatalysts, but their structures are almost confined with three‐dimensional (3D) structures such as perovskites. A phase‐pure Li₂LaTa₂O₆N with a layered perovskite structure was successfully prepared by thermal ammonolysis of a lithium‐rich oxide precursor. Li₂LaTa₂O₆N exhibited high crystallinity and visible‐light absorption up to 500 nm. As opposed to well‐known 3D oxynitride perovskites, Li₂LaTa₂O₆N supported by a binuclear Ru^II complex was capable of stably and selectively converting CO₂ into formate under visible light (λ>400 nm). Transient absorption spectroscopy indicated that, as compared to 3D oxynitrides, Li₂LaTa₂O₆N possesses a lower density of mid‐gap states that work as recombination centers of photogenerated electron/hole pairs, but a higher density of reactive electrons, which is responsible for the higher photocatalytic performance of this layered oxynitride.     

Temperature‐Selective Dual Radical Generation from Alkyl Diiodide: Applications to Synthesis of Asymmetric CABC Multi‐Block Copolymers and Their Unique Assembly Structures

Temperature‐selective radical generation from a newly designed alkyl diiodide (I?R²?R¹?I) was studied. R¹?I and I?R² had different reactivities for generating alkyl radicals in the presence of a tetraoctylammonium iodide (ONI) catalyst. Taking advantage of the temperature selectivity, we used the alkyl diiodide as a dual initiator in ONI‐catalyzed living radical polymerization to uniquely synthesize CABC non‐symmetric multi‐block copolymers. Because of their non‐symmetric structure, CABC multi‐block copolymers form unique assemblies, that is, Janus‐type particles with hetero‐segment coronas and flower‐like particles with hetero‐segment petals.