Visible-light-driven photoreactions of [(bpy)2Ru(II)L]Cl2 in aqueous solutions (bpy = bipyridine, l = 1,2-bis(4-(4'-methyl)-2,2'-bipyridyl) ethene)

Visible-light-induced photoreactions of [(bpy)2Ru(II)L]Cl2 (bpy = bipyridine, L = trans-1,2-bis(4-(4'-methyl)-2,2'-bipyridyl) ethene) in aqueous solution are examined. From pH titrations, it is found that the Ru complex is a stronger base (pKa* = 6) in the excited state than in the ground state (pKa = 4). Photolysis of the [(bpy)2Ru(II)L] complex in solutions at pH 7 and 12 led to formation of species with increased emission quantum yields, approximately 55 nm blue-shift of the emission maximum to 625 nm, and disappearance of the absorption band at 330 nm, the latter arising from the olefinic bond of the L ligand. No spectral changes are observed in solutions at pH < or = 4. With the help of chromatography, mass spectroscopy, Raman spectroscopy, and NMR, photoproducts formed at neutral pH have been analyzed. It is found that the major product is a dimer of [(bpy)2Ru(II)L], dimerizing around the double bond. Photoreactions do not occur in the dark or in the aprotic solvent acetonitrile. We propose that a Ru(III) radical intermediate is formed by photoinduced excited-state electron and proton transfer, which initiates the dimerization. The radical intermediate can also undergo photochemical degradative reductions. Below pH 4, the emission quenching is proposed to arise via protonation of the monoprotonated [(bpy)2Ru(II)LH] followed by electron transfer to the viologen-type moiety created by protonation. The products of photodegradation at pH > 12 are different from those of pH 7, but the mechanism of the degradation at pH > 12 was not elucidated.     

Viscosity of sodium carboxymethylcellulose in ethylene glycol–water mixed solvent media: Separation of the influences of polyion conformation and electrostatic interactions on the reduced viscosity

Precise measurements on the viscosities of the solutions of sodium carboxymethylcellulose in water and three ethylene glycol–water mixtures containing 10, 20, and 30 mass % of ethylene glycol have been reported at 35 °C. Isoionic dilutions were performed at total ionic strengths in the range of 0.0002–0.0008 eqv L^?1 using sodium chloride to obtain the intrinsic viscosities along with the Huggins constants. The influence of the medium and the ionic strength on the intrinsic viscosities have been interpreted from the points of view of the counterion condensation and expansion/contraction of the polyion chains in solution. The variations of Huggins constants, on the other hand, provided information on the intermolecular interactions in these solutions. A convenient method has been proposed to decompose the reduced viscosity of a polyelectrolyte solution into its conformational and electrostatic components. The electrostatic reduced viscosities obtained in the present study, purely from experimental considerations, quantitatively corroborates the conclusions derived from the Huggins constants. Using the Hess and Klein theoretical approach, an expression for the reduced viscosity due to the electrostatic interactions as a function of polyelectrolyte concentration could be obtained and the reported experimental electrostatic contributions could be nicely described with the help of this approach. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1196–1202, 2010     

Renormalization-group analysis of the R(I)-R(V) rotator phase transition

A model for coupled tilt angle and lattice distortion parameter is proposed to describe the R(I)-R(V) transition in n-alkane. The model is treated in the framework of a Landau mean-field theory and renormalization-group theory. The influence of gauche conformations and molecular flexibility on the R(I)-R(V) transition is discussed within the mean-field theory. The fluctuations on the R(I)-R(V) transition are discussed by the renormalization-group theory. Renormalization-group theory predicts that the R(I)-R(V) transition can be driven first order by fluctuations and becomes second order at a tricritical point. Available experimental data are consistent with our model.     

Synthesis of amphiphilic azo-anion-radical complexes of chromium(III) and the development of ultrathin redox-active surfaces by the Langmuir-Schaefer technique

Neutral tris-chelated chromium complex [Cr(L(a))(3)] (1a), and its surfactant derivatives [Cr(L(b))(3)] (1b), [Cr(L(c))(3)] (1c), and [Cr(L(d))(3)] (1d) (where L(a)=2-(4'-methoxyphenylazo)pyridine, L(b)=2-(4'-butyloxyphenylazo)pyridine, L(c =2-(4'-octyloxyphenylazo)pyridine, and L(d)=2-(4'-dodecyloxyphenylazo)pyridine) were synthesized. The molecular structure of compound 1a, determined by X-ray diffraction, showed that the local geometry around the metal center is a distorted octahedral with meridional coordination of the ligands. The structural parameters, spectroscopic data, and density functional theory (DFT) calculations on representative complex 1a suggest that ligand L(a) is predominantly an azo-anion-radical-type, and so the complex can be represented as [Cr(III)(L(a.-))(3)]. An assessment of their physicochemical and surface properties was performed with the aim of using these triple-tailed metallosurfactants as precursors for redox-responsive films. The surface-pressure-molecular-area isotherm measurement for compound 1d shows that the complex forms a stable Langmuir film at the air/water interface. The monolayer and multilayers were successfully transferred onto the quartz substrate and the platinum working electrode at a surface pressure of 10 mN m(-1) by the Langmuir-Schaefer (LS) technique. The LS films were studied by UV/Vis spectrometry, infrared spectroscopy, field-emission scanning electron microscopy, and atomic force microscopy. A good linear relationship between the absorbance at 370 nm and the thickness of the layers against the number of deposited layers indicated the uniformity and reproducibility of this transfer process. Voltammograms for platinum-surface-bound LS film of compound 1d showed that the redox response owing to the first oxidation is stable and reproducible after many cycles (>300 cycles). Spectroscopic studies and electrochemical measurements of compound 1d on the LS films revealed that these complexes are potential candidates for molecular devices.     

