Oscillating frequency of piezoelectric quartz crystal in solutions

Oscillating frequencies of a piezoelectric crystal were measured in various solutions. One side of the crystal surface was coated with a silicon sealant. This coating was useful for measuring the oscillation of crystals in solutions for a wide range of products of density (?) and viscosity (η) and in electrolyte solutions. For measurement in solutions, the frequency change depended on the circuit used, whereas for measurements in air the circuit did not influence the frequency change. All experimental data showed that the frequency change from pure water, ΔF_w, followed ΔF_w = ? K(√?η ? √?_wη_w) except for electrolyte and polymer solutions, where K is a proportionality constant, η_w the density of pure water and η_w the viscosity of water.     

Fixed charge density effective to membrane phenomena

Summary Mobilities and activity coefficients of small ions in membranes were determined experimentally for collodion based polystyrene sulfonic acid membrane in aqueous KCl solution in a wide range of concentrations. The activity coefficients were measured by analyzing the amounts of co- and counter-ions taken into the membranes, while the mobilities were determined by a proper combination of the membrane potential and ion permeability data in conjunction with the analytical data of small ions in the membranes. It was found that the mobility of the coions was not very different from that in bulk solution in the range of KCl concentrations studied, while the mobility of counterions decreased very much in comparison with that in bulk solution. The concentration dependence of the product of mobilities of positive and negative ions in the membrane was the same as that of activity coefficients of small ions in the membrane. The depressions of mobility and activity coefficient of the counterions in the membrane were represented by the similar formulas as that in the polyelectrolyte solutions, i.e. the empirical additivity rule held formally, although the effective charge density of the membrane or fraction of counterions not bounded in the vicinity of fixed charges of the membrane skeleton was found to be dependent upon the salt concentration of the external solution when the concentration was lower than the stoichiometric density of charges fixed in the membrane.

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Zusammenfassung Beweglichkeiten und Aktivitätskoeffizienten kleiner Ionen in Membranen wurden experimentell für auf der Basis Polystyrene-Polystyrolsulfosäure hergestellte kolloide Membranen in wäßriger KCl-Lösungineinem weiten Bereich der Konzentrationen bestimmt. Die Aktivitätskoeffizienten wurden durch analytische Bestimmung der Beträge von Ko- und Gegenionen, die in den Membranen enthalten waren, gemessen, während die Beweglichkeiten durch geeignete Kombinationen von Daten des Membranpotentials und der Ionenpermeabilität in Verbindung mit analytischen Daten kleiner Ionen in den Membranen vermittelt wurden. Es wurde gefunden, daß die Beweglichkeit des Ko-Ions nicht sehr verschieden von derjenigen der reinen Lösung im Bereich der untersuchten KCl-Konzentrationen ist, während die Mobilität des Gegenions sehr stark im Vergleich zu der in der reinen Lösung abnahm. Die Konzentrationsabhängigkeit des Produktes von Beweglichkeiten positiver und negativer Ionen in Membranen war dieselbe wie die der Aktivitätskoeffizienten kleiner Ionen in den Membranen. Die Herabsetzung der Beweglichkeit und des Aktivitätskoeffizienten des Gegenions in der Membran werden durch ähnliche Formeln dargestellt wie die in Polyelektrolyt-Lösungen. Zum Beispiel gilt formal die empirisch Additivitätsregel, obgleich die effektive Ladungsdichte in der Membran der Nachbarschaft der fixierten Ladungen am Membranskelett als abhängig von der Salzkonzentration in der äußeren Lösung gefunden wurde, wenn die Konzentration geringer war als die stöchiometrische Dichte der fixierten Ladung an der Membran.

     

Multicolor photochromism of two- and three-component diarylethene crystals

Novel photochromic single crystals composed of three different kinds of diarylethenes, 1,2-bis(3,5-dimethyl-2-thienyl)perfluorocyclopentene (1a), 1,2-bis(2,5-dimethyl-3-thienyl)perfluorocyclopentene (2a), and 1,2-bis(2-methyl-5-p-methoxyphenyl-3-thienyl)perfluorocyclopentene (3a), have been prepared. The three-component crystals turned yellow, orange, red, purple, blue, green, or black upon irradiation with light of appropriate wavelengths. The colors of the crystals were thermally stable in the dark and completely bleached by irradiation with visible light. Such multicolored photochromic crystals have potential for the application to optoelectronic devices, such as multifrequency three-dimensional optical memory media or full-color displays.     