Macroscopic description of the ferromagnetic superconductors

We present an improved analysis of the phase transitions in spin-triplet ferromagnetic superconductors within Ginzburg–Landau theory. We put special emphasis on the phase transitions from normal phase to the mixed phase of coexistence of ferromagnetism and unconventional superconductivity. We present a detailed analysis of the different phases that can occur and analyze the question under which conditions the phase transitions from normal phase to the mixed phase of coexistence of ferromagnetism and unconventional superconductivity are possible when compared to other phase transitions. The conditions for the phase transitions and the stability conditions are calculated. On the basis of this model, it is argued that the transition from normal phase to the mixed phase of coexistence is always of first order. It was observed from the theoretical calculations that the transition from the ferromagnetic phase to the coexistence phase can cross over from the first to the second order at the tricritical point.     

Isotropic to ferroelectric and antiferroelectric liquid crystals phase transitions

This review is an attempt towards a unified picture of the direct transitions from the isotropic liquid to ferroelectric and antiferroelectric liquid crystalline phases formed by rod-like and bent-core molecules. The Landau–Ginzburg theories of the phase transitions between the isotropic liquid to ferroelectric and antiferroelectric liquid crystalline phases in compounds composed of chiral rod-like molecules and achiral bent-core molecules are presented. This includes a discussion of the nature of the order parameters and the nature of the various types of phase transitions. The various predictions are compared with the available experimental results.     

Some useful upper bounds for the selection of optimal profiles

In enhanced oil recovery by chemical flooding within tertiary oil recovery, it is often necessary to choose optimal viscous profiles of the injected displacing fluids that reduce growth rates of hydrodynamic instabilities the most thereby substantially reducing the well-known fingering problem and improving oil recovery. Within the three-layer Hele–Shaw model, we show in this paper that selection of the optimal monotonic viscous profile of the middle-layer fluid based on well known theoretical upper bound formula [P. Daripa, G. Pasa, A simple derivation of an upper bound in the presence of a viscosity gradient in three-layer Hele–Shaw flows, Journal of Statistical Mechanics (2006) 11. http://dx.doi.org/10.1088/1742-5468/2006/01/P01014] agrees very well with that based on the computation of maximum growth rate of instabilities from solving the linearized stability problem. Thus, this paper proposes a very simple, fast method for selection of the optimal monotonic viscous profiles of the displacing fluids in multi-layer flows.     

Surface-Enhanced Raman Scattering of Rhodamine 123 in Silver Hydrosols and in Langmuir-Blodgett Films on Silver Islands

Surface-enhanced Raman scattering(SERS) of the Rhodamine 123 (Rh 123) molecule on ion-induced silver colloids has been studied. A time-dependent study of the SER spectra at a particular pH confirms charge transfer interaction between the probe molecule and the metal. The SER spectra of Rh 123 in Ag sol is compared with that of the molecules organized in a monolayer on silver island films by the Langmuir-Blodgett (LB) technique. The origin of high SERS activity of Rh 123 molecules in a monolayer on a silver island film is shown to be due to physisorption whereas in the ion-induced colloidal SERS both physisorption and chemisorption machanisms are involved. From these results, the contribution of charge transfer interaction to SERS in Ag sol has been estimated. In monolayer SERS, all the in-plane and out-of-plane (of xanthene ring) modes are more or less equally enhanced. This indicates that the xanthene plane of Rh 123 molecule organized in a LB film is oriented neither flat nor perpendicular to the silver island surface but is tilted. Copyright 2001 Academic Press.     

Zeolite guest-host interactions: Implications in formation,catalysis, and photochemistry

This review primarily focuses on contributions of our research group in the area of zeolite guesthost chemistry. The perturbation of the Raman spectra of the organic structure-directing-agents during synthesis of zeolites ZK-4, ZSM-5, and ferrierite show clearly the entrapment of the organic by the aluminosilicate framework. The microordering around the organic coincides with the development of longrange-order typical of crystal formation. Using three examples involving zeolite entrapped organometallic complexes of manganese(III), cobalt(II), and ruthenium(II), we have demonstrated a wide range of chemistries using reactants varying from olefins to dioxygen to photogenerated electrons.     

Polymers containing anthraquinone and quinoxaline units: Polypyrrolones

Four ladder or partial ladder polypyrrolones containing anthraquinone recurring units have been synthesized by condensing the dianhydride of 1,2,5,6-bis(α,β-dicarboxyl-pyrazino)anthraquinone with four different tetraamines, 1,2,4,5-tetraaminobenzene tetrahydrochloride, 3,3′,4,4′-tetraaminodiphenyl, 3,3′,4,4′-tetraaminodiphenyl ether, and 1,2,5,6-tetraaminoanthraquinone in dimethylacetamide and tetramethylene sulfone as reaction media. A prepolymer with an open structure was first formed which on further heating gave a closed-ring structure. These polymers which were highly colored, powdery materials, were insoluble in common organic solvents and slightly soluble only in concentrated H₂SO₄. They could, however, be solubilized in alkali by reduction with sodium dithionite. These polymers with an inherent viscosity in the range of 0.2–0.5, showed good thermal stability.