Limits of detection and selectivity coefficients of liquid membrane electrodes

An equation has been derived theoretically describing the emf of a liquid membrane electrode: E = E(0) - (RT/F) ln[(C + radicalC (2) + A (x))/2]. Experimental data are in good agreement with this equation. The parameter A(x) is related to the limit of detection. When the ion-exchanger dissociates completely in the membrane phase, A(x) is given by 4sigma(2)/b(x). Here sigma represents the concentration of the ion-exchanger in the liquid membrane and b(x) is a quantity related to the ion-selectivity.     

Crystal engineering of photochromic diarylethene single crystals

Photochromic performance of diarylethene single crystals was controlled by crystal engineering using non-covalent aromatic-aromatic interactions as the directional intermolecular force. A diarylethene derivative with two pentafluorophenyl groups, 1,2-bis(2-methyl-5-pentafluorophenyl-3-thienyl)perfluorocyclopentene (1a), formed stoichiometric co-crystals with benzene (Bz) and naphthalene (Np) by aryl-perfluoroaryl interactions. Face-to-face pi-stacking interactions between the pentafluorophenyl groups of 1a and the aromatic molecules are responsible for 2:1 and 1:1 stoichiometric compositions in 1a/Bz and 1a/Np co-crystals, respectively. The diarylethene underwent thermally stable and photoreversible photochromic reactions in a homo-crystal of 1a and co-crystals 1a/Bz and 1a/Np. The absorption spectra of the photogenerated closed-ring isomers varied depending on the conformation of the diarylethene molecules packed in the crystals. The diarylethene 1a also formed 1:1 stoichiometric co-crystals with different kinds of diarylethenes, 1,2-bis(2-ethyl-5-phenyl-3-thienyl)perfluorocyclopentene (2a) and 1,2-bis[2-methyl-5-(1-naphthyl)-3-thienyl]perfluorocyclopentene (3a). Both co-crystals 1a/2a and 1a/3a showed photochromism. Although 1a, 2a, and 3a underwent efficient photocyclization reactions in their homo-crystals, highly selective photocyclization reactions of 2a or 3a were observed in the co-crystals. The selective reactions were confirmed by HPLC and X-ray crystallography. Excited energy transfers from 1a to 2a and from 1a to 3a are considered to occur and cause the selective reactions.     

Geometrical Evolution and Formation of the Photoproduct in the Cycloreversion Reaction of a Diarylethene Derivative Probed by Vibrational Spectroscopy

The geometrical evolution of the reactant and formation of the photoproduct in the cycloreversion reaction of a diarylethene derivative were probed using time-resolved absorption spectroscopies in the visible to near-infrared and mid-infrared regions. The time-domain vibrational data in the visible region show that the initially formed Franck-Condon state is geometrically relaxed into the minimum in the excited state potential energy surface, concomitantly with the low-frequency coherent vibrations. Theoretical calculations indicate that the nuclear displacement in this coherent vibration is nearly parallel to that in the geometrical relaxation. Time-resolved mid-infrared spectroscopy directly detected the formation of the open-ring isomer with the same time constant as the decrease of the closed-ring isomer in the excited state minimum. This observation reveals that no detectable intermediate, in which the population is accumulated, is present between the excited closed-ring isomer and the open-ring isomer in the ground state.     

Dithienylethenes with a novel photochromic performance

Dithienylethenes with low decoloration quantum yields and thermal reversibility at high temperature above 100 degrees C were prepared. Introduction of bulky alkoxy substituents at 2- and 2'-positions of the thiophene rings strongly suppressed the cycloreversion quantum yields. The quantum yields were lower than 10(-3), and the photogenerated color remained stable enough under room light. On the other hand, the bulky alkoxy substituent decreased the thermal stability of the colored closed-ring isomers at high temperature. The color of the dithienylethene with cyclohexyloxy substituents faded out in less than 1 min at 160 degrees C.     

Successive chelatometric titration of calcium and magnesium

A simple procedure for the successive chelatometric titration of calcium and magnesium in natural waters, with 3',3'-bis(2-hydroxy-3-carboxy-naphthaleneazo)phenolphthalein as indicator, is described.